BGP between Cisco routers on different subnets.

To illustrate this I will use GNS3, i used two Cisco Routers directly different subnets between them.

The topology is very simple:

Starting with the basic configuration, on R1:

NetworkLabs-1(config)#interface FastEthernet0/0
NetworkLabs-1(config-if)# ip address 10.0.1.1 255.255.255.0
NetworkLabs-1(config)# ip route 10.0.2.0 255.255.255.0 FastEthernet0/0

Same thing on R2

 NetworkLabs-2(config)#interface FastEthernet0/0
NetworkLabs-2(config-if)# (config-if)#ip address 10.0.2.1 255.255.255.0
NetworkLabs-2(config-)#ip route 10.0.1.0 255.255.255.0 FastEthernet0/0
 

At this stage we have ping back and forth between both Routers, now to the BGP

 NetworkLabs-1(config)#router bgp 1
NetworkLabs-1(config-router)# neighbor 10.0.2.1 remote-as 2
 NetworkLabs-2(config)#router bgp 2
NetworkLabs-2(config-router)#neighbor 10.0.1.1 remote-as 1
 

At this stage BGP will not come up, it will be stuck on idle state, to make it work all we need is to add " disable-connected-check" on both of the routers

 NetworkLabs-1(config-router)#neighbor 10.0.2.1 disable-connected-check
NetworkLabs-2(config-router)#neighbor 10.0.1.1 disable-connected-check

That's it.


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