From: Nick Shah (nshah@xxxxxxxxxxxxxx)
Date: Tue Jul 02 2002 - 21:07:46 GMT-3
I had written this explanation for an earlier thread ..
/snip/
say you want to block 200.200.x.x/24, then you would use 200.200.0.0/16 ge
24 le 24
the mask /16 saying you are matching the first 2 octets, and ge24 le24
guarantees that ur prefix is /24
if you use just 200.200.0.0/16 ge 24 - it permits/denies all 200.200.x.x/24
and above /25,/26 etc.
if you use just 200.200.0.0/16 le 24 - it permits / denies all
200.200.x.x/24 and below /23 , /21 etc. upto /16
so basically mask < ge < le
Few more examples...
block/permit 200.200.x.x prefix between /24 & /28 ----> 200.200.0.0/16 ge 24
le 28
block/permit any prefix smaller than /24 --- > 0.0.0.0/0 le 24
block/permit default gateway (0.0.0.0) -----> 0.0.0.0/0
block/permit any any -----> 0.0.0.0/0 le 32
permit/deny host routes ----> 192.168.1.1/32 (these are easy)
There is a generic explanation on this url..
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr
_c/ipcprt2/1cfbgp.htm#1002814
check out same url on the doc cd as well.
//snip//
If you still have questions, let me know
rgds
Nick
----- Original Message -----
From: "Hunt Lee" <ciscoforme3@yahoo.com.au>
To: <ccielab@groupstudy.com>
Sent: Tuesday, July 02, 2002 9:49 PM
Subject: ip prefix-list ....
> Could someone explain to me how is the "ge" and "le" options are used
> for in a prefix list statement?
>
> Example:
>
> ip prefix-list TEST permit 172.16.0.0/24
> ip prefix-list TEST permit 172.16.1.0/24
> ip prefix-list TEST permit 172.16.2.0/24
> ip prefix-list TEST permit 172.16.3.0/24
>
> I understand that these 4 prefix-lists together will permit the 4
> subnets.
>
> But how is it equal to:
>
> ip prefix-list TEST permit 172.16.0.0/22 ge 23
>
> I know how to get the /22
>
> 172.16.00000000.0/24 = 0.0
> 172.16.00000001.0/24 = 1.0
> 172.16.00000010.0/24 = 2.0
> 172.16.00000011.0/24 = 3.0
>
> So the common bits would be /22, but why ge 23? How is it
> calculated??
>
> Thanks!
>
> H.
>
> http://www.sold.com.au - SOLD.com.au
> - Find yourself a bargain!
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