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5. Redundancy Design of RRs
Redundant RRs increase network
robustness.
The Originator_ID and Cluster_list attributes are used to prevent routing loops
in redundant RR scenarios. The Cluster_IDs of the RRs must be the same to
prevent routing loops. In addition, establishing fully-meshed IBGP connections
among the RRs is recommended.
Each client receives routes from the two RRs shown in the following figure. How
does the client select the optimal route?
6. RR Configuration
IP addresses are planned according to the preceding figure. The IP addresses of loopback 0 interfaces on all routers are in the format of x.x.x.x/32, where x is the device ID. An OSPF process runs in AS 123 to advertise routes of directly connected interfaces and loopback 0 interfaces. An IBGP peer relationship is established between R1 and R2 and between R2 and R3. R1 imports the route 11.11.11.0/24 to BGP. In this case, R2 can learn the BGP route, but R3 cannot. Then R2 is configured as an RR, with R1 as its client. In this case, R3 learns the route 11.11.11.0/24.
# R1 configurations (excluding OSPF
and interface configurations):
[R1] bgp 123
[R1-bgp] router-id 1.1.1.1
[R1-bgp] peer 2.2.2.2 as-number 123
[R1-bgp] peer 2.2.2.2 connect-interface loopback0
[R1-bgp] network 11.11.11.0 24
# R2 configurations (excluding OSPF
and interface configurations):
[R2] bgp 123
[R2-bgp] router-id 2.2.2.2
[R2-bgp] peer 1.1.1.1 as-number 123
[R2-bgp] peer 1.1.1.1 connect-interface loopback0
[R2-bgp] peer 1.1.1.1 reflect-client
[R2-bgp] peer 3.3.3.3 as-number 123
[R2-bgp] peer 3.3.3.3 connect-interface loopback0
# R3 configurations (excluding OSPF
and interface configurations):
[R3] bgp 123
[R3-bgp] router-id 3.3.3.3
[R3-bgp] peer 2.2.2.2 as-number 123
[R3-bgp] peer 2.2.2.2 connect-interface loopback0
After the preceding configurations are performed, check detailed information about the route 11.11.11.0 on R3.
Before reflecting a route, each RR checks whether the route already carries the Originator_ID and Cluster_List attributes. If the route does not carry the two attributes, the RR adds the two attributes to the route. By default, the router ID of the RR is used as the Cluster_ID, and the Cluster_ID is placed in the Cluster_List. To change the Cluster_ID, run the reflector cluster-id command on the RR.
If the Cluster_ID attribute already exists in the route to be reflected, the RR places its own Cluster_ID on top of the existing Cluster_List.
7. RR Implementation
RR Planning Rules
· Divide each transit AS into RR clusters.
· Deploy RRs and clients in each RR cluster.
· Deploy the routers that do not support the RR function in a single router cluster or deploy them as RR clients.
IBGP Session Rules
· All clients in each RR cluster must establish IBGP connections only with the RRs in the cluster.
· IBGP connections must be established among RRs in an AS.
· Non-RR routers can be fully meshed as IBGP peers or be configured as RR clients.
The RR solution is a very good choice on large-scale networks with highly redundant and hierarchical network architectures. In the following figure, the hierarchical RR cluster structure improves network robustness and reduces the number of IBGP connections in the AS.
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