Foundry Networks Switch and Router Installation And Configuration Manual page 733

4. Click on the AS Path Filter link to display the BGP AS Path Filter panel.
• If the device does not have any BGP AS-path filters configured, the BGP AS Path Filter configuration
panel is displayed, as shown in the following example.
• 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 Layer 3 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 19-53.
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:
BigIron(config)# ip as-path access-list 1 permit 100
BigIron(config)# router bgp
BigIron(config-bgp-router)# neighbor 10.10.10.1 filter-list 1 in
The ip as-path command 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 Layer 3 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.
December 2000
Configuring BGP4
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