CompTIA Network+ (N10-009) · glossary

Network+ glossary

579 terms you need for CompTIA Network+ (N10-009), in plain words. Each one links to the lesson that teaches it. The acronym list is further down.

#A B C D E F G H I J K L M N O P Q R S T U V W Z Acronyms

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2.4 GHz: 2.4 GHz: longest range and best through walls, but crowded (microwaves, Bluetooth) with only 3 non-overlapping channels. Lesson: Frequency options: 2.4, 5 and 6 GHz
5 GHz: 5 GHz: many more channels and higher speeds, shorter range. Lesson: Frequency options: 2.4, 5 and 6 GHz
6 GHz: 6 GHz (Wi-Fi 6E/7): a large, clean band with wide channels and the shortest range; requires WPA3. Lesson: Frequency options: 2.4, 5 and 6 GHz
802.1D states: 802.1D states: blocking → listening → learning → forwarding (plus disabled). Lesson: Port roles and states
802.1Q tagging: 802.1Q tagging inserts a 4-byte tag with a 12-bit VLAN ID into each frame on the trunk. Lesson: Access ports, trunks, 802.1Q and the native VLAN
802.3: Wired Ethernet is IEEE 802.3. Lesson: 802.3 Ethernet over copper
802.3af: PoE standards: 802.3af (PoE) 15.4 W per port, 802.3at (PoE+) 30 W, 802.3bt (PoE++) 60 W (Type 3) and 90 W (Type 4, often sold as '100 W'), measured at the switch. Lesson: Power over Ethernet
802.3at: PoE standards: 802.3af (PoE) 15.4 W per port, 802.3at (PoE+) 30 W, 802.3bt (PoE++) 60 W (Type 3) and 90 W (Type 4, often sold as '100 W'), measured at the switch. Lesson: Power over Ethernet
802.3bt: PoE standards: 802.3af (PoE) 15.4 W per port, 802.3at (PoE+) 30 W, 802.3bt (PoE++) 60 W (Type 3) and 90 W (Type 4, often sold as '100 W'), measured at the switch. Lesson: Power over Ethernet
802.11: Wi-Fi is defined by the IEEE 802.11 family. Lesson: 802.11 Wi-Fi standards
802.11h: 802.11h adds DFS (dynamic frequency selection: the AP listens for radar and moves off the channel) and TPC (transmit power control: lowers power to the minimum needed). Lesson: Regulatory impacts: 802.11h
1000BASE-T: Names like 1000BASE-T mean speed (1000 Mbps), BASE = baseband, T = twisted pair. Lesson: 802.3 Ethernet over copper
A
A: A: name to IPv4 address Lesson: Record types
AAAA: AAAA: name to IPv6 address Lesson: Record types
Access control list (ACL): An access control list (ACL) is an ordered list of permit/deny rules matched on IPs, ports and protocols. Lesson: ACLs
Access layer: Access layer: switches users and APs plug into (PoE, port security, VLANs). Lesson: Three-tier hierarchical model
Access point (AP): A wireless access point (AP) bridges Wi-Fi clients onto the wired network (Layer 2). Lesson: Wireless: access points and controllers
Access port: An access port belongs to one VLAN and sends untagged frames to the device. Lesson: Access ports, trunks, 802.1Q and the native VLAN
Active-active: Active-active: both units carry traffic at once (load shared); if one fails, the other takes it all. Lesson: Active-active vs. active-passive
Active-passive: Active-passive: one unit works while the standby waits, synced and ready, and takes over on failure. Lesson: Active-active vs. active-passive
Ad hoc: Ad hoc: devices connect directly to each other with no AP (IBSS). Lesson: Network types
Address exhaustion: IPv6 is the real fix for address exhaustion: 128-bit addresses (2^128, about 3.4 x 10^38), enough for every device to have a globally unique address. Lesson: Why IPv6: mitigating address exhaustion
Administrative distance: If two sources offer the same prefix, the lower administrative distance wins (connected 0, static 1, OSPF 110, RIP 120); then the lower metric. Lesson: The routing table
Administrative distance (AD): (2) Administrative distance (AD): if the same prefix is learned from different sources, the most trusted (lowest AD) is installed. Lesson: Route selection: prefix length, AD, metric
Administratively down: Administratively down: someone typed 'shutdown'; fix with 'no shutdown' Lesson: Port status
Advanced distance-vector: EIGRP: Cisco-developed advanced distance-vector (often called hybrid). Lesson: Dynamic routing: OSPF, EIGRP, BGP
AH (Authentication Header, protocol 51): AH (Authentication Header, protocol 51) gives integrity and authentication but no encryption. Lesson: IPsec: AH, ESP and IKE
Alerts: An IDS (intrusion detection system) watches a copy of traffic (from a SPAN/mirror port or tap) and alerts on attacks; it is out of band, so it cannot stop them. Lesson: IDS vs IPS
Allocate the largest subnet first: Rule: allocate the largest subnet first, then the next largest, each starting on its own block boundary. Lesson: What VLSM means
alternate/backup: Roles: root port (each non-root switch's best path to root), designated port (forwarding port on each segment), blocked ports (RSTP: alternate/backup) that stand by. Lesson: Port roles and states
Anomaly alert: Once you know normal, set thresholds so the system raises an anomaly alert and notifies people (email, text, chat) when a metric goes far outside it, like the WAN link at 95% at 2 a.m. Lesson: Anomaly alerting and notification
Anycast: Anycast: one address configured in many places; routing delivers to the nearest one. Lesson: Unicast, broadcast, multicast, anycast
API: API: scripts and tools make changes programmatically (automation) Lesson: Connection methods
APIPA: APIPA (Automatic Private IP Addressing) gives a host an address in 169.254.0.0/16 when it is set for DHCP but gets no answer. Lesson: APIPA and loopback/localhost
Application aware: Application aware: it identifies apps (VoIP, POS, video) and steers each one to the best link based on latency, jitter and loss. Lesson: SD-WAN
Application layer: The application layer is where network services meet software: HTTP/HTTPS, DNS, SMTP, FTP, SSH, SNMP, DHCP. Lesson: Layer 7 - Application
Application programming interface (API): Modern gear and cloud services expose an application programming interface (API), usually REST over HTTPS with JSON. Lesson: API integration
Arp -a: arp -a shows the IP-to-MAC cache, handy for duplicate IPs and ARP poisoning. Lesson: ipconfig, ip, ifconfig and arp
ARP poisoning: In ARP spoofing, the attacker sends forged ARP replies claiming 'I am the gateway's IP, here's my MAC.' The result, victims' ARP caches filled with the false mapping, is ARP poisoning. Lesson: ARP spoofing and ARP poisoning
ARP spoofing: In ARP spoofing, the attacker sends forged ARP replies claiming 'I am the gateway's IP, here's my MAC.' The result, victims' ARP caches filled with the false mapping, is ARP poisoning. Lesson: ARP spoofing and ARP poisoning
Asset inventory: An asset inventory lists what you own so nothing is forgotten, lost or left unpatched. Lesson: Asset inventory
Attenuation: Attenuation: signal loss over distance; copper Ethernet is limited to 100 m Lesson: Signal degradation
Authentication: SNMPv3 adds real authentication (users and hashing) and encryption, so it is the secure choice. Lesson: Versions, community strings, authentication
Authentication server: Three roles: the supplicant (client), the authenticator (switch or AP) and the authentication server (usually RADIUS). Lesson: 802.1X
Authenticator: Three roles: the supplicant (client), the authenticator (switch or AP) and the authentication server (usually RADIUS). Lesson: 802.1X
Authoritative: An authoritative server holds the zone and gives the official answer. Lesson: Who answers: authoritative, primary, secondary
Authorization: Three ideas on the exam: policy-based authentication (identity plus context: device health, location, time, MFA, checked continuously), authorization for each request to each resource, and least privilege access… Lesson: Zero trust architecture (ZTA)
Auto-negotiation: Leave both ends on auto-negotiation or hard-code both ends the same. Lesson: Speed and duplex
Automatically: Elasticity is doing that automatically in both directions: add servers during the Black Friday spike, remove them when it ends so you stop paying. Lesson: Scalability, elasticity, multitenancy
Autonomous: An autonomous AP is standalone: it holds its own config and is managed one by one. Lesson: Autonomous vs lightweight APs
Availability: Availability: systems are up when needed (redundancy, DDoS protection) Lesson: The CIA triad
Availability monitoring: Availability monitoring: is it up? Lesson: Five things to watch
B
Backup configuration: Backup configuration: a saved copy you can restore after failure or a bad change Lesson: Configuration management
Band steering: Band steering lets the AP push dual-band clients off 2.4 GHz onto 5 or 6 GHz to spread the load. Lesson: Frequency options: 2.4, 5 and 6 GHz
Bandwidth: Bandwidth is a link's capacity (a 100 Mbps circuit). Lesson: Bandwidth vs. throughput
Baseline: A baseline records normal performance over time: bandwidth, CPU, memory, latency, error counts, by hour and day. Lesson: Baseline metrics
Baseline/golden configuration: Baseline/golden configuration: the approved standard every device of that type should match Lesson: Configuration management
BGP: BGP: path-vector exterior protocol that routes between autonomous systems; the routing protocol of the internet. Lesson: Dynamic routing: OSPF, EIGRP, BGP
Bits: The physical layer moves raw bits as signals: voltage on copper, pulses of light in fiber, radio waves in Wi-Fi. Lesson: Layer 1 - Physical
Block: An IPS (intrusion prevention system) sits inline, so it can block malicious traffic as it passes. Lesson: IDS vs IPS
Block size: Block size = 256 - mask value in that octet. Lesson: The magic number (block size)
Block-level: A SAN (storage area network) is a dedicated high-speed network that gives servers block-level storage, using Fibre Channel or iSCSI. Lesson: NAS vs SAN
Blocked: Each switch picks a root port (best path to root); each segment gets a designated port; the rest are blocked, ready to take over if a link fails. Lesson: Spanning tree (STP)
BNC: Older Ethernet and some video gear used BNC bayonet connectors on coax. Lesson: Coaxial cable
Bottleneck: A bottleneck is the single slowest point in the path, such as a 1 Gbps uplink feeding a 10 Gbps core. Lesson: Congestion/contention and bottlenecking
Bottom-to-top: Then consider multiple approaches: work through the OSI model top-to-bottom or bottom-to-top, or divide and conquer (start in the middle, like pinging the gateway, and move up or down based on the result). Lesson: Step 2: Establish a theory
Bottom-up: Bottom-up: link light, cable, then MAC/ARP, then IP/ping, then ports, then the app. Lesson: Troubleshooting by layer
Branching: Branching lets an engineer work on a change in a separate branch, test it, then merge after review. Lesson: Source control
Bridge ID: STP first elects a root bridge: the switch with the lowest bridge ID (priority, default 32768, plus VLAN, then MAC address as tie-breaker). Lesson: Root bridge selection
Broadcast: Broadcast: one to ALL hosts on the local network (IPv4 only), e.g. Lesson: Unicast, broadcast, multicast, anycast
Broadcast address: Two special addresses in every subnet: network address (all host bits 0) and broadcast address (all host bits 1). Lesson: Network part and host part
Broadcast storm: Ethernet frames have no TTL, so in a Layer 2 loop broadcasts circle forever and multiply: a broadcast storm. Lesson: Network loops
BSSID: The BSSID is the MAC address of one AP radio serving that SSID; it identifies one basic service set (one AP cell). Lesson: SSID, BSSID and ESSID
BYOD: BYOD: personal phones and laptops: limited access, often via NAC and a separate SSID. Lesson: Why segment
C
Cable map: A cable map (cable diagram) lists every run end to end: wall jack, patch panel port, switch port, label. Lesson: Rack diagrams and cable maps
Cable tester: A cable tester checks copper wiring: continuity, wire map (opens, shorts, split or crossed pairs) and often length. Lesson: Cable tester
CAM / MAC address table: A switch learns MAC addresses into its CAM / MAC address table. Lesson: MAC flooding
Cameras: Cameras deter and record who entered the closet. Lesson: Cameras and locks
Captive portal: A captive portal is the web page that appears before access is granted: accept the terms, enter a code or log in. Lesson: Guest networks and captive portals
Category 5/6/7/8: Category 5/6/7/8: Cat5e 1 Gbps; Cat6 10 Gbps to ~55 m; Cat6a 10 Gbps to 100 m; Cat7 10 Gbps, shielded; Cat8 25/40 Gbps to 30 m Lesson: Incorrect cable
CDN: A CDN is a group of servers spread around the world that cache copies of content (images, video, scripts) close to users. Lesson: Content delivery network (CDN)
CDP: LLDP (vendor-neutral, IEEE 802.1AB) and CDP (Cisco) let neighbors announce name, model, port and IP: great for mapping links without walking to the closet. Lesson: Where is that device?
