Sorry I am totally new to BGP.
I have a VPN connection, that uses BGP as a routing protocol (Amazon VPC).
When I look at my bgp neighbour, and issue the following commands :-
sh ip bgp all neighbors xx received-routes
sh ip bgp all neighbors xx advertised-routes
I see the same route that I recieved, begin advertised back to the neighbour.
Is there no split-horizon type rule in BGP ?
I thought that if the same AS path exists in a route then BGP will not advertise it back to the neighbour with that AS.
Indeed you shouldn't if you really receive that route from the same neighbor you are trying to advertise it to.
But as i mentioned above, if you receive the route from 2 routers, both in the same AS, you will advertise that upstream to the other one!
The router that receives that will drop it on it's side as it sees it's own AS path in the list.
If you want to control that use as path access-lists