Brocade Multi-Service IronWare Routing Configuration Guide (Supporting R05.6.00) - Manual (Page 105)

Multi-Service IronWare Routing Configuration Guide 77
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Filtering
The regular-expression parameter specifies the AS path information you want to permit or deny to
routes that match any of the match clauses within the ACL. You can enter a specific AS number or
use a regular expression.
The neighbor command uses the filter-list parameter to apply the AS-path ACL to the neighbor.
Refer to
“Configuring BGP4 neighbors” on page 47 and “Configuring a BGP4 peer group” on
page 60.
Using regular expressions
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.
You can also 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:
Brocade(config-bgp)# ip as-path access-list acl1 permit z
To filter on a string of multiple characters, enter the characters in brackets. For example, to filter on
AS-paths that contain “x”, “y”, or “z”, enter the following command.
Brocade(config-bgp)# ip as-path access-list acl1 permit [xyz]
Special characters
When you enter a single-character expression or a list of characters, you also can use the special
characters listed in
Table 4 . The description for each character includes an example. Some special
characters must be placed in front of the characters they control and others must be placed after
the characters they control. The examples show where to place the special character.
TABLE 4 BGP4 special characters for regular expressions
Character Operation
. The period matches on any single character, including a blank space. For example, the following
regular expression matches for “aa”, “ab”, “ac”, and so on, but not just “a”.
a.
* The asterisk matches on zero or more sequences of a pattern. For example, the following regular
expression matches on an AS-path that contains the string “1111” followed by any value:
1111*
+ The plus sign matches on one or more sequences of a pattern. For example, the following regular
expression matches on an AS-path that contains a sequence of “g”s, such as “deg”, “degg”,
“deggg”, and so on:
deg+
? The question mark matches on zero occurrences or one occurrence of a pattern. For example,
the following regular expression matches on an AS-path that contains “dg” or “deg”:
de?g
^ A caret (when not used within brackets) matches on the beginning of an input string. For
example, the following regular expression matches on an AS-path that begins with “3”:
^3