Route Reflector; Capabilities Negotiation - Cisco Nexus 3000 Series Configuration Manual

Chapter 6 Configuring Advanced BGP
S e n d d o c u m e n t c o m m e n t s t o n e x u s 3 k - d o c f e e d b a c k @ c i s c o . c o m
In this example, AS10 is split into two subautonomous systems, AS1 and AS2. Each subautonomous
system is fully meshed, but there is only one link between the subautonomous systems. By using AS
confederations, you can reduce the number of links compared to the fully meshed autonomous system
in Figure

Route Reflector

You can alternately reduce the iBGP mesh by using a route reflector configuration. route reflectors pass
learned routes to neighbors so that all iBGP peers do not need to be fully meshed.
Figure 6-1
Without route reflectors, when router A receives a route from an external neighbor, it advertises the route
to all three iBGP neighbors.
When you configure an iBGP peer to be a route reflector, it becomes responsible for passing iBGP
learned routes to a set of iBGP neighbors.
In Figure
router A, it advertises (reflects) the routes to routers C and D. Router A no longer has to advertise to both
routers C and D.
Figure 6-3
AS20
Z
The route reflector and its client peers form a cluster. You do not have to configure all iBGP peers to act
as client peers of the route reflector. You must configure any nonclient peer as fully meshed to guarantee
that complete BGP updates reach all peers.

Capabilities Negotiation

A BGP speaker can learn about BGP extensions supported by a peer by using the capabilities negotiation
feature. Capabilities negotiation allows BGP to use only the set of features supported by both BGP peers
on a link.
If a BGP peer does not support capabilities negotiation, Cisco NX-OS will attempt a new session to the
peer without capabilities negotiation if you have configured the address family as IPv4.
6-1.
shows a simple iBGP configuration with four meshed iBGP speakers (router A, B, C, and D).
6-3, router B is the route reflector. When the route reflector receives routes advertised from
Route Reflector
AS10
A
eBGP
iBGP
B
Cisco Nexus 3000 Series NX-OS Unicast Routing Configuration Guide, NX-OS Release 5.0(3)U1(1)
Information About Advanced BGP
C
iBGP
D
6-5