How to read ip addr output on Linux

Welcome to the next pikoTutorial !

ip command was designed to replace older networking tools like ifconfig, route or netstat. To show all the network interfaces use command:

ip addr

Example output:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever

In the output you can find a bunch of useful information about each of the interfaces:

1. 1: lo - interface index and name (lo stands for loopback)
2. <LOOPBACK,UP,LOWER_UP> - statuses of the interface. For other interfaces, you may find here values like BROADCAST, MULTICAST etc.
3. mtu 65536 - the maximum transmission unit size for the interface (in this case it's 65536 bytes, but e.g. for Ethernet networks 1500 is a typical value)
4. qdisc noqueue - the queuing discipline
5. state UNKNOWN - state of the interface (here UNKNOWN, but for other interfaces may be UP or DOWN)
6. group default - group name that this interface belongs to
7. qlen 1000 - length of the transmit queue (in this case it's 1000 packets)
8. link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 - MAC address and broadcast address
9. inet 127.0.0.1/8 scope host lo - IPv4 address with netmask (127.0.0.1/8) scope (host)
10. inet6 ::1/128 scope host - IPv6 address with netmask (::1/128) and scope (host)