Cisco Nexus 7000 Series - AS Confederations; Route Reflector

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11-5
Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 4.x
OL-20002-02
Chapter 11 Configuring Advanced BGP
Information About Advanced BGP
Figure 11-2 shows the BGP network from Figure 11-1, split into two subautonomous systems and one
confederation.
Figure 11-2 AS Confederation
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 11-1.
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 11-1 shows a simple iBGP configuration with four meshed iBGP speakers (router A, B, C, and
D). 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 11-3, router B is the route reflector. When the route reflector receives routes advertised from
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.
ZA
B
C
D
AS10AS20
Confederation
peers
eBGP
iBGP
iBGP
185056
AS1 AS2