6.1 Introduction to Static Routing  
  6.1.4 Configuring default route forwarding  
Default routes are used to route packets with destinations that do not match any of the other routes in the routing table. Routers are typically configured with a default route for Internet-bound traffic, since it is often impractical and unnecessary to maintain routes to all networks in the Internet. A default route is actually a special static route that uses this format:

ip route 0.0.0.0 0.0.0.0 [next-hop-address | outgoing interface]

The 0.0.0.0 mask, when logically ANDed to the destination IP address of the packet to be routed, will always yield the network 0.0.0.0. If the packet does not match a more specific route in the routing table, it will be routed to the 0.0.0.0 network.

Use the following steps to configure default routes:

  1. Enter global configuration mode.
  2. Type the ip route command with 0.0.0.0 for the destination network address and 0.0.0.0 for the subnet mask. The gateway for the default route can be either the local router interface that connects to the outside networks or the IP address of the next-hop router. In most cases, it is preferred that the IP address of the next hop router is specified.
  3. Exit global configuration mode.
  4. Save the active configuration to NVRAM by using the copy running-config startup-config command.

In the section Configuring Static Routes, static routes were configured on Hoboken to make networks 172.16.1.0 on Sterling and 172.16.5.0 on Waycross accessible. It should now be possible to route packets to both of these networks from Hoboken. However, neither Sterling nor Waycross will know how to return packets to any non-directly connected network. A static route could be configured on Sterling and Waycross for each of the non-directly connected destination networks. This would not be a scalable solution on a larger network.

Sterling connects to all non-directly connected networks via interface Serial 0. Waycross has only one connection to all non-directly connected networks. This is through interface Serial 1. A default route on both Sterling and Waycross will provide routing for all packets that are destined for non-directly connected networks.

 

Lab Activity

e-Lab Activity: Configuring Default Route Forwarding

In this lab, the students will configure a default static route.

 
 

Web Links

ip default-network Command

http://www.cisco.com/en/US/products/sw/ iosswrel/ps1835/products_command_reference_ chapter09186a00800ca75a.html#1017820