Adding an AS_Path Filter to an AS_Path List

Scenarios

This section describes how to add an AS_Path filter to an AS_Path list. Each AS_Path list can have multiple AS_Path filters.

Notes and Constraints

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

Prerequisites

An AS_Path list is available. You can create one by referring to Creating an AS_Path List.

Procedure

1. Go to the AS_Path Lists page.
2. Click the name of the target AS_Path list.

   The AS_Path filters are displayed.

3. Click Add AS_Path Filter in the upper left corner of the filter list.

   The Add AS_Path Filter dialog box is displayed.

4. Configure the parameters based on Table 1.

   Table 1 Parameters for adding an AS_Path filter

   Parameter	Description	Example Value
   Sequence Number	Mandatory An AS_Path list consists of one or more AS_Path filters that are applied to filter routes based on their sequence numbers, in ascending order. A sequence number can be from 0 to 65535.	10
   Action	Mandatory Select Allow or Deny. If a route matches an AS_Path filter with Action set to Allow, the route is allowed. If the AS_Path filter has Action set to Deny, the route is denied.	Allow
   Regular Expression	A regular expression is a string that describes a characteristic and verifies whether another string conforms to this characteristic. An AS_Path filter defines an AS_Path regular expression to match AS_Path attributes of BGP routes for filtering BGP routes. For details, see AS_Path Regular Expressions.	65+

5. Click OK.

   In the AS_Path filter list, you can view the created AS_Path filter.

Follow-Up Operations

Deleting an AS_Path Filter from an AS_Path List: An AS_Path filter cannot be modified after being added. You can delete an AS_Path filter that you do not need and add another one.