Dell Brocade DCX, Configuration Manual

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794 BigIron RX Series Configuration Guide
53-1001810-01
Filtering
26
The neighbor command uses the filter-list parameter to apply the AS-path ACL to the neighbor.
Refer to
“Configuring BGP4 neighbors” on page 769 and “Configuring a BGP4 peer group” on
page 776.
Using regular expressions
You 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.
In addition, you can 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.
BigIron RX(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.
BigIron RX(config-bgp)# ip as-path access-list acl1 permit [xyz]
Special characters
When you enter as single-character expression or a list of characters, you also can use the
following special characters. Table 26.2 on page 26-45 lists the special characters. The
description for each special character includes an example. Notice that you place some special
characters in front of the characters they control but you place other special characters after the
characters they control. In each case, the examples show where to place the special character.
TABLE 117 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
$ A dollar sign matches on the end of an input string. For example, the following regular
expression matches on an AS-path that ends with “deg”.
deg$