Cellular: Cellular networks (4G LTE, 5G) give wide-area wireless data from carrier towers. Lesson: Cellular
Central policy management: Central policy management: one console sets routing and security policy for every site at once. Lesson: SD-WAN: transport and policy
Central repository: A central repository is the single source of truth everyone pulls from. Lesson: Source control
Certificate: A certificate binds a public key to a name. Lesson: Certificates: PKI vs. self-signed
Certificate authority (CA): In a public key infrastructure (PKI), a trusted certificate authority (CA) signs certificates, so browsers and devices trust them. Lesson: Certificates: PKI vs. self-signed
Change default passwords: Change default passwords: admin/admin and 'public' are in every attacker's list Lesson: Device hardening
Change management: Change management controls how changes reach production. Lesson: Change management
Channel overlap: Channel overlap: in 2.4 GHz only channels 1, 6 and 11 don't overlap (in the US). Lesson: Interference and channel overlap
Channel width: Channel width: bonding channels to 40, 80 or 160 MHz (320 in Wi-Fi 7) raises throughput but leaves fewer non-overlapping channels and picks up more noise. Lesson: Channels, channel width and non-overlapping channels
CIDR: CIDR (Classless Inter-Domain Routing) writes the mask as a slash and the count of network bits: /24 = 24 ones. Lesson: CIDR: the slash number
Class A: Classes are mostly history now, but the exam still asks: Class A (huge, /8), Class B (/16), Class C (/24), Class D (multicast) and Class E (experimental). Lesson: Classful addressing: Classes A to E
Class B: Classes are mostly history now, but the exam still asks: Class A (huge, /8), Class B (/16), Class C (/24), Class D (multicast) and Class E (experimental). Lesson: Classful addressing: Classes A to E
Class C: Classes are mostly history now, but the exam still asks: Class A (huge, /8), Class B (/16), Class C (/24), Class D (multicast) and Class E (experimental). Lesson: Classful addressing: Classes A to E
Class D: Classes are mostly history now, but the exam still asks: Class A (huge, /8), Class B (/16), Class C (/24), Class D (multicast) and Class E (experimental). Lesson: Classful addressing: Classes A to E
Class E: Classes are mostly history now, but the exam still asks: Class A (huge, /8), Class B (/16), Class C (/24), Class D (multicast) and Class E (experimental). Lesson: Classful addressing: Classes A to E
Clear text: Telnet and FTP send everything, passwords included, in clear text; replace them with SSH and SFTP. Lesson: Moving files and managing devices
Client disassociation issues: Client disassociation issues: clients drop off an AP: weak signal, interference, power-saving bugs, or deauthentication attacks. Lesson: Client disassociation and roaming
Client-to-site: A client-to-site (remote access) VPN connects one user's device to the company network, usually with a VPN client using TLS/SSL or IPsec. Lesson: Client-to-site VPN
Client-to-site (remote access): Client-to-site (remote access): software on a laptop connects one user to HQ. Lesson: Virtual private network (VPN)
Clientless: Clientless VPN runs in a web browser over HTTPS: no software to install, but access is limited to web portals and published apps. Lesson: Client-to-site VPN
CNAME: CNAME: alias pointing to another name (shop -> web01) Lesson: Record types
Coaxial cable: Coaxial cable has one center conductor, insulation, a braided shield and a jacket. Lesson: Coaxial cable
Cold site: Cold site: space, power, cooling, maybe connectivity. Lesson: Cold, warm, hot sites
Collapsed core: A collapsed core merges the core and distribution layers into one pair of switches. Lesson: Collapsed core
Community strings: SNMPv2c uses community strings as simple shared passwords, sent in clear text. Lesson: Versions, community strings, authentication
Compatibility requirements: IPv4 and IPv6 cannot talk to each other directly, so there are three compatibility requirements strategies. Lesson: Compatibility: dual stack, tunneling, NAT64
Compliance: IaC tools compare live config to the code, report drift and push it back into compliance. Lesson: Drift, compliance, upgrades, dynamic inventories
Compression: The presentation layer makes data readable to the other side: character encoding (ASCII, Unicode), data formats (JPEG, MPEG), compression and encryption/decryption. Lesson: Layer 6 - Presentation
Confidentiality: Confidentiality: only authorized people see data (encryption, access control) Lesson: The CIA triad
Configuration drift: Configuration drift happens when someone makes a manual change and a device no longer matches its approved baseline. Lesson: Drift, compliance, upgrades, dynamic inventories
Configuration monitoring: Configuration monitoring: alerts when a config changes or drifts from golden Lesson: Five things to watch
Conflict identification: Conflict identification: if two people change the same lines, the merge is flagged as a conflict so a human decides instead of silently overwriting. Lesson: Source control
Congestion: Congestion happens when more traffic arrives than a link or device can forward: queues fill, latency climbs, packets drop. Lesson: Congestion/contention and bottlenecking
Consider multiple approaches: Then consider multiple approaches: work through the OSI model top-to-bottom or bottom-to-top, or divide and conquer (start in the middle, like pinging the gateway, and move up or down based on the result). Lesson: Step 2: Establish a theory
Console: Console: direct serial/USB cable to the console port; works with no network config at all Lesson: Connection methods
Content filtering: Content filtering inspects what is actually in the traffic: file types, keywords, malicious scripts. Lesson: URL and content filtering
Contention: Contention is many devices competing for the same shared medium or link. Lesson: Congestion/contention and bottlenecking
Control plane: Network devices have planes: the data (forwarding) plane moves packets, the control plane decides where they go (routing tables, STP), and the management plane is how admins configure them (SSH, SNMP, APIs). Lesson: Software-defined networking (SDN)
Controller: SDN separates the control plane from the hardware and centralizes it in a controller. Lesson: Software-defined networking (SDN)
Core layer: Core layer: a fast, redundant backbone that moves traffic between distribution blocks and to the data center/WAN. Lesson: Three-tier hierarchical model
Correlates: A security information and event management (SIEM) system goes beyond collecting: it normalizes logs from firewalls, servers, switches and apps, correlates events across them, alerts on suspicious patterns, and keeps… Lesson: SIEM
Cost: Metric = cost (based on bandwidth). Lesson: Dynamic routing: OSPF, EIGRP, BGP
CRC: CRC: frames failed the checksum: bad cable, interference, duplex mismatch Lesson: Increasing interface counters
Crosstalk: Crosstalk: signal bleeds between pairs (NEXT/FEXT), often from untwisted pairs at the connector Lesson: Signal degradation
D
Data (forwarding) plane: Network devices have planes: the data (forwarding) plane moves packets, the control plane decides where they go (routing tables, STP), and the management plane is how admins configure them (SSH, SNMP, APIs). Lesson: Software-defined networking (SDN)
Data at rest: Data at rest sits on disks, backups and phones; protect it with full-disk or database encryption. Lesson: Encryption: in transit and at rest
Data center interconnect (DCI): Big uses: multi-tenant clouds and data center interconnect (DCI), so a VM can move between data centers and keep its IP. Lesson: VXLAN
Data in transit: Data in transit moves across a network; protect it with TLS, IPsec, SSH. Lesson: Encryption: in transit and at rest
Data link layer: The data link layer packages bits into frames and delivers them on the local network using MAC addresses (48-bit, burned into each NIC; the first half is the vendor OUI). Lesson: Layer 2 - Data link
Data locality: Data locality (data residency) rules require certain data to be stored or processed inside a specific country or region, which affects where you put cloud servers and backups. Lesson: GDPR and data locality
Datagrams: The transport layer connects one application to another using port numbers and chops data into segments (TCP) or datagrams (UDP). Lesson: Layer 4 - Transport
De-encapsulation: The receiver does de-encapsulation, peeling one header off per layer on the way up. Lesson: Encapsulation: wrapping the data
Deception technologies: Deception technologies lure attackers. Lesson: Honeypots and honeynets
Default route: A default route (0.0.0.0/0, IPv6 ::/0) is used when nothing more specific matches: the 'gateway of last resort', usually toward the ISP. Lesson: Default routes
Denial-of-service (DoS): A denial-of-service (DoS) attack overwhelms a target so legit users can't reach it: floods of traffic or requests, or crashing a service. Lesson: DoS and DDoS
Designated port: Each switch picks a root port (best path to root); each segment gets a designated port; the rest are blocked, ready to take over if a link fails. Lesson: Spanning tree (STP)
DFS: 802.11h adds DFS (dynamic frequency selection: the AP listens for radar and moves off the channel) and TPC (transmit power control: lowers power to the minimum needed). Lesson: Regulatory impacts: 802.11h
DHCP relay: A DHCP relay (Cisco: ip helper-address) on the router interface catches the broadcast and forwards it as unicast to the DHCP server in another subnet. Lesson: Relay / IP helper
Dig: nslookup (Windows, Linux, macOS) and dig (Linux/macOS) query DNS directly. Lesson: nslookup and dig
Direct attach copper (DAC): A direct attach copper (DAC) cable is a short twinaxial copper cable with transceiver ends (SFP+, SFP28, QSFP) molded on. Lesson: DAC and twinaxial cable
Direct Connect: Direct Connect (a dedicated/private connection) is a private circuit from your site or colocation facility into the provider's network: consistent bandwidth and latency, does not cross the public internet, but costs… Lesson: Connecting the office to the cloud: VPN vs Direct Connect
Directional: A directional antenna (patch, Yagi, parabolic dish) focuses energy in one direction for longer range: long warehouse aisles, outdoor yards and point-to-point links between buildings. Lesson: Antennas: omnidirectional vs directional
Disable unused ports: Disable unused ports: shut them down (and park them in an unused VLAN) Lesson: Device hardening
Disable unused services: Disable unused services: Telnet, HTTP management, CDP on edge ports, unused SNMP Lesson: Device hardening
Distributed DoS (DDoS): A distributed DoS (DDoS) comes from many sources at once, often a botnet of infected devices, so blocking one IP does not help. Lesson: DoS and DDoS
Distribution layer: Distribution layer: aggregates access switches, routes between VLANs, applies policy. Lesson: Three-tier hierarchical model
Divide and conquer: Divide and conquer: start in the middle with ping (Layer 3); if ping works, layers 1-3 are probably fine, so go up. Lesson: Troubleshooting by layer
DNS over HTTPS (DoH): DNS over HTTPS (DoH) (port 443) and DNS over TLS (DoT) (port 853) encrypt queries so others on the path cannot read or alter them. Lesson: DNSSEC, DoH, DoT
DNS over TLS (DoT): DNS over HTTPS (DoH) (port 443) and DNS over TLS (DoT) (port 853) encrypt queries so others on the path cannot read or alter them. Lesson: DNSSEC, DoH, DoT
DNS poisoning: DNS poisoning (cache poisoning) plants a false record in a resolver's cache, so EVERY client using that resolver is misdirected until the TTL expires. Lesson: DNS spoofing and DNS poisoning
DNS spoofing: DNS spoofing sends a forged DNS answer so a victim goes to the wrong IP. Lesson: DNS spoofing and DNS poisoning
DNS TTL: DNS TTL: how many seconds a resolver may cache a record before asking again. Lesson: Time to live (TTL)
DNSSEC: DNSSEC adds digital signatures to records so resolvers can verify they are authentic and unchanged. Lesson: DNSSEC, DoH, DoT
Document: Document findings, actions, outcomes and lessons learned. Lesson: Steps 4-7 in practice
Double tagging: Two methods: switch spoofing (the attacker's device negotiates a trunk using DTP) and double tagging (two 802.1Q tags; the first switch strips the outer native-VLAN tag and forwards the inner one). Lesson: VLAN hopping
Drops: Drops: frames discarded, usually full buffers from congestion Lesson: Increasing interface counters
Dual stack: Dual stack: every device runs IPv4 and IPv6 side by side and uses whichever the destination supports. Lesson: Compatibility: dual stack, tunneling, NAT64
Dumpster diving: Dumpster diving: searching trash for passwords, diagrams, old configs Lesson: Social engineering
Duplex: Each port has a speed (10/100/1000/10G) and duplex: full duplex sends and receives at once; half duplex takes turns and can collide. Lesson: Speed and duplex
Duplex mismatch: A duplex mismatch (one full, one half) still links up, but is painfully slow: the half-duplex side logs late collisions and the full side logs CRC/runt errors. Lesson: Speed and duplex
Dynamic inventories: Dynamic inventories build the target list live from a source (cloud API, IPAM, CMDB) in place of a hand-maintained static list, so new devices are included automatically. Lesson: Drift, compliance, upgrades, dynamic inventories
Dynamic NAT: Dynamic NAT: private hosts borrow addresses from a public pool. Lesson: NAT and PAT
E
East-west: East-west traffic moves between servers inside the data center: the web tier calling the app tier, database replication, VM migration. Lesson: Traffic flows: north-south vs east-west
EIGRP: EIGRP: Cisco-developed advanced distance-vector (often called hybrid). Lesson: Dynamic routing: OSPF, EIGRP, BGP
Elasticity: Elasticity is doing that automatically in both directions: add servers during the Black Friday spike, remove them when it ends so you stop paying. Lesson: Scalability, elasticity, multitenancy
Encryption: SNMPv3 adds real authentication (users and hashing) and encryption, so it is the secure choice. Lesson: Versions, community strings, authentication
encryption/decryption: The presentation layer makes data readable to the other side: character encoding (ASCII, Unicode), data formats (JPEG, MPEG), compression and encryption/decryption. Lesson: Layer 6 - Presentation
End-of-life (EOL): End-of-life (EOL): the vendor stops selling the product. Lesson: EOL vs. EOS
End-of-support (EOS): End-of-support (EOS): the vendor stops patches, bug fixes and technical support. Lesson: EOL vs. EOS
Enterprise: Enterprise uses 802.1X: each user or device authenticates with its own credentials or certificate through an EAP method, checked by a RADIUS server. Lesson: Authentication: PSK vs Enterprise
Error disabled (err-disabled): Error disabled (err-disabled): the switch shut the port for a violation: port security, BPDU guard, flapping Lesson: Port status
Escalate: If it is not confirmed, establish a new theory or escalate. Lesson: Step 3: Test the theory
ESP (Encapsulating Security Payload, protocol 50): ESP (Encapsulating Security Payload, protocol 50) gives encryption plus integrity, so almost every VPN uses ESP. Lesson: IPsec: AH, ESP and IKE
ESSID: When many APs broadcast the same SSID with the same security, they form an extended service set, named by the ESSID, and clients can roam between APs without reconnecting. Lesson: SSID, BSSID and ESSID
Ethernet: It must match the protocol: Ethernet optics for LAN switches, Fibre Channel (FC) optics for SAN switches and storage arrays. Lesson: Transceivers: protocol and form factor
