ip Command: Manage IP Addresses, Network Devices, Routing Tables, and Network Namespaces

Overview

The ip command in Linux is a powerful utility for managing IP addresses, network interfaces, routing tables, and network namespaces. It provides granular control over various network configurations, making it an essential tool for system administrators.

Syntax

ip addr add|del IFADDR dev IFACE | show|flush [dev IFACE] [to PREFIX]
ip route list|flush|add|del|change|append|replace|test ROUTE
ip link set IFACE [up|down] [arp on|off] [multicast on|off] \
        [promisc on|off] [mtu NUM] [name NAME] [qlen NUM] [address MAC] \
        [master IFACE | nomaster] [netns PID]
ip tunnel add|change|del|show [NAME] \
        [mode ipip|gre|sit] [remote ADDR] [local ADDR] [ttl TTL]
ip neigh show|flush [to PREFIX] [dev DEV] [nud STATE]
ip rule [list] | add|del SELECTOR ACTION

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Key Features and Examples

Manage IP Addresses

View IP addresses:

ip addr

Add an IP address to a device:

ip addr add 192.168.1.1/24 dev eth0

Remove an IP address:

ip addr del 192.168.1.1/24 dev eth0

Flush all IP addresses for a device:

ip addr flush dev eth0

Manage Network Devices

Display all network interfaces:

ip link

Show specific device details:

ip link show dev eth0

Bring an interface up or down:

ip link set eth0 up
ip link set eth0 down

Set MTU for a device:

ip link set eth0 mtu 1450

Add or delete a bridge device:

ip link add br0 type bridge
ip link del br0

Create a virtual Ethernet pair:

ip link add veth0 type veth peer name veth1

Manage Routing Tables

Display the main routing table:

ip route show table main

Add a default route:

ip route add default via 10.8.1.1 dev eth0

Add a static route:

ip route add 10.8.1.0/24 via 10.8.1.1

Replace an existing route:

ip route replace 10.8.1.0/24 dev eth0

Flush the routing table:

ip route flush cache

Manage Routing Rules

Show routing rules:

ip rule

Add a rule to use a specific table:

ip rule add from 10.8.1.0/24 table 520

Blackhole traffic from a specific source:

ip rule add from 0/0 blackhole

Manage Network Namespaces
List network namespaces:

ip netns

Create a network namespace:

ip netns add s1

Delete a namespace:

ip netns del s1

Execute a command within a namespace:

ip netns exec s1 ip addr

Example: Setting MTU

MTU (Maximum Transmission Unit) defines the maximum packet size for data transmission on a network device. Adjusting MTU impacts performance and compatibility.

View the current MTU for eth0:

ip link show eth0

Set MTU to 1450 bytes:

ip link set eth0 mtu 1450

Common MTU Values:

• Ethernet: 1500 bytes (default)
• PPPoE: 1492 bytes (8 bytes for headers)
• Wi-Fi: Often 1500 bytes but can vary slightly.

Quick Tips with ip

Color-coded output:

ip -c addr
ip -c route

Compact display:

ip -brief link
ip -brief addr

For detailed configuration guides, check the official documentation.