Foundry Networks FESX User Manual

Foundry Configuration Guide for the FESX, FSX, and FWSX
21 - 42 © Foundry Networks, Inc. December 2005
FESX424 Router(config-bgp-router)# as-path-filter 4 permit 2500
Syntax: as-path-filter <num> permit | deny <as-path>
The <num> parameter identifies the filter’s position in the AS-path filter list and can be from 1 – 100. Thus, the
AS-path filter list can contain up to 100 filters. The Foundry 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’s 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:
FESX424 Router(config)# ip as-path access-list 1 permit 100
FESX424 Router(config)# router bgp
FESX424 Router(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’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 in a route map, use the match as-path
command. See “Matching Based on AS-Path ACL” on page 21-51.
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, see “Using Regular Expressions” on page 21-42.
The neighbor command uses the filter-list parameter to apply the AS-path ACL to the neighbor. See “Adding
BGP4 Neighbors” on page 21-12.
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:

Foundry Networks FESX Specifications

General

Brand	Foundry Networks
Model	FESX
Category	Switch
Language	English