Administrator Guide

1344 BGP
Communities
Dell Networking BGP supports BGP standard communities as defined in
RFC 1997. Dell Networking supports community lists for matching routes
based on community, and supports matching and setting communities in
route maps. Dell 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 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 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