Hi Lads,

I Used to Filter based on AS paths and reject any prefix that had private
or reserved AS numbers in the AS Path, I have to say that my experience is
that on Software routers such as Mikrotik, even on fast x86 processor based
routers that it increased convergence times by up to 5x in some case, and
8x/ 10x on Cloud core versions of Mikrotik Hardware,

in short the benefit of removing prefixes whos as path appears to be non
standard conforming, was far , by fa,r out weighed, by the cost of the time
it took my routers to recover from a blip or even just starndard regular
maintainence,


I would agree (now that I learned the hard way) with all those who say
filtering via AS Path and Reg ex is not such a hot idea...

I hope this helps,

Tom Smyth

On Wed, Nov 4, 2015 at 11:09 AM, James Bensley <jwbens...@gmail.com> wrote:

>
> On 31 Oct 2015 18:59, "Nick Hilliard" <n...@foobar.org> wrote:
> >
> > um, apologies for the tactlessness of this email, which didn't come out
> at
> > all as intended, oops :-/
> >
> > -n
>
> No problems. If I wasn't clear, I'm not saying prefixes and AS paths are
> the same. See earlier post about being in mobile and multi-AS consolidation
> work.
>
> I have 5 full table provides, if someone is sending me a prefix with AS
> path that contains XYZ-AS which I'd a private AS, someone has made a boo
> boo somewhere and I don't want that to become my best path as that operator
> potentially has a network full of problems. Nuking the prefix with a bad AS
> path then allows me to learn it from somewhere else.
>
> Yes, caveat corner cases for a customer with single upstream somewhere so
> we will see their prefixes the same via all my transit providers. I have
> taken a dump of the full table, I'll be scanning it. Off the top of my
> head, I'm confident that they're few and far between enough that it's no
> problems for me.
>
> James
>



-- 
Kindest regards,
Tom Smyth

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