Static routing

A route is a rule, set in the kernel, used to determine which physical network interface or gateway is needed in order to reach a particular network (or single host). There are many types of routed protocols; this article simply Article description::covers routing of the IP protocol in the Linux kernel.

Although IP routes are stored in the kernel, they are modifiable by userspace tools as described in the following examples.

Showing routes
Show the routing table with iproute2:

Or show the routing table using :

Adding a static route
The IP address, subnet mask (CIDR), and gateway are necessary prerequisite information before adding a static route.

In this example the 10.10.10.0 network with a 255.255.255.0 subnet mask will be routed to the 192.168.1.50 gateway. CIDR style netmasks are required when adding routes using commands from the package. The following example will add the 10.10.10.0/24 route:

Show the routing table using the command:

Older systems may possibly only have the or  commands (via ) instead of  used in the above example.

Adding the same static route as described above using the command:

Show routing table using :

The routing table is sorted from most specific routes to most general. This is how it is read by the routing process. Longest prefix match - means the the smallest network, or the network with the largest netmask, or the most specific route f.e. 255.255.255.255 is at first position in the routing table.

Adding a permanent static route
For users of the netifrc scripts (OpenRC's standard network tools), permanent static routes can be added by opening a preferred text editor to and adjusting the file accordingly.

Reference the current routing table for help.

With dhcpcd as network manager the static route goes into Dhcpcd instead.

Both statements above mean:


 * 1) IP packets destined to the 10.10.10.0/24 network are send to 192.168.1.50.
 * 2) IP packets destined to all 0.0.0.0/0 other networks are send to 192.168.1.1.

The default route 0.0.0.0/0 is used if:


 * The host has no physical or logical IP interface in the target network segment.
 * The host has to send IP packets outside of its own IP network segment, and there is no specific route found in the routing table for target IP network.

External resources

 * Longest prefix match (on Wikipedia)