route

Understanding Routing Tables

Before diving into the commands, let’s briefly understand routing tables. These tables act as a directory for your system’s network connections, mapping destination networks to the interfaces and gateways needed to reach them. When your system needs to send data to a destination, it consults the routing table to determine the best path.

Key ip route Commands and Options

The ip route command offers a wealth of options, allowing you to view, add, delete, and modify routing entries. Let’s look at some common commands and their usage:

1. Viewing Routing Tables

The simplest use of ip route is to display the current routing table:

ip route

This will output a list of routes, including the destination network, netmask, gateway, and interface.

2. Adding Static Routes

Adding a static route is essential for directing traffic to networks not automatically discovered by your system. The syntax is as follows:

ip route add <destination> via <gateway> dev <interface>

For example, to add a route to the 192.168.1.0/24 network via the gateway 192.168.0.1 using the eth0 interface:

sudo ip route add 192.168.1.0/24 via 192.168.0.1 dev eth0

You’ll need sudo privileges to modify routing tables. The /24 denotes the subnet mask.

3. Deleting Routes

Removing a route is equally important for network management. The command is:

sudo ip route del <destination> via <gateway> dev <interface>

To delete the route added in the previous example:

sudo ip route del 192.168.1.0/24 via 192.168.0.1 dev eth0

4. Specifying Metric

Routes can have associated metrics, influencing route selection. Lower metrics are preferred.

sudo ip route add 10.0.0.0/8 via 10.10.10.1 dev eth1 metric 20

This adds a route to 10.0.0.0/8 with a metric of 20.

5. Default Gateway

Setting a default gateway directs all traffic not explicitly routed otherwise:

sudo ip route add default via 192.168.0.1 dev eth0

This sets 192.168.0.1 as the default gateway on the eth0 interface.

6. Showing specific routes

You can filter the output by specifying a particular destination or interface

ip route show to 192.168.1.0/24
ip route show dev eth0

7. Using ip route list (synonym for ip route show)

ip route list functions identically to ip route show. It provides the same functionality with a slightly different command syntax.

These examples illustrate some core ip route functionalities. Exploring the man ip-route page provides a complete reference to all its capabilities, including advanced features like policy routing and route tables manipulation. Understanding and utilizing ip route is critical for effective Linux network administration.