Re: [Idr] WGLC on draft-ietf-idr-as-private-reservation-00

[Nick Hilliard <[e-mail]>]

On 12/12/2012 18:52, Brian Dickson wrote:
> Okay, in as-plain, here goes:

ah, thanks - that's saved me the bother of sitting down and exercising the
grey matter of an evening.  In fact you can optimise it by taking
characters out from the front, which I've done below.  On some systems with
recursive RE libs, you can do more of this and shorter the RE string.  On
other RE libs which support specifying the atom instance count, you can
replace sequences of dots with squiggly braces, but that won't help much
with readability and it's not portable across all of the various vendor
regexp libs (and it will just make it look like modem-induced line-noise).
 I've taken out the 42 and cut-n-pasted it into a cisco router, and it now
looks like this:

> ip as-path access-list 499 permit _42(781900[8-9].|78190[1-9]..|7819[1-9]...|78[2-9].....|79......|8.......|9[0-3]......|94[0-8].....|949[0-5]....|9496[0-6]...|94967[0-1]..|949672[0-8].|9496729[0-4])_

It will be similar but not the same on other vendors.

If we aim for a decimal-aligned system, in the worst case this is reduced to:

> ip as-path access-list 499 permit _XXX......._

... for some simple numeric value of XXX.

I know which regular expression I'd prefer to deal with.

Nick