Category Archives: BGP

BGP

BGP backdoor

From the above caption, you can see by default the traffic from AS64513 to AS64512 will transit over at AS65000 which can utilize 2Gbps, to use an optimize route between AS64512 and AS64513 is either change the AD of BGP … Continue reading

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BGP: Load balancing using ebgp multihop and loopback interface.

1841-1 configuration 1841-1#sh run | s router bgp router bgp 64512 no synchronization bgp log-neighbor-changes network 172.16.1.0 mask 255.255.255.0 neighbor 110.1.1.1 remote-as 64513 neighbor 110.1.1.1 ebgp-multihop 2 neighbor 110.1.1.1 update-source Loopback64512 no auto-summary 1841-1#sh run | i ip route ip … Continue reading

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Tshoot BGP: Path unchanged despite local preference has been modified.

All routers within their own AS has been configured with IGP, routers within their own AS are reachable to one another (imagine the above diagram is part of an AS network). The border routers are connected to each other AS … Continue reading

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BGP: update source

Just a note to remind myself that to establish eBGP connection if loopback is used as the source then neighbor <peer’s ip address> update-source loopback<id>is necessary. By default BGP will use the interface ip as the source address to establish … Continue reading

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BGP route selection

I thought it will be useful as a quick reference for myself during troubleshooting BGP related issue. BGP path decision in order 1.  Prefer the path with the highest weight. Weight is not a BGP attribute, it is Cisco’s proprietary. … Continue reading

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BGP: Path selection lab

The lab is from my friend, Andrey, you can find the lab objective here: http://eccentric.mae.cornell.edu/~andrey/labs/BGP%20Dual-connected%20AS%20with%20OSPF.pdf R1: 1841-1 R2: 2651-1 R3: 2651-2 R4: 1841-2 R5: 3825-1 Subnet at segment between R1 and R2: 192.168.1.0/24 Subnet at segment between R2 and R3: … Continue reading

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BGP message

3825-1(config)# *Jan 27 16:00:39.591: BGP: 172.16.2.1 passive open to 172.16.1.1 *Jan 27 16:00:39.591: BGP: 172.16.2.1 went from Active to Idle The state from Active to Idle was caused by BGP reset using clear ip bgp * *Jan 27 16:00:39.591: BGP: … Continue reading

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