Re: PREFIX LISTS

From: gladston@br.ibm.com
Date: Mon Dec 06 2004 - 17:16:20 GMT-3


Hello,

Hope somebody correct me if I am wrong.

By Halabi definition:

"Supernet is any network that contains fewer bits than a network's natural mask"

ip prefix-list test17 seq 5 deny 0.0.0.0/1 le 7
 matches 0 to 127, with mask less than 8 (127 loopback and le meaning 7 and less)

ip prefix-list test17 seq 10 deny 128.0.0.0/2 le 15
 matches 128 to 191 with mask less than 16

ip prefix-list test17 seq 15 deny 192.0.0.0/3 le 23
 matches 191 to 223 with mask less than 24

So far, so good. Denies any supernet of all Classfull.

Permit everything else:

ip prefix-list test17 seq 20 permit 0.0.0.0/0 le 32

===================
quoted
Can this also be answered as follows?
===================

ip prefix-list test17 seq 5 permit 0.0.0.0/1 ge 8
 matches 1 to 127 with mask greater than 7
 will match classfull and subnets of the range 1 to 127

ip prefix-list test17 seq 10 permit 128.0.0.0/2 ge 16
 matches 128 to 191 with mask greater than 15

ip prefix-list test17 seq 15 permit 192.0.0.0/3 ge 24
 matches 192 to 223 with mask greater than 23

ip prefix-list test17 seq 20 deny 0.0.0.0/0 ge 32
 matches everything else

Yeah, I think you reach your goal both ways.



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