Configuration Guide User guide

1396 FastIron Configuration Guide
53-1002494-02
Filtering
Defining an AS-path filter
To define AS-path filter 4 to permit AS 2500, enter the following command.
Brocade(config-bgp-router)#as-path-filter 4 permit 2500
Syntax: as-path-filter <num> permit | deny <as-path>
The <num> parameter identifies the filter position in the AS-path filter list and can be from 1
through 100. Thus, the AS-path filter list can contain up to 100 filters. The Brocade Layer 3 switch
applies the filters in numerical order, beginning with the lowest-numbered filter. When a filter
match is true, the Layer 3 switch stops and does not continue applying filters from the list.
NOTE
If the filter is referred to by a route map match statement, the filter is applied in the order in which
the filter is listed in the match statement.
The permit | deny parameter indicates the action the router takes if the filter match is true.
• If you specify permit, the router permits the route into the BGP4 table if the filter match is true.
• If you specify deny, the router denies the route from entering the BGP4 table if the filter match
is true.
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.
Brocade(config)#ip as-path access-list 1 permit 100
Brocade(config)#router bgp
Brocade(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 1406.
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 to filter” on page 1397.