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| 3.2 |  | Default Routing |
| 3.2.2 |  | Configuring static default routes |

Creating an ip route to 0.0.0.0/0 is the simplest way to configure a default route. This is done using the following syntax:

> Router(config)#ip route 0.0.0.0 0.0.0.0 [next-hop-ip-address | exit-interface]

To the Cisco IOS, network 0.0.0.0 /0 has special meaning as the gateway of last resort. All destination addresses match this route because a mask of all 0s requires none of the 32 bits in an address to be an exact match.

A route to 0.0.0.0 /0 is often called a quad-zero route. Manually configuring 0.0.0.0/0 routes on every router might suffice in a simple network. Routers may need to dynamically exchange default routes in more complex situations. The exchange of default information works differently depending on the routing protocol being used and can create severe problems when improperly configured. Default routes typically point outside the network. Therefore, default routes are noticeable when they fail.

Static routes to 0.0.0.0/0 are automatically propagated to other routers in RIP updates. The only way to stop this automatic update is to use a route filter. A route filter configuration option is discussed in Module 8, Route Optimization.

In IOS releases 12.1 and later, RIP does not propagate a static default route automatically. When using RIP and IOS 12.1, the RIP process must be manually configured to advertise the static default route by issuing the network 0.0.0.0 command.

Alternately, the default-information originate or the redistribute static command may be used to configure static default route propagation. Regardless of the IOS version, the OSPF requires the default-information originate command to propagate the static default routes. The following example illustrates this configuration for RIP. Figure .

> RTY(config)#ip route 0.0.0.0 0.0.0.0 172.16.1.2
> RTY(config)#router rip
> RTY(config-router)#default-information originate

Using the default-information originate command, an administrator can statically configure a single RIP router with a 0.0.0.0/0 route, and that default route will be propagated to other routers. The default-information originate command can also be used with OSPF to achieve the same effect.

| Lab Activity e-Lab Activity: Configuring Static Default Routers This lab is to create a static default route and let RIP propagate the route to other routers.