BGP route advertisement

Hi!

Just like our IGPs we can use the network command to advertise something or we can redistribute networks into BGP. There’s one big difference though, the network command for BGP behaves differently.
When you use any of the IGPs then the network command is used to activate the IGP on all interfaces that fall within the range of the network command.
But when we use the network command in BGP then BGP will only look at the routing table. When it finds the network that matches the network command, it will install it in the BGP table and follow the next advertisement rules:
1. When multiple feasible routes to a destination exist, BGP advertises only the optimal route to its peers.
2. BGP advertises only routes that it uses.
3. BGP advertises routes learned from an EBGP peer to all BGP peers, including both EBGP and IBGP peers.
4. BGP advertises routes learned from an IBGP peer to EBGP peers, rather than other IBGP peers.

After establishing a session with a new BGP peer, BGP advertises all the routes matching the above rules to the peer. After that, BGP advertises only incremental updates to the peer.

Hope it helps you!

Hello user! hope it can help:

- A BGP Speaker advertises all BGP routes to new peers immediately after they establish BGP connections.
- Generally, when multiple routes exist, a BGP Speaker adds only the optimal route into its routing table.
-  A BGP speaker advertises the routes learned from an EBGP peer to all BGP peers, including EBGP peers and IBGP peers.

Thanks!