Peer-groups
All members MUST share a common outbound policy.
The same UPDATE message is sent to all the peers.
Examples:
RR-clients, but not a mixture of clients and iBGP peers
iBGP OR eBGP peers, but not both in the same peer-group
NEXT_HOP is an exception to the rule. Peers A and B can be in a peer-group and receive a different NEXT_HOP for an UPDATE. Accomplished by doing the NEXT_HOP re-write at the last minute