Dell PowerConnect FCS624S Configuration Guide - Page 1078

30 Filtering The 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 [seq ] deny | permit The parameter specifies the ACL name. (If you enter a number, the CLI interprets the number as a text string.) The seq 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 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 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 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] 1036 PowerConnect B-Series FCX Configuration Guide 53-1002266-01