Brocade Virtual ADX Switch and Router Guide (Supporting ADX v03.1.00) - Manual (Page 263)

Brocade Virtual ADX Switch and Router Guide 249
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Filtering
8
To filter for a special character instead of using the special character as described in Table 36 ,
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 “\*”.
Virtual ADX(config-bgp)# 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 “\\”.
Virtual ADX(config-bgp)# ip as-path access-list acl2 deny \\
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 – 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 - refer to “Filtering communities” on page 249.
• 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.
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.
Community filters or ACLs can be referred to by match clauses 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. 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)?)
TABLE 36 BGP4 special characters for regular expressions (Continued)
Character Operation