ip Command in Linux: Addresses and Routes

The ip command replaced ifconfig and route a decade ago, and it is the tool every modern distro actually ships. Addresses, links, routes, neighbours — one command, consistent grammar, and a shorthand form that makes daily use fast.

The grammar #

Every ip command is ip OBJECT COMMAND: which table to look at, then what to do — addr show, link set, route add. The words abbreviate freely as long as they stay unambiguous (a = addr, r = route, l = link).

The four everyday reads

$ ip addr show                 # addresses on every interface
$ ip -br addr                  # the same, one line per interface
$ ip route                     # the routing table
$ ip link                      # interface states

-br (brief) is the flag nobody forgets after seeing it once — one line per interface with state and address:

Brief mode: the whole network at a glance

$ ip -br addr
lo               UNKNOWN        127.0.0.1/8
wlan0            UP             192.168.1.42/24
docker0          DOWN           172.17.0.1/16

Reading the output #

Anatomy of one address line

$ ip addr show wlan0
2: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 ...
    inet 192.168.1.42/24 brd 192.168.1.255 scope global wlan0

The /24 is the prefix — network size in CIDR notation; scope global means routable (contrast scope host for loopback). Flags <UP,LOWER_UP> answer "is the link actually alive" in one glance, which troubleshooting always wants first.

The changes you will make #

Task	Command
Bring an interface up/down	`ip link set eth0 up`
Add an address	`ip addr add 10.0.0.5/24 dev eth0`
Remove an address	`ip addr del 10.0.0.5/24 dev eth0`
Add a route	`ip route add 10.10.0.0/16 via 10.0.0.1`
Default route	`ip route add default via 192.168.1.1`
Routing cache flush	`ip route flush cache`

Manual changes vanish at reboot or reconnect — deliberate persistence belongs in NetworkManager, systemd-networkd, or your distro's netplan, which write these same commands for you.

The diagnostics worth knowing #

Who is on my network segment?

$ ip neigh                     # the ARP table: IP -> MAC, reachable or stale

The neighbour table tells you what the machine believes is nearby — STALE entries explain one-way connectivity mysteries, and FAILED entries mean ARP itself is not answering, which is a link-level problem before it is an IP one.

ip -br a on arrival, ip r for "why does this go that way", ip neigh for "is the peer even there" — three reads cover nearly every first-minute network diagnosis on a Linux box.

From here: ping tests reachability, ss lists the sockets, and dig checks the name layer. The network series continues.