From: Usankin, Andrew (Andrew.Usankin@twtelecom.com)
Date: Thu Nov 29 2007 - 15:29:47 ART
Dunno how to put it right, but you missing the point here. Nobody thinks
about confederation routes neither about aggregates with as-set applied.
For example aggregate route may look like:
Network Next Hop Metric LocPrf Weight Path
*> 172.16.0.0/22 192.168.1.1 0 0 1 {65530,2}
i
And "}" is actually a character and takes place in expression.
Confederates have "(" and ")". So what I'm saying is that "_" sign is in
fact matches all those characters. Here is a quote from "BGP4 handbook":
_ (underscore) Matches a comma (,), left brace ({), right brace (}),
left parenthesis ((), right parenthesis ()), the beginning of the
string, the end of the string, or a space.
(Pay attention here to "beginning of the string and the end of the
string")
So if you say "_200$" it will actual match as those routes originated in
AS 200 as well as those passing through this AS. I like to always make
it as more specific as it possible, so if I want to filter "routes
originated in AS 200" I make expression as "^200$" not "_200$".
Andrew
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Tandou Mohamed
Sent: Wednesday, November 28, 2007 8:01 AM
To: Gupta, Gopal (NWCC); smorris@ipexpert.com; ccielab@groupstudy.com
Subject: RE: Regular Expression
Thanks a lot everyone to clear this out for me.
"Gupta, Gopal (NWCC)" <gopal.gupta@hp.com> wrote:
Hi Tandou,
B means Routes originated in 200,
just think it logically and go behind the syntax, go behind the original
string and then apply the syntax logically.
We have As-path like this (100 300 200) (Original string)
B (_200$) now look at the string we want to match out of the original
string what original string says is the route has traversed 100 300 and
has originated in 200 coz 200 is the first AS in the original string.
Now "_" means any AS number in the start of the string and $ means the
end of the string.
In case of B we have $ but with 200 and in the start we have mentioned
any AS number using "_"
Hope I have tried to make you understand........
HTH
Gops
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Tandou Mohamed
Sent: Wednesday, November 28, 2007 19:41
To: smorris@ipexpert.com; ccielab@groupstudy.com
Subject: RE: Regular Expression
Importance: Low
Now i understand D. what about B? the origin of the routes will be AS
200 only or can be any adjacent neighbor to AS 200 ?
Thanks,
Mohamed
Scott Morris wrote:
D would be routes LEARNED FROM AS 690 (your peer)
HTH,
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713,
JNCIE-M #153, JNCIS-ER, CISSP, et al.
CCSI/JNCI-M/JNCI-ER
VP - Technical Training - IPexpert, Inc.
IPexpert Sr. Technical Instructor
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Telephone: +1.810.326.1444
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-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Tandou Mohamed
Sent: Wednesday, November 28, 2007 8:34 AM
To: ccielab@groupstudy.com
Subject: Regular Expression
Hello GS,
can someone check this out if i am correct about these definition also
any comment on B,C,D and E those really confuse me sometimes.
Thanks,
Mohamed
A) ip as-path access-list 1 permit _109_ => routes containing or
transiting AS 109
B) ip as-path access-list 2 permit _200$ => routes originated in AS 200
C) ip as-path access-list 2 permit ^100$ => routes originated by a
neighbor in AS 100
D) ip as-path access-list 3 permit ^690_ => routes originating from AS
690
E) ip as-path access-list 3 permit ^$ => routes originating from this AS
(my AS)
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