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Free Cisco Lab GNS3 Scenario BGP Route Reflectors

Posted by: admin  :  Category: BGP, CCIE, CCNA

In the following Free Cisco Lab Scenario you will configure BGP over 15 routers in 8 AS, as well as multiple route reflectors in multiple clusters as shown in the network diagram. This is a very advanced lab requiring an advanced knowledge of routing and routing protocols namely BGP, therefore little instructions are provided but I have provided the GNS3 configuration.

The main objective of this lab is to demonstrate how route reflectors work and how to configure multiple route reflectors and clusters within an autonomous system. To refresh your knowledge on these topics the following is a brief description of BGP route reflectors and how react within clusters and autonomous systems.

Internal BGP peering does not have IBGP peers forward advertised routes learned by other IBGP peers to a third IBGP peer. IBGP peers providing learned routes to other IBGP routers within the Autonomous System (AS) are called route reflectors. AN IBGP router acting as a Route Reflector (RR) performs a function much like a hub and spoke configuration. The router used for this function has peer connections with all the routers in the AS and updates their tables. All non RR routers within the AS only have connection with the RR router.

A router is configured as a RR by using the neighbor ip-address route-reflector-client command where the ip-address is the IP address of a BGP neighbor router to become a client of the RR.

More than one RR can be defined in an AS and communicates with other RRs as though they where IBGP peers. Multiple RRs can be defined in a single or multiple clusters. Although the RR may peer with each other and form a full mesh communications between clusters, the clients of a RR within a cluster do not peer with clients of a different cluster.

When a RR receives a route from a non client peer it will reflect that route to all client routers within the cluster. If the RR receives a route from a client peer it will then reflect the route to all non client peers as well as all other client peers within the cluster. Lastly if a RR receives a route from an external BGP peer, the RR sends the update to all clients and non client peers alike.

Due to the fact the routes are reflected, it is possible for internal learned BGP routes to cause routing information loops. The BGP schema has two methods of addresses this problem. First the method employs the optional originator-id attribute which is four bytes in length and is actually the route-id of the route originator in the local AS. If the route has looped back to itself the route is then ignored and not added to the routing table update.

The second method is to use a cluster list, a RR can determine if a loop exist by discovering its own cluster ID in the cluster list, and the advertisement is then ignored. If the cluster list is empty, the RR creates a new cluster list. Cluster IDs are defined using the bgp cluster-id cluster-id command. The cluster-id variable is the ID assigned to the cluster by the RR; this value can be up to four bytes. The cluster-id is important when configuring redundancy to avoid a single point of failure of a RR within a cluster.

If the clients of a cluster are fully meshed, then route reflectors are not needed. By default the RR has client-to-client reflection enabled, to disable this use the no bgp client-to-client reflection command. Note that peer groups may not be used if client-to-client reflection is enabled. Any clients of a RR cannot be members of a BGP peer group. This is because clients being part of a peer group may cause invalid routes to be reflected to clients that are not part of the peer group.


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4 Responses to “Free Cisco Lab GNS3 Scenario BGP Route Reflectors”

  1. Tweets that mention Free Cisco Lab Advanced BGP Route Reflectors -- Says:

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  2. Tom Keagle Says:

    “Thx for this constructive information. Please keep up the neat work. I will be returning often.”

  3. gm.chip Says:

    Make sure you have
    If not, notepad 😛

    Oh , and hello Barry Burdette 😛

  4. Atif Siddiqui Says:

    Hello all, where can i find this IOS c3660-a3js-mz.124-15.T13.bin, and is there any way some body can share it with me.

    Best Regards,


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