Evil twin: An evil twin is a rogue AP that copies a real SSID (like 'Kibble-Guest'), often with a stronger signal, so users connect to the attacker instead. Lesson: Evil twin
Exclusions: Exclusions are addresses inside the scope the server must never hand out, such as ones you assigned statically to printers or the gateway. Lesson: Scope, lease time, exclusions
Exploit: An exploit is the actual method or code that takes advantage of the weakness. Lesson: Risk, threat, vulnerability, exploit
F
F-type: RG-6 carries cable TV and cable-modem internet (DOCSIS) with F-type screw-on connectors. Lesson: Coaxial cable
FCS: The frame trailer holds an FCS (frame check sequence, a CRC): the receiver recomputes it and discards damaged frames. Lesson: Layer 2 - Data link
Fiber distribution panel: A fiber distribution panel does the same for fiber: it terminates and protects trunk fibers and splices and gives LC/SC adapters for patching to switches. Lesson: Cabling: patch panels and fiber distribution panels
Fibre Channel (FC): It must match the protocol: Ethernet optics for LAN switches, Fibre Channel (FC) optics for SAN switches and storage arrays. Lesson: Transceivers: protocol and form factor
Files: NAS (network-attached storage) is a storage device on the regular network that shares files using SMB or NFS. Lesson: NAS vs SAN
Fire suppression: Fire suppression: use clean agent gas systems (inert gas or chemical agents) or pre-action/dry-pipe sprinklers in equipment rooms, not just wet pipes over the racks. Lesson: Environmental factors
Firewall: A firewall permits or denies traffic by rules. Lesson: Firewall
Firmware: Firmware: low-level code on APs, NICs, transceivers, UPS cards Lesson: Software management
First Hop Redundancy Protocol (FHRP): A First Hop Redundancy Protocol (FHRP) lets two or more routers share a virtual IP (VIP) and virtual MAC. Lesson: FHRP and the virtual IP
First match wins: Rules are checked top to bottom; the first match wins, and an implicit deny at the end drops anything not permitted. Lesson: ACLs
Flapping: Symptoms: all port lights blazing, CPU at 100%, MAC addresses flapping between ports, network unusable. Lesson: Network loops
Floating static route: A floating static route has a higher administrative distance so it is used only if the main route disappears. Lesson: Static routing
Flow data: Flow data (NetFlow, IPFIX, sFlow) summarizes conversations: source and destination IP, ports, protocol, bytes, times. Lesson: Flow data
Form factors: Form factors: SFP (1 Gbps), SFP+ (10), SFP28 (25), QSFP (quad: QSFP+ 40, QSFP28 100 Gbps). Lesson: Transceivers: protocol and form factor
Forward proxy: A forward proxy sits in front of users: it filters URLs, caches content and hides internal addresses when staff browse the web. Lesson: Proxy
Forward zone: A forward zone answers name-to-IP questions (A, AAAA, CNAME, MX). Lesson: Zones: forward and reverse
Frames: The data link layer packages bits into frames and delivers them on the local network using MAC addresses (48-bit, burned into each NIC; the first half is the vendor OUI). Lesson: Layer 2 - Data link
Full mesh: In a full mesh, every node links to every other node: maximum redundancy and direct paths, but links grow fast: n(n-1)/2. Lesson: Mesh
Full tunnel: Split tunnel sends only company traffic through the tunnel; full tunnel sends everything. Lesson: Virtual private network (VPN)
G
General Data Protection Regulation (GDPR): The General Data Protection Regulation (GDPR) is EU law protecting personal data of people in the EU: consent, rights to access and erasure, breach notification. Lesson: GDPR and data locality
Geofencing: Geofencing uses location (GPS, IP geolocation, Wi-Fi) to allow, block or change access. Lesson: Geofencing
Geostationary (GEO): Geostationary (GEO) satellites sit about 35,786 km up, so a round trip takes roughly 600 ms or more: bad for VoIP and gaming. Lesson: Satellite
Giants: Giants: frames over 1518 bytes, often an MTU/jumbo frame mismatch Lesson: Increasing interface counters
GLBP: Protocols: HSRP (Cisco), VRRP (open standard), GLBP (Cisco, also load-balances). Lesson: FHRP and the virtual IP
GRE (Generic Routing Encapsulation, IP protocol 47): GRE (Generic Routing Encapsulation, IP protocol 47) wraps one packet inside another to create a point-to-point tunnel between two routers. Lesson: GRE: the generic tunnel
Guest: Guest: visitors get internet only, isolated from internal systems. Lesson: Why segment
Guest network: A guest network is a separate SSID mapped to its own VLAN that reaches only the internet, never internal subnets; client isolation stops guests from seeing each other. Lesson: Guest networks and captive portals
GUI: GUI: a web interface over HTTPS; friendly but slower for bulk changes Lesson: Connection methods
H
Hardening: Hardening removes easy ways in: Lesson: Device hardening
Hardware: Hardware: model, serial number, location, owner Lesson: Asset inventory
Health checks: It runs health checks and stops sending to dead servers, so it adds both capacity and fault tolerance. Lesson: Load balancer
Heat map: The result is usually a heat map: a floor plan colored by signal strength, showing dead spots and overlap. Lesson: Wireless survey and heat map
Hextet: An IPv6 address is 8 groups (hextets) of 4 hex digits separated by colons. Lesson: Reading and shortening IPv6
High availability (HA): High availability (HA) pairs devices so one failure does not stop service. Lesson: Active-active vs. active-passive
Honeynet: A honeynet is a whole network of honeypots. Lesson: Honeypots and honeynets
Honeypot: A honeypot is a fake system that looks valuable (an 'old file server') but has no real data; any connection to it is suspicious. Lesson: Honeypots and honeynets
Host bits: Host bits h = 32 minus the prefix. Lesson: Hosts = 2^h - 2
Host portion: Every address has a network portion (which network) and a host portion (which device). Lesson: Network part and host part
Hosts file: Before DNS, most OSes check the local hosts file (Windows: C:\Windows\System32\drivers\etc\hosts, Linux: /etc/hosts). Lesson: Recursive lookups and the hosts file
hot aisle / cold aisle: Data centers use hot aisle / cold aisle: equipment pulls cool air from the cold aisle and blows hot air into the hot aisle. Lesson: Airflow: port-side intake vs port-side exhaust
Hot site: Hot site: fully equipped and running with near-real-time data. Lesson: Cold, warm, hot sites
HSRP: Protocols: HSRP (Cisco), VRRP (open standard), GLBP (Cisco, also load-balances). Lesson: FHRP and the virtual IP
Hub and spoke: The WAN version is hub and spoke: every branch (spoke) connects to HQ (hub), and branch-to-branch traffic goes through the hub. Lesson: Star / hub and spoke
Hubs, repeaters, media converters: It defines cables, connectors, pinouts, signal timing and the devices that only repeat signals: hubs, repeaters, media converters. Lesson: Layer 1 - Physical
Humidity: Humidity: too dry causes static discharge, too humid causes condensation and corrosion; keep it moderate (commonly about 40-60% relative humidity) and monitor it. Lesson: Environmental factors
Hundreds of meters: Multimode fiber (MMF) has a wider 50 or 62.5 micron core, cheaper optics (LED/VCSEL), and runs hundreds of meters: inside buildings and data centers. Lesson: Single-mode vs multimode fiber
Hybrid: A hybrid topology mixes two or more types: Kibble is a star inside each building, hub and spoke to the stores, and point to point to the warehouse. Lesson: Point to point and hybrid
Hybrid cloud: A hybrid cloud connects private/on-premises resources with a public cloud so workloads and data can move between them. Lesson: Deployment models: public, private, hybrid
I
IaaS: IaaS (infrastructure): the provider gives you virtual machines, storage and networks; you manage the OS and up. Lesson: Service models: SaaS, PaaS, IaaS
ICMP: Also here: ICMP (ping, traceroute errors), fragmentation, and the IP TTL that drops looping packets. Lesson: Layer 3 - Network
IDF: An IDF (intermediate distribution frame) is a smaller closet closer to users, on each floor or wing, holding access switches and patch panels, with an uplink (often fiber) back to the MDF. Lesson: MDF and IDF locations
IDS (intrusion detection system): An IDS (intrusion detection system) watches a copy of traffic (from a SPAN/mirror port or tap) and alerts on attacks; it is out of band, so it cannot stop them. Lesson: IDS vs IPS
IEEE 802.1X: IEEE 802.1X is port-based NAC. Lesson: 802.1X
Ifconfig: ip (Linux: 'ip addr', 'ip route') replaces the older ifconfig. Lesson: ipconfig, ip, ifconfig and arp
IKE (Internet Key Exchange, UDP 500): IKE (Internet Key Exchange, UDP 500) authenticates the peers and negotiates keys, building the security associations. Lesson: IPsec: AH, ESP and IKE
Implicit deny: Rules are checked top to bottom; the first match wins, and an implicit deny at the end drops anything not permitted. Lesson: ACLs
Improper termination: Improper termination: wrong pin order (split or mixed-up pairs, or T568A on one end and T568B on the other of a straight-through run), too much untwisted wire, or a loose crimp. Lesson: Improper termination and TX/RX transposed
In-band: In-band management uses the same production network as user traffic: if the network breaks, you lose access. Lesson: In-band vs. out-of-band
Incorrect standard: Two classic problems: power budget exceeded (the switch's total PoE supply is used up) and incorrect standard (a PoE+ AP on an 802.3af-only port boots partially or not at all). Lesson: Power over Ethernet
Industrial control systems (ICS): Operational technology (OT) includes industrial control systems (ICS) and SCADA (supervisory control and data acquisition, which monitors and controls processes across sites). Lesson: OT is different
Infrastructure as code (IaC): With infrastructure as code (IaC) you describe network and cloud config in text files and let tools apply it, so every build is repeatable. Lesson: IaC and automation
Infrastructure mode: Infrastructure mode: clients connect through an AP. Lesson: Network types
Inline: An IPS (intrusion prevention system) sits inline, so it can block malicious traffic as it passes. Lesson: IDS vs IPS
Insufficient wireless coverage: Insufficient wireless coverage: areas with no usable signal at all, found with a site survey and heat map. Lesson: Signal degradation and coverage
Integrity: Integrity: data isn't changed without detection (hashes, signatures) Lesson: The CIA triad
Interesting octet: Find the interesting octet: the one where the mask is not 255 or 0. Lesson: The magic number (block size)
Interference: Interference (EMI): motors, fluorescent lights, power cables Lesson: Signal degradation
Internet gateway: An internet gateway connects a VPC to the internet in both directions; resources with public IPs in a public subnet use it. Lesson: Cloud gateways
IoT and IIoT: IoT and IIoT: cameras, thermostats, sensors; industrial IoT on factory floors. Lesson: Why segment
Ip addr: ip (Linux: 'ip addr', 'ip route') replaces the older ifconfig. Lesson: ipconfig, ip, ifconfig and arp
IP address: A router connects different networks and forwards packets by destination IP address (Layer 3) using its routing table. Lesson: Router
IP address management (IPAM): IP address management (IPAM) tracks your address space: which subnets exist, which addresses are used, reserved or free, and often ties into DHCP and DNS. Lesson: IPAM
Ip helper-address: A DHCP relay (Cisco: ip helper-address) on the router interface catches the broadcast and forwards it as unicast to the DHCP server in another subnet. Lesson: Relay / IP helper
IP TTL: IP TTL: a hop counter in every packet; each router subtracts 1, and at 0 the packet is dropped and an ICMP "time exceeded" is sent back. Lesson: Time to live (TTL)
Ipconfig: ipconfig (Windows; /all for MAC, DHCP, DNS; /release, /renew, /flushdns). Lesson: ipconfig, ip, ifconfig and arp
IPS (intrusion prevention system): An IPS (intrusion prevention system) sits inline, so it can block malicious traffic as it passes. Lesson: IDS vs IPS
IPsec: IPsec secures IP packets, usually for site-to-site VPNs. Lesson: IPsec: AH, ESP and IKE
IPv4 address: An IPv4 address is 32 bits, written as four 8-bit octets in dotted decimal. Lesson: Binary in 60 seconds
J
Jitter: Jitter: VARIATION in latency between packets. Lesson: Latency, packet loss, jitter
Jumbo frames: Jumbo frames (up to about 9000 bytes) cut overhead for storage (iSCSI), backups and VM migration. Lesson: MTU and jumbo frames
Jump box: A jump box is a hardened server that admins connect to first, then manage devices from there. Lesson: Jump box / jump host
K
Key management: Key management is the life of cryptographic keys: generate, store securely, distribute, rotate, revoke and destroy. Lesson: Key management
Kilometers: Single-mode fiber (SMF) has a tiny ~9 micron core, uses lasers, and runs kilometers (10 km, 40 km and more): campus and WAN links. Lesson: Single-mode vs multimode fiber
L
LACP: LACP (IEEE 802.3ad, now 802.1AX) negotiates the bundle. Lesson: Link aggregation
Latency: Latency: time for a packet to travel (ms). Lesson: Latency, packet loss, jitter
Layer 1: Layer 1: cables, ports, media, patch panels (the physical paths) Lesson: Network diagrams by layer
Layer 2: Layer 2: switches, VLANs, trunks, MAC-level links, spanning tree Lesson: Network diagrams by layer
Layer 2 encapsulation: It is Layer 2 encapsulation: original Ethernet frames are wrapped in UDP/IP (UDP port 4789) by VTEPs (tunnel endpoints) and routed anywhere. Lesson: VXLAN
Layer 3: Layer 3: routers, subnets, IP addresses, routing and gateways Lesson: Network diagrams by layer
LC (local connector): LC (local connector): small form factor, latch like RJ45, usually duplex pairs. Lesson: Fiber connectors
LDAP: LDAP (TCP 389; LDAPS 636) queries directory services such as Active Directory for users and groups. Lesson: SSO, LDAP, SAML
Leading zeros: Two rules to shorten it: (1) drop leading zeros in any group; (2) replace one run of consecutive all-zero groups with ::. Lesson: Reading and shortening IPv6
Leaf: Every leaf switch (top of rack, servers plug in) connects to every spine switch; leaves never connect to leaves and spines never to spines. Lesson: Spine and leaf
Lease time: The lease time is how long a client may keep an address; clients try to renew at 50% of the lease. Lesson: Scope, lease time, exclusions
Least privilege: Least privilege: give only the access needed for the job, nothing more. Lesson: Authorization: least privilege and RBAC
Least privilege access: Three ideas on the exam: policy-based authentication (identity plus context: device health, location, time, MFA, checked continuously), authorization for each request to each resource, and least privilege access… Lesson: Zero trust architecture (ZTA)
Licensing: Licensing: how many seats you own vs. Lesson: Asset inventory
Lightweight: A lightweight AP is managed by a wireless LAN controller (on site or in the cloud), usually via CAPWAP. Lesson: Autonomous vs lightweight APs
Link aggregation: Link aggregation bundles several physical links into one logical link (port channel / EtherChannel): more bandwidth and redundancy, and spanning tree sees it as one link so nothing gets blocked. Lesson: Link aggregation
Link-state: OSPF: open-standard link-state protocol. Lesson: Dynamic routing: OSPF, EIGRP, BGP
LLDP: LLDP (vendor-neutral, IEEE 802.1AB) and CDP (Cisco) let neighbors announce name, model, port and IP: great for mapping links without walking to the closet. Lesson: Where is that device?
