ip prefix list - ge le usage

[philip2008]

I have a question about the two examples below. From what I can gather is that these two preform the exact same task, that is to deny updates for this network with mask greater than /23.

If this is correct, which is the more standard/preferred practice, ge or le?

ip prefix-list test seq 5 deny 223.223.222.0/23 le 32

ip prefix-list test seq 5 deny 223.223.222.0/23 ge 24

[Harold Ritter]

Philip,

These two commands do not have the same end result.

The first statement would match on prefix 223.223.222.0/23 and the second one would not (ge 24).

As far as your second question is concerned, I would say that there is not one form preferred over the other. It depends on what needs to be accomplished.

Regards,

[philip2008]

thanks for reply,

if the second statement is:

ip prefix-list test seq 5 deny 223.223.222.0/23 ge 23

would this then be an identical statement?

Phil

[Harold Ritter]

Phil,

Both statements would indeed match the specific prefix in this case.

Bear in mind that there are still different though.

The way the

prefix-list

works is that it tries to match the

first portion (223.223.222.0/23) to the prefix

it self. It then tries to match the second portion (ge 23 or le 32 or /23 if nothing is specified) to the

prefix-length

So using ge 23 or le 32 can lead to different results.

Regards,

[philip2008]

I'm working hard to make this click!

This link gives me a good understanding of prefix lists

http://www.groupstudy.com/archives/ccielab/200105/msg00474.html

however it only fortifies my belief that the previous two examples produce the same results.

Another two examples below are listed with more details at which you may easily be able to show me the mistake I make.

I appreciate your replies.

ip prefix-list mylist seq 10 permit 10.64.0.0/16 le 32

This list specifies any subnet within the 10.64.0.0/16 range that has a

mask between /16 and /32, inclusive (255.255.0.0 to 255.255.255.255).

ip prefix-list mylist seq 10 permit 10.64.0.0/16 ge 16

This list specifies any subnet within the 10.64.0.0/16 range that has a

mask of /16 or greater (255.255.0.0 to 255.255.255.255).

[Harold Ritter · Accepted solution]

Philip,

Correct. As long as the range you are using is the same (i.e. 16 to 32 for both ge or le), the results will be the same either you use the GE or LE form.

Regards,

[Lassek]

Hi

a ´bit´old but since I came across it I thought to add a comment.

regarding: ip prefix-list mylist seq 10 permit 10.64.0.0/16 ge 16

´ge´ can´t be equal to the prefix length. So the statement is not correct.