A BGP message consists of a BGP header and a data portion. BGP runs by sending five types of messages: Open, Update, Notification, Keepalive, and Route-refresh. These messages use the same header format. BGP messages are transmitted based on TCP (port 179). The message length varies from 19 octets to 4096 octets. The header of each BGP message is 19 octets, consisting of three fields.