Network Configuration and Services
This domain covers how macOS selects interfaces, obtains addresses, resolves names, and applies per-network settings. Questions often test service order, DHCP behavior, DNS resolution, 802.1X, VPN, and proxy configuration rather than obscure commands.
Interfaces, locations, and service order
A Mac can have Wi-Fi, Ethernet, Thunderbolt Bridge, and VPN interfaces active at once. Network Locations let you switch sets of settings for different environments. Service order determines the primary interface and the order in which DNS servers are queried. Use networksetup -listallnetworkservices and networksetup -listnetworkserviceorder to inspect it. A self-assigned address in 169.254.0.0/16 means DHCP did not complete; it is not a DNS failure. ipconfig getpacket en0 and ipconfig getsummary en0 show lease details.
Naming and authentication
DNS problems look like slow or failed name resolution while IP connectivity still works. Test with scutil --dns, dscacheutil -q host -a name example.com, and ping by IP address. 802.1X Wi-Fi profiles should be delivered by configuration profile so the identity certificate and trust chain are installed correctly. VPN service order matters when split tunneling sends only some traffic through the tunnel.
Worked example
A Mac on Wi-Fi gets 169.254.10.23 and cannot reach the internet, but Ethernet works. Reasoning: the Wi-Fi link associated, but DHCP did not supply a lease. Check the Wi-Fi service’s DHCP setting, VLAN, and DHCP server reachability before changing DNS. Renew the lease or reconnect; if the address remains self-assigned, the fault is upstream or in the Wi-Fi configuration, not in the DNS cache.
Traps
- A self-assigned address is not fixed by flushing DNS.
- Service order affects default routing and DNS query order, not just icon order.
- A captive portal can make the network appear connected while blocking normal traffic.
- Deleting a VPN configuration may remove its credentials; confirm before removing it.