When does a BGP router need an eBGP connection?
A BGP router needs to establish a connection (on TCP port 179) to each of it’s BGP peers before BGP updates can be exchanged. The BGP session between two BGP peers is said to be an external BGP (eBGP) session if the BGP peers are in different autonomous systems (AS) .
Which is iBGP router belongs to eBGP multihop?
If they are not directly connected, the neighbor ebgp-multihop ( registered customers only) command must be used and a path through an IGP or static route to reach the peer must exist in order for the routers to establish neighbor relationship. In the configuration above, R1-AGS router belongs to AS 300 while R6-2500 router belongs to AS 400.
How is the peer relationship established in iBGP?
By default, the peer relationship is established using the IP address of the interface closest to the peer router. However, using the neighbor update-source ( registered customers only) command, any operational interface, including the loopback interface, can be specified to be used for establishing TCP connections.
What makes a BGP session an internal iBGP session?
A BGP session between two BGP peers is said to be an internal BGP (iBGP) session if the BGP peers are in the same autonomous systems. By default, the peer relationship is established using the IP address of the interface closest to the peer router.
Why does BGP only peer with a matching neighbor?
Using loopback addresses for our neighbor statements leads to a common gotcha with BGP. BGP has a security mechanism where it will only peer with another router if it has a matching neighbor statement for that peer. The source address in the packets received from the neighbor must match the exact IP address in the neighbor statement on this router.
What do you need to know about iBGP and eBGP?
Peers must be directly connected when using eBGP. If they are not directly connected, the neighbor ebgp-multihop ( registered customers only) command must be used and a path through an IGP or static route to reach the peer must exist in order for the routers to establish neighbor relationship.
How to configure eBGP using a loopback address?
You can also configure eBGP using a loopback address (or any other operational interface) as shown in this section.
Which is the IP address of iBGP R2?
By issuing the “show ip bgp summary” command we can see under neighbor column the IP address 10.10.12.2. This is the IP address of R2 with which R1 has established the peering relationship. We can see also that local AS number is 10. This means that both R1 and R2 are iBGP neighbors with each other, since the AS is the same.