Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

Prefix-list question

Hi expert,

How can I count the actual IP range of below prefix list

ip prefix-list abc seq 10 deny 10.100.64.0/18 ge 24
ip prefix-list abc seq 20 permit 10.100.0.0/16 ge 24
ip prefix-list abc seq 30 deny 10.100.0.0/14 ge 16
ip prefix-list abc seq 40 deny 10.104.0.0/13 ge 16
ip prefix-list abc seq 50 deny 10.112.0.0/13 ge 16
ip prefix-list abc seq 100 permit 0.0.0.0/0 le 32

5 REPLIES

Re: Prefix-list question

Not sure what your question is.

You have a list of prefix lists each one with different instructions.

You want to know which IP ranges are matched by the permit statements? Please clarify.

Federico.

New Member

Re: Prefix-list question

Yes, you are right

Thank you!

Re: Prefix-list question

Hi,

ip prefix-list abc seq 10 deny 10.100.64.0/18 ge 24 is matching any prefix within 10.100.64.0/18 (=10.100.64.0 - 10.100.127.255) but the prefix mask length must be greater or equal /24. Which means 10.100.66.0/24 is matched, but 10.100.66.0/23 is not, e.g.

The deny keyword is inverting the prefix acceptance logic though, i.e., the matching prefixes are being dropped by the router.


ip prefix-list abc seq 20 permit 10.100.0.0/16 ge 24 is matching any prefix within 10.100.0.0/16 (=10.100.0.0 - 10.100.255.255) but the prefix mask length must be greater or equal /24.

For

ip prefix-list abc seq 30 deny 10.100.0.0/14 ge 16
ip prefix-list abc seq 40 deny 10.104.0.0/13 ge 16

ip prefix-list abc seq 50 deny 10.112.0.0/13 ge 16

the logic is similar to the first line.


ip prefix-list abc seq 100 permit 0.0.0.0/0 le 32 is matching any prefix.

BR,

Milan

New Member

Re: Prefix-list question

Hi ,

For ip prefix-list abc seq 10 deny 10.100.64.0/18 ge 24, is it means that

Within the IP range  10.100.64.0 - 10.100.127.255

if route is 10.100.64.0 /24, then is match and will be dropped

if route is 10.100.65.0/ 24, then is match and will be dropped

if route is 10.100.67.0/ 26, then is match and will be dropped

if route is 10.100.64.0/ 22, then is not match and will not dropped

if route is 10.100.72.0/ 22, then is not match and will not dropped

Re: Prefix-list question

Hi,

yes, correct.

This line does not match it.

The final dropping/accepting depends on the following prefix-list lines finally.

BR,

Milan

625
Views
0
Helpful
5
Replies
CreatePlease login to create content