Configuring BGP4
•If BGP AS-path filters are already configured and you are adding a new one, click on the Add AS Path Filter link to display the BGP AS Path Filter configuration panel, as shown in the following example.
•If you are modifying an existing BGP AS-path filter, click on the Modify button to the right of the row describing the filter to display the BGP AS Path Filter configuration panel, as shown in the following example.
5.Enter the filter ID in the ID field. You can specify a number from 1 – 100.
6.Select the action you want the routing switch to perform if the filter is true:
•If you select Deny, the router denies the route from entering the BGP4 table if the filter match is true.
•If you select Permit, the router permits the route into the BGP4 table if the filter match is true.
7.Enter the AS path you want to filter in the Regular Expression field. As indicated by the field’s title, you can use regular expressions for the AS path. See “Using Regular Expressions” on page 10-49.
8.Click the Add button to apply the changes to the device’s running-config file.
9.Select the Save link at the bottom of the dialog. Select Yes when prompted to save the configuration change to the startup-config file on the device’s flash memory.
Defining an AS-Path ACL
To configure an AS-path ACL, use either of the following methods.
USING THE CLI
To configure an AS-path list that uses ACL 1, enter a command such as the following:
HP9300(config)# ip as-path access-list 1 permit 100 HP9300(config)# router bgp
HP9300(config-bgp-router)# neighbor 10.10.10.1 filter-list 1 in
The ip as-pathcommand configures an AS-path ACL that permits routes containing AS number 100 in their AS paths. The neighbor command then applies the AS-path ACL to advertisements and updates received from neighbor 10.10.10.1. In this example, the only routes the routing switch permits from neighbor 10.10.10.1 are those whose AS-paths contain AS-path number 100.
Syntax: ip as-path access-list <num> [seq <seq-value>] deny permit <as-regular-expression>
The <num> parameter specifies the ACL number and can be from 1 – 199.
The seq <seq-value> parameter is optional and specifies the AS-path list’s sequence number. You can configure up to 199 entries in an AS-path list. If you do not specify a sequence number, the software numbers them in increments of 5, beginning with number 5. The software interprets the entries in an AS-path list in numerical order, beginning with the lowest sequence number.
The deny permit parameter specifies the action the software takes if a route’s AS-path list matches a match statement in this ACL. To configure the AS-path match statements, use the match as-pathcommand. See “Matching Based on AS-Path ACL” on page 10-63.
