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New Member

iBGP vs eBGP

I would like to know if there are any benefits and/or differences by using eBGP or iBGP in a particular scenario. I am running GRE over IPSec accross the internet. I am setting up BGP between the two routers that are terminating the GRE/IPSec tunnel, with the loopbacks as the neighbor addresses. Are there any benefits/ differences using iBGP or eBGP in this scenario?


Re: iBGP vs eBGP

I am very confused by your question... eBGP and iBGP are the same protocol, all that differs is whether the two end points are in the same ASN. Furthermore, there is no need to use a GRE tunnel if the routing protocol is BGP.

That said, there are differences in how BGP behaves within an ASN (iBGP) and between ASNs (eBGP). In particular, iBGP tends to be more trusting while eBGP does not have a concept of "synchronization." The default administrative distance for learned routes is also different.

In general, if you are using BGP for multihoming with your ISPs, your choice of eBGP vs iBGP for your locations is already determined. If this is your first foray into BGP, plan on doing some heavy reading to learn the protocol and how it works (curling up with Halabi's book for a week would be a good start :-).

Good luck and have fun!

Vincent C Jones

New Member

Re: iBGP vs eBGP

Vincent, I do not think that explained this so that is completely understandable. I will have two IPSec tunnel connections across the internet with two separate routers on each side. I will be sending routing updates through these tunnels, and preferring one path over the other as they are going to two separate data centers, and want the ability to failover. This is a minor question as to which would be a better method to peer these two routers. I personally do not think it matters as to whether I configure these as internal peers or external, but I wanted to ask if there are actually any benefits of one over the other in this scenario.

Just an FYI, I am very familiar with configuring BGP, so I wil not need a lesson for configuration, and no this is not my first foray into BGP. I suppose that I deserved your condescending response because I provided half the details. If this is still not clear, you are not obligated to respond.

Thank you for your effort.


Re: iBGP vs eBGP

I don't know what is going on here, because I posted a response this morning and its gone now, nor is it the first time this message board has dropped postings.

Briefly, what I said was that based on your statements, there would be no functional difference between iBGP and eBGP as long as they were correctly configured, and that I would choose iBGP just in case sometime in the future there was a requirement for "real" eBGP.

I also pointed out that iBGP does not need multihop set and does not need a GRE tunnel to set up peering, so the only reason I could see to use a GRE tunnel was to fake a larger MTU than the IPsec tunnel supports.

Vincent C Jones

New Member

Re: iBGP vs eBGP


Controlling route preference with eBGP tends to be easier because you can prepend the appropriate advertised ASN to create a "longer" apparent path to that destination.

Hope this helps.