Difference between IBGP and EBGP

[Nabarun Halder]

What is the Difference between IBGP and EBGP  ?

[Harold Ritter]

Hi Nabarun,

eBGP stands for external BGP and is typically used to exchange routes with routers outside of your control (i.e. service provider, partners, etc).

iBGP stands for internal BGP and is used to dissiminate the information in your internal network.

Regards

[JohnTylerPearce]

Nabarun,

There are two types of BGP (If you will). iBGP and eBGP.

iBGP stands for Internal Border Gateway Protocol (iBGP), and includes routers within the same Autonomous System (AS). So if 5 routers were part of BGP AS 500, that will all be iBGP routers.

eBGP stands for Exterior Border Gateway Protocol (eBGP), and includes routers that have connections to Autonomous Systems (ASes) with a different AS value then it's own.

[Richard Burts]

It may also be helpful to note that there are a number of behavior differences between an IBGP router and an EBGP router.  For example if we learn a route from an EBGP neighbor then we will advertise that route to all BGP neighbors (does not matter whether the neighbor is IBGP or EBGP) but if we learn a route from an IBGP neighbor we will not advertise that route to other IBGP neighbors.

Another difference is that for an EBGP neighbor the default is to set TTL to 1 while for an IBGP neighbor the TTL is set to a higher value. Also in the path selection process there are differences depending on whether the prefix was learned via IBGP or by EBGP (EBGP is preferred over IBGP).

HTH

Rick

[Joseph W. Doherty]

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Posting

Just to clarify a little what Rick wrote about iBGP an eBGP routers, one router running BGP can have both iBGP and eBGP peers.  As Rick notes, there are differences in behavior depending on which kind of BGP peer you're interacting with, and which generated the BGP routes you're working with.

Which is which?  If the BGP peers are in different Autonomous Systems, then peers are eBGP, same Autonomous System, then peers are iBGP.