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 _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/ This message contains information that may be confidential, privileged or otherwise protected by law from disclosure. It is intended for the exclusive use of the addressee(s). Unless you are the addressee or authorized agent of the addressee, you may not review, copy, distribute or disclose to anyone the message or any information contained within. If you have received this message in error, please contact the sender by electronic reply and immediately delete all copies of the message. _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
