From: Leo Seto (lseto@xxxxxxxxxxxxx)
Date: Mon Aug 19 2002 - 03:43:54 GMT-3
if you mean to represent ^4 [0-9]*$ I'm thinking
^4 [0123456789]*$ and
^4 .*$ would both work.
-Leo Seto
On Mon, 19 Aug 2002, Jason Sinclair wrote:
> There is another way to represent 4[0-9]*$ - anyone care to take a guess?
>
> Jason Sinclair CCIE #9100
> Manager, Network Control Centre
> POWERTEL
> 55 Clarence Street,
> SYDNEY NSW 2000
> AUSTRALIA
> office: + 61 2 8264 3820
> mobile: + 61 416 105 858
> email: sinclairj@powertel.com.au
>
> -----Original Message-----
> From: ccie candidate [mailto:ccie1@lycos.com]
> Sent: Monday, 19 August 2002 14:32
> To: 'Omer Ansari'; Michael Snyder
> Cc: ccielab@groupstudy.com
> Subject: RE: Filtering BGP updates using ip as-path access-lists
>
> guys ;
>
> i want to participate in this
>
> regular experssions are actually work with the Finite state machine concept
> ..it means that when you want to have a match ..the conditios must come in
> the provided sequence of the regular expression
>
>
> to explain this lets take Michael question ..is 4 is the same ^4$ ..the
> answer is absolutely NOT.
>
> the first one (^4$) tells the router that the strings that will match me
> (the expression ) should be like that
> "when they start with begining of the string ,
> it should follow that the number 4 , then it should follow with end of the
> line "
>
> now only AS path of 4 will match ,no other strings can fit or match here
>
> i think that one is clear .
>
> now about the second regular expression ..it actually tells the router
> nothing more than
> " if the number 4 appears in the string , this is a match !! "
>
> so strings like 49 , 354 , 12 4 5
> will all match
>
>
> this will explain also why expression like _2_ means to match AS paths that
> contains 2
> the expression says
> " when space(or begining of line) followed by 2 followed by space (or end of
> line )appears ..this is a match "
>
> so strings like 33 2 44 , 2 , 13 2 will all match .
>
>
> now to some of the expressions mentioned in the previous posts
>
> [0-9]* will match the null string
> (* means zero or more of the occurence)
>
> so the regular expression
> ^4 [0-9]*$ will match AS 4 and any other AS attached to it ...the only thing
> which i have to test is the space if it match the space of not ..i will come
> back with that soon ..
>
>
>
> i hope this help
>
>
>
>
>
>
> --
>
> On Sun, 18 Aug 2002 19:43:47
> Michael Snyder wrote:
> >I wouldn't say that the expression nullifies routes from as4. Routes
> >originating from AS4 would only have the string ^4$. The expression in
> >question ^4 [0-9]* [0-9]*$ requires that only paths that start with as4
> >and have two more wildcard paths will match.
> >
> >I don't believe [0-9]* will match a null string. Therefore there's a
> >problem with my string I didn't see before, the problem is that isn't
> >inclusive of paths that are only one or two AS's long.
> >
> >If my requirement was to get the directly connected neighbors of AS4,
> >and those directly connected to the neighbors, then I think I would need
> >three expressions.
> >
> >^4$ ; Need a path to AS4
> >^4 [0-9]*$ ; Need AS4's neighbors
> >^4 [0-9]* [0-9]*$ ; Need AS4's neighbor's neighbors
> >
> >About when to us a space char (ascii 32) vs using an underscore _ (acsii
> >95), I just use my own experience. After reading the BGP tables for a
> >few months during labs, I know what string I want to match.
> >
> >Your last question about confederations, they use braces. Acsii 123,125
> >
> >Don't think I've seen a comma in an AS path yet.
> >
> >Your question, has brought another question to my mind. Wonder if ^4$
> >and 4 would do the same thing. I'll lab it this week.
> >
> >
> >-----Original Message-----
> >From: Omer Ansari [mailto:omer@ansari.com]
> >Sent: Sunday, August 18, 2002 12:08 PM
> >To: Michael Snyder
> >Cc: steven.j.nelson@bt.com; ccielab@groupstudy.com
> >Subject: RE: Filtering BGP updates using ip as-path access-lists
> >
> >Mike,
> >the spaces in your regexp automatically nullify any routes originating
> >from AS4 right?
> >
> >a little digression: anyone care to explain the difference between a
> >comma
> >(,) and a space ( ) in a regexp?
> >
> >are commas there for confederations?
