Re: How long AS-PATH policies have you used

["Jakob Heitz (jheitz) via NANOG" <nanog () lists nanog org>]

That was fixed in IOS-XR about 5 years ago.
Previously, we could only do it with as-path-set in route-policy.
as-path-set allows whole paths to be specified, so it's slow.
If all you want is to match on a single ASN, it can be done much faster using a tree lookup instead of linear.
So, I invented the as-set for route-policy configuration.
Here is a config sample:

as-set asset1
  2914,
  174,
  3356
end-set
!
route-policy asd
  if as-path originates-from asset1 then
    pass
  endif
end-policy

If that doesn't meet your needs, let me know.
Kind Regards,
Jakob Heitz

Date: Tue, 24 Feb 2026 20:15:00 +0200
From: Saku Ytti <saku () ytti fi>


For SROS, IOSXR 90k would be quite a ridiculous attempt, and it's
probably cheaper just to expand to a million lines of prefix-list,
since prefix-list scale is more tested than AS_PATH scale.
In SROS as-path-group can contain only 128 lines, so if you match a
single ASN per line, you'd need 700 terms just to check the origin,
unless you use regexp OR in the lines to put multiple origins per
line.

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