Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide - Manual (Page 440)

BGP4 special characters for regular expressions (Continued) TABLE 91
Character Operation
| 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. Refer to 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)?)
To filter for a special character instead of using the special character as described in "Using regular
expressions," 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 "\*".
device(config-bgp-router)# ip as-path access-list acl2 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 "\\".
device(config-bgp-router)# ip as-path access-list acl2 deny \\
BGP4 filtering communities
You can filter routes received from BGP4 neighbors based on community names.
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 a route attribute. Each
string in the community name can be a number from 0 through 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 device provides the following methods for filtering on community information.
• Community filters
• Community list ACLs
NOTE
The device cannot actively support community filters and community list ACLs at the same time. Use
one method or the other but do not mix methods.
BGP4 filtering communities
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