Load balancer: A load balancer spreads client requests across a pool of servers behind one virtual address. Lesson: Load balancer
Localhost: Loopback is 127.0.0.0/8; 127.0.0.1 (name localhost) always means "this machine". Lesson: APIPA and loopback/localhost
Lockable: Network gear should be physically secured: lockable rack doors and side panels, locked closets with badge or key control, and logs of who entered. Lesson: Lockable racks and rooms
Locks: Locks (keys, badge readers, keypads, locked racks and cages) keep people away from switches and console ports. Lesson: Cameras and locks
Log aggregation: Devices write logs; log aggregation gathers them in one place. Lesson: Log aggregation: syslog collector
Logical address (IP): The network layer gives every host a logical address (IP) and moves packets between different networks. Lesson: Layer 3 - Network
Logical diagram: A logical diagram shows how traffic flows: subnets, VLANs, routing, which device is the default gateway. Lesson: Physical vs. logical diagrams
Longest prefix match: A router picks the route with the longest prefix match (most specific). Lesson: The routing table
Loopback: Loopback is 127.0.0.0/8; 127.0.0.1 (name localhost) always means "this machine". Lesson: APIPA and loopback/localhost
Loops: Redundant switch links create Layer 2 loops: broadcasts circle forever (broadcast storm) and MAC tables flap. Lesson: Spanning tree (STP)
Low Earth orbit (LEO): Low Earth orbit (LEO) constellations orbit a few hundred km up and give much lower latency (tens of ms). Lesson: Satellite
M
MAC address: A switch forwards frames inside one network by MAC address (Layer 2). Lesson: Switch
MAC addresses: The data link layer packages bits into frames and delivers them on the local network using MAC addresses (48-bit, burned into each NIC; the first half is the vendor OUI). Lesson: Layer 2 - Data link
MAC filtering: MAC filtering allows or blocks devices by MAC address on a switch or AP. Lesson: MAC filtering
MAC flooding: MAC flooding sends thousands of frames with fake source MACs until the table is full. Lesson: MAC flooding
Malware: Malware is malicious software: viruses, worms (self-spreading across the network), trojans, ransomware (encrypts data for ransom), spyware, botnets. Lesson: Malware
Management information base (MIB): The management information base (MIB) is the database of values an agent can report, like interface counters, CPU, temperature. Lesson: MIBs and OIDs
Management plane: Network devices have planes: the data (forwarding) plane moves packets, the control plane decides where they go (routing tables, STP), and the management plane is how admins configure them (SSH, SNMP, APIs). Lesson: Software-defined networking (SDN)
MDF: The MDF (main distribution frame) is the central wiring room: the ISP demarc, core switches, routers and the links out to every IDF. Lesson: MDF and IDF locations
Mean time between failures (MTBF): Mean time between failures (MTBF): average running time between failures of a repairable device. Lesson: MTTR and MTBF
Mean time to repair (MTTR): Mean time to repair (MTTR): average time to fix a failed component and return it to service. Lesson: MTTR and MTBF
Mesh: Mesh: APs link to each other wirelessly; only some need a cable. Lesson: Network types
Metric: (3) Metric: between routes from the same protocol, the lowest metric (OSPF cost, EIGRP composite) wins. Lesson: Route selection: prefix length, AD, metric
Mismatch: Mismatch: both ends must use compatible optics: same wavelength and type (e.g., 10GBASE-SR multimode vs. Lesson: Transceivers
MPO (multi-fiber push on): MPO (multi-fiber push on): one rectangular ferrule with 12 or 24 fibers; used for 40/100G and trunk cables. Lesson: Fiber connectors
MTU: The MTU (maximum transmission unit) is the largest payload a link carries in one frame: 1500 bytes by default on Ethernet. Lesson: MTU and jumbo frames
Multicast: Multicast: one to a group that joined (224.0.0.0/4 in IPv4, ff00::/8 in IPv6). Lesson: Unicast, broadcast, multicast, anycast
Multifactor authentication (MFA): Multifactor authentication (MFA) needs two or more DIFFERENT factor types: something you know (password), have (phone, token), are (fingerprint), plus somewhere you are. Lesson: Authentication factors and MFA
Multimode fiber (MMF): Multimode fiber (MMF) has a wider 50 or 62.5 micron core, cheaper optics (LED/VCSEL), and runs hundreds of meters: inside buildings and data centers. Lesson: Single-mode vs multimode fiber
Multitenancy: Multitenancy means many customers (tenants) share the same physical cloud hardware, kept separate by logical isolation. Lesson: Scalability, elasticity, multitenancy
MX: MX: mail server for the domain, with priority (lower = preferred) Lesson: Record types
N
N hosts: For N hosts, find the smallest h where 2^h - 2 is at least N; prefix = 32 - h. Lesson: Sizing: pick the prefix from the need
N subnets: For N subnets, find the smallest s where 2^s is at least N and add s to the starting prefix. Lesson: Sizing: pick the prefix from the need
NAS (network-attached storage): NAS (network-attached storage) is a storage device on the regular network that shares files using SMB or NFS. Lesson: NAS vs SAN
NAT: NAT translates IP addresses as packets cross a router or firewall, usually private (RFC1918) inside to public outside. Lesson: NAT and PAT
NAT gateway: A NAT gateway lets instances in a private subnet start connections out to the internet (to download patches, for example) while blocking connections started from the internet. Lesson: Cloud gateways
NAT64: NAT64: a translator lets IPv6-only clients reach IPv4-only servers, usually with DNS64 creating synthetic IPv6 answers. Lesson: Compatibility: dual stack, tunneling, NAT64
Native VLAN: Frames in the native VLAN cross the trunk untagged. Lesson: Access ports, trunks, 802.1Q and the native VLAN
Netstat: netstat shows a host's own connections and listening ports. Lesson: netstat
Network address: Two special addresses in every subnet: network address (all host bits 0) and broadcast address (all host bits 1). Lesson: Network part and host part
Network discovery: Network discovery finds what is connected: devices, IPs, open services, neighbors. Lesson: Network discovery
Network layer: The network layer gives every host a logical address (IP) and moves packets between different networks. Lesson: Layer 3 - Network
Network portion: Every address has a network portion (which network) and a host portion (which device). Lesson: Network part and host part
Network security groups: Network security groups attach to individual instances or their virtual NICs and define allowed inbound/outbound traffic (typically stateful: replies are allowed automatically). Lesson: Network security groups vs security lists
Network security lists: Network security lists (network ACLs on some clouds) apply to a whole subnet, so every instance in it inherits the rules. Lesson: Network security groups vs security lists
Next-generation firewall (NGFW): A next-generation firewall (NGFW) also identifies applications and users and can inspect content up to Layer 7. Lesson: Firewall
NFV: NFV replaces dedicated network hardware with software: virtual routers, firewalls, load balancers and WAN optimizers running as VMs. Lesson: NFV: network functions virtualization
Nmap: Nmap scans hosts and ports: which devices are up, which ports are open, which services and versions run. Lesson: Nmap
No encryption: GRE has no encryption, so it is often run inside IPsec (GRE over IPsec) when it crosses the internet. Lesson: GRE: the generic tunnel
Non-authoritative: A non-authoritative answer comes from some server's cache. Lesson: Who answers: authoritative, primary, secondary
Non-overlapping: In the US, the 2.4 GHz non-overlapping 20 MHz channels are 1, 6 and 11. Lesson: Channels, channel width and non-overlapping channels
Non-plenum: Non-plenum (PVC, CM/CMR riser) is cheaper and fine in walls, conduit and non-air spaces. Lesson: Plenum vs non-plenum cable
North-south: North-south traffic enters or leaves the data center: users or the internet talking to servers (crossing the edge firewall). Lesson: Traffic flows: north-south vs east-west
Not routed on the internet: Private addresses (RFC1918) can be used by anyone internally and are not routed on the internet; NAT translates them to a public address on the way out. Lesson: Public vs private (RFC1918)
Notifies: Once you know normal, set thresholds so the system raises an anomaly alert and notifies people (email, text, chat) when a metric goes far outside it, like the WAN link at 95% at 2 a.m. Lesson: Anomaly alerting and notification
NS: NS: which name servers are authoritative for the zone Lesson: Record types
Nslookup: nslookup (Windows, Linux, macOS) and dig (Linux/macOS) query DNS directly. Lesson: nslookup and dig
NTP: NTP (UDP 123) syncs clocks to within milliseconds using a hierarchy of strata (stratum 0 = atomic/GPS source, 1 = server attached to it). Lesson: NTP, PTP, NTS
NTS: NTS (Network Time Security) adds TLS-based authentication to NTP so clients can trust the time source. Lesson: NTP, PTP, NTS
O
Object identifier (OID): Each value has an object identifier (OID), a dotted number such as 1.3.6.1.2.1.2.2.1.10 (ifInOctets). Lesson: MIBs and OIDs
Octet: An IPv4 address is 32 bits, written as four 8-bit octets in dotted decimal. Lesson: Binary in 60 seconds
Omnidirectional: An omnidirectional antenna radiates in all directions horizontally, like a donut: right for ceiling APs covering a room or open area. Lesson: Antennas: omnidirectional vs directional
On-path attack: In an on-path attack (formerly man-in-the-middle), the attacker sits between two parties, reading or changing traffic. Lesson: On-path attack
Operating system (OS): Operating system (OS): the network OS image on switches, routers, firewalls Lesson: Software management
Operational technology (OT): Operational technology (OT) includes industrial control systems (ICS) and SCADA (supervisory control and data acquisition, which monitors and controls processes across sites). Lesson: OT is different
Options: Options are the extra settings handed out with the address. Lesson: DHCP options
OSI (Open Systems Interconnection) reference model: The OSI (Open Systems Interconnection) reference model splits network communication into 7 layers. Lesson: Seven layers, one trip
OSPF: OSPF: open-standard link-state protocol. Lesson: Dynamic routing: OSPF, EIGRP, BGP
Out-of-band (OOB): Out-of-band (OOB) uses a separate path: a dedicated management network, a console server, or a cellular modem attached to console ports. Lesson: In-band vs. out-of-band
P
PaaS: PaaS (platform): the provider also runs the OS and runtime; you deploy your code. Lesson: Service models: SaaS, PaaS, IaaS
Packet capture: Packet capture records full packets, headers and payload, with a protocol analyzer like Wireshark or tcpdump. Lesson: Packet capture
Packet loss: Packet loss: packets that never arrive (congestion, errors). Lesson: Latency, packet loss, jitter
Packets: The network layer gives every host a logical address (IP) and moves packets between different networks. Lesson: Layer 3 - Network
Partial mesh: A partial mesh links only the important sites redundantly. Lesson: Mesh
PAT: PAT (port address translation, "NAT overload"): many private hosts share one public IP, kept apart by unique source port numbers. Lesson: NAT and PAT
Patch panel: A patch panel is where horizontal copper runs from wall jacks terminate (punched down on the back). Lesson: Cabling: patch panels and fiber distribution panels
Path-vector: BGP: path-vector exterior protocol that routes between autonomous systems; the routing protocol of the internet. Lesson: Dynamic routing: OSPF, EIGRP, BGP
Payment Card Industry Data Security Standard (PCI DSS): The Payment Card Industry Data Security Standard (PCI DSS) applies to anyone who stores, processes or transmits card data. Lesson: PCI DSS
PDU: A PDU (power distribution unit) is the rack power strip that feeds each device; metered and switched PDUs show the load and can remotely power-cycle outlets. Lesson: UPS and PDU
Performance monitoring: Performance monitoring: latency, throughput, utilization, errors vs. Lesson: Five things to watch
Phishing: Phishing: fake emails or messages that trick users into clicking or giving credentials Lesson: Social engineering
Physical appliance: Every network function can come as a physical appliance (dedicated hardware in a rack) or a virtual appliance (the same software running as a VM or container on a hypervisor or in the cloud). Lesson: Physical vs virtual appliances
Physical diagram: A physical diagram shows where things really are: which closet, which rack, which cable runs to which jack. Lesson: Physical vs. logical diagrams
Physical layer: The physical layer moves raw bits as signals: voltage on copper, pulses of light in fiber, radio waves in Wi-Fi. Lesson: Layer 1 - Physical
Ping: ping sends ICMP echo requests: is it reachable, how fast, any loss? Lesson: ping and traceroute/tracert
Playbooks: Automation pieces on the exam: playbooks (ordered steps to run, e.g. Lesson: IaC and automation
Plenum: A plenum is a space used to move air for heating and cooling, such as above a drop ceiling used as a return air path or under a raised floor. Lesson: Plenum vs non-plenum cable
Plenum-rated: Plenum-rated cable (CMP) has a fire-retardant, low-smoke jacket and is required by fire code there. Lesson: Plenum vs non-plenum cable
PoE: PoE standards: 802.3af (PoE) 15.4 W per port, 802.3at (PoE+) 30 W, 802.3bt (PoE++) 60 W (Type 3) and 90 W (Type 4, often sold as '100 W'), measured at the switch. Lesson: Power over Ethernet
Point to point: Point to point is a direct link between exactly two endpoints: a leased line, a fiber between two buildings, a wireless bridge. Lesson: Point to point and hybrid
Policy-based authentication: Three ideas on the exam: policy-based authentication (identity plus context: device health, location, time, MFA, checked continuously), authorization for each request to each resource, and least privilege access… Lesson: Zero trust architecture (ZTA)
Polls: The manager polls agents on UDP 161. Lesson: How SNMP works
Port: A port is a 16-bit number (0-65535) that identifies a service on a host. Lesson: Ports 101
Port mirroring: Port mirroring (Cisco calls it SPAN) copies traffic from one or more ports or VLANs to a monitor port where your analyzer or IDS listens. Lesson: Port mirroring
Port numbers: The transport layer connects one application to another using port numbers and chops data into segments (TCP) or datagrams (UDP). Lesson: Layer 4 - Transport
Port security: Port security limits which and how many MAC addresses may use a switch port. Lesson: Port security
Port-side exhaust: Port-side intake pulls air in at the port side; port-side exhaust blows air out of the port side. Lesson: Airflow: port-side intake vs port-side exhaust
Port-side intake: Port-side intake pulls air in at the port side; port-side exhaust blows air out of the port side. Lesson: Airflow: port-side intake vs port-side exhaust
Potential effects: Plan the fix and its potential effects (will rebooting the core drop the stores?), get approval through change management if needed, then implement or escalate. Lesson: Steps 4-7 in practice
Power budget exceeded: Two classic problems: power budget exceeded (the switch's total PoE supply is used up) and incorrect standard (a PoE+ AP on an 802.3af-only port boots partially or not at all). Lesson: Power over Ethernet
Power load: Add up the power load of everything in the rack (watts) and keep it under the rating of the UPS, PDU and circuit, with headroom (a common rule is 80% of a circuit). Lesson: Power load and voltage
Prefix length: (1) Prefix length: the longest (most specific) match wins, always. Lesson: Route selection: prefix length, AD, metric
Presentation layer: The presentation layer makes data readable to the other side: character encoding (ASCII, Unicode), data formats (JPEG, MPEG), compression and encryption/decryption. Lesson: Layer 6 - Presentation
Preventive measures: Verify full system functionality, not just the one symptom, and add preventive measures. Lesson: Steps 4-7 in practice
Primary: The primary server holds the editable copy of the zone; secondary servers keep read-only copies via zone transfers for redundancy. Lesson: Who answers: authoritative, primary, secondary
Private: You choose its private IP range (for example 10.50.0.0/16), carve it into subnets, and decide which subnets are public (reachable via an internet gateway) and which are private (no direct inbound internet). Lesson: Virtual private cloud (VPC)
Private cloud: A private cloud is cloud-style infrastructure (self-service, automated) used by only one organization, on site or hosted. Lesson: Deployment models: public, private, hybrid
Probe: A toner puts a tone on a cable at one end; the probe picks it up so you can find the other end in a bundle or patch panel. Lesson: Toner (tone generator and probe)
Production configuration: Production configuration: what is running live right now Lesson: Configuration management
Protect: On a violation the port can shutdown (err-disabled), restrict (drop and log) or protect (drop silently). Lesson: Port security
Protocol: It must match the protocol: Ethernet optics for LAN switches, Fibre Channel (FC) optics for SAN switches and storage arrays. Lesson: Transceivers: protocol and form factor
Protocol analyzer: A protocol analyzer (Wireshark) decodes captured packets so you can see retransmissions, resets, slow handshakes and which app floods the link. Lesson: Protocol analyzer and tcpdump
