Route Reflector - Lenovo RackSwitch G8264 Application Manual

Route Reflector

© Copyright Lenovo 2016
Typically, an AS has one or more border routers—peer routers that exchange routes
with other ASs—and an internal routing scheme that enables routers in that AS to
reach every other router and destination within that AS. When you advertise routes
to border routers on other autonomous systems, you are effectively committing to
carry data to the IPv4 space represented in the route being advertised. For
example, if you advertise 192.204.4.0/24, you are declaring that if another router
sends you data destined for any address in 192.204.4.0/24, you know how to carry
that data to its destination.
The Enterprise NOS implementation conforms to the BGP Route Reflection
specification defined in RFC 4456.
As per RFC 1771 specification, a route received from an iBGP peer cannot be
advertised to another iBGP peer. This makes it mandatory to have full‐mesh iBGP
sessions between all BGP routers within an AS. A route reflector—a BGP router—
breaks this iBGP loop avoidance rule. It does not affect the eBGP behavior. A route
reflector is a BGP speaker that advertises a route learnt from an iBGP peer to
another iBGP peer. The advertised route is called the reflected route.
A route reflector has two groups of internal peers: clients and non‐clients. A route
reflector reflects between these groups and among the clients. The non‐client peers
must be fully meshed. The route reflector and its clients form a cluster.
When a route reflector receives a route from an iBGP peer, it selects the best path
based on its path selection rule. It then does the following based on the type of peer
it received the best path from:
 A route received from a non‐client iBGP peer is reflected to all clients.
 A route received from an iBGP client peer is reflected to all iBGP clients and
iBGP non‐clients.
Chapter 34: Border Gateway Protocol
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