eBGP Multihop neighbors

kcgeorge1218 · ‎05-01-2007

Hello -

Are there any issues to be taken into consideration when implementing BGP peering over eBGP-multihop?

mohammedmahmoud · ‎05-01-2007

Hi,

Only one issue, if you are going to do peering using loopback, you'll need to use the "neighbor x.x.x.x ebgp-multihop 2" command for the neighbor ship to build up, plus of course "neighbor x.x.x.x update-source loopback0".

Another thing to put in mind in any eBGP peering is the route filtering, you should decide whether you need to receive all the routes that this neighbor sends or not.

HTH, please do rate if it does help,

Mohammed Mahmoud.

kcgeorge1218 · ‎05-02-2007

Thx,Mohammed. I meant to ask if there are any service implications to be considered when implementing multihop peering.

Reason being that there are pt-pt links between the Rtrs but the client has decided to use multihop rather than peer directly with the physical interfaces. I am trying to understand why this was implemented this way.

Thx in advance

Danilo Dy · ‎05-02-2007

Hi,

Sry to bump in.

One of the reason could be the client router that is directly connected to your BGP router via point-to-point link is not capable of running BGP, the BGP router might be behind it (one hop away). One of the reason this could happen is the BGP router is not able to connect to point-to-point link as it does not support the media or not enough slot to put a module or interface for the point-to-point link, I see a lot of these happens.

Don't forget to put a password for all eBGP multihop implementation.

Dandy

mohammedmahmoud · ‎05-02-2007

Hi,

Most probably the client is trying to achieve load sharing and thats why he is going to peer with loopbacks, and the answer is no there is no any implications for using multihop eBGP, all it does is increase the TTL value of the sent BGP messages.

HTH, please rate if it does help,

Mohammed Mahmoud.

kcgeorge1218 · ‎05-02-2007

I checked a couple of these external routers and they are all connected over a Pt-Pt FR Ckt. Initially I thought that the far-end routers were behind somewhere in the providers cloud, but they they are connected via a T1/FR.