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Routing & Switching · Intermediate

Prefix List

A Cisco filter that matches routes by prefix and prefix length range, preferred over ACLs for route filtering.

Definition

Each prefix-list entry has a sequence, permit or deny, a prefix and optional ge (greater than or equal) and le (less than or equal) length qualifiers. Without ge or le, only the exact prefix length matches. Like ACLs, prefix lists end with an implicit deny.

Example

ip prefix-list LAN seq 5 permit 10.0.0.0/8 ge 24 le 24 matches all /24s inside 10.0.0.0/8.

Exam tip

10.0.0.0/8 le 32 matches everything in 10/8; 0.0.0.0/0 le 32 matches all routes.

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