If you want a router to serve as a default destination for traffic from other routers that do not know where to forward traffic, you can configure the router to advertise a default route. Use the neighbor default-originate command to specify the neighbors to which this router will advertise the default route. Said another way, these neighbors will dynamically learn the default route from the router you configure.
If you issue the neighbor default-originate command, BGP sends the default route to that neighbor regardless of whether the default route exists in the IP forwarding table.
In Figure 15, router NY originates the default route 0.0.0.0/0 to router Albany only. Router Chicago does not receive the default route.
Figure 15: Advertising a Default Route
To configure router NY:
- host1(config)#router bgp 200
- host1(config-router)#network 192.168.42.0
mask 255.255.254.0
- host1(config-router)#neighbor 10.3.3.1 remote-as
300
- host1(config-router)#neighbor 192.168.10.2
remote-as 100
- host1(config-router)#neighbor 192.168.10.2
default-originate
You can also specify a route map to modify the attributes of the default route. If the default route does not match the route map, then the default route is not advertised.
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