Protocol number: Inside the IP header a protocol number says what is carried. Lesson: TCP vs UDP vs ICMP
Proxy: A proxy makes requests on behalf of someone else. Lesson: Proxy
PSK (Personal): PSK (Personal): everyone shares one passphrase. Lesson: Authentication: PSK vs Enterprise
PTP: PTP (Precision Time Protocol, IEEE 1588) uses hardware timestamps for sub-microsecond accuracy, used in finance, telecom and industrial systems. Lesson: NTP, PTP, NTS
PTR: PTR: IP address back to a name (reverse lookup) Lesson: Record types
Public: You choose its private IP range (for example 10.50.0.0/16), carve it into subnets, and decide which subnets are public (reachable via an internet gateway) and which are private (no direct inbound internet). Lesson: Virtual private cloud (VPC)
Public cloud: A public cloud is owned by a provider and shared by many customers over the internet; you pay for what you use. Lesson: Deployment models: public, private, hybrid
Public key infrastructure (PKI): In a public key infrastructure (PKI), a trusted certificate authority (CA) signs certificates, so browsers and devices trust them. Lesson: Certificates: PKI vs. self-signed
Q
QoS: QoS decides who goes first when a link is busy. Lesson: Quality of service (QoS)
QSFP: Form factors: SFP (1 Gbps), SFP+ (10), SFP28 (25), QSFP (quad: QSFP+ 40, QSFP28 100 Gbps). Lesson: Transceivers: protocol and form factor
Question the obvious: Question the obvious (is it plugged in? Lesson: Step 2: Establish a theory
R
Rack diagram: A rack diagram shows each device's position in the rack by rack unit (U), front and back, plus power. Lesson: Rack diagrams and cable maps
Rack unit (U): A rack diagram shows each device's position in the rack by rack unit (U), front and back, plus power. Lesson: Rack diagrams and cable maps
Rack units: Racks are measured in rack units: 1U = 1.75 inches (44.45 mm) of height. Lesson: Rack size
RADIUS: Enterprise uses 802.1X: each user or device authenticates with its own credentials or certificate through an EAP method, checked by a RADIUS server. Lesson: Authentication: PSK vs Enterprise
Recovery point objective (RPO): Recovery point objective (RPO): how much data you can afford to lose, measured in time. Lesson: RPO and RTO
Recovery time objective (RTO): Recovery time objective (RTO): how long until the service must be running again. Lesson: RPO and RTO
Recursive: Your PC asks a recursive resolver to do the full work: the resolver queries root, then TLD, then the authoritative server, caches the result and returns it. Lesson: Recursive lookups and the hosts file
Request: A request (service request or change request) describes what, why, risk, rollback plan and timing. Lesson: Change management
Request process tracking: Request process tracking keeps a record of every step. Lesson: Change management
Reservation: A reservation ties one address to one client's MAC address, so that device always gets the same IP from DHCP. Lesson: Reservations
Restrict: On a violation the port can shutdown (err-disabled), restrict (drop and log) or protect (drop silently). Lesson: Port security
Reusable tasks: "configure a new store switch"), templates (a config with variables like VLAN or hostname) and reusable tasks (small blocks such as "set NTP" used by many playbooks). Lesson: IaC and automation
Reverse proxy: A reverse proxy sits in front of servers: internet users talk to it, and it passes requests to internal servers (often with caching and TLS offload). Lesson: Proxy
Reverse zone: A reverse zone answers IP-to-name with PTR records, under in-addr.arpa for IPv4 (10.1.8.20 -> 20.8.1.10.in-addr.arpa) and ip6.arpa for IPv6. Lesson: Zones: forward and reverse
RG-6: RG-6 carries cable TV and cable-modem internet (DOCSIS) with F-type screw-on connectors. Lesson: Coaxial cable
RG-59: RG-59 is thinner, for short video runs. Lesson: Coaxial cable
Risk: Risk is the likelihood and impact of a threat exploiting a vulnerability. Lesson: Risk, threat, vulnerability, exploit
RJ11: RJ11: smaller, 6 positions with 2 or 4 wired; analog phone lines, DSL, alarm/fax lines. Lesson: Copper connectors
RJ45: RJ45: 8 pins (8P8C), twisted-pair Ethernet. Lesson: Copper connectors
Roaming misconfiguration: Roaming misconfiguration: clients should move between APs seamlessly. Lesson: Client disassociation and roaming
Rogue AP: A rogue AP is an unauthorized access point plugged into the network, opening a back door around the firewall. Lesson: Rogue devices and services
Rogue DHCP server: A rogue DHCP server hands out bad settings, such as itself as the gateway or DNS, sending traffic to the attacker or breaking connectivity. Lesson: Rogue devices and services
Role-based access control (RBAC): Role-based access control (RBAC): permissions attach to roles (Help Desk, Network Admin), and users get roles, which makes joiners, movers and leavers easy. Lesson: Authorization: least privilege and RBAC
Roles: Roles: root port (each non-root switch's best path to root), designated port (forwarding port on each segment), blocked ports (RSTP: alternate/backup) that stand by. Lesson: Port roles and states
Root bridge: Switches elect a root bridge (lowest bridge ID = priority, default 32768, then lowest MAC). Lesson: Spanning tree (STP)
Root port: Each switch picks a root port (best path to root); each segment gets a designated port; the rest are blocked, ready to take over if a link fails. Lesson: Spanning tree (STP)
Router: A router connects different networks and forwards packets by destination IP address (Layer 3) using its routing table. Lesson: Router
Router Advertisement (RA): The router sends a Router Advertisement (RA) with the /64 prefix; the host adds its own 64-bit interface ID (EUI-64 from its MAC, or a random value for privacy) and checks for duplicates with Duplicate Address Detection. Lesson: SLAAC
Runts: Runts: frames under 64 bytes, often collisions or duplex mismatch Lesson: Increasing interface counters
S
SaaS: SaaS (software): you just use the finished app in a browser; the provider runs everything. Lesson: Service models: SaaS, PaaS, IaaS
SAE: WPA3 replaces the PSK handshake with SAE (Simultaneous Authentication of Equals), which resists offline guessing and gives forward secrecy, makes Protected Management Frames mandatory, and offers a 192-bit Enterprise… Lesson: Encryption: WPA2 vs WPA3
SAML: SAML is an XML standard that passes authentication assertions from an identity provider (IdP) to web apps (service providers): common for web and cloud SSO. Lesson: SSO, LDAP, SAML
SAN (storage area network): A SAN (storage area network) is a dedicated high-speed network that gives servers block-level storage, using Fibre Channel or iSCSI. Lesson: NAS vs SAN
SASE: SASE (Secure Access Service Edge) combines SD-WAN networking with cloud-delivered security in one service at provider points of presence near users: secure web gateway (SWG), cloud access security broker (CASB), zero… Lesson: SASE and SSE
Satellite: Satellite internet reaches places with no cable or cell service. Lesson: Satellite
SC (subscriber connector): SC (subscriber connector): square, push-pull, snaps in. Lesson: Fiber connectors
SCADA: Operational technology (OT) includes industrial control systems (ICS) and SCADA (supervisory control and data acquisition, which monitors and controls processes across sites). Lesson: OT is different
SCADA, ICS, OT: SCADA, ICS, OT: systems that control physical processes (conveyors, HVAC, power). Lesson: Why segment
Scalability: Scalability is the ability to grow capacity to handle more load: scale up/vertical (a bigger VM) or scale out/horizontal (more VMs). Lesson: Scalability, elasticity, multitenancy
Scheduled: Run it ad hoc (on demand, like when you inherit a new site) or scheduled (nightly or weekly) to catch new and rogue devices. Lesson: Network discovery
Scope: A scope is the range of addresses a DHCP server hands out for one subnet, plus its settings. Lesson: Scope, lease time, exclusions
Screened subnet: A screened subnet (formerly DMZ) sits between them for public-facing servers like the web shop: reachable from the internet, but walled off from the internal network. Lesson: Zones and the screened subnet
SD-WAN: SD-WAN applies SDN ideas to the wide area network. Lesson: SD-WAN
SDN: SDN separates the control plane from the hardware and centralizes it in a controller. Lesson: Software-defined networking (SDN)
Secondary: The primary server holds the editable copy of the zone; secondary servers keep read-only copies via zone transfers for redundancy. Lesson: Who answers: authoritative, primary, secondary
Security half: SSE (Security Service Edge) is just the security half of SASE without the SD-WAN part. Lesson: SASE and SSE
Security information and event management (SIEM): A security information and event management (SIEM) system goes beyond collecting: it normalizes logs from firewalls, servers, switches and apps, correlates events across them, alerts on suspicious patterns, and keeps… Lesson: SIEM
Segmentation: Segmentation splits the network into zones (VLANs, subnets, firewalls, ACLs) so one compromised device can't reach everything. Lesson: Why segment
Segments: The transport layer connects one application to another using port numbers and chops data into segments (TCP) or datagrams (UDP). Lesson: Layer 4 - Transport
Self-signed: A self-signed certificate is signed by its own key: traffic is still encrypted, but clients warn because no trusted CA vouches for it. Lesson: Certificates: PKI vs. self-signed
Service-level agreement (SLA): A service-level agreement (SLA) is a contract that defines the service a provider must deliver: uptime (like 99.9%), response and repair times, and penalties if they miss. Lesson: SLA
Session layer: The session layer sets up, manages and tears down the conversation (session) between two applications. Lesson: Layer 5 - Session
Severity: Each message has a severity from 0 to 7. Lesson: Log aggregation: syslog collector
SFP: Form factors: SFP (1 Gbps), SFP+ (10), SFP28 (25), QSFP (quad: QSFP+ 40, QSFP28 100 Gbps). Lesson: Transceivers: protocol and form factor
Shoulder surfing: Shoulder surfing: watching someone type a password or PIN Lesson: Social engineering
Show arp: On network devices: show route (Cisco: show ip route) prints the routing table and default route; show arp (show ip arp) lists IP-to-MAC mappings the router has learned, so you can find who is using an address. Lesson: show route and show arp
Show config: show config (show running-config) shows the active config. Lesson: Where is that device?
Show interface: show interface gives status, speed/duplex, rates and error counters. Lesson: show interface and show power
Show mac-address-table: show mac-address-table shows which MAC is learned on which port and VLAN. Lesson: Where is that device?
Show power: show power (Cisco: show power inline) lists the PoE budget and per-port power. Lesson: show interface and show power
Show route: On network devices: show route (Cisco: show ip route) prints the routing table and default route; show arp (show ip arp) lists IP-to-MAC mappings the router has learned, so you can find who is using an address. Lesson: show route and show arp
Show vlan: show vlan lists VLANs and their access ports. Lesson: Where is that device?
Shutdown: On a violation the port can shutdown (err-disabled), restrict (drop and log) or protect (drop silently). Lesson: Port security
Signal strength: Signal strength: optics report transmit and receive power in dBm. Lesson: Transceivers
Simple Network Management Protocol (SNMP): Simple Network Management Protocol (SNMP) lets a manager (the monitoring server, NMS) read and sometimes set values on agents (switches, routers, printers, UPS). Lesson: How SNMP works
Single sign-on (SSO): Single sign-on (SSO): log in once, reach many apps. Lesson: SSO, LDAP, SAML
Single-mode fiber (SMF): Single-mode fiber (SMF) has a tiny ~9 micron core, uses lasers, and runs kilometers (10 km, 40 km and more): campus and WAN links. Lesson: Single-mode vs multimode fiber
Single-mode vs. multimode: **Single-mode vs. Lesson: Incorrect cable
Site-to-site: Site-to-site: two firewalls/routers connect whole offices (HQ to the stores), users never notice. Lesson: Virtual private network (VPN)
Site-to-site VPN: A site-to-site VPN links two networks over the internet through an encrypted tunnel, usually IPsec between firewalls or VPN concentrators at each site. Lesson: Site-to-site VPN
SNMPv2c: SNMPv2c uses community strings as simple shared passwords, sent in clear text. Lesson: Versions, community strings, authentication
SNMPv3: SNMPv3 adds real authentication (users and hashing) and encryption, so it is the secure choice. Lesson: Versions, community strings, authentication
Software: Software: what runs where, including versions Lesson: Asset inventory
Source control: IaC files live in source control (such as Git). Lesson: Source control
Spanning tree: Spanning tree (802.1D; Rapid STP 802.1w) blocks redundant paths. Lesson: Spanning tree (STP)
Spanning Tree Protocol (STP, 802.1D): Spanning Tree Protocol (STP, 802.1D) prevents loops by blocking redundant paths. Lesson: Network loops
Speed: Each port has a speed (10/100/1000/10G) and duplex: full duplex sends and receives at once; half duplex takes turns and can collide. Lesson: Speed and duplex
Speed tester: A speed tester measures throughput, latency and sometimes jitter to a test server. Lesson: Bandwidth vs. throughput
Spine: Every leaf switch (top of rack, servers plug in) connects to every spine switch; leaves never connect to leaves and spines never to spines. Lesson: Spine and leaf
Spine and leaf: Modern data centers use spine and leaf. Lesson: Spine and leaf
Split tunnel: Split tunnel sends only company traffic through the tunnel; full tunnel sends everything. Lesson: Virtual private network (VPN)
SSE: SSE (Security Service Edge) is just the security half of SASE without the SD-WAN part. Lesson: SASE and SSE
SSH: SSH (TCP 22): encrypted command line. Lesson: Connection methods
SSID: The SSID is the network name users see ("Kibble-Staff"). Lesson: SSID, BSSID and ESSID
ST (straight tip): ST (straight tip): round bayonet, push and twist. Lesson: Fiber connectors
Star: In a star every device connects to one central device (a switch). Lesson: Star / hub and spoke
Stateful: A basic firewall filters on IP addresses, protocol and ports (Layers 3-4) and is usually stateful: it remembers sessions so return traffic is allowed automatically. Lesson: Firewall
Stateless address autoconfiguration (SLAAC): Stateless address autoconfiguration (SLAAC) lets an IPv6 host build its own address. Lesson: SLAAC
Static NAT: Static NAT: one private to one public, permanent; used to publish a server. Lesson: NAT and PAT
Static route: A static route is typed in by an admin: "to reach network X, send to next hop Y." It uses no CPU or bandwidth for updates, is predictable and secure, but does not react to failures and does not scale. Lesson: Static routing
STP vs. UTP: **STP vs. Lesson: Incorrect cable
Strata: NTP (UDP 123) syncs clocks to within milliseconds using a hierarchy of strata (stratum 0 = atomic/GPS source, 1 = server attached to it). Lesson: NTP, PTP, NTS
Subinterface: A subinterface is a logical interface carved out of one physical interface. Lesson: Subinterfaces (router on a stick)
Subnet: Network security lists (network ACLs on some clouds) apply to a whole subnet, so every instance in it inherits the rules. Lesson: Network security groups vs security lists
Subnet mask: The subnet mask shows the split: 1 bits = network, 0 bits = host. Lesson: Network part and host part
Supernet: CIDR also works the other way: combining contiguous networks into one shorter prefix (a supernet or summary route) so routers carry fewer routes. Lesson: CIDR summarization
Supplicant: Three roles: the supplicant (client), the authenticator (switch or AP) and the authentication server (usually RADIUS). Lesson: 802.1X
Suspended: Suspended: a port-channel (LACP) member whose settings don't match the bundle is held out of it Lesson: Port status
SVI: An SVI is a virtual Layer 3 interface for a VLAN on a switch ("interface vlan 30"). Lesson: Switch virtual interface (SVI)
Switch: A switch forwards frames inside one network by MAC address (Layer 2). Lesson: Switch
Switch spoofing: Two methods: switch spoofing (the attacker's device negotiates a trunk using DTP) and double tagging (two 802.1Q tags; the first switch strips the outer native-VLAN tag and forwards the inner one). Lesson: VLAN hopping
Syslog collector: A syslog collector receives syslog messages (usually UDP 514) from many devices. Lesson: Log aggregation: syslog collector
T
Tabletop exercise: Tabletop exercise: the team walks through a scenario around a table, talking through who does what, with no systems touched. Lesson: Testing the plan
TACACS+: TACACS+ (TCP 49, Cisco-made) separates authentication, authorization and accounting and encrypts the whole payload; it is the favorite for logging admins into network devices with per-command control. Lesson: RADIUS vs. TACACS+
Tailgating: Tailgating: following an authorized person through a secure door Lesson: Social engineering
Tap: A network tap is a hardware device inserted in a link that copies all traffic to a monitor port, including errors, without the drops a busy mirror port can have. Lesson: Visual fault locator and taps
TCP: TCP is connection-oriented and reliable: three-way handshake (SYN, SYN-ACK, ACK), sequence numbers, acknowledgments, retransmissions and windowing for flow control. Lesson: Layer 4 - Transport
