RANGER GAMEZ

CompTIA A+ Core 1 (220-1201) · chapter 14 of 15

Week 14: The network is slow (again)

In this chapter Objectives 5.5

  1. Network symptoms and causes
  2. Practice questions
  3. Chapter recap

Objective 5.5

Network symptoms and causes

Intermittent wireless and external interference

Intermittent wireless connectivity: weak signal at the edge of coverage, roaming between APs, channel overlap with neighbors, power-saving on the NIC, or external interference. On 2.4 GHz the classic sources are microwave ovens, cordless phones, Bluetooth and baby monitors; thick walls, metal shelves and water also absorb signal. Use a Wi-Fi analyzer: move clients to 5/6 GHz, change channels (1/6/11), add or move APs.

Exam tip Drops only when the microwave runs = 2.4 GHz interference. Move clients to 5 GHz.

Limited connectivity

Limited connectivity (no internet, local only): usually an APIPA 169.254.x.x address from a failed DHCP request, a wrong gateway, or a VLAN issue. Check with ipconfig: renew the lease (ipconfig /release then /renew), then ping the gateway, then a public IP, then a name.

C:\> ipconfig
   IPv4 Address. . . : 169.254.12.80
   Default Gateway . :
C:\> ipconfig /renew
An error occurred while renewing
interface Wi-Fi : unable to contact
your DHCP server.

Exam tip Order: ping loopback, own IP, gateway, a public IP, then a name. Fails at the name only = DNS.

Slow speeds and high latency

Slow network speeds: a saturated link (backups, cloud sync, video), a port negotiated at 100 Mbps or half duplex (bad cable/old Cat), weak Wi-Fi, or a limited ISP plan. High latency is delay (ms): congested links, long or satellite paths, overloaded routers or a busy Wi-Fi channel. Use ping and tracert to see where delay starts.

C:\> ping 8.8.8.8
Reply from 8.8.8.8: time=412ms TTL=115
Reply from 8.8.8.8: time=388ms TTL=115
C:\> tracert 8.8.8.8
 1    2 ms   1 ms   2 ms  192.168.10.1
 2  395 ms 401 ms 389 ms  gw.isp.example

Exam tip Latency jumps at hop 2 = past your router, at the ISP link. Call the provider.

Jitter and poor VoIP quality

Jitter is variation in latency between packets. Real-time traffic hates it. Poor VoIP quality (robotic voice, gaps, echo, dropped calls) comes from jitter, packet loss and latency (aim for under ~150 ms one way and low jitter). Fix with QoS to prioritize voice, a separate voice VLAN, wired phones, and enough bandwidth (watch the upload).

Exam tip Robot voice on calls = jitter/packet loss. Answer: QoS for voice traffic.

Port flapping

Port flapping: a switch port goes up and down again and again (link up/link down in the switch log). Causes: a damaged cable or connector, a bad NIC or switch port, speed/duplex mismatch, or a loose patch. Users see short, repeated drops. Swap the cable, try another port, test with a cable tester.

SW1 log
10:02:11 Gi1/0/14 link down
10:02:13 Gi1/0/14 link up 1000/full
10:02:40 Gi1/0/14 link down
10:02:42 Gi1/0/14 link up 100/full

Exam tip Port flapping is physical first: cable, then ports.

Authentication failures and intermittent internet

Authentication failures: wrong Wi-Fi passphrase, an expired or changed domain password saved on the device, expired certificate on 802.1X/enterprise Wi-Fi, wrong date/time (breaks certificates), or a locked-out account on the RADIUS/AAA server. Intermittent internet connectivity with a stable LAN: ISP outages, a failing modem/ONT, bad coax/DSL line, or an overheating router. Check the modem lights and logs, and test from the router.

Exam tip Wi-Fi fails right after a password change on every phone = saved old credentials.

Check yourself 1Users say VoIP calls sound choppy and robotic every afternoon when large cloud backups run. Bandwidth tests are otherwise fine. What is the BEST fix?

  1. Configure QoS to prioritize voice traffic
  2. Change the access point to Wi-Fi channel 11
  3. Replace the phones' patch cables with Cat 6a
  4. Increase the DHCP lease time
Show the answer

Answer: A. Configure QoS to prioritize voice traffic

Backups fill the link and cause jitter and loss. QoS gives voice packets priority so calls stay clear.

Practice questions

Answer in your head, then open the answer. Ranger's Help Desk has 436 questions like these for A+ Core 1, with mock exams.

Question 1Users on a 2.4 GHz wireless network lose their connection every day around lunch time, near the break room. What is the MOST likely cause?

  1. A duplex mismatch on the AP's uplink
  2. A wrong DNS server
  3. Interference from the microwave oven
  4. An expired DHCP lease on the clients
Show the answer

Answer: C. Interference from the microwave oven

Microwave ovens operate near 2.4 GHz and cause external interference. Moving users to 5 GHz or moving the AP fixes it.

Question 2A wireless network keeps dropping in one area. Which tool should the technician use to find sources of interference and overlapping channels?

  1. A Wi-Fi analyzer
  2. A crimper
  3. A tone generator
  4. A loopback plug
Show the answer

Answer: A. A Wi-Fi analyzer

A Wi-Fi analyzer shows signal strength, channels in use and nearby networks, which helps find interference.

Question 3In an office building, several 2.4 GHz access points are set to channels 3, 5 and 9. Users report intermittent wireless connectivity. What should the technician change?

  1. Set all APs to the same channel, 6
  2. Turn off WPA3 encryption on the APs
  3. Use channels 1, 6 and 11
  4. Raise every AP to maximum transmit power
Show the answer

Answer: C. Use channels 1, 6 and 11

In the 2.4 GHz band only channels 1, 6 and 11 do not overlap. Overlapping channels interfere with each other.

Question 4A user's wired connection is far slower than coworkers' on the same switch. Based on the exhibit, what should the technician do FIRST?

  1. Run a full malware scan
  2. Change the DNS server to a public one
  3. Replace the switch with a gigabit model
  4. Swap in a known-good patch cable
Show the answer

Answer: D. Swap in a known-good patch cable

A gigabit NIC linking at 100 Mbps often has a damaged cable or a pair problem. Testing with a known-good cable is the quickest check.

Question 5Based on the exhibit, why does the user have only limited connectivity?

  1. The Wi-Fi signal is too strong
  2. No DHCP server answered the PC
  3. The DNS server is down for the network
  4. The default gateway is set to the wrong address
Show the answer

Answer: B. No DHCP server answered the PC

A 169.254.x.x address is APIPA. Windows assigns it when no DHCP server answers, so the PC can reach only local APIPA hosts.

Practice it in Ranger's Help DeskThe same lessons as a story, with drills, hands-on labs and mock exams. Free, in your browser.
Play free

CompTIA, A+, Network+, Security+ and Linux+ are trademarks of CompTIA, Inc. Ranger Gamez is not affiliated with or endorsed by CompTIA. The practice questions are written to the published exam objectives; they are not real exam questions.