8.3 BGP Neighbor Negotiation
8.3.4 KEEPALIVE message
KEEPALIVEs are sent periodically at a rate that ensures the hold time will not expire. A recommended rate is one-third of the hold time interval. If the hold time interval is zero, periodic KEEPALIVE messages will not be sent. The KEEPALIVE message is a 19-byte BGP message header with no data following it.