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Re: expectations for bgp peering?
From: "Patrick W. Gilmore" <patrick () ianai net>
Date: Wed, 21 Jan 2009 00:35:17 -0500

On Jan 21, 2009, at 12:25 AM, mike wrote:

So I am just wondering what my expecations should be in a bgp peering scenario where I am multihomed with my own ASN and arin assigned ip space. At issue is the fact that my backup isp forced me to use ebgp multihop to peer with a router internal to their network and not the border router I am directly attached to, and secondly, that they say I am not allowed to prepend at all - they will do it for me, and from the looks of things they have established a route- map that just prepends their AS 6 times to my announcement.

This smells of bad engineering. I have looked up the bgp report for my provider and they have 0 downstream AS's, and the week that this project has taken (and it's still not up and working) has left me with less than absolute confidence in the provider. I want to know if anyone has an opinion on ebgp multihop for external customers, and wether I should really have an expectation to be able to assign my prepends as suits my needs? Are there any conditions that could make this fail that I should be aware of?

First, Rule Number One: Your network, your decision. (Okay, rule number one not about spam. :) Your transit provider owns your transit provider's network, he can run it as he pleases. There is nothing "wrong" with multi-hop or not allowing you to prepend. Bits are flowing, and you are connected.

Now that we know he _can_ run his network like that, I would never buy transit from someone who _does_ run a network like that. I've seen multi-hop before, but it is usually when something unusual is happening. For instance, if you are in a strange location and the edge router near you does not speak BGP. It is not horrible, but certainly not something I personally would prefer. Multi-hop can present more or at least different failure modes than direct BGP, but those can be managed with clue and effort.

The non-prepending thing though, that's Just Plain Silly. And hints at a general lack of clue. Which means that multi-hop is dangerous as it requires more clue, not less, to manage properly.


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