Networking Concepts and Configuration
Networking Concepts and Configuration tests whether you can reason from interface to route to name resolution to service. Questions cover IPv4 subnetting, TCP and UDP ports, DNS, DHCP, routing, and the tools used to prove each layer.
Addressing and routes
- IPv4 addresses are 32-bit; /24 means 24 network bits and 8 host bits. Private ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.
- The default gateway is the next hop for non-local destinations; ip route shows it.
- ip addr shows addresses; ip link shows interface state; nmcli manages NetworkManager connections.
Names and services
- Resolution order is typically determined by /etc/nsswitch.conf, then /etc/hosts, then DNS servers in /etc/resolv.conf.
- dig example.com A queries DNS directly; getent hosts example.com follows the system resolver.
- ss -tlnp lists listening TCP sockets with process names; ping tests ICMP reachability, not a specific port.
Worked example
A server cannot reach https://intranet.example.com. Run ip addr and ip route; ping the gateway; dig intranet.example.com; curl -vk https://intranet.example.com; and on the target run ss -tlnp | grep 443. Reasoning: this isolates link or address, routing, DNS, TLS and HTTP, and listener problems in order. A DNS failure shows as a name resolution error while ping to an IP still works.
Traps
- Treating a failed ping as proof the host is down; ICMP is often filtered.
- Editing /etc/resolv.conf on a NetworkManager host where it is regenerated.
- Confusing a port with a protocol.
- Miscalculating subnet boundaries or broadcast addresses.