Tuesday, February 28, 2006

 

BGP neighbors stuck in ACTIVE. (Question #25)

Consider two routers connected back to back via their serial interfaces. The configurations on the routers are

Router1

interface Loopback0
ip address 10.10.10.10 255.255.255.255
!
interface Serial2
ip address 192.168.16.1 255.255.255.252
no fair-queue
!
router bgp 1
no synchronization
bgp log-neighbor-changes
neighbor 20.20.20.20 remote-as 2
neighbor 20.20.20.20 ebgp-multihop 2
neighbor 20.20.20.20 update-source Loopback0
no auto-summary
!
ip route 0.0.0.0 0.0.0.0 192.168.16.2



Router2

interface Loopback0
ip address 20.20.20.20 255.255.255.255
!
interface Serial2
ip address 192.168.16.2 255.255.255.252
no fair-queue
!
router bgp 2
no synchronization
bgp log-neighbor-changes
network 20.20.20.20 mask 255.255.255.255
network 172.16.1.0 mask 255.255.255.0
neighbor 10.10.10.10 remote-as 1
neighbor 10.10.10.10 ebgp-multihop 2
neighbor 10.10.10.10 update-source Loopback0
no auto-summary
!
ip route 0.0.0.0 0.0.0.0 192.168.16.1



These BGP neighbors are stuck in active and never come up. Note that the two routers can ping each other's serial and loopback interfaces with their own serial and loopback interface addresses as the source address. Why are these routers unable to establish BGP neighborship?

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