ip Command Linux: Complete Guide to Advanced Network Configuration and Management

The ip command is one of the most powerful and versatile networking tools in Linux, serving as the modern replacement for legacy commands like ifconfig, route, and arp. This comprehensive guide will take you through every aspect of the ip command, from basic usage to advanced network configuration scenarios.

What is the ip Command?

The ip command is part of the iproute2 package and provides a unified interface for network configuration and monitoring in Linux systems. It allows administrators to configure network interfaces, manage routing tables, set up tunnels, and perform various network-related tasks with precision and flexibility.

Key Advantages Over Legacy Tools

• Unified Interface: Single command for multiple networking tasks
• More Features: Advanced capabilities not available in older tools
• Better Performance: More efficient communication with the kernel
• Future-Proof: Actively maintained and updated
• Scriptable: Better suited for automation and scripting

Basic Syntax and Structure

The ip command follows a consistent syntax pattern:

ip [OPTIONS] OBJECT { COMMAND | help }

Common Objects

• link – Network interfaces
• addr – IP addresses
• route – Routing table
• neigh – Neighbor/ARP table
• tunnel – Tunnel interfaces
• rule – Routing policy database

Common Options

• -c – Colorize output
• -s – Show statistics
• -d – Show detailed information
• -j – JSON output format
• -p – Pretty print (human-readable)

Managing Network Interfaces

Viewing Network Interfaces

To display all network interfaces:

ip link show

Example Output:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 52:54:00:12:34:56 brd ff:ff:ff:ff:ff:ff
3: wlan0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether 00:11:22:33:44:55 brd ff:ff:ff:ff:ff:ff

Viewing Specific Interface

ip link show eth0

Enabling and Disabling Interfaces

To bring an interface up:

sudo ip link set eth0 up

To bring an interface down:

sudo ip link set eth0 down

Changing Interface Properties

Modify MTU size:

sudo ip link set eth0 mtu 1400

Change MAC address:

sudo ip link set eth0 address 00:11:22:33:44:66

Rename interface:

sudo ip link set eth0 name ethernet0

IP Address Management

Viewing IP Addresses

Display all IP addresses:

ip addr show

Or use the shorthand:

ip a

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
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 52:54:00:12:34:56 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.100/24 brd 192.168.1.255 scope global dynamic eth0
       valid_lft 86359sec preferred_lft 86359sec
    inet6 fe80::5054:ff:fe12:3456/64 scope link 
       valid_lft forever preferred_lft forever

Adding IP Addresses

Add a static IP address:

sudo ip addr add 192.168.1.150/24 dev eth0

Add multiple IP addresses to the same interface:

sudo ip addr add 10.0.0.10/24 dev eth0
sudo ip addr add 172.16.1.10/24 dev eth0

Removing IP Addresses

Remove a specific IP address:

sudo ip addr del 192.168.1.150/24 dev eth0

Remove all IP addresses from an interface:

sudo ip addr flush dev eth0

Routing Management

Viewing Routing Table

Display the main routing table:

ip route show

Or use shorthand:

ip r

Example Output:

default via 192.168.1.1 dev eth0 proto dhcp metric 100 
169.254.0.0/16 dev eth0 scope link metric 1000 
192.168.1.0/24 dev eth0 proto kernel scope link src 192.168.1.100 metric 100

Adding Routes

Add a default gateway:

sudo ip route add default via 192.168.1.1

Add a specific network route:

sudo ip route add 10.0.0.0/24 via 192.168.1.254 dev eth0

Add a host route:

sudo ip route add 203.0.113.10 via 192.168.1.1

Deleting Routes

Delete a specific route:

sudo ip route del 10.0.0.0/24

Delete default gateway:

sudo ip route del default

Advanced Routing Examples

Route with specific metric:

sudo ip route add 172.16.0.0/16 via 192.168.1.2 metric 200

Route through specific interface:

sudo ip route add 192.168.2.0/24 dev eth1

Neighbor (ARP) Table Management

Viewing ARP Table

Display neighbor table:

ip neigh show

Example Output:

192.168.1.1 dev eth0 lladdr aa:bb:cc:dd:ee:ff REACHABLE
192.168.1.50 dev eth0 lladdr 11:22:33:44:55:66 STALE
192.168.1.25 dev eth0 lladdr 77:88:99:aa:bb:cc DELAY

Adding ARP Entries

Add a static ARP entry:

sudo ip neigh add 192.168.1.200 lladdr 00:11:22:33:44:55 dev eth0

Deleting ARP Entries

Delete a specific ARP entry:

sudo ip neigh del 192.168.1.200 dev eth0

Flush ARP table for an interface:

sudo ip neigh flush dev eth0

Advanced Network Configuration

VLAN Configuration

Create a VLAN interface:

sudo ip link add link eth0 name eth0.100 type vlan id 100
sudo ip link set eth0.100 up
sudo ip addr add 192.168.100.10/24 dev eth0.100

Bridge Configuration

Create a bridge:

sudo ip link add name br0 type bridge
sudo ip link set br0 up
sudo ip link set eth0 master br0
sudo ip addr add 192.168.1.10/24 dev br0

Bonding/Teaming Configuration

Create a bonding interface:

sudo ip link add bond0 type bond mode 802.3ad
sudo ip link set eth0 master bond0
sudo ip link set eth1 master bond0
sudo ip link set bond0 up

Policy-Based Routing

Routing Rules

View routing rules:

ip rule show

Example Output:

0:	from all lookup local 
32766:	from all lookup main 
32767:	from all lookup default

