nanog mailing list archives

Re: How long AS-PATH policies have you used

From: James Bensley via NANOG <nanog () lists nanog org>
Date: Wed, 25 Feb 2026 19:09:57 +0000

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On Monday, February 23rd, 2026 at 17:52, Saku Ytti via NANOG <nanog () lists nanog org> wrote:

...

I'd like to hear about operational experiences, how long AS-PATH
policies people have successfully run and in which NOS.

...

How many ASN can I iterate, before I become market leading and have to
work with vendors to fix bugs?


The largest AS path filter I can find on our network, is for one of our customers. The filter is 9002 permit entries 
long, each entry matches 8 ASNs, so 72016 ASNs in total.

To clarify, one "entry" is matching 8 possible origin ASNs:

permit (1|2|3|4|5|6|7|8)$ any

^ 9k of those.

This is on EOS, it works fine.

...

So I don't really need to check the prefix again, after it passed
RPKI. AS_PATH check is equally strong.


This is exactly why we have AS path filters too. We're looking into dropping prefix filters but keeping AS path filters 
until such time as ASPA (or some other method) covers that part of the path filtering space, and we're also working on 
RFC9234 adoption right now. Prefix filters are yucky.


Cheers,
James.
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Current thread:

How long AS-PATH policies have you used Saku Ytti via NANOG (Feb 23)
- Re: How long AS-PATH policies have you used Tom Beecher via NANOG (Feb 24)
  - Re: How long AS-PATH policies have you used Saku Ytti via NANOG (Feb 24)
- Re: How long AS-PATH policies have you used James Bensley via NANOG (Feb 25)
  - Re: How long AS-PATH policies have you used Saku Ytti via NANOG (Feb 25)
    - Re: How long AS-PATH policies have you used Job Snijders via NANOG (Feb 26)
    - Re: How long AS-PATH policies have you used Saku Ytti via NANOG (Feb 26)
    - Re: How long AS-PATH policies have you used Saku Ytti via NANOG (Feb 26)
    - Re: How long AS-PATH policies have you used Saku Ytti via NANOG (Feb 26)
    - Re: How long AS-PATH policies have you used Job Snijders via NANOG (Feb 26)
    - Re: How long AS-PATH policies have you used Saku Ytti via NANOG (Feb 26)
    - Securing EBGP while getting rid of big IRR-based prefix-list-filters (Was: How long AS-PATH policies have you used) Job Snijders via NANOG (Feb 26)
    - Re: Securing EBGP while getting rid of big IRR-based prefix-list-filters (Was: How long AS-PATH policies have you used) James Bensley via NANOG (Feb 27)
    - Re: Securing EBGP while getting rid of big IRR-based prefix-list-filters (Was: How long AS-PATH policies have you used) Saku Ytti via NANOG (Feb 27)

(Thread continues...)