From: BRZYSKI, ADAM E (SWBT) (ab1723@xxxxxxx)
Date: Mon Nov 12 2001 - 19:49:19 GMT-3
You are correct. I made a typo.
Adam Brzyski
Design Engineer II
CCIE #8082, NNCDE
-----Original Message-----
From: afiddler [mailto:afiddler@wi.rr.com]
Sent: Monday, November 12, 2001 4:36 PM
To: BRZYSKI, ADAM E (SWBT)
Subject: Re: BGP regular expression help
_1$ Originated from 100
Shouldn't this be:
_100$
----- Original Message -----
From: "BRZYSKI, ADAM E (SWBT)" <ab1723@sbc.com>
To: "Krake, Kris" <KKrake@aegonusa.com>; <ccielab@groupstudy.com>
Sent: Monday, November 12, 2001 2:57 PM
Subject: RE: BGP regular expression help
> Note the following
>
> ^ means begins with
> $ means ends with
>
> Keep in mind how the AS path is formed by BGP. Each time a BGP update
> transverses from a particular AS to another AS the AS number of the
exiting
> AS is added to the AS path attribute. Boy that sentence is a mouthful. I
> hope I did not confuse you. In case I did lets do an example. Lets say
> that a route originated in AS 1 and has gotten propagated to AS 10 through
> the following topology:
>
> AS1-AS5-AS6-AS10
>
> Within AS10 when looking at the BGP table you should see the following AS
> path for all updates that originated in AS1
>
> 6 5 1
>
> Note that the originating AS is the left most number. With that said the
> definitions above for ^ and $ are given from the perspective of what is
> displayed in the BGP table. However in reality that perspective is
reverse
> of how the BGP process constructs the AS path attribute. Look at the
> following examples
>
> .* any
> ^$ Local AS
> ^1$ Only from AS 1
> ^6_ Received directly from AS 6
> _1$ Originated from 100
> _5_ via AS 5
>
> Look at the following link for more help
>
>
http://www.cisco.com/univercd/cc/td/doc/product/atm/c8540/12_0/13_19/cmd_ref
> /appc.htm#xtocid68796
>
> Note the following command is very useful in checking the validity of your
> regular expressions
>
> show ip bgp regexp (regular expression)
>
>
> Adam Brzyski
> Design Engineer II
> CCIE #8082, NNCDE
>
>
> -----Original Message-----
> From: Krake, Kris [mailto:KKrake@aegonusa.com]
> Sent: Monday, November 12, 2001 2:12 PM
> To: BRZYSKI, ADAM E (SWBT); ccielab@groupstudy.com
> Subject: RE: BGP regular expression help
>
>
> I am more interested in the show ip bgp regexp command to go through the
bgp
> route table. Therefore I need the logical not in the regular expression.
> As for the expressions below: I know I'm green on regexp's but doesn't
the
> "^" mean originate. I would have thought the opposite of what you stated
> below.
>
> -----Original Message-----
> From: BRZYSKI, ADAM E (SWBT) [mailto:ab1723@sbc.com]
> Sent: Monday, November 12, 2001 2:48 PM
> To: ccielab@groupstudy.com
> Subject: RE: BGP regular expression help
>
>
> ip as-path access-list 1 deny _123_1$
> ip as-path access-list 1 permit .*
>
> note that the access-list above will filter out any updates that
originated
> in AS 1 and directly went through AS 123
>
> ip as-path access-list 1 deny ^1_123_
> ip as-path access-list 1 permit .*
>
> note that this access-list will filter out any updates that have arrived
> into the local AS directly through AS 1 and 123.
>
> In order for the filters to work they need to be applied to a neighbor
> statement within your BGP configuration.
>
> Hope this helps.
>
> Adam Brzyski
> Design Engineer II
> CCIE #8082, NNCDE
>
> -----Original Message-----
> From: Krake, Kris [mailto:KKrake@aegonusa.com]
> Sent: Monday, November 12, 2001 1:26 PM
> To: ccielab@groupstudy.com
> Subject: BGP regular expression help
>
>
> How would you write the regular expression for the following:
>
> all paths NOT starting with the 1 123 pattern (AS 1 followed by AS 123)
>
> I know that ^1_123 would show me those patterns with 1 123 but I need the
> opposite of that (logical not)...
>
> I have tried ^[^1_123] and [^^1_123]
>
> Thanks for guidance...
>
> Kris
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