Re: How long AS-PATH policies have you used

I've always gotten plenty of mileage out of as-path regexes on Junos.
Usually don't ever need to be more than 4 long.

On Mon, Feb 23, 2026 at 11:52 AM Saku Ytti via NANOG <[email protected]>
wrote:

> We've had problems in various NOS in generating large prefix-lists. In
> absolute configuration size, as well as prefix-set sizes.
>
> I'd like to hear about operational experiences, how long AS-PATH
> policies people have successfully run and in which NOS.
>
>
> I am not interested in exact AS_PATH contents, I am only interested
> that it contains a named set of AS numbers, in any order and any
> repetition. In Junos speak ^[1 42 500 1212]*$
>
> How many ASN can I iterate, before I become market leading and have to
> work with vendors to fix bugs?
>
>
>
> The interest is because of RPKI we could get rid of prefix-lists, but
> we might still want to verify AS_PATH. Consider AS-YTTI having
> AS43792.
>
> a) They advertise google with invalid origin
> b) They advertise google with valid origin
>
> Maybe these come from some BGP optimization tool they run. A) is
> dropped by RPKI, B) is passed.
> But B) can be dropped by prefix-list filter or AS-PATH filter which
> doesn't allow Google ASN to exist in the AS_PATH.
>
> So I don't really need to check the prefix again, after it passed
> RPKI. AS_PATH check is equally strong.
>
> --
>   ++ytti
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