Linux route Command

Linux 命令大全Linux Command Reference

1. Overview of the route Command

The route command is a powerful tool in Linux systems for viewing and manipulating the IP routing table. As a basic command for network configuration, it allows administrators to:

  • Display current routing table information
  • Add/delete static routes
  • Modify existing routing rules
  • Manage the transmission path of network packets

Basic Syntax

route [选项] [操作] [目标] [命令参数]

2. Basic Concepts of the Routing Table

1. What is a Routing Table

The routing table is a data structure maintained by the operating system kernel that determines how network packets are transmitted from the source address to the destination address. It can be compared to:

"An urban traffic navigation system: when you want to go to a destination, the system tells you which road to take is the fastest and most efficient"

2. Key Fields of the Routing Table

Viaroute -nWhen viewing the routing table, the following important columns are displayed:

Column Name Description Example Value
Destination Destination network or host 192.168.1.0
Gateway Next-hop gateway 192.168.1.1
Genmask Network mask 255.255.255.0
Flags Route flags U (route is enabled)
Metric Route cost 0
Iface Outgoing interface eth0

3. Common Operations of the route Command

1. View the Routing Table

Example

# Display the complete routing table (without resolving hostnames)
route -n

# Example output:
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.1.1     0.0.0.0         UG    0      0        0 eth0
192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0 eth0

2. Add a Route

Example

# Add a route to a specific host
route add -host 192.168.1.100 dev eth0

# Add a route to a network
route add -net 192.168.2.0 netmask 255.255.255.0 gw 192.168.1.1

# Add a default gateway
route add default gw 192.168.1.1

3. Delete a Route

Example

# Delete a specific route
route del -net 192.168.2.0 netmask 255.255.255.0

# Delete the default gateway
route del default gw 192.168.1.1

4. Detailed Explanation of Command Options

The route command supports the following common options:

Option Description
-n Display addresses in numeric form (do not resolve hostnames)
-e Display the routing table using netstat format
-v Display detailed operation information
-A family Specify the address family (inet, inet6, etc.)
-F Display the kernel FIB routing table
-C Display the route cache

Special command parameters:

  • add: Add a route
  • del: Delete a route
  • -host: Operation targets a specific host
  • -net: Operation targets an entire network
  • gw: Specify the gateway
  • dev: Specify the network interface

5. Practical Application Scenarios

Scenario 1: Multi-NIC Route Configuration

When a server has multiple network interfaces, you need to specify the egress for different networks:

Example

# Make traffic destined for 10.0.0.0/24 go through the eth1 interface
route add -net 10.0.0.0 netmask 255.255.255.0 dev eth1

Scenario 2: VPN Route Settings

After connecting to a VPN, you need to add specific routes:

Example

# Only let a specific subnet go through the VPN tunnel
route add -net 172.16.0.0 netmask 255.240.0.0 dev tun0

Scenario 3: Temporary Route Testing

Example

# Temporarily add a route for testing (will be lost after reboot)
route add -host 8.8.8.8 gw 192.168.1.254
ping 8.8.8.8  # Test whether the route is effective
route del -host 8.8.8.8  # Delete after testing is complete

6. Persistent Route Configuration

Routes added via the route command will be lost after a reboot. To make them take effect permanently:

1. Debian/Ubuntu Systems

Edit/etc/network/interfaces：

Example

auto eth0
iface eth0 inet static
    address 192.168.1.100
    netmask 255.255.255.0
    gateway 192.168.1.1
    up route add -net 10.0.0.0 netmask 255.0.0.0 gw 192.168.1.2

2. RHEL/CentOS Systems

Create a route configuration file/etc/sysconfig/network-scripts/route-eth0：

10.0.0.0/8 via 192.168.1.2

7. Troubleshooting Common Issues

1. Steps to Check When a Route Is Not Effective

2. Typical Error Resolution

Error 1："SIOCADDRT: Network is unreachable"

  • Cause: The gateway is not within the direct broadcast domain of the local network
  • Solution: First make sure you can ping the gateway address

Error 2："RTNETLINK answers: File exists"

  • Cause: Attempting to add an already existing route
  • Solution: Delete the old route first and then add it, or use thereplaceoption

8. Alternative Command: ip route

Modern Linux systems recommend using theip routecommand:

Example

# Display the routing table
ip route show

# Add a route
ip route add 10.0.0.0/8 via 192.168.1.2

# Delete a route
ip route del 10.0.0.0/8

Althoughip routeis more powerful, but theroutecommand is still widely used because it is simple and intuitive.

Through this guide, you should have mastered the core usage of the route command. It is recommended to practice these commands more in a real environment and observe the impact of route changes on network connections. When encountering complex routing problems, you can combine them withtracerouteandpingand other tools for comprehensive diagnosis.

Linux 命令大全Linux Command Reference

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