BGP – Part 3 (IBGP, IBGP Topologies and EBGP)

In the previous post, we have talked about BGP generally. In this post we will handle IBGP and EBGP detailed.

IBGP (Internal Border Gateway Protocol)

* BGP, which is used in the same Autonomous System. Neighborship is established with the peer which is in the same Autonomous System.

* IBGP peers do not need direct connection. But, there must be some IGP that runs and allows the two neighbors to reach one another.

* Routes learned from the internal peers, must not sent back to other internal peers. It can only sent to the external peers.

* Internal peers must be full mesh. But you can get over this full mesh , by two other feature of BGP. These features are AS Confederations and Route Reflectors.

* AS-PATH and NEXT-HOP attributes must not updated when passing updates to internal peers.

* iBGP peers are dependent on the underlying IGP of the AS to connect peers together.

* In iBGP, full mesh topology is required by default. By using route reflectors or bgp confederations this can be by passed.

Now Let’s check the iBGP topologies.

IBGP Full Mesh Topology

In this topology, all the routers used in IBGP must be connected together as mull mesh.This type of configuration is difficult to configure and complex. In this type of configuration, adding one router to the topology is also difficult, because you need to update all routers on IBGP topology for this router.

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