Long AS Path

jim deleskie deleskie at gmail.com
Thu Jun 22 12:47:20 CST 2017


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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