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Chapter 9
BGP Scalability and Advanced Features
concentration router for the entire network. All the other BGP routers in the
AS need only peer with the concentration router; they become known as clients.
Route reflectors reduce the number of BGP neighbor peering relationships in
an AS by maintaining a single central source for updates to their route reflec-
tor clients.
Some of the main things to remember when using route reflectors are
listed below:
Route reflectors are used when the internal neighbor statements
become excessive.
Route reflectors do not affect the paths that IP packets take through
the network; they only identify how the routing information is distrib-
uted through the network.
Route reflectors relieve iBGP of a full-mesh requirement.
An IGP is still used in order to carry local routes and next-hop
addresses.
Route reflectors receive updates from their configured peers whether
they are clients or non-clients.
Non-client refers to any iBGP peer that is not participating in the route reflec-
tor cluster as a client.
Non-client updates are sent to route reflector clients in the cluster only.
Updates from eBGP peers are sent to all clients and non-clients.
Updates that the route reflector receives from a route reflector client
are sent to all non-client peers and all route reflector clients, with the
exception of the client listed in the ORIGINATOR_ID attribute field.
You can configure multiple route reflectors for redundancy purposes.
Other iBGP and eBGP peers can co-exist.
Route reflectors modify the BGP split-horizon rule by allowing the
router configured as the route reflector (the concentration router) to
be the only router that propagates routes learned by iBGP to other
iBGP peers.
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