In BGP, neighboring routers are often configured with the same update policies. For example, the neighboring routers may have the same filtering applied. On Cisco routers, neighboring routers with the same update policies can be grouped into peer groups to simplify configuration and to make updating more efficient and improve performance. Members of the peer group inherit all the configuration options of the peer group.
Peer groups are more efficient because updates are generated only once per peer group rather than repetitiously for each neighboring router. The generated update is replicated for each neighbor that is part of the internal peer group. Peer groups save processing time in generating the updates for all IBGP neighbors. The peer group name is local to the router on which it is configured, and it is not passed to any other router. Peer groups make the router configuration easier to read and manage.
BGP supports Message Digest 5 (MD5) neighbor authentication. MD5 sends a "message digest" (also called a "hash") which is created using the key and a message. The message digest is then sent instead of the key. The key itself is not sent, preventing it from being read while it is being transmitted. This ensures that nobody can eavesdrop on the line and learn keys during transmission.
If there is an asterisk (*) in first column of the show ip bgp output, it means that the next-hop address (in the fifth column) is valid.