Users Guide

1420 BGP
Communities
Dell EMC Networking BGP supports BGP standard communities as defined
in RFC 1997. Dell EMC Networking supports community lists for matching
routes based on community, and supports matching and setting communities
in route maps. Dell EMC Networking BGP recognizes and honors the
following well-known communities (RFC 1997):
• NO_EXPORT — A route carrying this community is not advertised to
external peers.
• NO_ADVERTISE — A route carrying this community is not advertised to
any peer.
• NO_EXPORT_SUBCONFED — A route carrying this community is not
advertised to external peers.
If Dell EMC Networking receives an UPDATE message with more than 512
communities, a NOTIFICATION message is returned to the sender with
error UPDATE message/attribute length error.
Routing Table Overflow
BGP Routing Table
Device configuration errors and other network transients can cause temporary
or sustained spikes in the BGP routing table size. To protect the router from
allocating too much memory in these scenarios, Dell EMC Networking BGP
limits the BGP routing table size. The limit is set to the number of routes
supported by the routing table (RTO). BGP imposes separate limits for each
address family it supports. Once the BGP routing table is full, new routes
computed in phase 2 of the decision process are not added to RTO and are
not used for forwarding, but are advertised to neighbors. When the BGP
routing table becomes full, a log message is written to the log warning the
administrator. While BGP remains in this state, it periodically writes a log
message that states the number of NLRI routes that could not be added to
the routing table.
BGP automatically recovers from a temporary spike in BGP routes above this
limit. When BGP cannot add a route to the BGP routing table, it sets the
phase 2 pending flag on that NLRI in the Accept RIB. While there are NLRI