GP neighbors use a KEEPALIVE message to confirm that the con-
nection between the neighbors is still active. A BGP speaker sends a KEE- PALIVE to each peer, usually at an interval of one-third of the agreed hold time, which is no more than once per second. If an UPDATE message is not sent during the established hold time, a KEEPALIVE message is sent in its place. A KEEPALIVE message consists only of a 19-byte header and can be turned off by setting the hold time to zero.
his chapter focused on BGP terminology and the basics components
of BGP. Let's quickly review what this chapter covered:
Autonomous systems, which are used to identify routers operating in a common network.
Transit autonomous systems, which are between two autonomous systems.
AS routing loop or looping prefix error
Invalid NEXT_HOP prefix
Optional attribute error
Invalid network field when processing a prefix update
Error encountered processing the AS_PATH attribute
T A B L E 7 . 8
Error Subcodes for UPDATE Message Errors (continued)