Default Originate vs Network 0.0.0.0

[Joe Lee]

All-

Can anyone please explaing to me what the difference between" neighbor x.x.x.x default originate" and "network 0.0.0.0" in the bgp routing?

Regards,

Joe

[Peter Paluch]

Hi Joe,

The neighbor default-originate command would advertise a default route only to the selected neighbor, regardless of whether the advertising router has a default route in its own routing table.

The network 0.0.0.0 command would search for a default route in the router's routing table and it would inject it into BGP table, subsequently advertising it to all BGP neighbors. If a default route is removed from the router's routin table, it will also be withdrawn from all BGP neighbors.

Best regards,

Peter

[Jose Jara]

Joe,

Other things to take into account:

- The default route advertised via default-originate does not pass by the filters (Adj-Rib-Out), so it will be advertised regardless of any filter you are applying to the neighbor. For example, if you are applying a filter to the neighbor like route-map, as-path filter list, distribute-list or prefix-list denying everything, the default route will still be advertised. Be aware of that in case you are manipulating any BGP attribute, as in this case it will have no effect.

The way you should manipulate the attributes to the default is via neighbor default-originate route-map.

Also, you may do a conditional default with the route-map. For example, advertising the default route in case a specific prefix exists in the route-table.

Best Regards,

Jose.

[Peter Paluch]

Hello Jose,

Very good points indeed. Rated as deserved, and I am glad you've joined this thread!

Best regards,

Peter