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Overview:
Normally in IBGP, a full mesh of BGP relationships is required (because of the BGP split horizon rule). A BGP router will not advertise a route learned via another IBGP router to a third IBGP router. By relaxing this restriction and by providing additional control, we can allow a router to advertise (reflect) IBGP learned routes to other IBGP routers. This will reduce the number of IBGP peers within an AS.
Here we are demonstrating how few relationships can be configured in a given topology. If we were not using route reflectors AS 1 will have needed: 6(6-1)/2 = 15 neighbor relationships. Now have only got 7 with full redundancy
Our Diagram:
Physical Topology
BGP Topology
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R1 Config:
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router bgp 2
no synchronization
bgp router-id 1.1.1.1
network 1.1.1.1 mask 255.255.255.255
network 10.1.1.1 mask 255.255.255.0
network 10.1.9.0 mask 255.255.255.0
network 11.1.1.1 mask 255.255.255.255
neighbor 2.2.2.2 remote-as 1
neighbor 2.2.2.2 ebgp-multihop 255
neighbor 2.2.2.2 update-source Loopback0
neighbor 6.6.6.6 remote-as 1
neighbor 6.6.6.6 ebgp-multihop 255
neighbor 6.6.6.6 update-source Loopback0
no auto-summary
!
ip classless
ip route 2.2.2.2 255.255.255.255 10.1.1.2
ip route 6.6.6.6 255.255.255.255 10.1.9.2
no ip http server
!
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R2 Config:
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router ospf 1
router-id 2.2.2.2
network 2.2.2.2 0.0.0.0 area 0
network 10.0.0.0 0.255.255.255 area 0
!
router bgp 1
no synchronization
bgp router-id 2.2.2.2
network 2.2.2.2 mask 255.255.255.255
network 10.1.2.0 mask 255.255.255.0
network 10.1.4.0 mask 255.255.255.0
network 10.1.5.0 mask 255.255.255.0
neighbor 1.1.1.1 remote-as 2
neighbor 1.1.1.1 ebgp-multihop 255
neighbor 1.1.1.1 update-source Loopback0
neighbor 3.3.3.3 remote-as 1
neighbor 3.3.3.3 update-source Loopback0
neighbor 3.3.3.3 next-hop-self
neighbor 4.4.4.4 remote-as 1
neighbor 4.4.4.4 update-source Loopback0
neighbor 4.4.4.4 route-reflector-client
neighbor 4.4.4.4 next-hop-self
neighbor 5.5.5.5 remote-as 1
neighbor 5.5.5.5 update-source Loopback0
neighbor 5.5.5.5 route-reflector-client
neighbor 5.5.5.5 next-hop-self
neighbor 6.6.6.6 remote-as 1
neighbor 6.6.6.6 update-source Loopback0
neighbor 6.6.6.6 next-hop-self
no auto-summary
!
ip classless
ip route 1.1.1.1 255.255.255.255 10.1.1.1
no ip http server
ip bgp-community new-format
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R3 Config:
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router ospf 1
router-id 3.3.3.3
network 3.3.3.3 0.0.0.0 area 0
network 10.0.0.0 0.255.255.255 area 0
!
router bgp 1
no synchronization
bgp router-id 3.3.3.3
network 3.3.3.3 mask 255.255.255.255
network 10.1.4.0 mask 255.255.255.0
network 10.1.6.0 mask 255.255.255.0
network 10.1.8.0 mask 255.255.255.0
neighbor 2.2.2.2 remote-as 1
neighbor 2.2.2.2 update-source Loopback0
neighbor 4.4.4.4 remote-as 1
neighbor 4.4.4.4 update-source Loopback0
neighbor 4.4.4.4 route-reflector-client
neighbor 4.4.4.4 next-hop-self
neighbor 5.5.5.5 remote-as 1
neighbor 5.5.5.5 update-source Loopback0
neighbor 5.5.5.5 route-reflector-client
neighbor 5.5.5.5 next-hop-self
neighbor 6.6.6.6 remote-as 1
neighbor 6.6.6.6 update-source Loopback0
no auto-summary
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R4 Config:
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router ospf 1
router-id 4.4.4.4
network 4.4.4.4 0.0.0.0 area 0
network 10.0.0.0 0.255.255.255 area 0
!
router bgp 1
no synchronization
bgp router-id 4.4.4.4
network 4.4.4.4 mask 255.255.255.255
network 10.1.5.0 mask 255.255.255.0
network 10.1.7.0 mask 255.255.255.0
neighbor 2.2.2.2 remote-as 1
neighbor 2.2.2.2 update-source Loopback0
neighbor 3.3.3.3 remote-as 1
neighbor 3.3.3.3 update-source Loopback0
neighbor 3.3.3.3 route-map setnexthop in
no auto-summary
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R5 Config:
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router ospf 1
router-id 5.5.5.5
network 5.5.5.5 0.0.0.0 area 0
network 10.0.0.0 0.255.255.255 area 0
!
router bgp 1
no synchronization
bgp router-id 5.5.5.5
network 5.5.5.5 mask 255.255.255.255
network 10.1.6.0 mask 255.255.255.0
network 10.1.7.0 mask 255.255.255.0
neighbor 2.2.2.2 remote-as 1
neighbor 2.2.2.2 update-source Loopback0
neighbor 3.3.3.3 remote-as 1
neighbor 3.3.3.3 update-source Loopback0
no auto-summary
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R6 Config:
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router bgp 1
no synchronization
bgp router-id 6.6.6.6
network 6.6.6.6 mask 255.255.255.255
network 10.1.2.0 mask 255.255.255.0
network 10.1.3.0 mask 255.255.255.0
network 10.1.9.0 mask 255.255.255.0
neighbor 1.1.1.1 remote-as 2
neighbor 1.1.1.1 ebgp-multihop 255
neighbor 1.1.1.1 update-source Loopback0
neighbor 2.2.2.2 remote-as 1
neighbor 2.2.2.2 update-source Loopback0
neighbor 2.2.2.2 route-reflector-client
neighbor 2.2.2.2 next-hop-self
neighbor 3.3.3.3 remote-as 1
neighbor 3.3.3.3 update-source Loopback0
neighbor 3.3.3.3 route-reflector-client
neighbor 3.3.3.3 next-hop-self
neighbor 7.7.7.7 remote-as 1
neighbor 7.7.7.7 update-source Loopback0
neighbor 7.7.7.7 route-reflector-client
neighbor 7.7.7.7 next-hop-self
no auto-summary
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R7 Config:
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router ospf 1
network 7.7.7.7 0.0.0.0 area 0
network 10.0.0.0 0.255.255.255 area 0
!
router bgp 1
no synchronization
network 7.7.7.7 mask 255.255.255.255
network 10.1.3.0 mask 255.255.255.0
network 10.1.8.0 mask 255.255.255.0
neighbor 6.6.6.6 remote-as 1
neighbor 6.6.6.6 update-source Loopback0
no auto-summary
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R1 Output:
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R2 Output:
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R3 Output:
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R4 Output:
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R5 Output:
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R6 Output:
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*********************************************************************************************
TO PROVE REDUNDANCY:
*********************************************************************************************
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R4 Output:
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Kill link between R5 and R3 (10.1.6.0 network)
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Link up:
Link down:
Lost only one ping!!!
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Kill link between R2 and R1 (network 10.1.1.0)
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Start ping:
Kill link:
Lost two pings:
Trace:
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Kill link between R1 and R2 , between R7 and R6
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Start ping:
Kill links:
Kill link on R1
Kill link on R7
Ping:
Therefore lost 36 pings = +- 1 min
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