Add a routing rule:

sudo ip rule add from 192.168.1.0/24 table 100

Custom Routing Tables

Create routes in custom table:

sudo ip route add 10.0.0.0/8 via 192.168.1.1 table 100
sudo ip route add default via 192.168.1.254 table 100

Tunnel Configuration

GRE Tunnel

Create a GRE tunnel:

sudo ip tunnel add gre1 mode gre remote 203.0.113.1 local 203.0.113.2
sudo ip link set gre1 up
sudo ip addr add 10.0.0.1/30 dev gre1

IPIP Tunnel

Create an IPIP tunnel:

sudo ip tunnel add ipip1 mode ipip remote 198.51.100.1 local 198.51.100.2
sudo ip link set ipip1 up
sudo ip addr add 172.16.0.1/30 dev ipip1

Network Statistics and Monitoring

Interface Statistics

Show detailed interface statistics:

ip -s link show eth0

Example Output:

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 52:54:00:12:34:56 brd ff:ff:ff:ff:ff:ff
    RX: bytes  packets  errors  dropped overrun mcast   
    1234567    9876     0       0       0       123     
    TX: bytes  packets  errors  dropped carrier collsns 
    2345678    8765     0       0       0       0

Route Statistics

Show route cache statistics:

ip -s route show

Troubleshooting Network Issues

Common Diagnostic Commands

Check connectivity to default gateway:

ip route get 8.8.8.8

Example Output:

8.8.8.8 via 192.168.1.1 dev eth0 src 192.168.1.100 uid 1000 
    cache

Monitoring Real-time Changes

Monitor network events in real-time:

ip monitor all

Monitor only route changes:

ip monitor route

Practical Examples and Use Cases

Network Interface Backup and Restore

Save current network configuration:

# Save interface configuration
ip addr show > /tmp/network-backup.txt

# Save routing table
ip route show > /tmp/routes-backup.txt

# Save ARP table
ip neigh show > /tmp/arp-backup.txt

Multi-homed Server Configuration

Configure a server with multiple network connections:

# Configure first interface (internal network)
sudo ip addr add 192.168.1.10/24 dev eth0
sudo ip route add 192.168.0.0/16 via 192.168.1.1 dev eth0

# Configure second interface (DMZ network)
sudo ip addr add 10.0.1.10/24 dev eth1
sudo ip route add 10.0.0.0/8 via 10.0.1.1 dev eth1

# Default route through external interface
sudo ip route add default via 203.0.113.1 dev eth2

Load Balancing Setup

Configure load balancing across multiple interfaces:

# Add multiple default routes with different metrics
sudo ip route add default via 192.168.1.1 dev eth0 metric 100
sudo ip route add default via 192.168.2.1 dev eth1 metric 200

# Or use equal-cost multi-path routing
sudo ip route add default nexthop via 192.168.1.1 dev eth0 weight 1 \
                           nexthop via 192.168.2.1 dev eth1 weight 1

Security Considerations

Best Practices

• Use sudo: Always use appropriate privileges for network changes
• Backup configurations: Save current settings before making changes
• Test changes: Verify connectivity after modifications
• Document changes: Keep records of network modifications
• Avoid conflicts: Check for conflicting routes and addresses

Securing Network Interfaces

Disable unused interfaces:

sudo ip link set wlan0 down

Remove unnecessary IP addresses:

sudo ip addr flush dev eth1

Automation and Scripting

JSON Output for Scripts

Get structured output for automation:

ip -j addr show | jq '.[] | select(.ifname=="eth0")'

Batch Configuration Script

#!/bin/bash
# Network configuration script

# Function to configure interface
configure_interface() {
    local interface=$1
    local ip_addr=$2
    local gateway=$3
    
    echo "Configuring $interface..."
    
    # Bring interface up
    ip link set $interface up
    
    # Add IP address
    ip addr add $ip_addr dev $interface
    
    # Add route if gateway provided
    if [ ! -z "$gateway" ]; then
        ip route add default via $gateway dev $interface
    fi
    
    echo "$interface configured successfully"
}

# Configure multiple interfaces
configure_interface eth0 "192.168.1.10/24" "192.168.1.1"
configure_interface eth1 "10.0.0.10/24"

Migration from Legacy Commands

Command Equivalents

Performance Optimization

Interface Optimization

Optimize network interface settings:

# Increase interface queue length
sudo ip link set eth0 txqueuelen 2000

# Set interface to promiscuous mode
sudo ip link set eth0 promisc on

# Configure interface buffer sizes
sudo ip link set eth0 mtu 9000  # Jumbo frames for LAN

Routing Optimization

Optimize routing performance:

# Add specific routes to avoid table lookups
sudo ip route add 192.168.100.0/24 dev eth1

# Use different metrics for load balancing
sudo ip route add 0.0.0.0/0 via 192.168.1.1 metric 100
sudo ip route add 0.0.0.0/0 via 192.168.2.1 metric 200

Conclusion

The ip command is an essential tool for Linux system administrators and network engineers. Its comprehensive feature set allows for sophisticated network configurations, from simple interface management to complex routing scenarios and tunnel setups.

Key takeaways from this guide:

• The ip command provides a unified interface for all network configuration tasks
• It offers more features and better performance than legacy networking tools
• Understanding object-based syntax is crucial for effective usage
• Advanced features like policy routing and tunneling enable complex network architectures
• Proper documentation and testing are essential for network changes

By mastering the ip command, you’ll be equipped to handle virtually any network configuration challenge in Linux environments. Practice with these examples in a test environment to build confidence before applying changes to production systems.

Remember to always backup your current network configuration before making significant changes, and test connectivity thoroughly after any modifications. The ip command’s power comes with responsibility – use it wisely to maintain stable and secure network operations.