Re: Long AS Path

[Pierfrancesco Caci <pf () tippete net>]

> > > > > "Mel" == Mel Beckman <mel () 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