From: Gregg Malcolm (greggm@xxxxxxxxxxxxx)
Date: Wed Mar 27 2002 - 18:01:04 GMT-3
> Thanks Clay. Think the light is finally getting somewhat brighter for me.
> I set up a bunch of AS prepends on a router then played with filtering AS
> paths.
>
> From what I can see, there are a few important reg exp's to remember : _ ^
> and $
>
> _ matches any instance. Good for filtering transit AS info.
> ^ matches the beginning. Used for filtering paths beginning with an AS
> number
> $ matches ends with. Used for filtering paths that end with an AS number.
> I find I must use _ then path then $ (eg _30$) to filter path that
> originated at path 30.
>
> I think these 3 along with .* and ^$ will hopefully get me thru the lab.
I
> believe that I can do any filtering with multiples of these. Let's say
that
> I was asked to deny all routes that originated in path 50 and all routes
> that passed thru 150 :
> ip as-path access-list 1 deny _50$
> ip as-path access-list 1 deny _150 (same as just 150 tho.. I need to test
> some more)
> ip as-path access-list 1 permit .*
>
> Sound right ? I'm certain that other expressions are very useful but I'm
not
> sure that I can remember them all. Plus, I'm not really sure that they
will
> be needed on the lab test.
>
> I've also found that sh ip bgp reg <expression> helps a bunch to test the
> expression before placing it in an as-path list. A great feature that I
> never really used before.
>
> Gregg
>
>
>
> ----- Original Message -----
> From: "Clay Maney" <clay@openworldinc.com>
> To: "Gregg Malcolm" <greggm@sbcglobal.net>
> Sent: Wednesday, March 27, 2002 11:09 AM
> Subject: Re: BGP Reg Expressions
>
>
> > I'm not the guru here by any measure, but I can tell you this for sure:
> >
> > the ^ means "beginning with" and the $ means "ending with".
> >
> > so, ^30 means "where 30 is the first AS in the list", etc.
> >
> > hope that helps (and please let me know if I'm wrong)
> >
> > Clay
> >
> > On Wed, Mar 27, 2002 at 10:44:35AM -0800, Gregg Malcolm wrote:
> > > Folks,
> > >
> > > Does anyone have any good tips to help to remember reg expressions ?
> > > Unfortunately, my Unix background is pretty weak. I can remember some
> of the
> > > simple stuff like .* is all paths, ^$ is local routes (empty), _30_ is
> routes
> > > that passed thru path 30 , etc.
> > >
> > > The CD is very limited with info regarding this. Best CD info I've
> found is
> > > an appendix in the dial section :
> > >
>
http://127.0.0.1:8080/cc/td/doc/product/software/ios121/121cgcr/dial_r/drdap
> p
> > > /index.htm
> > >
> > > Mostly related to chat scripts from what I see. BTW - I swear that if
I
> see a
> > > chat script on the lab I'll get up and leave immediately.
> > >
> > > My confusion is not so much with the meaning of the expressions, but
> with how
> > > they are interpreted by BGP. For instance, what's the difference
> between ^30$
> > > and ^30_ ? Is it that ^30$ only matches 30 and nothing else and ^30_
> matches
> > > any path with 30 anywhere in it ?
> > >
> > > Does anyone have a standard set that they use that is somewhat easy to
> > > remember ?
> > >
> > > TIA, Gregg
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