Adding a Prefix Rule to an IP Address Prefix List

Scenarios

This section describes how to add prefix rules to an IP prefix list. Each IP prefix list can have multiple prefix rules.

Notes and Constraints

• IP prefix rules change the path through which network traffic passes. If the route policy of a prefix rule has already been associated with an enterprise router, evaluate the impact on services before adding a prefix rule to the policy.
• Each prefix rule in an IP prefix list must have its unique sequence number and IP prefix.

Prerequisites

An IP prefix list is available. You can create one by referring to Creating an IP Prefix List.

Procedure

1. Go to the Prefix Lists page.
2. Click the name of the target IP prefix list.

   The prefix rule list is displayed.

3. Click Add Prefix Rule in the upper left corner of the list.

   The Add Prefix Rule dialog box is displayed.

4. Configure the parameters based on Table 1.

   Table 1 Parameters for adding a prefix rule

   Parameter	Description	Example Value
   Configuration	Mandatory Choose Quick or Advanced. Quick Enter the IP prefix in the CIDR format. An IP prefix specifies the first bits of an IP address range that a route destination must match. The following are parameters that you do not need to configure: Sequence Number: Automatically generated. The sequence number increases by a multiple of 10, with that of the first rule set to 10. The subsequent numbers are 20, 30, and so on. Action: Allow by default Min. Netmask Length and Max. Netmask Length Advanced Sequence Number: An IP prefix list consists of one or more prefix rules that are applied to filter routes based on their sequence numbers, in ascending order. A sequence number can be from 0 to 65535. You are advised to set the sequence number of the first rule to 20. Action: Select Allow or Deny. If a route matches a prefix rule with Action set to Allow, the route is allowed. If the prefix rule has Action set to Deny, the route is denied. IP Prefix: Enter the IP prefix in the CIDR format. This parameter specifies the first bits of an IP address range that a route destination must match. Min. Netmask Length: It cannot be smaller than the netmask length of the IP prefix. For example, if the netmask length of the IP prefix is 16, the min. netmask length must be greater than or equal to 16 (for example, 18). Max. Netmask Length: It cannot be smaller than the min. netmask length. For example, if the min. netmask length is 18, the max. netmask length must be from 18 to 32 (for example, 20).	Sequence Number: 10 Action: Allow IP Prefix: 10.0.0.0/16 Min. Netmask Length: 20 Max. Netmask Length: 28

5. Click OK.

   You can view the added prefix rule.