RE: regular expression

From: asadovnikov (asadovnikov@comcast.net)
Date: Sat Aug 30 2003 - 01:45:05 GMT-3

If you look at Internet routing table you will be surprised how many routes
of that kind are actually there. Prepending AS path with a number of the AS
is a standard Internet practice of announcing "backup" route. I.e. if my AS
is 456, and I am dual-homed to 123 and 124, and I prefer inbound traffic to
come via 124, I will send my prefixes 'as is' to 124 and prepend them with
456 several times when sending to 123. So say I am announcing 10.0.0.0/8
(which I obviously would not to Internet), then the following to entries
will be seen (from upstream):

10.0.0.0/8 124 456
                123 456 456 456 456 456

The following modification of reg-exp should take care of this situation:
        (_123_([0-9]+_)*(456_)+[0-9]+_)|(_456_([0-9]+_)*(123)+_[0-9]+_)

I have to say that now I am stretching my abilities to do reg-exp without
testing; still to lazy to try :)

Best regards,
Alexei

-----Original Message-----
From: Nathaly Landry [mailto:lnathaly@cisco.com]
Sent: Friday, August 29, 2003 11:13 PM
To: 'asadovnikov'
Subject: RE: regular expression

Thank you

        If you have an as-path that has 123 456 456, one might have more
pressing issues than worrying about reg exp!! ;-)

nat

-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
asadovnikov
Sent: Friday, August 29, 2003 10:24 PM
To: 'Cristian Henry H'; 'Nathaly Landry'
Cc: 'Chepuri Roshan'; 'Ram Shummoogum'; ccielab@groupstudy.com
Subject: RE: regular expression

I am a little to lazy right now to try it but I think the following will
work:
        (_123_([0-9]+_)*456_[0-9]+_)|(_456_([0-9]+_)*123_[0-9]+_)

([0-9]+_)* - in the middle will match zero and more AS numbers between
123 & 456, and
[0-9]+_ - at the end will ensure that the 123/456 is not the last AS
number
             (it would match though 123 456 456, which is only
limitation of this
             reg-exp)

-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Cristian Henry H
Sent: Thursday, August 28, 2003 9:36 AM
To: Nathaly Landry
Cc: 'Chepuri Roshan'; 'Ram Shummoogum'; ccielab@groupstudy.com
Subject: Re: regular expression

My opinion

^([1-9]+_)*(123|456)_([1-9]+_)*(123|456)_([1-9]+_)*$

Nathaly Landry ha escrito:
>
> Cleaning up my folder, did not see an answer for that one, I
> think that the reg expression is: Reg exp to only accept routes that
> have transitted thru AS 123 AND AS 456
>
> ^((.+_)*123(_.+)*_456(_.+)*)$|((.+_)*123(_.+)*_456(_.+)*$)
>
> Any idea?
> Nat
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of Chepuri Roshan
> Sent: Thursday, February 20, 2003 11:55 PM
> To: Ram Shummoogum
> Cc: ccielab@groupstudy.com
> Subject: Re:
>
> Try _[1,4][2,5][3,6]_
>
> At 10:34 PM 2/20/2003 -0500, Ram Shummoogum wrote:
> >Hi ALL:
> >
> >
> >I need some help on this BGP regular expression.
> >
> >
> >Make a router only accept routes that has transit AS 123 and AS 456.

> >The keyword here is "and" and not or.
> >
> >
> >Ex: {34 5 6 456 7 99 123 88}
> > {45 123 89 456 7}
> >
> >
> >
> >
> >
> >I know "OR" is | but what is AND.
> >
> >
> >
> >
> >
> >Thanks for your help
> >
> >
> >RAM
>
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--
Cristian E. Henry
REUNA

E-mail: chenry@reuna.cl
Fono: 56-2-3370336

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