10.4 Routing

Just because a host can communicate with other hosts of the same network does not mean it can communicate with hosts outside the network. In order for a host to communicate with hosts outside the network, it must be configured to route traffic properly.

Executing the command /sbin/route displays the current settings for routing purposes. There are several columns:

• Destination
  this is the distination network address for the rest of the row. A special address is default, which specifies all addresses other than the ones explicitly listed.
• Gateway
  this is the gateway machine to communicate with the state Destination network. A symbol of * means not applicable (no need to use a gateway).
• Genmask
  this is the netmask for the network address of the same row.
• Flags
  this specifies the kind of target/destination. Read the manual page of route to know more. The most common symbols are U for ‘up’ and G for ‘use gateway’. ‘Up’ simply means it is active.
• Iface
  this specifies the interface being associated with the row.

The command route should display a row like the following:

This designates <some-host> as the “default gateway” of the host.

If this line is missing, you can add your own default gateway as follows: