Users Guide

1418 BGP
in this state, BGP periodically checks if there is space available in the BGP
routing table, and if so, runs phase 2. When space becomes available in the
BGP routing table, these routes are added.
RTO Full Condition
If BGP computes a new route but the routing table does not accept the route
because it is full, BGP flags the route as one not added to RTO. BGP
periodically tries to add these routes to RTO. BGP will continue to advertise
the best routes to neighbors, even if they are not added to RTO. The only
necessary condition for forwarding a route to the neighbor is that the route is
the best route in the BGP database. When used in conjunction with VRFs,
this rule may make routing black holes likely unless the network capacity is
planned correctly.
Route Reflection
Dell EMC Networking BGP can be configured as a route reflector as
described in RFC 4456. Like any BGP implementation, Dell EMC
Networking BGP can also act as a route reflector client. Route reflection
eliminates the need to configure a full mesh of iBGP peering sessions. As its
name implies, this feature allows a router to reflect a route received from an
internal peer to another internal peer. Under conventional BGP rules, a router
can only send routes learned from an external peer or routes locally originated
to an internal peer. A route reflector will advertise routes learned from an
iBGP speaker designated as a route reflector client to other iBGP speakers.
The administrator can configure an internal BGP peer to be a route reflector
client. Alternatively, the administrator can configure a peer template to make
any inheriting peers route reflector clients. The client status of a peer can be
configured independently for IPv4 and IPv6.
A cluster may have multiple route reflectors. Route reflectors within the same
cluster are configured with a cluster ID. When a route reflector reflects a
route, it prepends its cluster ID to a list of cluster IDs in the CLUSTER_LIST
attribute.
RFC 4456 notes that:
"...when a RR reflects a route, it SHOULD NOT modify the following path
attributes: NEXT_HOP, AS_PATH, LOCAL_PREF, and MED. Their
modification could potentially result in routing loops."