Month 4: Macs, signals and hotspots

The Network pane

Open System Settings > Network. Each network service (Wi-Fi, Ethernet, Thunderbolt Bridge, an iPhone USB connection) has a status dot.

• Green: on and connected
• Yellow: active but not connected (for example, no IP address)
• Red: not set up or needs configuring
• Gray: turned off or unavailable

Dev: Yellow dot means the cable's in but no address came back. Check DHCP first.

Exam tip VPN, Firewall and content filters also appear in the Network pane in recent macOS versions.

Details for a service

Click a service, then Details. Tabs include TCP/IP (Configure IPv4: Using DHCP, DHCP with manual address, Manually; Renew DHCP Lease), DNS, WINS, 802.1X, Proxies and Hardware (MAC address, speed, MTU). The Action (...) menu below the list adds services, deletes them, sets the service order and manages Locations: saved sets of network settings, such as Office and Home.

Exam tip To test a clean network setup without losing the old one, create a new Location and switch to it.

Who goes first

A Mac can have several services active at once, such as Ethernet and Wi-Fi. macOS uses the highest active service in the service order first for its default route and DNS, then falls back down the list if that one isn't available. VPN connections always take precedence and can't be reordered.

Exam tip Purpose in one line: the service order decides which connected interface the Mac prefers.

Changing it

Choose Set Service Order from the Action (...) menu, drag the services into the order you want, click OK, and apply. Typical reasons: prefer wired Ethernet over Wi-Fi at a desk, or push a slow or metered connection (such as an iPhone USB tether) below Wi-Fi so it's used only as a backup. Each Location can have its own order.

Dev: Plugging in Ethernet doesn't help if Wi-Fi is still at the top of the list.

Scope first

Ask who and where. All devices failing on one network points to the network (router, DHCP, internet outage). One device failing everywhere points to the device. One device on one network points to that network's saved settings: password, private address, manual IP, DNS or proxy.

• Can't join: check the password, Forget This Network and rejoin; check MAC filtering
• Joined but no internet: check for a captive portal, then IP, router and DNS
• Slow or dropping: signal strength, interference, distance, channel congestion

Read the IP settings

In the network's Info (iPhone) or Details > TCP/IP (Mac), check that there's an IP address, subnet mask and router. An address starting with 169.254 is self-assigned: DHCP didn't answer. Renew the lease (Mac: Renew DHCP Lease), rejoin, or have the network admin check the DHCP server. Wrong manual IP, DNS or proxy settings also break a working connection.

Exam tip 169.254.x.x on an Apple device = no DHCP response. The Wi-Fi link is up, but the network gave no address.

Bigger hammers, in order

Restart the device and the router. On iPhone or iPad, Reset Network Settings (Settings > General > Transfer or Reset > Reset) clears all saved Wi-Fi networks, VPN and cellular settings. On Mac, try a new Location or remove and re-add the Wi-Fi service. Keep routers on Apple's recommended settings: WPA3 or WPA2 with AES, one network name across bands, and one DHCP server.

Dev: Reset Network Settings forgets every Wi-Fi password. Warn the user first.

Option-click the Wi-Fi icon

Holding Option while clicking the Wi-Fi icon shows the connection's details: IP address, router, security, BSSID, channel and band, RSSI (signal strength) and noise in dBm, Tx Rate and PHY mode. RSSI closer to 0 is stronger: about -50 dBm is excellent, and a Mac starts looking for a stronger access point around -75 dBm. The gap between RSSI and noise is the signal-to-noise ratio; bigger is better.

RSSI:     -81 dBm
Noise:    -89 dBm
Tx Rate:  13 Mbps
Channel:  6 (2.4 GHz, 20 MHz)
PHY Mode: 802.11n

Exam tip RSSI -81 and noise -89 = only 8 dB of signal-to-noise ratio. Expect slow, unreliable Wi-Fi.

Running Wireless Diagnostics

From the same Option-click menu, open Wireless Diagnostics (the item reads Open Wireless Diagnostics or Create Diagnostics Report, depending on the version). Its assistant tests the connection, can monitor for drops, and ends with a summary of issues and recommendations. It saves a report named WirelessDiagnostics_...tar.gz in /private/var/tmp (/var/tmp) for the network team or AppleCare.

• Window menu tools include Info, Logs, Scan (nearby networks and best channels) and Performance (signal, noise and rate over time)
• Find the report: Finder > Go > Go to Folder > /var/tmp

Hotspot basics

Personal Hotspot shares an iPhone's or cellular iPad's mobile data over Wi-Fi, Bluetooth or USB. It must be allowed by the carrier and the plan; if it's missing from Settings, ask the carrier. Turn on Allow Others to Join in Settings > Personal Hotspot and set a password there. Family members and the user's own devices (Instant Hotspot, same Apple Account with Bluetooth and Wi-Fi on) can join without the password.

Exam tip MDM can also restrict Personal Hotspot on managed devices. Check the profile if the switch is dimmed.

When devices can't connect

Work through the connection type.

• Wi-Fi: keep the Personal Hotspot screen open while the other device joins; check the password; turn on Maximize Compatibility (2.4 GHz) for older devices
• Bluetooth: pair the devices; stay on Settings > Bluetooth while connecting; forget and re-pair if needed
• USB: Trust the computer; on Mac, the iPhone must appear as a service in Network settings
• Still failing: restart both, update carrier settings, then Reset Network Settings on the hotspot device

Exam tip Non-Apple devices are dropped after about 90 seconds with no traffic. Reconnect them; it's normal.

Where they live

Open System Settings > Network. Each service (Wi-Fi, Ethernet, Thunderbolt Bridge, VPN) is listed with its status. Select one and choose Details to change its settings. Use the Action (…) menu to add a service, set the service order (which connection the Mac prefers) or manage locations (sets of network settings, if shown).

• TCP/IP: Configure IPv4 using DHCP or Manually (IP address, subnet mask, router); Renew DHCP Lease
• DNS: add DNS servers and search domains
• Proxies: web proxies, automatic proxy configuration
• Hardware: MTU and speed (Ethernet)
• Wi-Fi: Known Networks list, Ask to join networks, Limit IP address tracking, Private Wi-Fi address

Troubleshooting order

Green dot = connected; yellow = connected without a usable address (often a self-assigned 169.254.x.x address: DHCP failed); red = not connected. Try in order: check the service order, Renew DHCP Lease, check DNS, forget and rejoin a Wi-Fi network, and remove a VPN or profile that changes routing. Use Wireless Diagnostics (hold Option and click the Wi-Fi menu) for Wi-Fi problems.

Exam tip A Mac with a 169.254 address can't reach the router; a Mac with a good IP that can't load websites usually has a DNS problem.