BSCI - BGP - Message Types

As with all routing protocols there are a number of different messages types with differing duties/purposes.

For BGP we have:

1. OPEN - Includes BGP version number, AS number (ASN), Hold Time, BGP router-id, other optional parameters such as Authentication criteria
2. Keepalives - Exchanged to prevent the hold time expiring, where hold time is 0 keepalives are not sent. Keepalives are sent every 60seconds
3. UPDATE - information on 1 path only. Multiple paths require multiple update messages. All attributes in an update refer to the path. This includes - Withdrawn routes, Path attributes, Network Layer Reachability (list of ip prefixes reachable via the path)
4. Notification Messages - sent due to error condition being met. BGP connection is closed immediately after one of these is sent.