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1036 PowerConnect B-Series FCX Configuration Guide
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The <as-path> parameter indicates the AS-path information. You can enter an exact AS-path string
if you want to filter for a specific value. You also can use regular expressions in the filter string.
Defining an AS-path ACL
To configure an AS-path list that uses ACL 1, enter a command such as the following.
PowerConnect(config)#ip as-path access-list 1 permit 100
PowerConnect(config)#router bgp
PowerConnect(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 <string> [seq <seq-value>] deny | permit <regular-expression>
The <string> parameter specifies the ACL name. (If you enter a number, the CLI interprets the
number as a text string.)
The seq <seq-value> parameter is optional and specifies the AS-path list 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 AS-path list matches
a match statement in this ACL. To configure the AS-path match statements in a route map, use the
match as-path command. Refer to “Matching based on AS-path ACL” on page 1045.
The <regular-expression> parameter specifies the AS path information you want to permit or deny
to routes that match any of the match statements within the ACL. You can enter a specific AS
number or use a regular expression. For the regular expression syntax, refer to “Using regular
expressions” on page 1036.
The neighbor command uses the filter-list parameter to apply the AS-path ACL to the neighbor.
Refer to “Adding BGP4 neighbors” on page 993.
Using regular expressions
You use a regular expression for the <as-path> parameter to specify a single character or multiple
characters as a filter pattern. If the AS-path matches the pattern specified in the regular
expression, the filter evaluation is true; otherwise, the evaluation is false.
In addition, you can include special characters that influence the way the software matches the
AS-path against the filter value.
To filter on a specific single-character value, enter the character for the <as-path> parameter. For
example, to filter on AS-paths that contain the letter “z”, enter the following command.
PowerConnect(config-bgp-router)#as-path-filter 1 permit z
To filter on a string of multiple characters, enter the characters in brackets. For example, to filter on
AS-paths that contain “x”, “y”, or “z”, enter the following command.
PowerConnect(config-bgp-router)#as-path-filter 1 permit [xyz]