Networking and Troubleshooting
Networking and Troubleshooting
This domain tests network types, topologies, devices, addressing and systematic fault finding. Questions may cover LAN and WAN, star and bus topologies, hubs, switches, routers, IP addressing, DHCP, DNS and diagnostic commands.
Core rules
- A hub repeats signals to all ports; a switch forwards frames to the intended port; a router connects networks and chooses paths.
- IPv4 addresses have four octets. Private ranges include 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16.
- A subnet mask separates network and host bits. The default gateway is the router used to reach other networks. DNS resolves names; DHCP assigns addresses automatically.
- An address beginning 169.254 usually means DHCP failed and the device self-assigned a link-local address.
- ping tests reachability, ipconfig shows configuration, tracert shows the path, and nslookup queries DNS.
Worked example
One PC cannot reach websites. ipconfig shows 169.254.10.5. That address suggests DHCP did not supply a valid configuration. Check the cable or Wi-Fi link, then renew the address. Test the local stack with ping 127.0.0.1, ping the default gateway, then ping a public IP such as 8.8.8.8. If the public IP responds but names fail, suspect DNS. The reasoning is to isolate local, gateway and name-resolution faults in order.
Traps
Do not describe a switch as a router; it does not normally connect different networks. A private IP is not directly reachable from the internet. ping may be blocked by a firewall even when the host is up. Do not confuse DNS with DHCP. Check cable type and connector before replacing hardware.