[c-nsp] Is it LE or GE in prefix-lists?

Matthew Crocker matthew at crocker.com
Wed Aug 16 08:50:20 EDT 2006



Howdie,

  I always screw this up,

Lets say I have a customer with a /16 that is announcing that /16 to  
me.  He has a customer with a /24 from that /16 and is announcing  
that /24 to him and to another ISP.   I would like to accept both  
the /16 & /24 routes so that the /24 can survive through my network  
and compete with the /24 going through the other ISPs network.   I  
have a prefix-list inbound on my customer currently configured to  
allow only the /16,  how do I change it to allow the /16 and /24s  
inside it?

Is it

ip prefix-list CUSTOMER_A seq 10 permit 10.11.0.0/16 ge 24

OR

ip prefix-list CUSTOMER_A seq 10 permit 10.11.0.0/16 le 24

Is the LE on the subnet length (less than or equal to 24 bits i.e. / 
16 - /24) or is it GE on the number of IPs (greater than or equal to  
256 IPs (i.e. 256 - 64k IP)

I would like to accept the /16 in any form from /16 - /24,  I don't  
want to accept /25 - /32

-Matt

--
Matthew S. Crocker
Vice President
Crocker Communications, Inc.
Internet Division
PO BOX 710
Greenfield, MA 01302-0710
http://www.crocker.com



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