BGP neighbor route-reflector-client

BGP Route Reflection: An Alternative to Full Mesh Internal BGP (IBGP)

Typically, all BGP speakers within a single AS must be fully meshed and any external routing information must be re-distributed to all other routers within that AS. For n BGP speakers within an AS that requires to maintain n*(n-1)/2 unique Internal BGP (IBGP) sessions. This "full mesh" requirement clearly does not scale when there are a large number of IBGP speakers each exchanging a large volume of routing information, as is common in many of today's networks. Use the neighbor route-reflector-client command to configure the local router as the route reflector and the specified neighbor as one of its clients. All the neighbors configured with this command will be members of the client group and the remaining iBGP peers will be members of the nonclient group for the local route reflector.

NOTE: BGP route reflectors relax the prohibition on advertising internally learned routes to other iBGP peers, but dividing peers into two separate classes of peers: route-reflector clients and non-clients, which are regular iBGP peers with the restrictions intact. Routes learned from clients will be advertised to other clients and to non-clients. However, routes learned from non-clients will be advertised only to the clients. This situation opens up interesting loop and failure scenarios that may need special handling.

Video Demonstration

from: Cisco IOS IP Routing: BGP Command Reference

neighbor route-reflector-client

To configure the router as a BGP route reflector and configure the specified neighbor as its client, use the neighbor route-reflector-client command in address family or router configuration mode. To indicate that the neighbor is not a client, use the no form of this command.

neighbor {ip-address | ipv6-address | peer-group-name} route-reflector-client

no neighbor {ip-address | ipv6-address | peer-group-name} route-reflector-client

Syntax Description

ip-address	IP address of the BGP neighbor being identified as a client.
ipv6-address	IPv6 address of the BGP neighbor being identified as a client.
peer-group-name	Name of a BGP peer group.

Command Default

There is no route reflector in the autonomous system.

Command Modes

Address family configuration (config-router-af)
Router configuration (config-router)

Command History

Release	Modification
11.1	This command was introduced.
12.0(7)T	Address family configuration mode was added.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2(33)SRB	The ipv6-address and peer-group-name arguments were added.
12.2(33)SB	This command was integrated into Cisco IOS Release 12.2(33)SB.
12.2(33)SXI	This command was integrated into Cisco IOS Release 12.2(33)SXI.
Cisco IOS XE Release 3.1S	This command was updated. It was integrated into Cisco IOS XE Release 3.1S.

Usage Guidelines

By default, all internal BGP (iBGP) speakers in an autonomous system must be fully meshed, and neighbors do not readvertise iBGP learned routes to neighbors, thus preventing a routing information loop. When all the clients are disabled, the local router is no longer a route reflector.

If you use route reflectors, all iBGP speakers need not be fully meshed. In the route reflector model, an Interior BGP peer is configured to be aroute reflector responsible for passing iBGP learned routes to iBGP neighbors. This scheme eliminates the need for each router to talk to every other router.

Use the neighbor route-reflector-client command to configure the local router as the route reflector and the specified neighbor as one of its clients. All the neighbors configured with this command will be members of the client group and the remaining iBGP peers will be members of the nonclient group for the local route reflector.

The bgp client-to-client reflection command controls client-to-client reflection.

Files:
Topology
Configs
BGP Configuration