12-15-2013 02:52 PM - edited 03-04-2019 09:52 PM
Hello All,
I have been trying to understand Prefix lists. I understand why they are used, but having difficulty in understanding what networks a certain prefix list actually covers. I have pasted a couple of examples that I have come across below, and I am hoping somebody can explain what networks are covered by them;-
ip prefix-list test 1 seq 10 permit 10.0.0.0/11 ge 24
ip prefix-list test 2 seq 10 permit 10.150.0.0/16 ge 24
ip prefix-list test 3 seq 10 permit 10.128.0.0/24 ge 25
Also, if anybody knows of a good tuition page, please could you let me know
Many Thanks
Russ
Solved! Go to Solution.
12-15-2013 03:00 PM
Hi Russ,
ip prefix-list test 1 seq 10 permit 10.0.0.0/11 ge 24
This entry permits all subnetworks of 10.0.0.0/11 (i.e. 10.0.0.0/255.224.0.0, or any subnet in the range 10.0.0.0 - 10.31.255.255) whose netmask is at least /24.
For example, 10.10.0.0/24 would pass, 10.8.0.0/25 would pass, but 10.6.0.0/23 would not pass because the netmask is not at least /24, although this network is a subnet of 10.0.0.0/11. Also, 10.40.0.0/24 would not pass because this is no longer a subnet of 10.0.0.0/11.
ip prefix-list test 2 seq 10 permit 10.150.0.0/16 ge 24
This entry permits all subnetworks of 10.150.0.0/16 whose netmask is at least /24. The examples would be analogous as before.
ip prefix-list test 3 seq 10 permit 10.128.0.0/24 ge 25
This entry permits all subnetworks of 10.128.0.0/24 whose netmask is at least /25.
Also, if anybody knows of a good tuition page, please could you let me know
I do not know if it is good but have a look at this thread:
https://supportforums.cisco.com/message/3568328#3568328
Best regards,
Peter
12-15-2013 03:00 PM
Hi Russ,
ip prefix-list test 1 seq 10 permit 10.0.0.0/11 ge 24
This entry permits all subnetworks of 10.0.0.0/11 (i.e. 10.0.0.0/255.224.0.0, or any subnet in the range 10.0.0.0 - 10.31.255.255) whose netmask is at least /24.
For example, 10.10.0.0/24 would pass, 10.8.0.0/25 would pass, but 10.6.0.0/23 would not pass because the netmask is not at least /24, although this network is a subnet of 10.0.0.0/11. Also, 10.40.0.0/24 would not pass because this is no longer a subnet of 10.0.0.0/11.
ip prefix-list test 2 seq 10 permit 10.150.0.0/16 ge 24
This entry permits all subnetworks of 10.150.0.0/16 whose netmask is at least /24. The examples would be analogous as before.
ip prefix-list test 3 seq 10 permit 10.128.0.0/24 ge 25
This entry permits all subnetworks of 10.128.0.0/24 whose netmask is at least /25.
Also, if anybody knows of a good tuition page, please could you let me know
I do not know if it is good but have a look at this thread:
https://supportforums.cisco.com/message/3568328#3568328
Best regards,
Peter
12-15-2013 11:45 PM
Thanks Peter!
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide