Users Guide

Table Of Contents
1382 BGP
At startup, when the saved configuration is applied, there could potentially be
a lot of churn to outbound update groups and filtering of routing
information. This startup churn is avoided by keeping BGP globally disabled
until after the entire configuration is applied and the status of all routing
interfaces is known.
BGP Timers
Dell EMC Networking BGP supports the five mandatory timers described in
RFC 4271 section 10. Dell EMC Networking BGP employs the optional
IdleHoldTimer, but does not support a DelayOpenTimer.
When Dell EMC Networking BGP initiates a TCP connection to a peer, it
starts a retry timer (ConnectRetryTimer from RFC 4271). If the connection
is not established before the retry timer expires, BGP initiates a new TCP
connection attempt. Up to 3 retries are attempted with an exponential back-
off of the retry time. The initial retry time is configurable per neighbor.
The IDLE hold timer runs when a peer has automatically transitioned to the
IDLE state. When the IDLE hold timer expires, BGP attempts to form an
adjacency. The IDLE hold time is a jittered to avoid synchronization of
retries. The idle hold time varies depending on the event that triggered the
transition to IDLE.
Dell EMC Networking BGP starts hold and keep-alive timers for each peer.
When BGP establishes an adjacency, the neighbors agree to use the
minimum hold time configured on either neighbor. BGP sends KEEPALIVE
messages at either 1/3 of the negotiated hold time or the configured keepalive
interval, whichever is more frequent. Keepalive times are jittered.
RFC 4271 section 9.2.1.1 specifies a “minimum amount of time that must
elapse between an advertisement and/or withdrawal of routes to a particular
destination by a BGP speaker to a peer.” In Dell EMC Networking BGP, this
advertisement interval is configurable independently for each peer, defaulting
to 30 seconds for external peers and 5 seconds for internal peers. The
advertisement interval may be configured to 0. Dell EMC Networking BGP
enforces the advertisement interval by limiting how often phase 3 of the
decision process can run for each outbound update group. The advertisement
interval is applied to withdrawals as well as active advertisements.