Internal
Border Gateway Protocol - iBGP
iBGP is a
term used to describe an area of BGP operation that runs within an organisation
or autonomous system. Routes can be injected from the iGBP into eBGP, vise
versa.
To be able
to connect to another autonomous system, it is essential to configure the
following:
• The
start of the routing process
• The
networks to be advertised
• The BGP
neighbor that the routing process will be synchronizing routing tables with over a TCP session.
Configuring
iBGP
iBGP basic configuration slightly differs from to that of eBGP
configuration. The configuration is not to identify and form neighborship with
an eBGP peer, instead, the iBGP neighbor’s ASN is listed on the neighbor...
remote-as. The neighbor-asn command lists the same
ASN as the local router’s router bgp command. However, eBGP neighbor
remote-as commands list a different ASN.
To simplify
this, the remote ASN is the same ASN as the local router bgp ASN.We use the diagram below as an example.
iBGP configuration commands:
The above topology
and configuration shows two iBGP router peering.
Both refer
to the other router’s IP address on the Serial, FastEthernet or loopback interface
between the two routers, and both refer to ASN 556. The two routers then
realize the neighbor is an iBGP neighbor
because the neighbor’s ASN (556) matches the local router’s ASN, as seen on the router bgp 556 command.
