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408 Nokia Network Voyager for IPSO 4.0 Reference Guide
distributed to other neighbors. The following table displays some special community attributes
that a BGP speaker can apply.
For further details, refer to the communities documents, RFCs 1997 and 1998.
Route Reflection
Generally, all border routers in a single AS need to be internal peers of each other; all nonborder
routers frequently need to be internal peers of all border routers. While this configuration is
usually acceptable in small networks, it can lead to unacceptably large internal peer groups in
large networks. To help address this problem, BGP supports route reflection for internal and
routing peer groups (BGP version 4).
When using route reflection, the rule that specifies that a router can not readvertise routes from
internal peers to other internal peers is relaxed for some routers called route reflectors. A typical
use of route reflection might involve a core backbone of fully meshed routers. This means that
all the routers in the fully meshed group peer directly with all other routers in the group. Some of
these routers act as route reflectors for routers that are not part of the core group.
Two types of route reflection are supported. By default, all routes received by the route reflector
that originate from a client are sent to all internal peers (including the client group but not the
client). If the no-client reflect option is enabled, routes received from a route reflection client are
sent only to internal peers that are not members of the client group. In this case, the client group
must be fully meshed. In either case, all routes received from a non-client internal peer are sent
to all route reflection clients.
Typically, a single router acts as the reflector for a set, or cluster, of clients; for redundancy, two
or more routers can also be configured to be reflectors for the same cluster. In this case, a cluster
ID should be selected to identify all reflectors serving the cluster, using the cluster ID keyword.
Note
Nokia recommends that you not use multiple redundant reflectors unnecessarily as it
increases the memory required to store routes on the peers of redundant reflectors.
Community attribute Description
NO_EXPORT (0xFFFFFF01) Not advertised outside a BGP confederation boundary. A
stand-alone autonomous system that is not part of a
confederation should be considered a confederation itself.
NO_ADVERTISE (0xFFFFFF02) Not advertised to other BGP peers.
NO_EXPORT_SUBCONFED(0xFFFFFF03) Not advertised to external BGP peers. This includes peers
in other members’ autonomous systems inside a BGP
confederation.