# Creating a prefix list

Use the following procedure to create a new prefix list.

Prefix lists are the base item in a routing policy. Prefix lists contain lists of IP addresses with their associated masks that support the comparison of ranges of masks.

## Procedure steps

1. From the navigation tree, double-click IP.

2. In the IP tree, click Policy.

3. In the work area, click the Prefix List tab.

4. On the toolbar, click Insert.

5. Using the fields provided, create a new prefix list.

6. Click Insert.

## Variable definitions

The following table describes the fields of the Prefix List tab.

Field | Definition
--- | ---
Id | Specifies the unique identifier of this prefix list.
Prefix | Specifies the IP address associated with this prefix list.
PrefixMaskLen | Specifies the subnet mask length associated with this prefix list.
Name | Specifies the name associated with this prefix list.
MaskLenFrom | Specifies the lower bound of the mask length. This value, when combined with the higher bound mask length (MaskLenUpto), specifies a subnet range covered by the prefix list. The default value is the mask length (PrefixMaskLen).
MaskLenUpto | Specifies the higher bound of the mask length. This value, when combined with the lower bound mask length (MaskLenFrom), specifies a subnet range covered by the prefix list. Default value is the mask length (PrefixMaskLen).