Quick IP Prefix List Question

[wpalumbo06]

Hello,

I would like to filter BGP routes using a route map and ip prefix list but am curious what is the best methid to accomplish the following:

I want the prefix list to filter out these networks:

172.39.8.0/24

172.39.8.0/25

172.39.8.0/26

172.39.8.0/27

172.39.8.0/28

172.39.8.0/29

172.39.8.0/30

Which option makes the most sense: (if either)

seq 50 permit 172.39.8.0/24

seq 51 permit 172.39.8.0/24 ge 25

or

seq 50 permit 172.39.8.0/23 ge 24

Thanks,

Bill

[Peter Paluch · Accepted solution]

Hi Bill,

The most simple way of doing this is by having the prefix-list in the form:

seq 50 permit 172.39.8.0/24 le 30

This says that the network which will be matched must be either the 172.39.8.0/24 or any subnet thereof, and the mask at the same time must be between /24 and /30 inclusive.

Does this meet your needs?

Best regards,

Peter

[Giuseppe Larosa · Accepted solution]

Hello Bill,

first option would be preferred as the second one would match also for any 192.168.9.0/x x >= 24 so it less  specific.

Personally I would use

seq 50 permit 192.168.8.0/24 le 32

to be sure that any prefix within 192.168.8./24 included the base block 192.168.8.0/24 is a match

Hope to help

Giuseppe

[wpalumbo06]

Thanks guys - didnt even occur to me to use le vice ge for this...guess I need to increase my caffeine intake today

[Peter Paluch]

Bill,

A good sleep is better than any amount of coffee Having a good deserved rest is a must. Anyway, we're glad to have helped!

Best regards,

Peter

[wpalumbo06]

Lol - I work in the financial sector - sleep is not permitted

Thanks again for the help!

Bill

[Peter Paluch]

Bill,

Lol - I work in the financial sector - sleep is not permitted 

I am a teacher - how well I know what you're talking about Take care!

Best regards,

Peter