[c-nsp] BGP Regex to allow ISP customers

[Robert Blayzor]

Most SP’s support community tags of their directly connected customer prefixes.

That may be your path of lease resistance.


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> On Oct 17, 2016, at 4:14 PM, Nick Cutting <ncutting at edgetg.com> wrote:
> 
> Good Afternoon Masters of the BGP,
> 
> I am not good at BGP regex.
> 
> I need to come up with an ip as-path access-list that will only accept customer routes that belong to a certain provider, the ISP in question does not have a way of differentiating, so I was hoping to use a regex.
> 
> So for example if the server provider has an AS of 100, I need to be able to accept all routes originating from 100 (for their customers that do not have BGP) and all routes that have originated from a customer AS, that is a customer of the ISP in question.  The tricky part is if that client is prepending their AS.
> 
> e.g.
> If 55 and 56 are Customer AS's connected to AS 100 (our ISP)
> need to allow:
> 
> 100 55 i
> 100 56 i
> 
> Or 100 55 55 55 I (to allow for prepending)
> 
> But NOT
> 
> 100 55 something else
> 
> Is this possible?
> Any help greatly appreciated.
> 
> Nick
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