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BGP Support for Multi-Topology Routing

Today I am going to talk about Multi-Topology routing using Border Gateway Protocol (BGP). What is the purpose of Multi-Topology routing? We will discuss the same in this article followed by sample configuration in BGP.Multi-Topology routing supports multiple unicast topologies and a separate multicast topology. Multi-Topology routing offers independent forwarding abilities on a per topology basis. Multi-Topology Routing permits the device configuration of service differentiation through class-based forwarding.

An independent forwarding table is preserved for each topology, permitting us to largely apply independent forwarding configurations or add a level of granularity to independent forwarding configurations.

IP routing should be allowed on the router in order for MTR to function.Dynamic routing can be allowed per-topology to provision inter-domain and intra-domain routing. Route computation and forwarding are independent for each topology. Multi-Topology routing is supported on BGP, EIGRP, IS-IS and OSPF dynamic routing protocol. 

In OSPF, EIGRP, and IS-IS, the topology ID is inserted through the first configuration of the topology command for a class-specific topology. In BGP, the topology ID is configured by entering the “bgp tid” command under the topology configuration.

BGP Support for Multi-Topology Routing
As we earlier discuss above that BGP supports Multi-Topology routing by using the command “bgp tid” We are taking a topology and configure the Multi-Topology routing in the BGP. 

Fig 1.1- Multi-Topology Routing in BGP
Configuration on RouteXP_R2 router
!
router bgp 300 
scope global
bgp default ipv4-unicast
neighbor 172.16.10.2 remote-as 300 
neighbor 192.168.20.2 remote-as 200
address-family ipv4 unicast 
topology NB1
bgp tid 100 
neighbor 172.16.10.2 activate 
exit
address-family ipv4 multicast 
topology base 
neighbor 192.168.20.2 activate 
exit 
!
scope vrf DATA 
neighbor 192.168.10.2 remote-as 100 
address-family ipv4 
neighbor 192.168.10.2 activate 
end
!

Verification
RouteXP_R2# show ip bgp topology NB1 summary
RouteXP_R2# show ip bgp topology NB1 neighbors 172.16.10.2

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