Users Guide

1402 BGP
Dell EMC Networking BGP supports manual start and stop events. A manual
start event occurs when the user first configures a peer (neighbor remote-as)
or administratively enables a peer (no neighbor shutdown). A manual stop
event occurs when the user administratively disables a neighbor (neighbor
shutdown).
Of the optional events in RFC 4271 section 8.1.2 - 8.1.5, the following events
are supported:
• AutomaticStart_with_DampPeerOscillations (Event 6)
• AutomaticStop (Event 8)
• IdleHoldTimer_Expires (Event 13)
When an attempt to establish an adjacency fails, Dell EMC Networking puts
the adjacency in the IDLE state and starts the idle hold timer. When the idle
hold timer expires, Dell EMC Networking moves the adjacency to the
CONNECT state and initiates a new TCP connection. If the neighbor does not
respond to the connection request, Dell EMC Networking retries three times.
The first retry is done after the configured retry interval. Each subsequent retry
doubles the previous retry interval. So by default, the TCP connection is retried
after 2, 4, and 8 seconds. Configuring the initial retry interval to a large value
can prevent retries. The TCP stack times out a connection attempt in 20
seconds (after retransmitting the SYN segment according to normal retransmit
procedures), sends a TCP reset, and notifies the application of the connection
failure. The connection failure resets the BGP connect retry timer, puts the
adjacency in IDLE state, and starts the idle hold timer.
Dell EMC Networking BGP allows multiple BGP sessions between the same
two routers. However, each session must be established between different
pairs of IP addresses.
Dell EMC Networking BGP includes two capabilities in every OPEN message
it sends. The first is the Route Refresh capability described in RFC 2918. The
second is the multiprotocol capability described in RFC 4760. Dell EMC
Networking always advertises the IPv4/unicast AFI/SAFI pair. If the user has
activated IPv6 for the peer, the OPEN also includes the IPv6/unicast pair.
Even though Dell EMC Networking BGP does not support any AFI/SAFI
pairs other than IPv4/unicast when IPv6 is not enabled, Dell EMC
Networking advertises the multiprotocol capability with IPv4/unicast because
some other implementations appear to require this in order to establish an
adjacency.