During normal BGP operation, peer routers redistribute routes from each other. However, in some specific situations it may be best to not advertise routes from one peer, such as if the peer is redundant with another peer (they share the same routes exactly), if it might be unreliable in some way, or some other reason. The FortiGate can also take routes it learns from other protocols and advertise them in BGP, for example OSPF or RIP. If your Company hosts its own web or email servers, external locations will require routes to your networks to reach those services.

In this example the Company has an internal network in an OSPF area, and is connected to a BGP AS and two BGP peers. Company goes through these two peers to reach the Internet. However, Peer 1 routes will not be advertised to Peer 2. The Company internal user and server networks are running OSPF, and will redistribute those routes to BGP so external locations can reach the web and email servers.

This section includes the following topics: