BGP Neighbor Relationship:
o BGP neighbors are routers forming TCP connection for exchanging BGP updates.
o Border gateway protocol (BGP) neighbors also called BGP peers or BGP speakers.
o There are two types of BGP neighbor relationship internal BGP and External BGP.
o BGP first forms neighbor relationship with Border gateway protocol Speakers (Peer).
o Than its learns information from its peer, BGP place that information in its BGP table.
o Local Router’s Autonomous System Number must match neighboring Router’s ASN.
o Ensure that Border gateway protocol (BGP) peers have IP reachability to each other.
o Configure basic External Border gateway protocol (eBGP) on each Cisco Router.
o Transmission Control Protocol (TCP) three 3-Way Handshake must be completed.
o The Border Gateway Protocol Peering must be completed & BGP Update Exchange.
o Source IP address of incoming TCP connection must be from configured BGP peer.
o Peer’s advertisement of his Border gateway protocol AS# must be what we expect.
o If Border gateway protocol authentication is used, same password must configured.
o The BGP peers must have unique Border Gateway Protocol (BGP) Router-IDs.
o The BGP Peers must use the same Border Gateway Protocol (BGP) version only.
Use the setting of the bgp router-id <x.x.x.x> router subcommand.
To configure BGP Peers, use the following commands:
router bgp asn (Global Command)
neighbor ip-address remote-as remote-asn (BGP Subcommand)
Overview of Internal BGP (iBGP) and External BGP (eBGP).
Let us check the BGP Peering Overview in below image.
R1 Basic Configuration
R1(config)#interface e0/0
R1(config-if)#ip add 192.168.12.1 255.255.255.0
R1(config-if)#no shut
R1(config-if)#exit
R1(config)#interface loopback 1
R1(config-if)#ip add 1.1.1.1 255.255.255.255
R2 Basic Configuration
R2(config)#interface e0/0
R2(config-if)#ip add 192.168.12.2 255.255.255.0
R2(config-if)#no shut
R2(config-if)#exit
R2(config)#interface loopback 2
R2(config-if)#ip add 2.2.2.2 255.255.255.0
BGP Configuration
R1(config)#router bgp 1
R1(config-router)#neighbor 192.168.12.2 remote-as 2
R1(config-router)#network 1.1.1.1 mask 255.255.255.255
R1(config-router)#neighbor 192.168.12.2 password cisco
BGP Configuration
R2(config)#router bgp 2
R2(config-router)#neighbor 192.168.12.1 remote-as 1
R2(config-router)#network 2.2.2.0 mask 255.255.255.0
R2(config-router)#neighbor 192.168.12.2 password cisco
Keep the Same Router ID in R1
R1(config)#router bgp 1
R1(config-router)#bgp router-id 2.2.2.2
Mismatch Authentication R1
R1(config)#router bgp 1
R1(config-router)#neighbor 192.168.12.2 password cisco1
