In standard internal BGP implementations, all BGP systems within the AS are fully meshed so that any external routing information is redistributed among all routers within the AS. This type of implementation can present scaling issues when an AS has a large number of internal BGP systems because of the amount of identical information that BGP systems must share with each other. Route reflection provides one means of decreasing BGP control traffic and minimizing the number of update messages sent within the AS.
In route reflection, BGP systems are arranged in clusters. Each cluster consists of at least one system that acts as a route reflector, along with any number of client peers. BGP peers outside the cluster are called nonclient peers. The route reflector reflects (redistributes) routing information to each client peer (intracluster reflection) and to all nonclient peers (intercluster reflection). Because the route reflector redistributes routes within the cluster, the BGP systems within the cluster do not have to be fully meshed.
When the route reflector receives a route, it selects the best path. Then, if the route came from a nonclient peer, the route reflector sends the route to all client peers within the cluster. If the route came from a client peer, the route reflector sends it to all nonclient peers and to all client peers except the originator. In this process, none of the client peers send routes to other client peers.
To configure route reflection, you specify a cluster identifier only on the BGP systems that are to be the route reflectors. These systems then determine, from the network reachability information they receive, which BGP systems are part of its cluster and are client peers, and which BGP systems are outside the cluster and are nonclient peers.
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Note: When you configure route reflection on a Juniper router, you can apply policy changes to the following attributes: NEXT_HOP, AS_PATH, LOCAL_PREF, and MED. Other vendors might not support policy changes to these attributes and so care must be taken with policy when migrating route reflection configurations from non-Juniper to Juniper routers. |
To configure a router to be a route reflector, you must do the following:
To configure the route reflector, include the following statements in the configuration:
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group group-name {
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type internal;
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peer-as autonomous-system;
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neighbor address1;
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neighbor address2;
- }
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group group-name {
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type internal;
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peer-as autonomous-system;
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cluster cluster-identifier;
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neighbor address3;
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neighbor address4;
- }
For a list of hierarchy levels at which you can include this statement, see the statement summary section for this statement.
By default, the BGP route reflector performs intracluster reflection because it assumes that all the client peers are not fully meshed. However, if the client peers are fully meshed, intracluster reflection results in the sending of redundant route advertisements. In this case, you can disable intracluster reflection by including the no-client-reflect statement within the group statement:
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group group-name {
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type internal;
-
peer-as autonomous-system;
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cluster cluster-identifier;
-
no-client-reflect;
-
neighbor address3;
-
neighbor address4;
- }
For a list of hierarchy levels at which you can include this statement, see the statement summary section for this statement.
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Note: BGP route reflection is not supported for VPN routing and forwarding (VRF) routing instances. |
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