Long AS Path

Mel Beckman mel at beckman.org
Thu Jun 22 14:25:40 CST 2017


You don't have to wonder. You can call and ask them. 

-mel via cell

> On Jun 22, 2017, at 5:47 AM, jim deleskie <deleskie at gmail.com> wrote:
> 
> I see 5+ prepends as maybe not reason to have your "BGP driving license
> revoked" but if I can continue with the concept that you have your BGP
> learners permit.
> If I think back to when I learned to code or when making ACL's,  we still
> used line number and practice would be to give ourselves lots
> of space 5 or 10 numbers in case we have to insert something in the middle.
> ie I need 2 sets of prepends, I'm still learning this stuff
> so I'll go with 5 and 10. We all started somewhere, we all did dumb stuff,
> hopefully, we all learned.
> 
> 12AS hops, I have to go see how they are connected now, maybe someone in
> that chain needs to be invited by an IX to a NANOG or GPF or some such,
> that can't be super efficient.
> 
> -jim
> 
> On Thu, Jun 22, 2017 at 3:09 AM, Pierfrancesco Caci <pf at tippete.net> wrote:
> 
>>>>>>> "Mel" == Mel Beckman <mel at beckman.org> writes:
>> 
>> 
>>    Mel> Why not ask the operator why they are pretending this path?
>> Perhaps
>>    Mel> they have a good explanation that you haven't thought of. Blindly
>>    Mel> limiting otherwise legal path lengths is not a defensible
>> practice, in
>>    Mel> my opinion.
>> 
>>    Mel>  -mel beckman
>> 
>> 
>> A prepend like that is usually the result of someone using the IOS
>> syntax on a XR or Junos router.
>> 
>> Long ago, someone accidentally prepending 255 times hit a bug (or was it
>> a too strict bgp implementation? I don't remember) resulting in several
>> networks across the globe dropping neighbors. One has to protect against
>> these things somehow.
>> 
>> As a data point, here is how many prefixes I see on my network for each
>> as-path length, after removing prepends:
>> 
>> 
>> aspath length   count
>> -------------------------
>>        0:      340
>>        1:      47522
>>        2:      292879
>>        3:      227822
>>        4:      58390
>>        5:      10217
>>        6:      2123
>>        7:      638
>>        8:      48
>>        9:      58
>>        11:     20
>>        12:     2
>> 
>> 
>> So, does your customer have a legitimate reason to prepend more than 5
>> times? Maybe. I still think that anyone that does should have their BGP
>> driving licence revoked, though.
>> 
>> Pf
>> 
>> 
>> 
>> 
>> --
>> Pierfrancesco Caci, ik5pvx
>> 


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