Tcpdump: tcpdump is the command-line capture tool on Linux and network appliances; save with -w and open the file in an analyzer. Lesson: Protocol analyzer and tcpdump
Temperature: Temperature: keep intake air cool and steady; ASHRAE recommends about 18-27 C (64-81 F); watch hot spots. Lesson: Environmental factors
Templates: "configure a new store switch"), templates (a config with variables like VLAN or hostname) and reusable tasks (small blocks such as "set NTP" used by many playbooks). Lesson: IaC and automation
Threat: A threat is something that could exploit it (an attacker, malware, a flood). Lesson: Risk, threat, vulnerability, exploit
Throughput: Throughput is what you actually get through it, after overhead, errors and contention. Lesson: Bandwidth vs. throughput
Time-based authentication: Time-based authentication typically means a TOTP code that changes every 30 seconds; access can also be limited to certain hours. Lesson: Authentication factors and MFA
Toner: A toner puts a tone on a cable at one end; the probe picks it up so you can find the other end in a bundle or patch panel. Lesson: Toner (tone generator and probe)
Top-down: Top-down: start at the app when the network looks fine. Lesson: Troubleshooting by layer
Top-to-bottom: Then consider multiple approaches: work through the OSI model top-to-bottom or bottom-to-top, or divide and conquer (start in the middle, like pinging the gateway, and move up or down based on the result). Lesson: Step 2: Establish a theory
TOTP: Time-based authentication typically means a TOTP code that changes every 30 seconds; access can also be limited to certain hours. Lesson: Authentication factors and MFA
TPC: 802.11h adds DFS (dynamic frequency selection: the AP listens for radar and moves off the channel) and TPC (transmit power control: lowers power to the minimum needed). Lesson: Regulatory impacts: 802.11h
Traceroute: tracert (Windows) / traceroute (Linux/macOS) lists each router hop to a destination, showing where the path stops or slows. Lesson: ping and traceroute/tracert
Tracert: tracert (Windows) / traceroute (Linux/macOS) lists each router hop to a destination, showing where the path stops or slows. Lesson: ping and traceroute/tracert
Traffic analysis: Traffic analysis: what protocols and hosts use the bandwidth (flows, captures) Lesson: Five things to watch
Transceiver: A transceiver (optic) plugs into a switch port and converts electrical signals to light or copper signals. Lesson: Transceivers: protocol and form factor
Transport: Modes: tunnel (whole packet wrapped, site-to-site) and transport (payload only, host-to-host). Lesson: IPsec: AH, ESP and IKE
Transport agnostic: Transport agnostic: it does not care if the link is MPLS, cable broadband, fiber or LTE/5G. Lesson: SD-WAN: transport and policy
Transport layer: The transport layer connects one application to another using port numbers and chops data into segments (TCP) or datagrams (UDP). Lesson: Layer 4 - Transport
Traps: Agents send unrequested alerts called traps to the manager on UDP 162. Lesson: How SNMP works
Trunk: A trunk carries many VLANs between switches (or to a router or AP). Lesson: Access ports, trunks, 802.1Q and the native VLAN
Trusted: Trusted zones are internal networks you control; untrusted is the internet. Lesson: Zones and the screened subnet
TTL: Also here: ICMP (ping, traceroute errors), fragmentation, and the IP TTL that drops looping packets. Lesson: Layer 3 - Network
Tunnel: Modes: tunnel (whole packet wrapped, site-to-site) and transport (payload only, host-to-host). Lesson: IPsec: AH, ESP and IKE
Tunneling: Tunneling: carry IPv6 packets inside IPv4 packets across an IPv4-only network (6to4, Teredo, GRE tunnels). Lesson: Compatibility: dual stack, tunneling, NAT64
Twinaxial: A direct attach copper (DAC) cable is a short twinaxial copper cable with transceiver ends (SFP+, SFP28, QSFP) molded on. Lesson: DAC and twinaxial cable
Two-tier: It is a two-tier design: access plus a combined core/distribution. Lesson: Collapsed core
TX/RX transposed: TX/RX transposed: the transmit and receive sides are swapped, common with fiber patch cords. Lesson: Improper termination and TX/RX transposed
TXT: TXT: free text, used for SPF, DKIM, domain verification Lesson: Record types
U
UDP: UDP is connectionless: no handshake, no retransmits, very low overhead. Lesson: Layer 4 - Transport
UDP 161: The manager polls agents on UDP 161. Lesson: How SNMP works
UDP 162: Agents send unrequested alerts called traps to the manager on UDP 162. Lesson: How SNMP works
UDP 514: A syslog collector receives syslog messages (usually UDP 514) from many devices. Lesson: Log aggregation: syslog collector
Unicast: Unicast: one sender to one receiver. Lesson: Unicast, broadcast, multicast, anycast
Untagged: Frames in the native VLAN cross the trunk untagged. Lesson: Access ports, trunks, 802.1Q and the native VLAN
Untrusted: Trusted zones are internal networks you control; untrusted is the internet. Lesson: Zones and the screened subnet
Upgrades: Upgrades: firmware rolled out to devices in automated, staged batches. Lesson: Drift, compliance, upgrades, dynamic inventories
UPS: A UPS (uninterruptible power supply) keeps equipment running from batteries during an outage or sag, long enough for a generator to start or for a clean shutdown. Lesson: UPS and PDU
URL filtering: URL filtering allows or blocks web access by address or category (gambling, malware sites). Lesson: URL and content filtering
Usable hosts: Usable hosts per subnet = 2^h - 2: subtract the network address (host bits all 0) and the broadcast address (host bits all 1). Lesson: Hosts = 2^h - 2
V
Validation test: Validation test: actually perform steps, such as restoring backups or failing over to the DR site, to prove the plan works and meets RTO/RPO. Lesson: Testing the plan
Version control: Version control keeps every change: who, what, when, and rollback to any version. Lesson: Source control
Virtual appliance: Every network function can come as a physical appliance (dedicated hardware in a rack) or a virtual appliance (the same software running as a VM or container on a hypervisor or in the cloud). Lesson: Physical vs virtual appliances
Virtual IP (VIP): A First Hop Redundancy Protocol (FHRP) lets two or more routers share a virtual IP (VIP) and virtual MAC. Lesson: FHRP and the virtual IP
Visual fault locator (VFL): A visual fault locator (VFL) shines bright red laser light into fiber; breaks, tight bends and bad connectors glow where light leaks out. Lesson: Visual fault locator and taps
VLAN: A VLAN splits one physical switch into separate logical networks; each VLAN is its own broadcast domain and IP subnet. Lesson: VLANs and the VLAN database
VLAN database: The switch keeps VLAN IDs and names in its VLAN database (vlan.dat on Cisco); a port cannot carry a VLAN that does not exist there. Lesson: VLANs and the VLAN database
VLAN hopping: VLAN hopping lets an attacker reach a VLAN they shouldn't. Lesson: VLAN hopping
VLSM: VLSM (variable length subnet masking) lets you use different prefix lengths inside one address block, so each subnet is only as big as it needs to be. Lesson: What VLSM means
Voice VLAN: A voice VLAN lets one access port carry two VLANs: the phone tags its voice traffic with the voice VLAN (learned via CDP/LLDP), and the PC plugged into the phone sends untagged data VLAN traffic. Lesson: Voice VLAN
Voltage: Check voltage: US offices use 120 V; data centers often use 208 V or 230 V, which needs matching PDUs, plugs and power supplies. Lesson: Power load and voltage
VPC: A VPC is your own logically isolated network inside a public cloud. Lesson: Virtual private cloud (VPC)
VPN: A VPN builds an encrypted tunnel across an untrusted network such as the internet. Lesson: Virtual private network (VPN)
VRRP: Protocols: HSRP (Cisco), VRRP (open standard), GLBP (Cisco, also load-balances). Lesson: FHRP and the virtual IP
Vulnerability: A vulnerability is a weakness (unpatched firmware). Lesson: Risk, threat, vulnerability, exploit
VXLAN: VXLAN (Virtual Extensible LAN) stretches Layer 2 segments across a Layer 3 network. Lesson: VXLAN
W
Warm site: Warm site: hardware and connectivity in place, data needs restoring from backup. Lesson: Cold, warm, hot sites
Warranty support: Warranty support: coverage end dates and support contracts Lesson: Asset inventory
Well-known ports: Well-known ports are 0-1023, registered 1024-49151, and dynamic/ephemeral 49152-65535 (the random source port your PC picks). Lesson: Ports 101
Wi-Fi analyzer: A Wi-Fi analyzer shows nearby SSIDs/BSSIDs, channels, signal strength (RSSI), noise and channel use. Lesson: Wi-Fi analyzer
Wireless LAN controller: A lightweight AP is managed by a wireless LAN controller (on site or in the cloud), usually via CAPWAP. Lesson: Autonomous vs lightweight APs
Wireless LAN controller (WLC): A wireless LAN controller (WLC) centrally manages many APs: one place for SSIDs, security, channel and power plans, firmware and roaming. Lesson: Wireless: access points and controllers
Wireless site survey: A wireless site survey measures real signal strength, noise and interference around a building. Lesson: Wireless survey and heat map
WPA2: WPA2 uses AES (CCMP) encryption. Lesson: Encryption: WPA2 vs WPA3
WPA3: WPA3 replaces the PSK handshake with SAE (Simultaneous Authentication of Equals), which resists offline guessing and gives forward secrecy, makes Protected Management Frames mandatory, and offers a 192-bit Enterprise… Lesson: Encryption: WPA2 vs WPA3
Z
Zero trust (ZTA): Zero trust (ZTA): never trust, always verify, no matter where the request comes from. Lesson: Zero trust architecture (ZTA)
Zero-touch provisioning: Zero-touch provisioning: ship the box to the store, plug it in, it calls home and downloads its config. Lesson: SD-WAN
Zone transfers: The primary server holds the editable copy of the zone; secondary servers keep read-only copies via zone transfers for redundancy. Lesson: Who answers: authoritative, primary, secondary
Zones: Firewalls group interfaces into zones. Lesson: Zones and the screened subnet

Acronyms

Acronym	Stands for	What it means
A	Address (DNS record)	DNS record that maps a host name to an IPv4 address.
AAA	Authentication, Authorization, and Accounting	The security trio: prove who you are, decide what you may do, and log what you did.
AAAA	IPv6 Address (DNS record)	DNS record that maps a host name to an IPv6 address.
ACK	Acknowledgment	A TCP flag (and packet) that confirms data or a connection request was received.
ACL	Access Control List	An ordered list of allow and deny rules on a router, firewall or file, checked from the top down.
AD	Administrative Distance	How much a router trusts a source of routes. When two sources know the same route, the lower number wins.
ADSL	Asymmetric Digital Subscriber Line	DSL with faster download than upload, over phone lines.
AES	Advanced Encryption Standard	The standard symmetric cipher today: one shared key (128, 192 or 256 bits) encrypts and decrypts data in 128-bit blocks.
AH	Authentication Header	IPsec protocol that proves packets are authentic and unchanged but does not encrypt them.
AP	Access Point	A device that connects wireless clients to the wired network.
API	Application Programming Interface	A defined way for one program to ask another for data or actions, such as web requests that return JSON.
APIPA	Automatic Private Internet Protocol Addressing	A self-assigned 169.254.x.x address a device gives itself when no DHCP server answers. Seeing one means DHCP failed.
APU	Audio Processing Unit	A processor that handles sound. (AMD also says APU for a CPU with graphics built in.)
ARP	Address Resolution Protocol	Finds the MAC address that goes with an IPv4 address on the local network. Fake replies enable ARP poisoning.
AS	Autonomous System	A network run by one organization with one routing policy, known on the internet by its AS number in BGP.
ASCII	American Standard Code for Information Interchange	An old standard that maps 128 letters, digits and symbols to numbers.
ASHRAE	American Society of Heating, Refrigerating and Air-Conditioning Engineers	The engineering group whose guidelines set safe temperature and humidity ranges for data centers.
AUP	Acceptable Use Policy	The rules users agree to about what they may and may not do on company devices and networks.
AXFR	Full Zone Transfer	A DNS request that copies a whole zone from the primary server to a secondary. Lock it down to stop data leaks.
BCP	Business Continuity Planning	Planning that keeps the business's critical work going during and after a disruption.
BGP	Border Gateway Protocol	The routing protocol between autonomous systems that ties the internet together.
BLE	Bluetooth Low Energy	A low-power Bluetooth mode for sensors, beacons and wearables.
BNC	Bayonet Neill-Concelman	A twist-lock bayonet connector for coaxial cable.
BPDU	Bridge Protocol Data Unit	The messages switches trade for Spanning Tree. BPDU guard shuts an edge port that suddenly receives them.
BSS	Basic Service Set	One access point and the wireless clients joined to it.
BSSID	Basic Service Set Identifier	The MAC address of an access point's radio, identifying one cell (BSS) of a wireless network.
BYOD	Bring Your Own Device	Staff use their own phones and laptops for work, under company security rules.
CA	Certificate Authority	A trusted organization that checks identities and signs digital certificates.
CAM	Content-addressable Memory	The fast lookup table a switch keeps of which MAC address lives on which port.
CAPWAP	Control and Provisioning of Wireless Access Points	The protocol lightweight access points use to tunnel to and be run by a wireless LAN controller.
CASB	Cloud Access Security Broker	Sits between users and cloud apps to see which cloud services are used and enforce security policy on them.
CCMP	Counter Mode with Cipher Block Chaining Message Authentication Code Protocol	The AES-based encryption and integrity protocol used by WPA2.
CCTV	Closed-circuit Television	Video cameras that record to a private system for watching and evidence.
CDN	Content Delivery Network	Servers spread around the world that cache a site's content close to users for speed and to soak up DDoS traffic.
CDP	Cisco Discovery Protocol	Cisco's protocol that lets directly connected Cisco devices learn each other's name, model, port and address.
CERT	Computer Emergency Response Team	A team that handles computer security incidents for an organization or a country.
CIA	Confidentiality, Integrity, and Availability	The three goals of security: keep data secret (confidentiality), correct (integrity) and reachable (availability).
CIDR	Classless Inter-domain Routing	Writes a network as an address plus a prefix length, like 192.168.1.0/24, instead of fixed classes.
CLI	Command-line Interface	A text screen where you type commands instead of clicking.
CMDB	Configuration Management Database	A database of IT assets and how they connect, used to plan changes and solve incidents.
CNAME	Canonical Name	DNS record that makes one name an alias of another name.
CoS	Class of Service	A 3-bit priority value in a VLAN (802.1Q) tag that lets switches favor some frames, such as voice.
CPU	Central Processing Unit	The main processor chip that runs program instructions.
CRC	Cyclic Redundancy Check	A checksum in each frame that catches corruption; rising CRC errors usually mean bad cabling or interference.
CSF	Cybersecurity Framework	NIST's framework for managing security risk in core functions: govern, identify, protect, detect, respond, recover.
CSMA/CA	Carrier Sense Multiple Access with Collision Avoidance	Wi-Fi's way of sharing the air: listen first, then wait a random time before sending to avoid collisions.
CSMA/CD	Carrier Sense Multiple Access with Collision Detection	How old half-duplex Ethernet shared a cable: listen, send, detect a collision, back off and retry.
CVE	Common Vulnerabilities and Exposures	A public list that gives each known vulnerability an ID, like CVE-2021-44228 (Log4Shell).
DAC	Direct Attach Copper	A short twinax copper cable with SFP-style ends built on: a cheap way to link switches and servers in the same rack.
DAI	Dynamic ARP Inspection	A switch feature that drops ARP replies that don't match the DHCP snooping table, stopping ARP poisoning.
DAS	Direct-attached Storage	Storage plugged straight into one server (inside it or by cable), not shared over the network.
DCI	Data Center Interconnect	High-speed links that join two or more data centers so they can work as one.
DDoS	Distributed Denial-of-service	Floods a target from many machines at once (often a botnet) so real users can't reach it.
DF	Don't Fragment	An IPv4 header flag that tells routers not to split the packet; too-big packets are dropped instead.
DFS	Dynamic Frequency Selection	5 GHz Wi-Fi rule: access points listen for radar and move off a channel when they hear it.
DHCP	Dynamic Host Configuration Protocol	Hands devices an IP address, subnet mask, gateway and DNS server automatically (Discover, Offer, Request, Acknowledge).
DHCPv4	Dynamic Host Configuration Protocol for IPv4	Hands devices an IPv4 address, mask, gateway and DNS server automatically.
DHCPv6	Dynamic Host Configuration Protocol for IPv6	Hands out IPv6 addresses and settings from a server, instead of or alongside SLAAC.
DKIM	DomainKeys Identified Mail	Signs outgoing email so receiving servers can check, with a key in DNS, that it came from the domain unchanged.
DLP	Data Loss Prevention	Tools that find sensitive data and stop it leaving by email, upload, USB or print.
