IP Routing Configuration Guide, Cisco Catalyst IE3x00 Rugged, IE3400 Heavy Duty, and ESS3300 Series Switches

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IP Routing Configuration Guide, Cisco Catalyst IE3x00 Rugged, IE3400 Heavy Duty, and ESS3300 Series Switches

Configure prefix lists for BGP filtering

Updated: June 25, 2026

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Configure prefix lists to control BGP route filtering by specifying permitted or denied network prefixes.

Prefix lists efficiently filter BGP routes. You can specify which network prefixes should be permitted or denied during BGP updates.

You do not need to specify a sequence number when removing a configuration entry. The show commands include the sequence numbers in their output.

Before using a prefix list in a command, you must set up the prefix list.

Procedure

1.

Use the configure terminal command to enter global configuration mode.

Example:

Device# configure terminal
2.

Use the ip prefix-list list-name [seq seq-value] deny | permit network/len [ge ge-value] [le le-value] command to create a prefix list with an optional sequence number to deny or permit access for matching conditions.

Example:

Device(config)# ip prefix-list BLUE permit 192.0.2.0/25

At least one permit or deny clause must be entered.

  • network/len is the network number and length (in bits) of the network mask.

  • (Optional) ge and le values specify the range of the prefix length to be matched. The specified ge-value and le-value must satisfy this condition: len < ge-value < le-value < 32
3.

Use the ip prefix-list list-name seq seq-value deny | permit network/len [ge ge-value] [le le-value] command to add an entry to a prefix list, and assign a sequence number to the entry. This step is optional.

Example:

Device(config)# ip prefix-list BLUE seq 10 permit 192.0.2.128/25
4.

Use the end command to return to privileged EXEC mode.

Example:

Device(config)# end
5.

Use the show ip prefix list [detail | summary] name [network/len] [seq seq-num] [longer] [first-match] command to verify the configuration by displaying information about a prefix list or prefix list entries.

Example:

Device# show ip prefix list summary test