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
Example
Configure a prefix-list. Display the prefix list.
Switch> enable Switch# configure terminal Switch(config)# ip prefix-list LIST1 192.0.2.1/255.255.255.0 Switch(config)# show ip prefix-list LIST1 ================================================================================ Prefix List - GlobalRouter ================================================================================ PREFIX MASKLEN FROM TO -------------------------------------------------------------------------------- List 1 LIST1: 192.0.1.2.1 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:
|
ge <0–32> |
Specifies the minimum length to match. Lower bound and higher bound mask lengths together can define a range of networks. |
id <1-2147483647> |
Specifies the Prefix list ID. |
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. |
Use the data in the following table to use 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. |