Chapter 4. Configuring Static Routes and the Default Gateway

Routing is a mechanism that allows a system to find the network path to another system. Routing is often handled by devices on the network dedicated to routing (although any device can be configured to perform routing). Therefore, it is often not necessary to configure static routes on Red Hat Enterprise Linux servers or clients. Exceptions include traffic that must pass through an encrypted VPN tunnel or traffic that should take a specific route for reasons of cost or security. A host's routing table will be automatically populated with routes to directly connected networks. The routes examine when the network interfaces are “up”. In order to reach a remote network or host, the system is given the address of a gateway to which traffic should be sent.

When a host's interface is configured by DHCP, an address of a gateway that leads to an upstream network or the Internet is usually assigned. This gateway is usually referred to as the default gateway as it is the gateway to use if no better route is known to the system (and present in the routing table). Network administrators often use the first or last host IP address in the network as the gateway address; for example, 192.168.10.1 or 192.168.10.254. Not to be confused by the address which represents the network itself; in this example, 192.168.10.0, or the subnet's broadcast address; in this example 192.168.10.255. The default gateway is traditionally a network router. The default gateway is for any and all traffic which is not destined for the local network and for which no preferred route is specified in the routing table.