IP Command in Linux: The Modern Replacement for ifconfig

Introduction

The ip command is a powerful and versatile networking utility in Linux systems that serves as the modern replacement for traditional networking tools like ifconfig, route, and arp. Part of the iproute2 package, the ip command provides a unified interface for configuring and managing various aspects of network settings in modern Linux distributions.

Unlike its predecessors, the ip command offers more features, better performance, and a more consistent syntax for managing network interfaces, routing tables, addresses, and more. This comprehensive documentation explores the capabilities, syntax, and practical applications of the ip command.

Basic Syntax

The general syntax of the ip command follows this pattern:

ip [OPTIONS] OBJECT {COMMAND | help}

Where:

• OPTIONS: Additional parameters that modify the behavior of the command
• OBJECT: The networking component you want to interact with (e.g., link, address, route)
• COMMAND: The action you want to perform on the specified object
• help: Displays help information about the specified object or command

Common Objects in the IP Command

The ip command works with several objects, each representing a different aspect of network configuration:

Key IP Command Operations

1. Managing Network Interfaces with ip link

The ip link object allows you to view and manage network interfaces at the link layer.

Displaying Network Interfaces

To list all network interfaces:

ip link show
# or shorter form
ip l

This command displays information about all network interfaces, including their state (UP/DOWN), MAC address, and other link-layer details.

Activating or Deactivating an Interface

To bring an interface up (activate it):

sudo ip link set dev eth0 up

To bring an interface down (deactivate it):

sudo ip link set dev eth0 down

Changing Interface Properties

To change the MTU (Maximum Transmission Unit) of an interface:

sudo ip link set dev eth0 mtu 1500

To change the MAC address of an interface:

sudo ip link set dev eth0 address 00:11:22:33:44:55

2. Managing IP Addresses with ip address

The ip address (or ip addr) object allows you to view and manage IP addresses assigned to network interfaces.

Displaying IP Addresses

To show IP addresses for all interfaces:

ip address show
# or shorter form
ip a

To show IP addresses for a specific interface:

ip address show dev eth0

Adding an IP Address to an Interface

To add an IPv4 address to an interface:

sudo ip address add 192.168.1.100/24 dev eth0

To add an IPv6 address to an interface:

sudo ip address add 2001:db8::1/64 dev eth0

Removing an IP Address from an Interface

To remove an IPv4 address from an interface:

sudo ip address del 192.168.1.100/24 dev eth0

3. Managing Routing with ip route

The ip route object allows you to view and manage the routing table.

Displaying Routes

To show the routing table:

ip route show
# or shorter form
ip r

Adding a Route

To add a default route (gateway):

sudo ip route add default via 192.168.1.1 dev eth0

To add a route to a specific network:

sudo ip route add 10.0.0.0/24 via 192.168.1.254 dev eth0

Deleting a Route

To delete a route:

sudo ip route del 10.0.0.0/24

Finding the Route for a Specific Destination

To find which route would be used to reach a specific IP address:

ip route get 8.8.8.8

4. Managing ARP Cache with ip neigh

The ip neigh object allows you to view and manage the ARP (Address Resolution Protocol) cache.

Displaying ARP Cache

To show the ARP cache:

ip neigh show

Adding an ARP Entry

To add a static ARP entry:

sudo ip neigh add 192.168.1.5 lladdr 00:11:22:33:44:55 dev eth0

Deleting an ARP Entry

To delete an ARP entry:

sudo ip neigh del 192.168.1.5 dev eth0

Advanced IP Command Features

1. Network Namespaces

Network namespaces allow for isolated network environments within a single Linux system. The ip netns command is used to manage these namespaces.

# Create a new namespace
sudo ip netns add mynetns
 
# List all namespaces
ip netns list
 
# Execute a command in a namespace
sudo ip netns exec mynetns ip addr

2. Virtual Ethernet Interfaces

Virtual Ethernet (veth) interfaces are used to create tunnels between network namespaces.

# Create a veth pair
sudo ip link add veth0 type veth peer name veth1
 
# Move one end to a namespace
sudo ip link set veth1 netns mynetns

3. Traffic Control

The ip command can be used with the tc (Traffic Control) subsystem to manage network traffic.

# Add a queueing discipline
sudo tc qdisc add dev eth0 root netem delay 100ms
 
# Show queueing disciplines
tc qdisc show dev eth0

Practical Examples

Example 1: Setting Up a Secondary IP Address

# Add a secondary IP address to eth0
sudo ip addr add 192.168.2.10/24 dev eth0
 
# Verify the configuration
ip addr show dev eth0

Example 2: Creating a Static Route for a Specific Network

# Add a route to the 10.0.0.0/8 network via a specific gateway
sudo ip route add 10.0.0.0/8 via 192.168.1.254 dev eth0
 
# Verify the route
ip route show

Example 3: Monitoring Interface Statistics

# Show detailed statistics for an interface
ip -s link show dev eth0

Comparison with Legacy Commands

Conclusion

The ip command is a powerful and versatile tool for network configuration and management in Linux systems. It provides a unified interface for managing various aspects of networking, from interfaces and addresses to routes and ARP cache entries. By mastering the ip command, system administrators and network engineers can efficiently configure and troubleshoot network-related issues in modern Linux environments.

As Linux networking continues to evolve, the ip command remains an essential tool in the administrator's toolkit, offering more features and better performance than its legacy counterparts. Whether you're configuring a simple home network or managing complex enterprise networking environments, the ip command provides the flexibility and power needed to get the job done efficiently.