EBGP Multihop or EBGP through a GRE tunnel ?

[Matthew burnley]

Hello,

Does anyone know what the advantages of announcing BGP routes through a GRE tunnel have over using EBGP multihop and no tunnel?  Im thinking about a backup ADSL line for a router, if i was to create a EBGP neighbor with my device on its public IP address over an ADSL line, there are surely many hops in the way, thus i will have to use EBGP multihop in the neighbor statement, or i could create a GRE tunnel between my two end points and build the BGP neighbor over the tunnel interface IP addresses.

What are the advantages of using one method over the other?  Does anybody have an answer?

[Joseph W. Doherty]

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Posting

Well, from a performance standpoint, using a GRE tunnels incurs extra processing to encapsulate and decapsuate packets, and you lose 24 bytes of transport capacity (to GRE overhead), which can also easily lead to fragmentation.

Consider iBGP is "naturally" multihop, I would lean toward using eBGP multihop, if peers weren't adjacent.

[Akash Agrawal]

Hi,

I second Joseph on it. Advantage of GRE tunnel is to carry multicast or broadcast traffic from one site to another like if you want to run IGP protocols like EIGRP, OSPF between two sites, non ip traffic over ip network or say if you want to do encryption of data and want to use ipsec over GRE. For protocol like BGP which supports multihop, we can avoid using GRE and save extra overhead.

Regards,

Akash