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Notes:
The RPSL policy of AS1 could be as follows :
RPSL policy for AS1
aut-num: AS1
import: from Cust1
action pref=100; community.append(AS1:Cust);
accept Cust1
from Peer1
action pref=500; community.append(AS1:Peer);
accept Peer1
from Prov1
action pref=1000; community.append(AS1:Prov);
accept ANY
export: to Cust1
announce ANY AND
( community.contains(AS1:Cust) OR community.contains(AS1:Peer)
OR community.contains(AS1:Prov) )
to Peer1 announce ANY AND community.contains(AS1:Cust)
to Prov1 announce ANY AND community.contains(AS1:Cust)
Instead of using the community attribute to indicate the type of peer from which a route has been learned, another possibility is to utilize one community value per type of peer to which the route should be learned. In this case, AS1, would utilize AS1:ToProvider to indicate that a route should be advertised to a provider, ... A route received from a customer site would be tagged with community values AS1:ToProvider, AS1:ToPeer, AS1:ToCustomer so that this route would be advertised over all eBGP sessions.