RE: Suggestion on BGP Prefix-list

From: OhioHondo (ohiohondo@columbus.rr.com)
Date: Thu Jun 05 2003 - 16:14:19 GMT-3


Carter

You are not wrong. The only prefix list that will specify ONLY the 3 listed
prefixes is:

prefix-list XXX seq 5 permit 192.168.1.0/24 ge 24 le 24
prefix-list XXX seq 5 permit 192.168.2.0/24 ge 24 le 24
prefix-list XXX seq 5 permit 192.168.5.0/24 ge 24 le 24

As I've noted several times on these types of questions --- the criteria for
the question leaves too much to assume. It's usually insufficient wording
for the word problem. For instance a more definitive question might be:

Given only the following routes write a single line prefix-list that denies
all routes except A,B,C.

-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Carter, Lee
Sent: Thursday, June 05, 2003 12:43 PM
To: 'Ram Shummoogum'; johnson_liu@corp.giga.net.tw
Cc: ccielab@groupstudy.com
Subject: RE: Suggestion on BGP Prefix-list

Correct me if I'm wrong but the

prefix-list XXX seq 5 permit 192.168.0.0/21 ge 24 le 24

will allow 192.168.0.0/24 thru 192.168.7.0/24

The question stated earlier sais to allow only 192.168.1.0/24,
192.168.2.0/24 and 192.168.5.0/24

-----Original Message-----
From: Ram Shummoogum [mailto:rshummoo@ca.ibm.com]
Sent: Thursday, June 05, 2003 9:44 AM
To: johnson_liu@corp.giga.net.tw
Cc: ccielab@groupstudy.com
Subject: RE: Suggestion on BGP Prefix-list

I guess you win..
Thanks

$BN-Gn?N(B <johnson_liu@corp.giga.net.tw> on 06/05/2003 10:33:56 AM

To: Ram Shummoogum/Quebec/IBM@IBMCA, <scotsman@rediffmail.com>
cc: <ccielab@groupstudy.com>
Subject: RE: Suggestion on BGP Prefix-list

How about this :

prefix-list XXX seq 5 permit 192.168.0.0/21 ge 24 le 24

--
Johnson Liu
Senior Network Engineer
Gigamedia Limited, Inc.
CCNP/CCDP/CCIE#11440

-----Original Message----- From: Ram Shummoogum [mailto:rshummoo@ca.ibm.com] Sent: 2003/6/5 [$B@14|;M(B] $B2<8a(B 08:01 To: scotsman@rediffmail.com Cc: ccielab@groupstudy.com Subject: Re: Suggestion on BGP Prefix-list

Let me give it a shot.

prefix-list XXX seq 5 deny 192.168.20.0/23 ge 24 le 24 prefix-list XXX seq 10 permit 0.0.0.0/0 le 32

RAM

"Scot Peter" <scotsman@rediffmail.com>@groupstudy.com on 06/05/2003 06:35:14 AM

Please respond to "Scot Peter" <scotsman@rediffmail.com>

Sent by: nobody@groupstudy.com

To: ccielab@groupstudy.com cc: Subject: Suggestion on BGP Prefix-list

Hello Group,

I have a scenario like this

AS254--(EBGP)----R4(AS1)---(IBGP)---R2(AS1)

AS 254 is advertising five routes to R4 in the range... 192.168.1.0/24 192.168.2.0/24 192.168.5.0/24 192.168.20.0/24 192.168.21.0/24 The requirement is to allow only 192.168.1.0/24, 192.168.2.0/24 and 192.168.5.0/24 ONLY; and filter all other routes. DO NOT use any access-lists / distribute lists; use only prefix lists with minimum number of lines.

I have configured the below on R4; but not sure on configuring minimum number of lines. Please advice.

Router bgp 1 neighbor 10.1.1.1 remot-as 254 neighbor 10.1.1.1 prefix-list XXX in

prefix-list XXX seq 5 permit 192.168.1.0/24 prefix-list XXX seq 10 permit 192.168.2.0/24 prefix-list XXX seq 15 permit 192.168.5.0/24

Is this config is OK with the minimum number of lines?

Thanks in advance SP

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