ip route - Linux IP Routing Management Guide

Table of Contents

• Overview
• Basic Usage
• Route Management
• Gateway Configuration
• Policy Routing
• Advanced Options
• Troubleshooting
• Best Practices

Overview

ip route is the modern command for managing IP routing tables in Linux systems. Part of the iproute2 package, it provides comprehensive routing control and network configuration capabilities.

Key Features

• Route table management
• Policy-based routing
• Multiple routing tables
• Advanced routing metrics
• VRF support
• MPLS routing
• Traffic control integration

Basic Usage

Display Routes

# Show all routes
ip route show
 
# Show route details
ip route show detail
 
# Show statistics
ip -s route show
 
# Watch route changes
watch -n1 'ip route show'

Basic Format

# General syntax
ip route {add|del|change|append|replace} prefix [via gateway] [dev interface]

Route Management

Add Routes

# Add network route
sudo ip route add 192.168.2.0/24 via 192.168.1.1
 
# Add route via interface
sudo ip route add 192.168.2.0/24 dev eth0
 
# Add default route
sudo ip route add default via 192.168.1.1

Delete Routes

# Delete specific route
sudo ip route del 192.168.2.0/24
 
# Delete route via gateway
sudo ip route del 192.168.2.0/24 via 192.168.1.1
 
# Delete default route
sudo ip route del default

Modify Routes

# Change existing route
sudo ip route change 192.168.2.0/24 via 192.168.1.2
 
# Replace route
sudo ip route replace 192.168.2.0/24 via 192.168.1.2
 
# Append route
sudo ip route append 192.168.2.0/24 via 192.168.1.2

Gateway Configuration

Default Gateway

# Add default gateway
sudo ip route add default via 192.168.1.1
 
# Add with metric
sudo ip route add default via 192.168.1.1 metric 100
 
# Add with interface
sudo ip route add default via 192.168.1.1 dev eth0

Multiple Gateways

# Primary gateway
sudo ip route add default via 192.168.1.1 metric 100
 
# Backup gateway
sudo ip route add default via 192.168.1.2 metric 200

Policy Routing

Routing Tables

# Show all tables
ip route show table all
 
# Add route to specific table
sudo ip route add 192.168.2.0/24 via 192.168.1.1 table 100
 
# Delete route from table
sudo ip route del 192.168.2.0/24 table 100

Route Rules

# Show rules
ip rule show
 
# Add rule
sudo ip rule add from 192.168.1.0/24 table 100
 
# Delete rule
sudo ip rule del from 192.168.1.0/24 table 100

Advanced Options

Route Metrics

# Add route with metric
sudo ip route add 192.168.2.0/24 via 192.168.1.1 metric 100
 
# Add with multiple metrics
sudo ip route add 192.168.2.0/24 via 192.168.1.1 metric 100 mtu 1500

Route Types

# Prohibit route
sudo ip route add prohibit 192.168.2.0/24
 
# Blackhole route
sudo ip route add blackhole 192.168.2.0/24
 
# Unreachable route
sudo ip route add unreachable 192.168.2.0/24

Route Caching

# Show route cache
ip route show cache
 
# Flush route cache
sudo ip route flush cache

Troubleshooting

Common Issues

1. Route Conflicts

# Check existing routes
ip route show
 
# Check specific network
ip route show match 192.168.2.0/24
 
# Check route details
ip route show 192.168.2.0/24 detail

2. Gateway Issues

# Verify gateway reachability
ping gateway_ip
 
# Check gateway routes
ip route get gateway_ip
 
# Monitor gateway
ip monitor route

3. Interface Problems

# Check interface status
ip link show dev eth0
 
# Verify interface routes
ip route show dev eth0
 
# Monitor interface
ip monitor route dev eth0

Best Practices

Route Management

# Backup current routes
ip route show > routes_backup.txt
 
# Verify changes
ip route get 192.168.2.1
 
# Monitor changes
ip monitor route

Security Considerations

# Block networks
sudo ip route add blackhole 10.0.0.0/8
 
# Monitor route changes
watch -n1 'ip route show'
 
# Log changes
ip monitor route | logger

Quick Reference

Essential Commands

# Show routes
ip route show
 
# Add route
sudo ip route add network/mask via gateway_ip
 
# Delete route
sudo ip route del network/mask
 
# Get specific route
ip route get destination_ip

Common Options

show    # Display routes
add     # Add route
del     # Delete route
change  # Modify route
replace # Replace route
get     # Get specific route

Example Configurations

Basic Network Setup

# Default gateway
sudo ip route add default via 192.168.1.1
 
# Local network
sudo ip route add 192.168.1.0/24 dev eth0
 
# Remote network
sudo ip route add 10.0.0.0/8 via 192.168.1.254

Advanced Routing

# Multiple paths
sudo ip route add 192.168.2.0/24 \
  nexthop via 192.168.1.1 weight 1 \
  nexthop via 192.168.1.2 weight 2
 
# Policy routing
sudo ip route add 192.168.2.0/24 via 192.168.1.1 table 100
sudo ip rule add from 192.168.1.100 table 100

VPN Configuration

# Add VPN route
sudo ip route add 10.0.0.0/8 dev tun0
 
# Split tunneling
sudo ip route add default via 10.8.0.1 table 200
sudo ip rule add from 192.168.1.0/24 table 200

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Remember:

• Always backup before changes
• Test changes thoroughly
• Document configurations
• Monitor route changes
• Consider security implications
• Use appropriate metrics

For detailed information, consult the man pages (man ip-route).