From: Jaroslaw Zak (jaroslawz@hotmail.com)
Date: Mon Nov 04 2002 - 17:18:23 GMT-3
Good one Brian, "advertise only whatever is between single parentheses".
Neat. I wonder if that would be doable timewise to come up with that formula
on ccie lab test.
Thanks
Jarek
>From: "Brian McGahan" <brian@cyscoexpert.com>
>To: "'Jaroslaw Zak'" <jaroslawz@hotmail.com>, <saralilin@hotmail.com>,
> <ccielab@groupstudy.com>
>Subject: RE: bgp question...help
>Date: Mon, 4 Nov 2002 12:58:09 -0600
>
>Jarek,
>
> That will work matching on each specific case, but it's much
>more fun to match all cases in one line. Suppose we have the following
>scenario:
>
>R1---R2--R3--R4---R5
>
>R1 is AS 100
>R2, R3, R4 are AS 200
>R5 is AS 300
>
>R2, R3, R4 are confederated, with sub as's 65002, 65003, and 65004
>respectively. They are also originating prefixes A, B, & C
>respectively. If AS 200 does not want to be transit, we must only
>advertise out prefixes originated in these three sub AS's.
>
>From R2's perspective, we see the following prefixes, and the following
>AS-Path's:
>
>A - EMPTY
>B - (65003)
>C - (65003,65004)
>
>From R4's perspective, we see the following prefixes, and the following
>AS-Path's:
>
>A - (65002,65003)
>B - (65003)
>C - EMPTY
>
>Now we must consider how to match all of these cases in a single line.
>Remember that parentheses are special characters within the as-path
>list.
>
>Our minimum case to match would be:
>
>^$
>
>This is our empty AS-PATH, which is prefixes locally originated in our
>sub-as.
>
>Our maximum case to match would be:
>
>\(X\)
>
>where X is any number of AS's, or a comma. Remember that we need to
>escape the parens.
>
>To satisfy our condition of X, we should be matching 1 or more instance
>of any character, which equates to:
>
>.+
>
>Therefore our maximum case is now:
>
>^\(.+\)$
>
>However, we must match the minimum case at the same time. Therefore,
>our current expression \(.+\) is either true or false. True or false
>(0 or 1 instance) is covered by the expression ?.
>
>Therefore, our final regular expression will read:
>
>^(\(.+\))?$
>
>Tada!
>
>Advertise only prefixes which match this expression outbound on your
>border routers, and your confederated AS's will not be transit.
>
>
>HTH
>
>Brian McGahan, CCIE #8593
>Director of Design and Implementation
>brian@cyscoexpert.com
>
>CyscoExpert Corporation
>Internetwork Consulting & Training
>Voice: 847.674.3392
>Fax: 847.674.2625
>
>
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
>Of
> > Jaroslaw Zak
> > Sent: Monday, November 04, 2002 12:11 PM
> > To: saralilin@hotmail.com; ccielab@groupstudy.com
> > Subject: RE: bgp question...help
> >
> > Sarah
> >
> > How about keeping it simple and advertising only routes originated by
> > myself
> > or other two sub-as (I'm tempted to use plural here: sub-as'es ;))
> >
> > from AS 6503 outgoing filter towards external neighbours:
> >
> > permit _6501$
> > permit _6502$
> > permit ^$
> >
> > Just a thought.
> > Jarek
> >
> >
> >
> >
> > >From: "Sara Li" <saralilin@hotmail.com>
> > >Reply-To: "Sara Li" <saralilin@hotmail.com>
> > >To: ccielab@groupstudy.com
> > >Subject: RE: bgp question...help
> > >Date: Mon, 04 Nov 2002 13:16:50 +0000
> > >
> > >solution 2: use as-path filter.
> > >
> > >advertise to as 100 deny _200_
> > >
> > >advertise to as 200 deny _100_
> > >
> > >will this work also right?
> > >
> > > >From: "Sara Li" >Reply-To: "Sara Li" >To: ccielab@groupstudy.com
> > > >Subject: RE: bgp question...help >Date: Mon, 04 Nov 2002 12:06:35
>+0000
> > > > >Janto, > your solution .. . hummm, i tried simplified it. >
> > > >R1(AS100)-----R2(AS300)-----R3(AS300)------R4(AS200) > >R1 has
>route
> > >172.16.1.0/24 in its BGP table. >R4 has route 192.168.1.0/24 in its
>BGP
> > >table. > >R2 >----- >neighbor R1 route-map setcommunity in >
> >route-map
> > >setcommunity permit 10 >set community no-export > >R3 >---- >neighbor
>R4
> > >route-map setcommunity in > >route-map setcommunity permit 10 >set
> > >community no-export > >i think this will work. so whatever routes
>from
> > >ebgp neighbor are tag >with no-export, so the routes will not exit
>as300.
> > > > >am i right? > > >From: "Janto Cin" >Reply-To: "Janto Cin" >To:
>"'Sara
> > >Li'" , >Subject: >RE: bgp question...help >Date: Mon, 4 Nov 2002
>17:43:47
> > >+0700 > > >R1(AS100)-----R2(AS300)-----R3(AS300)------R4(AS200) > >R1
>has
> > >route >172.16.1.0/24 in its BGP table. >R4 has route 192.168.1.0/24
>in
> > >its BGP >table. > >R2 >----- >neighbor R1 route-map setcommunity in
> > > >neighbor R1 >route-map deny_as200 out > >route-map setcommunity
>permit
> > >10 >match ip >address 1 >set community 100 > >route-map setcommunity
> > >permit 20 > > >access-list 1 permit 172.16.1.0 >ip community-list 99
> > >permit 200 > > >route-map deny_as200 deny 10 >match community-list 99
> >
> > > >route-map >deny_as200 permit 20 > >R3 >---- >neighbor R4 route-map
> > >setcommunity in > >neighbor R4 route-map deny_as100 out > >route-map
> > >setcommunity permit 10 > >match ip address 1 >set community 200 >
> > > >route-map setcommunity permit >20 > >access-list 1 permit
>192.168.1.0
> > > >ip community-list 99 permit 100 > > >route-map deny_as100 deny 10
> > >match
> > >community-list 99 > >route-map >deny_as100 permit 20 > >Please
>correct me
> > >if I'm wrong. > >Janto > > > >-----Original Message----- >From:
> > >nobody@groupstudy.com >[mailto:nobody@groupstudy.com] On Behalf Of
> >Sara
> > >Li >Sent: Monday, >November 04, 2002 3:25 PM >To:
>ccielab@groupstudy.com
> > > >Subject: bgp >question...help > >i have confederation AS 300 peer
>with
> > >AS100, AS 200. > >AS 300 got 3 sub-as 65501,65502,65503. and i dont
>want
> > >AS 300 to be a > >trasit as for AS100 and AS 200. >how should i
>filter
> > >it? initially i >thougt using as-path filter to allow >only ^$ local
>as,
> > >then it proves >only local sub-as routes will go out, >not allow the
> > >other two sub as go >out of AS 300. then i thoght of using >community
> > >no-export. but then, if >as100 or as 200 neighbor as want to >reach
>as
> > >300, they cant as AS 100 or >AS 200 wont advertise as 300's
> >routes.any
> > >idea? Sara > >
> > >
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