From: Troy Levin (troylevin@hotmail.com)
Date: Wed Mar 08 2006 - 00:29:04 GMT-3
Hi Mushtaq,
My test results show that a prefix list of "ip prefix-list permit
10.10.0.0/16 ge 30 le 30" will match ONLY on /30 subnets where the first 16
bits are 10.10
/16 means match the first 16 bits left to right without skipping must match.
ge 30 le 30 means that the subnet must be equal to /30 or 255.255.255.252.
R1#sh run | b router bgp
router bgp 1
no synchronization
bgp log-neighbor-changes
neighbor 131.108.50.2 remote-as 2
neighbor 131.108.50.2 prefix-list Filter in
no auto-summary
!
ip classless
no ip http server
!
!
!
ip prefix-list Filter seq 5 permit 10.10.0.0/16 ge 30 le 30
R2#sh run | B router bgp
router bgp 2
no synchronization
bgp log-neighbor-changes
network 10.10.0.0 mask 255.255.255.252
network 10.10.0.4 mask 255.255.255.252
network 10.10.13.0 mask 255.255.255.252 -----> also makes it through filter
on R1
network 12.12.0.0 mask 255.255.255.252 -----> /24 does not make it
through filter on R1
neighbor 131.108.50.1 remote-as 1
no auto-summary
R1#sh ip bgp
BGP table version is 10, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 10.10.0.0/30 131.108.50.2 0 0 2 i
*> 10.10.0.4/30 131.108.50.2 0 0 2 i
*> 10.10.13.0/30 131.108.50.2 0 0 2 i
HTH,
Troy
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Mushtaq A. Khan
Sent: Tuesday, March 07, 2006 3:00 PM
To: ccielab@groupstudy.com
Subject: IP Prefix-List issue
All,
I have recently read one very good posting on prefix-list in the groupstudy
and thought I now understand it very well but look like I still have some
confusions. Can someone help me out here.
For the prefix list "ip prefix-list permit 10.10.0.0/16 ge 30 le 30" I think
it will match the first 16 bits and will use a mask of 255.255.255.252. If
this is correct, will this permit 10.10.0.0 and 10.10.0.4 or only
10.10.0.4as the mask seems to limit to match the 30th bit.
Thanks,
Mushtaq
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