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what is difference between iBGP and EBGP ?

Any difference between iBGP and EBGP

4 REPLIES

Re: what is difference between iBGP and EBGP ?

There are many differences between IBGP and EBGP:

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.

But this is just a few things.

Vlad

Re: what is difference between iBGP and EBGP ?

IBGP is formed between Neighbors within the same AS whereas EBGP is formed between neighbors in different AS.

A route learnt from an IBGP peer will not be advertised back to another IBGP by default.

AS path is not prepended to the route when advertised to an IBGP peer.

Attributes like local preference are sent to the IBGP peers but not to an EBGP peer.

As VLAD has stated, under normal circumstances EBGP route is always preferred over an IBGP route (exception are if u configure BGP deterministic-med & BGP always-compare-med)

I will not agree with VLAD on the 1st point though. Even EBGP peers need not be directly connected. The only requirement is reachability to the remote peer with appropriate ebgp-multihop configuration

HTH, rate if it does

Narayan

Re: what is difference between iBGP and EBGP ?

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

regards

Devang

Re: what is difference between iBGP and EBGP ?

Hello,

in addition to the other posts, have a look at this link as well, which is a very comprehensive paper on BGP:

BGP Fundamentals

http://www.cisco.com/univercd/cc/td/doc/cisintwk/ics/icsbgp4.htm#wp10579

HTH,

GNT

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