expectations for bgp peering?

Warren Kumari warren at kumari.net
Wed Jan 21 14:21:27 UTC 2009

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

> Hello,
> 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.

Hmmm, this is distinctly unusual.

I'd suspect that the person that you are talking to is a: very new to  
BGP and is just applying the wrong canned route-map or b: the person  
is a little less new to BGP and has reached the "Oooh, now I know that  
I'm doing and can twiddle the knobs with the best of them" stage. I'd  
suggest trying to find someone else there to talk to....

Unless you have specifically bought the service as a "backup" service  
(and they are clumsily (and poorly) trying to make sure that you don't  
use it as your primary path) I cannot think of why your ISP would do  
this. This also seems a bit worrying  -- either they have enough  
capacity to carry your traffic when you need them to (and so should be  
happy to let you use them and bill you for the bits) or they don't and  
you will be unhappy when your primary goes away.

Are they really really cheap? If you need a "backup" ISP for  
regulatory reasons and don't really care, thats fine. If however you  
want good performance when your primary goes away, I'd suggest looking  
into this more...

>   This smells of bad engineering. I have looked up the bgp report  
> for my provider and they have 0 downstream AS's,

Yeah, that is worrying....

> 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?

While multihop is not in itself an issue, it does give one pause and  
it is worth finding out the reason. But, yes, you should expect to be  
able to prepend at will...


> Are there any conditions that could make this fail that I should be  
> aware of?
> Mike-

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