Cisco Systems 78-11741-02 Wireless Office Headset User Manual


 
Configuring BGP
Configuring Advanced BGP Features
IPC-317
Cisco IOS IP Configuration Guide
In order to treat the neighbors from other autonomous systems within the confederation as special eBGP
peers, use the following command in router configuration mode:
See the “BGP Community with Route Maps Examples” section at the end of this chapter for an example
configuration of several peers in a confederation.
For an alternative way to reduce the iBGP mesh, see the next section, “Configuring a Route Reflector.”
Configuring a Route Reflector
BGP requires that all iBGP speakers be fully meshed. However, this requirement does not scale well
when there are many iBGP speakers. Instead of configuring a confederation, another way to reduce the
iBGP mesh is to configure a route reflector.
Figure 55 illustrates a simple iBGP configuration with three iBGP speakers (Routers A, B, and C).
Without route reflectors, when Router A receives a route from an external neighbor, it must advertise it
to both routers B and C. Routers B and C do not readvertise the iBGP learned route to other iBGP
speakers because the routers do not pass on routes learned from internal neighbors to other internal
neighbors, thus preventing a routing information loop.
Figure 55 Three Fully Meshed iBGP Speakers
With route reflectors, all iBGP speakers need not be fully meshed because there is a method to pass
learned routes to neighbors. In this model, an iBGP peer is configured to be a route reflector responsible
for passing iBGP learned routes to a set of iBGP neighbors. In Figure 56, Router B is configured as a
route reflector. When the route reflector receives routes advertised from Router A, it advertises them to
Router C, and vice versa. This scheme eliminates the need for the iBGP session between Routers A
and C.
Command Purpose
Router(config-router)# bgp confederation peers
as-number [as-number]
Specifies the autonomous systems that belong to the
confederation.
S4217
External
BGP
speaker
Routes
advertised
Fully meshed
autonomous
system
Routes
Routes
Routes not
advertised
Router A Router A
Router B
Router C