Configuring prefix lists

Configure a prefix list to allow or deny specific route updates. A prefix list policy specifies route prefixes to match. After a match occurs, the system uses the route.

The prefix list contains a set of contiguous or noncontiguous routes. Reference prefix lists by name from within a routing policy.

About this task

Important

When you configure a prefix list for a route policy, add the prefix as a.b.c.d/32. You must enter the full 32-bit mask to exact a full match of a specific IP address.

You configure prefix lists on a VRF instance the same way you configure the GlobalRouter, except that you must use VRF Router Configuration mode.

Procedure

Enter Global Configuration mode:

enable

configure terminal
Configure a prefix list:

ip prefix-list WORD<1-64> {A.B.C.D/X} [ge <0–32>] [le <0–32>]
Optional: Rename an existing prefix list:

ip prefix-list WORD<1-64> name WORD<1-64>
Display the prefix list:

show ip prefix-list [prefix {A.B.C.D}] [vrf WORD<1-16>] [vrfids WORD<0-512>] [WORD <1-64>]

Example

Configure a prefix-list. Display the prefix list.

Switch:1>enable
Switch:1#configure terminal
Switch:1(config)#ip prefix-list LIST1 47.17.121.50/255.255.255.0
Switch:1(config)#show ip prefix-list LIST1
================================================================================
                           Prefix List - GlobalRouter
================================================================================

        PREFIX           MASKLEN FROM TO
--------------------------------------------------------------------------------

List 1    LIST1:
        47.17.121.50     24      24   24
1 Total Prefix List entries configured
--------------------------------------------------------------------------------
Name Appendix for Lists Converted from Old Config:
@A=conv addr list, @N=conv net list, @NR=conv net list modified as range

Variable definitions

The following table defines parameters for the ip prefix-list command.


Variable	Value
{A.B.C.D/X}	Specifies the IP address and the mask in one of the following formats: a.b.c.d/x a.b.c.d/x.x.x.x default
ge <0–32>	Specifies the minimum length to match. Lower bound and higher bound mask lengths together can define a range of networks.
le <0–32>	Specifies the maximum length to match. Lower bound and higher bound mask lengths together can define a range of networks.
name WORD<1-64>	Renames the specified prefix list. The name length is 1–64 characters.
WORD<1-64>	Specifies the name for a new prefix list.

The following table defines parameters for the show ip prefix-list command.


Variable	Value
{A.B.C.D}	Specifies the prefix to include in the command output.
vrf WORD<1-16>	Specifies the name of the VRF.
vrfids WORD<0-512>	Specifies the ID of the VRF and is an integer in the range of 0–512.
WORD<1-64>	Specifies a prefix list, by name, to use for the command output.

The following table defines parameters for the show ip prefix-list command output.


Variable	Value
PREFIX	Indicates the member of a specific prefix list.
MASKLEN	Indicates the prefix mask length in bits.
FROM	Indicates the prefix mask starting point in bits.
TO	Indicates the prefix mask endpoint in bits.