Quick Reference Guide

PowerConnect B-Series TI24X Configuration Guide 793
53-1002269-02
Filtering
25
If you want to filter for a special character instead of using the special character, enter “\”
(backslash) in front of the character. For example, to filter on AS-path strings containing an
asterisk, enter the asterisk portion of the regular expression as “\*”.
PowerConnect(config-bgp-router)# as-path-filter 2 deny \*
To use the backslash as a string character, enter two slashes. For example, to filter on AS-path
strings containing a backslash, enter the backslash portion of the regular expression as “\\”.
PowerConnect(config-bgp-router)# as-path-filter 2 deny \\
Filtering communities
You can filter routes received from BGP4 neighbors based on community names. Use either of the
following methods to do so.
A community is an optional attribute that identifies the route as a member of a user-defined class
of routes. Community names are arbitrary values made of two five-digit integers joined by a colon.
You determine what the name means when you create the community name as one of a route
attributes. Each string in the community name can be a number from 0 – 65535.
This format allows you to easily classify community names. For example, a common convention
used in community naming is to configure the first string as the local AS and the second string as
the unique community within that AS. Using this convention, communities 1:10, 1:20, and 1:30
can be easily identified as member communities of AS 1.
The Layer 3 Switch provides the following methods for filtering on community information:
• Community filters
• Community list ACLs
NOTE
The Layer 3 Switch cannot actively support community filters and community list ACLs at the same
time. Use one method or the other but do not mix methods.
NOTE
Once you define a filter or ACL, the default action for communities that do not match a filter or ACL
is “deny”. To change the default action to “permit”, configure the last filter or ACL entry as “permit
any any”.
Community filters or ACLs can be referred to by match statements in a route map.
| A vertical bar (sometimes called a pipe or a “logical or”) separates two alternative values or
sets of values. The AS-path can match one or the other value. For example, the following
regular expression matches on an AS-path that contains either “abc” or “defg”:
(abc)|(defg)
NOTE: The parentheses group multiple characters to be treated as one value. See the
following row for more information about parentheses.
( ) Parentheses allow you to create complex expressions. For example, the following complex
expression matches on “abc”, “abcabc”, or “abcabcabcdefg”, but not on “abcdefgdefg”:
((abc)+)|((defg)?)
TABLE 124 BGP4 special characters for regular expressions (Continued)
Character Operation