We've long had some feature requests open against JunOS for
as-path matching. The challenges faced are they don't treat these
AS numbers as strings, and certainly not in the case of some elements
like a paren (confed) or { for AS_SET.
In IOS-XR you can much more easily match against the origin-asn
in a policy as well which isn't quite as easy in other routing operating
systems.
- Jared
On Wed, Mar 11, 2015 at 05:28:06PM +0000, Mack McBride wrote:
> There is no back tracking in the junos regex nor would backtracking really
> help.
> Doing this is complicated on cisco due to the lack of negating a full as.
>
> However loop avoidance should prevent 64500 from occurring twice with an
> intervening AS.
> If you have turned off loop avoidance with allowas-in then you have a lot
> More complexity to worry about.
>
> I haven't tested this but it should work:
>
> (65400_)+([1-57-9][0-9]*_|6[01-35-9][0-9]*_|64[01-46-9][0-9]*_|645[1-9][0-9]*_|6450[1-9][0-9]*_|64500[0-9]+_)+
>
> Mack McBride | Network Architect | ViaWest, Inc.
> O: 720.891.2502 | [email protected] | www.viawest.com | LinkedIn |
> Twitter | YouTube
>
>
>
> -----Original Message-----
> From: cisco-nsp [mailto:[email protected]] On Behalf Of Saku
> Ytti
> Sent: Wednesday, March 11, 2015 10:38 AM
> To: [email protected]
> Subject: Re: [c-nsp] cisco regex puzzle of the day
>
> On (2015-03-10 20:29 +0100), Job Snijders wrote:
>
> > "^64500+ [^64500]"
> >
> > This junos beauty will match for example: "64500 64500 123 123 444",
> > but not "64500 64500" or "64500".
> >
> > Can any of you come up with a single line regex that works on IOS or
> > XR
> > (ios-regex) to mimick the above described behaviour?
>
> Follow-up question. Is there use-case for regular expression backtracking in
> AS_PATH?
> It would be simpler to implement without backtracking and it would fix this
> specific use-case, as simple '(64500_)+.+' would work. But perhaps it's still
> stupid idea, perhaps it'll break lot of really common use-cases.
>
> --
> ++ytti
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--
Jared Mauch | pgp key available via finger from [email protected]
clue++; | http://puck.nether.net/~jared/ My statements are only mine.
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