> >
> >
> >
> >On Thu, 15 Aug 2002, Michael Snyder wrote:
> >
> >> _ (Matches a comma (,), left brace ({), right brace (}), the beginning
> >> of the input string, the end of the input string, or a space.
> >>
> >> Steve I just wanted to match a space. Thats why I didn't use _ ,
> >Cisco
> >> shows examples of not using _ to match spaces. In other words, a
> >space
> >> char will match a space character.
> >>
> >> I stand by my expression of ^4 [0-9]* [0-9]*$
> >>
> >>
> >> I think another legal expression would be ^4 12 16 3$ notice that _
> >> isn't needed.
> >>
> >> -----Original Message-----
> >> From: steven.j.nelson@bt.com [mailto:steven.j.nelson@bt.com]
> >> Sent: Thursday, August 15, 2002 10:14 AM
> >> To: msnyder@ldd.net
> >> Subject: RE: Filtering BGP updates using ip as-path access-lists
> >>
> >> Michael
> >>
> >> You have missed out the _
> >>
> >>
> >> ^4_[0-9]*_[0-9]*$
> >>
> >> Steve
> >>
> >> -----Original Message-----
> >> From: Michael Snyder [mailto:msnyder@ldd.net]
> >> Sent: 15 August 2002 15:53
> >> To: 'Chaim Gev'
> >> Cc: ccielab
> >> Subject: RE: Filtering BGP updates using ip as-path access-lists
> >>
> >>
> >> ^4 [0-9]* [0-9]*$
> >>
> >> Would match any AS that was directly connected to an AS that was
> >> directly connected to AS 4. Is this correct?
> >>
> >> Also I think the expression you cited ^_4_[0-9]*$ is different than
> >> ^4_[0-9]*$. If they are the same, why not use the shorter one?
> >>
> >> Please Advise
> >>
> >>
> >> -----Original Message-----
> >> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> >Of
> >> Chaim Gev
> >> Sent: Thursday, August 15, 2002 8:13 AM
> >> To: msnyder@ldd.net; raj.bahad@totalise.co.uk
> >> Cc: ccielab@groupstudy.com
> >> Subject: RE: Filtering BGP updates using ip as-path access-lists
> >>
> >> The "*" means "match 0 or more sequences of the pattern" which is null
> >> in
> >> your suggestion.
> >> ^_4_[0-9]*$ is more accurate if you are asked to filter exactly AS4
> >(and
> >> not
> >> AS14).
> >>
> >>
> >>
> >>
> >> >From: "Michael Snyder" <msnyder@ldd.net>
> >> >Reply-To: "Michael Snyder" <msnyder@ldd.net>
> >> >To: "'Raj'" <raj.bahad@totalise.co.uk>
> >> >CC: <ccielab@groupstudy.com>
> >> >Subject: RE: Filtering BGP updates using ip as-path access-lists
> >> >Date: Thu, 15 Aug 2002 07:52:31 -0500
> >> >
> >> >I'm no expert on as-path access-lists.
> >> >
> >> >But, I believe the $ is the main difference.
> >> >
> >> >^4_ anything beginning with as path 4.
> >> >
> >> >^4_[0-9]*$ anything beginning with as path 4 and ENDS with one
> >> >additional AS.
> >> >
> >> >Which brings up a question of mine,
> >> >
> >> >Why wouldn't ^4_*$ do the same thing?
> >> >
> >> >
> >> >
> >> >-----Original Message-----
> >> >From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> >Of
> >> >Raj
> >> >Sent: Thursday, August 15, 2002 7:02 AM
> >> >To: ccielab@groupstudy.com
> >> >Subject: Filtering BGP updates using ip as-path access-lists
> >> >
> >> >Hi all,
> >> >
> >> >I've come across a scenario for which I require some clarification.
> >> >
> >> >I want to permit only networks originated from AS4, and AS's directly
> >> >attached to AS4. I use the following config to meet the requirements,
> >> >however I have come across documentation that has achieved the same
> >> >results
> >> >using a slightly different version. I've listed both of them below:
> >> >
> >> >ip as-path access-list 1 permit ^4_
> >> >
> >> >and the other being:
> >> >
> >> >ip as-path access-list 1 permit ^4_[0-9]*$
> >> >
> >> >Could someone please help clarify why one method would be preferred
> >> over
> >> >the
> >> >other?
> >> >
> >> >Thanks,
> >> >
> >> >Raj.
This archive was generated by hypermail 2.1.4 : Sat Sep 07 2002 - 19:48:29 GMT-3