BGP: Difference between revisions
→iBGP vs eBGP
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= iBGP vs eBGP =
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1. EBGP is peering between two different AS, whereas IBGP is between same AS (Autonomous System).
2. Routes learned from eBGP peer will be advertised to other peers (BGP or IBGP); however, routes learned from IBGP peer will not be advertised to other IBGP peers.
3. By default, EBGP peers are set with TTL = 1, which means neighbors are assumed to be directly connected, which is not in the case of IBGP. We can change this behavior for EBGP by using command “neighbor x.x.x.x ebgp-multihop <TTL>”. Multihop is the term used in EBGP only.
4. EBGP routes have administrative distance of 20, whereas IBGP has 200.
5. Next hop remains unchanged when route is advertised to IBGP peer; however, it is changed when it is advertised to EBGP peer by default.
This default behavior of IBGP can be changed by the command “neighbor x.x.x.x next-hop-self”; this changes the next hop, while advertising, as a local route.
For IBGP peers dont need to be directly connected.
Next-hop IP will not be changed when adv prefixes to another IBGP.
Also, if you check the way BGP choose the best route to put in the routing table you'll see that EBGP is preferred.
And BGP can run in two modes that each has a very different behavior when advertising routing information.
EBGP: external BGP runs between routers in different ASs.
IBGP: internal BGP runs between routers in the same AS.
EBGP: routes received from an EBGP peer can be advertised to EBGP and IBGP peers.
IBGP: routes received from an IBGP peer cannot be advertised to another IBGP peer but can be advertised to an EBGP peer.
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