Filtering communities – Brocade BigIron RX Series Configuration Guide User Manual
Page 951
BigIron RX Series Configuration Guide
873
53-1002484-04
Filtering
27
If you want to filter for a special character instead of using the special character as described in
Table 26.2 on page 26-45, 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 “\*”.
BigIron RX(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 “\\”.
BigIron RX(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 one of a route’s
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 BigIron RX provides the following methods for filtering on community information:
•
Community filters - refer to
•
Community list ACLs
NOTE
The BigIron RX 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 134
BGP4 special characters for regular expressions (Continued)
Character
Operation