DMARC	Domain-based Message Authentication, Reporting, and Conformance	A DNS policy telling receivers what to do with mail that fails SPF and DKIM checks, and where to send reports.
DMZ	Demilitarized Zone	A separate network zone for public-facing servers, between the internet and the internal network. Also called a screened subnet.
DNS	Domain Name System	The internet's phone book: it turns names like example.com into IP addresses.
DNS64	DNS for IPv6-to-IPv4 translation	Makes up IPv6 addresses for IPv4-only sites so IPv6-only clients can reach them through NAT64.
DNSKEY	DNS Key record	DNSSEC record that holds a zone's public signing key.
DNSSEC	Domain Name System Security Extensions	Adds digital signatures to DNS answers so resolvers can tell they are genuine. It does not encrypt them.
DOCSIS	Data Over Cable Service Interface Specification	The standard that carries internet over cable TV coax to a cable modem.
DoH	DNS over Hypertext Transfer Protocol Secure	DNS lookups sent inside encrypted HTTPS on port 443, so they blend in with web traffic.
DORA	Discover, Offer, Request, Acknowledge	The four DHCP steps a client and server go through to hand out an IP address.
DoS	Denial-of-service	An attack that overloads or crashes a service so legitimate users can't use it.
DoT	DNS over Transport Layer Security	DNS lookups encrypted with TLS on their own port, 853.
DP	DisplayPort	A digital video connector for monitors; it can daisy-chain screens and runs over USB-C (Alt Mode).
DR	Disaster Recovery	Getting IT systems and data back after a disaster such as a fire, flood or ransomware.
DS	Delegation Signer	DNSSEC record in a parent zone that vouches for the child zone's signing key, linking the chain of trust.
DSCP	Differentiated Services Code Point	Six bits in the IP header that mark a packet's QoS class, such as EF for voice.
DSL	Digital Subscriber Line	Internet service carried over ordinary telephone lines.
DSS	Data Security Standard	The rules part of PCI DSS: the security requirements for businesses that handle payment cards.
DTP	Dynamic Trunking Protocol	Cisco protocol that lets ports negotiate trunking on their own. Turn it off to block VLAN hopping.
DUAL	Diffusing Update Algorithm	How EIGRP finds loop-free best routes and keeps a ready backup (feasible successor).
EAP	Extensible Authentication Protocol	A framework of login methods (EAP-TLS, PEAP and others) used with 802.1X on Wi-Fi and wired ports.
EAP-TLS	Extensible Authentication Protocol-Transport Layer Security	An EAP method where both the client and the server prove themselves with certificates. The strongest common choice.
EAPoL	Extensible Authentication Protocol over LAN	Carries EAP login messages between a device and the switch or access point during 802.1X, before the port opens.
EIGRP	Enhanced Interior Gateway Routing Protocol	Cisco's advanced distance-vector routing protocol, fast to converge, with backup (feasible successor) routes.
EMI	Electromagnetic Interference	Electrical noise from motors, lights or power cables that corrupts signals on nearby copper cable.
EOL	End-of-life	The vendor stops making or selling a product; patches and support end soon after.
EOS	End-of-support	The vendor no longer supports the product: no more patches or fixes.
ESD	Electrostatic Discharge	A static electricity spark that can kill parts. Use an anti-static wrist strap and mat.
ESP	Encapsulating Security Payload	IPsec protocol that encrypts packets and also checks that they are authentic and unchanged.
ESS	Extended Service Set	Several access points with the same network name and settings, so clients can roam between them.
ESSID	Extended Service Set Identifier	The network name shared by several access points so clients can roam between them.
EUI-64	Extended Unique Identifier (64-bit)	Builds a 64-bit IPv6 interface ID from a MAC address: split it, insert FFFE in the middle, flip the 7th bit.
EULA	End-user License Agreement	The license terms you accept to use software: how many devices, and what you may and may not do.
FC	Fibre Channel	A fast, dedicated networking technology for storage area networks (SANs).
FCS	Frame Check Sequence	The 4-byte checksum at the end of an Ethernet frame; a mismatch means the frame was damaged.
FHRP	First Hop Redundancy Protocol	Lets two or more routers share one virtual gateway address so hosts keep working if one fails (HSRP, VRRP, GLBP).
FQDN	Fully Qualified Domain Name	A complete name with host and domain, like www.example.com.
FTP	File Transfer Protocol	Transfers files on ports 20 and 21 with no encryption; logins travel in clear text.
FTPS	File Transfer Protocol Secure	FTP with TLS encryption added. Not the same thing as SFTP.
GBIC	Gigabit Interface Converter	An older, larger hot-swappable 1 Gb transceiver module, replaced by SFP.
GCMP	Galois/Counter Mode Protocol	The AES-GCM based encryption protocol used by WPA3 (and Wi-Fi 6 and later).
GDPR	General Data Protection Regulation	The EU law that protects the personal data of people in the EU, with heavy fines for breaking it.
GEO	Geostationary Orbit	Satellites about 35,786 km up that stay over one spot; the distance gives high latency.
GLBP	Gateway Load Balancing Protocol	Cisco gateway redundancy that also shares the load across several routers.
GPS	Global Positioning System	Satellite system that tells a device where it is; used for maps, tracking and finding lost phones.
GRE	Generic Routing Encapsulation	Wraps one packet inside another to make a tunnel. It does not encrypt on its own.
GUI	Graphical User Interface	Windows, icons and menus you click, instead of typed commands.
HA	High Availability	A design with spare parts and automatic failover so a service stays up when something breaks.
HIPAA	Health Insurance Portability and Accountability Act	The US law that protects patients' health information (PHI).
HR	Human Resources	The department that hires people, onboards and offboards them, and keeps staff records.
HSM	Hardware Security Module	A tamper-resistant hardware device that creates, stores and uses crypto keys so they never leave it.
HSRP	Hot Standby Router Protocol	Cisco gateway redundancy: an active and a standby router share one virtual IP address.
HTTP	Hypertext Transfer Protocol	The protocol for web pages, port 80. Not encrypted.
HTTPS	Hypertext Transfer Protocol Secure	HTTP encrypted with TLS, port 443: the padlock in the browser.
HVAC	Heating, Ventilation, and Air Conditioning	Heating, cooling and airflow; keeps server rooms in a safe temperature and humidity range.
IaaS	Infrastructure as a Service	Rent virtual servers, storage and networks from a cloud; you still manage the OS and everything above it.
IaC	Infrastructure as Code	Defining servers, networks and settings in code files so they are built the same way every time.
IAM	Identity and Access Management	Managing who people are and what they can access: accounts, logins, roles and permissions.
iBGP	Internal Border Gateway Protocol	BGP running between routers inside the same autonomous system.
IBSS	Independent Basic Service Set	An ad hoc Wi-Fi network: devices talk directly with no access point.
ICMP	Internet Control Message Protocol	Carries network errors and tests, such as ping (echo) and the messages traceroute relies on.
ICS	Industrial Control System	Computers that run physical processes in factories, utilities and pipelines.
ID	Identifier	A name or number that identifies something, like a user ID or badge ID.
IDF	Intermediate Distribution Frame	A wiring closet on a floor or wing that links desks to the main distribution frame (MDF).
IdP	Identity Provider	The service that checks your login and vouches for you to other apps, for single sign-on.
IDS	Intrusion Detection System	Watches traffic or activity for attacks and raises alerts, but does not block.
IEEE	Institute of Electrical and Electronics Engineers	The body that writes networking standards such as 802.3 (Ethernet) and 802.11 (Wi-Fi).
IETF	Internet Engineering Task Force	The group that develops internet standards and publishes them as RFCs.
IGMP	Internet Group Management Protocol	How hosts tell routers which multicast groups they want to join.
IGP	Interior Gateway Protocol	A routing protocol used inside one organization's network, such as OSPF or EIGRP.
IIoT	Industrial Internet of Things	Internet-connected sensors and machines in factories, utilities and other industry.
IIS	Internet Information Services	Microsoft's web server for Windows.
IKE	Internet Key Exchange	Sets up IPsec: the two ends authenticate and agree on keys (UDP port 500).
IMAP	Internet Message Access Protocol	Reads email while keeping it on the server, synced across devices. Port 143, or 993 with TLS.
IOS	Internetwork Operating System	The operating system on Cisco routers and switches (not Apple's iOS).
IoT	Internet of Things	Everyday devices with network connections, such as cameras, thermostats and smart speakers.
IP	Internet Protocol	The protocol that addresses and routes packets between networks.
IPAM	Internet Protocol Address Management	A tool that tracks which IP addresses and subnets are used, free and assigned to what.
IPFIX	IP Flow Information Export	The standard version of NetFlow: summaries of who talked to whom, how much and when.
IPS	Intrusion Prevention System	Sits in the traffic path, spots attacks and blocks them.
IPSec	Internet Protocol Security	A suite that encrypts and authenticates IP packets, used for VPNs (AH, ESP, and IKE to set up keys).
IPTV	Internet Protocol Television	TV channels delivered over an IP network, often with multicast.
IPv4	Internet Protocol version 4	The original internet address: 32 bits, written like 192.168.1.10.
IPv6	Internet Protocol version 6	The newer internet address: 128 bits, written in hex like 2001:db8::1.
IS-IS	Intermediate System to Intermediate System	A link-state routing protocol like OSPF, popular with large service providers.
iSCSI	Internet Small Computer Systems Interface	Sends SCSI storage commands over IP, so servers can use SAN block storage over ordinary Ethernet.
ISL	Inter-Switch Link	Cisco's old trunking method that wrapped whole frames; replaced by the 802.1Q standard tag.
ISO	International Organization for Standardization	The international standards body behind standards such as ISO/IEC 27001 for security management.
ISP	Internet Service Provider	The company that connects you to the internet.
IT	Information Technology	Computers, networks and the people who run them.
IXFR	Incremental Zone Transfer	A DNS transfer that copies only the changes in a zone, not the whole zone.
JSON	JavaScript Object Notation	A simple text format for data, like {"name": "Ranger"}, used by most web APIs.
LACP	Link Aggregation Control Protocol	Bundles several physical links into one faster logical link with failover (IEEE 802.3ad).
LAN	Local Area Network	The network in one building or site.
LC	Local Connector	A small square fiber connector with a push-and-click latch, common on SFP modules.
LDAP	Lightweight Directory Access Protocol	The protocol for reading and searching a directory such as Active Directory. Port 389; LDAPS uses 636.
LDAPS	Lightweight Directory Access Protocol over SSL	LDAP protected with TLS (port 636), so directory logins and queries are encrypted.
LED	Light-Emitting Diode	A light-emitting diode: used as status lights and as the backlight in most LCD screens.
LEO	Low Earth Orbit	Satellites a few hundred to about 2,000 km up, like Starlink: much lower latency than geostationary.
LLDP	Link Layer Discovery Protocol	The vendor-neutral way neighboring network devices announce their name, port and abilities.
LLDP-MED	LLDP Media Endpoint Discovery	An LLDP extension that tells IP phones which voice VLAN and power settings to use.
LSA	Link-State Advertisement	The message OSPF routers flood to share what links and networks they know about.
LTE	Long-term Evolution	The 4G cellular data standard.
MAC	Media Access Control	The 48-bit hardware address burned into a network interface, written like 00:1A:2B:3C:4D:5E.
MDF	Main Distribution Frame	The main wiring room, where outside lines enter and the core equipment sits.
MDI	Medium Dependent Interface	The normal Ethernet port wiring on a PC or router (sends on pins 1 and 2).
MDIX	Medium Dependent Interface Crossover	The crossed Ethernet port wiring on switches, so a straight-through cable works. Auto-MDIX adjusts by itself.
MFA	Multifactor Authentication	Logging in with two or more different kinds of proof: something you know, have or are.
MIB	Management Information Base	The list of values a device can report or have set through SNMP, each with an ID (OID).
MIMO	Multiple Input, Multiple Output	Several antennas sending and receiving at once to carry more data.
MMF	Multimode Fiber	Fiber with a wide core that carries light on many paths: cheaper, for short runs inside buildings.
MOU	Memorandum of Understanding	A non-binding statement of shared intent between two parties.
MPLS	Multiprotocol Label Switching	Carrier WAN technology that forwards traffic by short labels instead of full IP lookups.
MPO	Multifiber Push On	A fiber connector holding 12 or more fibers at once, used for 40 and 100 Gb links in data centers.
MTBF	Mean Time Between Failures	The average time a repairable device runs between failures.
MTTR	Mean Time To Repair	The average time it takes to fix something and get it working again.
MTU	Maximum Transmission Unit	The largest packet a link can carry without splitting it. Ethernet's default is 1500 bytes.
MU-MIMO	Multi-user Multiple Input, Multiple Output	Lets an access point send to several clients at the same time instead of one after another.
MX	Mail Exchange	DNS record that names the mail server for a domain.
NaaS	Network as a Service	Renting networking (WAN, firewalls, switches) as a subscription service instead of buying it.
NAC	Network Access Control	Checks a device and its user before letting it on the network (is it patched, does it have antivirus?).
NAS	Network-attached Storage	A box on the network that shares files over SMB or NFS.
NAT	Network Address Translation	Swaps private internal IP addresses for a public one as traffic leaves the network.
NAT64	Network Address Translation IPv6-to-IPv4	Translation that lets IPv6-only devices reach IPv4 servers (works with DNS64).
NDA	Non-disclosure Agreement	A contract to keep confidential information secret.
NDP	Neighbor Discovery Protocol	IPv6's replacement for ARP and more: finds neighbors' addresses and routers, using ICMPv6.
NFS	Network File System	The Unix and Linux way to share folders over the network (like SMB on Windows).
NFV	Network Functions Virtualization	Running network functions such as firewalls and routers as software on ordinary servers.
NGFW	Next-generation Firewall	A firewall that also knows applications and users and has an IPS built in.
NIC	Network Interface Card	The hardware that connects a computer to a network.
NIST	National Institute of Standards and Technology	The US agency that publishes security standards and guides, such as the Cybersecurity Framework and SP 800.
NMS	Network Management System	The monitoring server that polls devices (often by SNMP) and collects their alerts.
NOC	Network Operations Center	The team and room that watch and run the network around the clock.
NS	Name Server	DNS record that names the authoritative name servers for a zone.
NTP	Network Time Protocol	Keeps device clocks in sync over the network (UDP 123), which logs and Kerberos rely on.
NTS	Network Time Security	Adds cryptographic checks to NTP so attackers can't fake the time.
NVR	Network Video Recorder	A box that records video from IP cameras.
OFDMA	Orthogonal Frequency-division Multiple Access	Wi-Fi 6 splits a channel into small slices so several clients can share one transmission.
OID	Object Identifier	A dotted number that names one value in an SNMP MIB, such as a port's traffic counter.
OOB	Out-of-band	Managing devices over a separate path (console server, management network) that works even when the main network is down.
OS	Operating System	The core software that runs a computer, such as Windows, macOS, Linux, Android or iOS.
OSI	Open Systems Interconnection	A 7-layer model of how network communication works, from cables (layer 1) to applications (layer 7).
OSPF	Open Shortest Path First	A link-state routing protocol for inside an organization; it picks paths by cost based on bandwidth.
OT	Operational Technology	Hardware and software that run physical equipment, such as factory lines, power and building systems.
OTDR	Optical Time-domain Reflectometer	A fiber tester that sends light pulses and times the reflections to find breaks, bends and bad splices.
