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 TCP connection. If update-source is not used then the BGP adjacency will never be formed, … Continue reading BGP: update source

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. The weight will not be propagated to another BGP speaking router. Weight influences the outbound … Continue reading BGP route selection

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: 192.168.2.0/24 Subnet at segment between R3 and R4: 192.168.3.0/24 subnet between R1 and R5: 100.10.10.0/24 … Continue reading BGP: Path selection lab

BGP: ebgp multihop

eBGP peering between AS777 and AS64512 AS64512 BGP status: 3825-1#sh ip bgp summ BGP router identifier 172.16.1.1, local AS number 64512 BGP table version is 1, main routing table version 1 Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd 172.16.2.1      4   777       0       0        0    0    0 never    Idle AS777 BGP status: 2651-1#sh … Continue reading BGP: ebgp multihop

BGP: Neighbour relationship

This lab demonstrates that BGP routers do not need to be directly connected to form neighbour relationship. 2651-1#sh run | section router bgp router bgp 6000 no synchronization bgp log-neighbor-changes network 50.1.1.0 mask 255.255.255.0 network 200.1.1.0 redistribute connected route-map bgp-filter-map1 neighbor 10.2.12.2 remote-as 5000 no auto-summary 2651-1#sh run | section route-map route-map bgp-filter-map1 permit 10 … Continue reading BGP: Neighbour relationship