RE: Reg Experts!

^200_300$ - must match exactly, originated in 300, passed through 200 and
that's it.
_200_300$ - some openness, just like above, originated in 300, passed
through 200, but could transit through other AS-es before reaching here.

^([0-9]+)?$ - could be any single AS# (string of digits) or no as# at all
(locally originated)
^([0-9]+)(_1\)*$ - this regexp is buggy, number of parenthesis does not
match. Without \ it will match anything originated in AS1 and passed through
one AS, or multiple times AS 1 (as prepend) or no AS 1 at all, just
originated in one AS. Another reason for \) could be if you could also match
\) for confederations.

_100+ - will match any as path that has _100, _1000, _10000 anywhere in it,
which means it has passed through that AS but it was not the last AS it
passed through.

^([0-9]+)(_\1)*$ - this is equivalent to ^([0-9]+)(_1)*$ and is similar to
the one explained above. \1 symbol has no meaning here otherwise, since
match and replace is not supported here as it is, for example, in voice
number translation rules.

Adel Abouchaev, CCIE# 12037, CISSP, MCSE

Technical Support Engineer
Netmasterclass LLC, Cisco Learning Partner
RFC821: adel_at_netmasterclass.net
E.164: +18886772669
HTTP: www.netmasterclass.net

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
Poplawski, James
Sent: Wednesday, June 09, 2010 10:19 AM
To: 'ccielab_at_groupstudy.com'
Subject: Reg Experts!

Just going through Narbik's Regular Expression listings and using INE
"Understanding BGP Regular Expressions" for reference.

I have some questions if anyone can explain in people terms. Here goes.

What's the difference between?
       deny ^200_300$
       deny _200_300$

       ^([0-9]+)?$
       ^([0-9]+)(_1\)*$

       _100+
       ^([0-9]+)(_\1)*$

In regards to ^([0-9]+)(_\1)*$ why is the number 1 chosen? Why have it at
all? Why not have a 0 or a 2 in there? I'm still looking through
documentation on \.

Any help is appreciated, thanks!
JB

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Received on Wed Jun 09 2010 - 11:47:30 ART