A brief note on the rules for originating a default route into BGP (copied from a posting made by Mohammed Mahmoud):
- default-information originate + redistribute static (or any dynamic routing protocol having the default route - you may filter only the default route)
- network command but must make sure the default route is present in the routing table
- issuing the neighbor default-originate command. This method does not require the presence of the 0.0.0.0/0 network in the routing table of the advertising router
Additional notes: The configuration of the default-information originate command in BGP is similar to the configuration of the network (BGP) command. The default-information originate command, however, requires explicit redistribution of the route 0.0.0.0. The network command requires only that the route 0.0.0.0 is present in the Interior Gateway Protocol (IGP) routing table. For this reason, the network command is preferred.