Prefix List Exercises

Prefix lists are a powerful tool for route filtering but they also may be a little confusing when learning them. Here are some prefix list examples to reinforce knowledge. Answers should be syntactically sound commands and using the most specific matching possible.

1. Filter the following routes:

* 10.1.5.1/24
* 10.2.2.1/24
* 10.5.7.1/24

1. Filter the following routes:

* 10.1.1.1/24
* 10.2.1.1/25
* 10.2.1.128/25
* 10.100.1.1/30

1. Filter all but the last route and allow no others

* 172.16.2.1/24
* 172.16.3.1/25
* 172.16.3.128/25
* 172.16.4.1/26
* 172.16.4.64/26
* 172.16.10.1/30

1. Filter all routes using one command

* 10.1.1.1/16
* 10.2.1.1/17
* 10.2.128.1/17
* 10.10.10.5/30

1. Filter all /30 routes

* 192.168.1.0/24
* 192.168.2.1/25
* 192.168.2.128/30
* 192.168.3.1/30

Answers are below so don’t scroll down too far!

Answers

1.

ip prefix-list 1 deny 10.0.0.0/13 ge 24 le 24
ip prefix-list 1 permit 0.0.0.0/0 le 32

2.

ip prefix-list 2 deny 10.0.0.0/8 ge 24 le 30
ip prefix-list 2 permit 0.0.0.0/0 le 32

3.

ip prefix-list 3 deny 172.16.0.0/20 ge 24 le 26
ip prefix-list 3 permit 172.16.10.0/30

4.

ip prefix-list 4 deny 10.0.0.0/12 ge 16 le 30
ip prefix-list 4 permit 0.0.0.0/0 le 32

5.

ip prefix-list 5 deny 192.168.2.0/23 ge 30 le 30
ip prefix-list 5 permit 0.0.0.0/0 le 32