OUI	Organizationally Unique Identifier	The first half (24 bits) of a MAC address, which identifies the manufacturer.
OWE	Opportunistic Wireless Encryption	Encrypts open Wi-Fi (Wi-Fi Enhanced Open) without a password.
PaaS	Platform as a Service	A cloud platform to run your code on; the provider manages the servers, OS and runtime.
PAT	Port Address Translation	Many inside devices share one public IP, told apart by port numbers (NAT overload).
PC	Personal Computer	A personal computer: a desktop or laptop.
PCAP	Packet Capture	A file of captured network packets, made by tools like tcpdump and opened in Wireshark.
PCI DSS	Payment Card Industry Data Security Standard	The security rules every business that takes payment cards must follow.
PDU	Power Distribution Unit; also Protocol Data Unit	A rack power strip (power distribution unit). In networking, also a protocol data unit: a frame, packet or segment.
PEAP	Protected Extensible Authentication Protocol	Wraps the Wi-Fi login in a TLS tunnel made with only a server certificate; users then log in with a password.
PIN	Personal Identification Number	A short secret number: something you know.
PKI	Public Key Infrastructure	The system of CAs, certificates and keys that lets strangers trust each other's identities online.
PLC	Programmable Logic Controller	A rugged industrial computer that runs machines on a factory floor.
PMF	Protected Management Frames	Wi-Fi feature (802.11w) that stops faked disconnect (deauthentication) frames; required in WPA3.
PoE	Power over Ethernet	Sends power over the Ethernet cable, so cameras, phones and access points need no separate plug.
POP3	Post Office Protocol version 3	Downloads email to one device, usually removing it from the server. Port 110, or 995 with TLS.
PPTP	Point-to-Point Tunneling Protocol	An old VPN protocol with broken security. Don't use it.
PSE	Power Sourcing Equipment	The switch or injector that supplies PoE power to devices.
PSK	Pre-shared Key	A shared password everyone types to join a network, as in WPA2-Personal.
PSU	Power Supply Unit	Turns wall AC power into the DC voltages a computer's parts need.
PTP	Precision Time Protocol	Keeps clocks in sync far more precisely than NTP, to microseconds or better, with hardware help.
PTR	Pointer	DNS record for reverse lookups: maps an IP address back to a name.
PVC	Polyvinyl Chloride	Ordinary cable jacket plastic. It gives off toxic smoke in a fire, so use plenum cable in air spaces.
QoS	Quality of Service	Giving important traffic, such as voice and video, priority over other traffic.
QSFP	Quad Small Form-factor Pluggable	A four-lane transceiver for 40 and 100 Gb links (QSFP28 for 100 Gb).
RA	Router Advertisement	An IPv6 router's message announcing the network prefix and itself as gateway; hosts use it for SLAAC.
RADIUS	Remote Authentication Dial-in User Service	A central login (AAA) service used by Wi-Fi, VPN and switches. UDP 1812 and 1813; only the password is encrypted.
RAID	Redundant Array of Independent Disks	Combines several disks for speed, redundancy or both (RAID 0, 1, 5, 6, 10). Not a backup.
RBAC	Role-based Access Control	Access by job role: people get the permissions of the roles they hold.
RC4	Rivest Cipher 4	An old stream cipher used by WEP and TKIP. Broken; don't use it.
RDP	Remote Desktop Protocol	Microsoft's remote desktop protocol, TCP port 3389. Don't expose it to the internet.
REST	Representational State Transfer	A simple style of web API: HTTP requests on URLs, usually with JSON replies.
RF	Radio Frequency	Radio signals, such as Wi-Fi and Bluetooth.
RFC	Request for Comments	The numbered documents that define internet standards, like RFC 1918 for private addresses.
RFID	Radio Frequency Identification	Reads tags by radio without line of sight, as in badges, inventory tags and toll passes.
RIP	Routing Information Protocol	An old distance-vector routing protocol that counts hops; 15 is the most, 16 means unreachable.
RIPv2	Routing Information Protocol version 2	The classless version of RIP: it sends subnet masks and uses multicast. Still a 15-hop limit.
RJ11	Registered Jack 11	The small phone-line connector (usually 2 or 4 wires).
RJ45	Registered Jack 45	The 8-pin connector on Ethernet cables.
RMA	Return Merchandise Authorization	The vendor's approval to send back a faulty part for repair or replacement.
RPO	Recovery Point Objective	How much data, in time, you can afford to lose; it sets how often you back up.
RRSIG	Resource Record Signature	DNSSEC record holding the digital signature for a set of DNS records.
RSA	Rivest, Shamir, and Adleman	A public-key algorithm based on the difficulty of factoring large numbers; used for signatures and key exchange.
RSSI	Received Signal Strength Indicator	How strong a received Wi-Fi signal is, in dBm; closer to 0 is stronger (-50 is great, -80 is weak).
RST	Reset	A TCP flag that abruptly ends a connection or refuses one, as a closed port does.
RSTP	Rapid Spanning Tree Protocol	The faster version of Spanning Tree (802.1w), recovering in seconds instead of up to 50.
RTO	Recovery Time Objective	How long a system can be down before the business is badly hurt; the target time to restore it.
RTP	Real-time Transport Protocol	Carries real-time audio and video, as in VoIP calls, usually over UDP.
RX	Receiver	The receive side of a link or cable pair.
SaaS	Software as a Service	Finished software you use over the internet, like webmail; the provider runs everything.
SAE	Simultaneous Authentication of Equals	The WPA3 password handshake (Dragonfly), which stops offline password guessing.
SAML	Security Assertion Markup Language	XML messages an identity provider sends to web apps saying who you are, for single sign-on.
SAN	Storage Area Network	A dedicated network that gives servers block-level storage, as if the disks were local.
SASE	Secure Access Service Edge	Networking (SD-WAN) and security (SWG, CASB, ZTNA, firewall) delivered together from the cloud.
SC	Subscriber Connector	A square fiber connector that pushes in and pulls out.
SCADA	Supervisory Control and Data Acquisition	Systems that monitor and control industrial processes, often spread over large areas like pipelines and grids.
SCTP	Stream Control Transmission Protocol	A transport protocol with several streams and paths per connection, used in phone networks.
SD-WAN	Software-defined Wide Area Network	Manages WAN links between sites from one controller and picks the best path (broadband, LTE, MPLS) per app.
SDN	Software-defined Network	Network control moved into central software that programs the switches and routers.
SFP	Small Form-factor Pluggable	A small hot-swappable module that gives a switch port fiber or copper at up to 1 Gb.
SFP+	Enhanced Small Form-factor Pluggable	The 10 Gb version of the small form-factor pluggable module.
SFTP	Secure File Transfer Protocol	File transfer through SSH on port 22, encrypted. Not the same as FTPS.
SHA	Secure Hash Algorithm	A family of hash functions; SHA-256 is common today, SHA-1 is broken.
SIEM	Security Information and Event Management	Collects logs from across the network in one place, links related events and raises alerts.
SIM	Subscriber Identity Module	The small card (or eSIM) that ties a phone to a cellular account and number.
SIP	Session Initiation Protocol	Sets up, manages and ends VoIP calls (ports 5060, and 5061 with TLS).
SLA	Service-level Agreement	A contract's promised service level, such as 99.9% uptime or a 4-hour response.
SLAAC	Stateless Address Autoconfiguration	An IPv6 device builds its own address from the prefix a router advertises, with no DHCP server.
SMB	Server Message Block	Windows file and printer sharing protocol, TCP port 445. Turn off the old SMBv1.
SMF	Single-mode Fiber	Fiber with a tiny core that carries one path of laser light, for long distances.
SMTP	Simple Mail Transfer Protocol	Sends email between mail servers (port 25) and from apps to their server (587).
SMTPS	Simple Mail Transfer Protocol Secure	SMTP protected with TLS, such as port 465.
SNMP	Simple Network Management Protocol	Lets a monitoring system read and change device settings and receive alerts (traps). UDP 161 and 162.
SNMPv1	Simple Network Management Protocol version 1	The first SNMP: community strings travel in clear text. Insecure.
SNMPv3	Simple Network Management Protocol version 3	The secure SNMP: user logins, integrity checks and encryption.
SNR	Signal-to-Noise Ratio	How far a signal stands above background noise, in dB; higher is better.
SNTP	Simple Network Time Protocol	A lighter, less precise version of NTP for simple devices.
SOA	Start of Authority	The first DNS record in a zone: the main name server, admin contact, serial number and timers.
SOHO	Small Office/Home Office	A small office or home office, usually with one all-in-one router.
SOX	Sarbanes-Oxley Act	The US law that requires public companies to keep accurate financial records and controls.
SPAN	Switched Port Analyzer	A switch feature that copies (mirrors) traffic from some ports to a monitoring port.
SPF	Sender Policy Framework	A DNS TXT record listing which servers may send email for a domain.
SQL	Structured Query Language	The language for querying and changing data in relational databases.
SRV	Service record	DNS record that tells clients which host and port offer a service, such as a domain controller.
SSE	Security Service Edge	The security half of SASE: web filtering (SWG), CASB and ZTNA delivered from the cloud.
SSH	Secure Shell	An encrypted remote command line, TCP port 22. Replaces Telnet.
SSHv2	Secure Shell version 2	The current, secure version of SSH. Version 1 has known flaws.
SSID	Service Set Identifier	The name of a Wi-Fi network.
SSL	Secure Sockets Layer	The old protocol that came before TLS. Every version is broken; "SSL certificates" today are really TLS.
SSO	Single Sign-on	Log in once and get into many apps without signing in again.
ST	Straight Tip	A round fiber connector with a twist-lock bayonet, found on older installs.
STP	Shielded Twisted Pair; also Spanning Tree Protocol	Shielded twisted pair: copper cable with foil for noisy places. Also Spanning Tree Protocol, which stops switch loops.
SVI	Switch Virtual Interface	A virtual interface on a layer 3 switch that gives a VLAN an IP address, for routing between VLANs.
SWG	Secure Web Gateway	Filters users' web traffic, blocking malicious and banned sites wherever the users are.
SYN	Synchronize	The TCP flag that opens a connection: the first step of the three-way handshake.
TACACS+	Terminal Access Controller Access Control System Plus	Cisco's central login (AAA) protocol over TCP 49: encrypts the whole message and controls each admin command.
TCP	Transmission Control Protocol	Reliable, connection-based delivery: a three-way handshake, then data is acknowledged and resent if lost.
TDR	Time-domain Reflectometer	Finds where a copper cable is broken or shorted by timing a pulse's echo.
TFTP	Trivial File Transfer Protocol	Very simple file transfer on UDP 69 with no login, used to load device configs and boot images.
TKIP	Temporal Key Integrity Protocol	WPA's stopgap encryption, built on RC4. Deprecated and weak.
TLD	Top-Level Domain	The last part of a domain name, such as .com, .org or .uk.
TLS	Transport Layer Security	Encrypts and authenticates connections, such as HTTPS. Use TLS 1.2 or 1.3.
ToR	Top of Rack (switch)	A switch at the top of each server rack that connects the servers in that rack.
TOTP	Time-based One-time Password	A login code made from a shared secret and the current time, changing about every 30 seconds.
TPC	Transmit Power Control	Wi-Fi feature (802.11h) that adjusts an access point's power to meet rules and reduce interference.
TTL	Time to Live	In IP, a hop count each router lowers so lost packets die; in DNS, how long an answer may be cached.
TV	Television	A television; cable TV and modems use coax with F-type connectors.
TX	Transmitter	The transmit side of a link or cable pair.
TXT	Text (DNS record)	DNS record that holds text; SPF, DKIM, DMARC and domain checks are published this way.
UDP	User Datagram Protocol	Fast, connectionless delivery with no handshake or resending; used for DNS, VoIP and streaming.
UNII	Unlicensed National Information Infrastructure	The 5 GHz bands (UNII-1 to UNII-3, plus UNII-4) set aside for unlicensed use such as Wi-Fi.
UPS	Uninterruptible Power Supply	A battery that keeps equipment running through short outages and allows a safe shutdown.
URL	Uniform Resource Locator	A web address, like https://www.example.com/page.
USB	Universal Serial Bus	The common plug for keyboards, drives, phones and chargers.
UTM	Unified Threat Management	One box that combines firewall, IPS, antivirus, web filtering and more.
UTP	Unshielded Twisted Pair	Ordinary Ethernet cable: twisted copper pairs with no shield.
VCSEL	Vertical-Cavity Surface-Emitting Laser	A cheap laser used in multimode fiber transceivers for short runs.
VFL	Visual Fault Locator	Shines a bright red laser into fiber so breaks and tight bends glow, on short runs.
VIP	Virtual IP	A shared address that clients use, which moves between servers or routers (load balancing, failover).
VLAN	Virtual Local Area Network	Splits one physical switch into separate logical networks.
VLSM	Variable Length Subnet Mask	Cutting one address block into subnets of different sizes so fewer addresses are wasted.
VM	Virtual Machine	A software computer running on a hypervisor, with its own OS, sharing the real hardware.
VNC	Virtual Network Computing	Cross-platform remote desktop sharing, usually on port 5900.
VNI	VXLAN Network Identifier	The 24-bit number that names one VXLAN segment (about 16 million possible).
VoIP	Voice over IP	Phone calls carried over IP networks instead of phone lines.
VPC	Virtual Private Cloud	Your own isolated private network inside a public cloud.
VPN	Virtual Private Network	An encrypted tunnel across an untrusted network, such as the internet.
VRF	Virtual Routing and Forwarding	Several separate routing tables on one router, keeping networks apart.
VRRP	Virtual Router Redundancy Protocol	The open-standard way for routers to share one virtual gateway address with failover.
VTEP	VXLAN Tunnel Endpoint	The device that wraps and unwraps VXLAN traffic.
VTP	VLAN Trunking Protocol	A Cisco protocol that copies VLAN lists from one switch to the others.
VTY	Virtual Teletype	The virtual lines on a router or switch used for remote logins by SSH or Telnet.
VXLAN	Virtual Extensible Local Area Network	Carries layer 2 networks inside UDP over a layer 3 network, with about 16 million segment IDs.
WAF	Web Application Firewall	A firewall for web apps: inspects HTTP traffic and blocks attacks like SQL injection and XSS.
WAN	Wide Area Network	A network that links sites across long distances.
WAP	Wireless Access Point	A device that connects wireless clients to the wired network.
WEP	Wired Equivalent Privacy	The original Wi-Fi encryption, broken within minutes. Never use it.
WLAN	Wireless Local Area Network	A local network over Wi-Fi.
WLC	Wireless LAN Controller	A central box that configures and manages many lightweight access points.
WPA	Wi-Fi Protected Access	Wi-Fi Protected Access: the original version used TKIP and is outdated.
WPA2	Wi-Fi Protected Access 2	Wi-Fi security with AES (CCMP). Personal mode uses a shared password; Enterprise uses 802.1X logins.
WPA3	Wi-Fi Protected Access 3	The newest Wi-Fi security: SAE stops offline password guessing, and stronger encryption.
WPS	Wi-Fi Protected Setup	Push-button or PIN Wi-Fi setup. The PIN can be brute-forced, so turn it off.
XML	Extensible Markup Language	A text format that marks up data with tags; used by SAML and SOAP.
ZTA	Zero Trust Architecture	Trust nothing by default: check every user, device and request, every time.
ZTNA	Zero Trust Network Access	Gives users access to one app at a time after checking who and what they are, instead of whole-network VPN access.
ZTP	Zero-Touch Provisioning	A new device downloads its configuration automatically when first powered on.

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