What is IP prefix-list? How to configure IP prefix-list?

 IP Prefix List

An IP prefix list is a network filtering tool used primarily in routing protocols to control which routes are accepted or rejected based on their network prefixes.

Key Characteristics

·        Prefix-based filtering: Matches routes based on their network address and prefix length.

·        Ordering processing: Entries are processed top-down until a match is found.

·        Implicit deny: if no match is found, the prefix is denied by default

 

R1(config)#ip prefix-list NAME seq 10 deny 192.168.1.1/24?

  ge  Minimum prefix length to be matched

  le  Maximum prefix length to be matched

  <cr>

Parameters

·        Network/len: The network address and prefix length to match.

·        Ge: “greater than or equal to” – minimum prefix length to match.

·        Le: “less than or equal to” – maximum prefix length to match.

·        Seq: optional sequence number for ordering entries.

Prefix lists are widely used in routing protocols like BGP, OSPF, and EIGRP for precise control over route advertisements and redistributions. 

Topology:-

Goal:.Configure the topology as per the diagram

1. Configure the IP addresses as per the topology
2. Configure IGP protocol EIGRP 100
3. Advertise the directly connected routes 
4. configure IP Prefix list name INTERNET
5. Deny 192.168.31.0/24 - 192.168.32.0/24
6. rest permit
7. deny 192.168.11.0/24 adjust the SEQ number.
8. make sure router 2 deny192.168.31.1/24 & 192.168.32.1/24 and 192.168.11.1/24 
9. change the SEQ