Foundry Configuration Guide for the FESX, FSX, and FWSX
21 - 44 © Foundry Networks, Inc. December 2005
If you want to filter for a special character instead of using the special character as described in Table 21.3 on
page 21-43, 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 “\*”.
FESX424 Router(config-bgp-router)# as-path-filter 2 deny \*
_ An underscore matches on one or more of the following:
• , (comma)
• { (left curly brace)
• } (right curly brace)
• ( (left parenthesis)
• ) (right parenthesis)
• The beginning of the input string
• The end of the input string
• A blank space
For example, the following regular expression matches on “100” but
not on “1002”, “2100”, and so on.
_100_
[ ] Square brackets enclose a range of single-character patterns. For
example, the following regular expression matches on an AS-path that
contains “1”, “2”, “3”, “4”, or “5”:
[1-5]
You can use the following expression symbols within the brackets. These
symbols are allowed only inside the brackets.
• ^ – The caret matches on any characters except the ones in the
brackets. For example, the following regular expression matches on
an AS-path that does not contain “1”, “2”, “3”, “4”, or “5”:
[^1-5]
• - The hyphen separates the beginning and ending of a range of
characters. A match occurs if any of the characters within the range is
present. See the example above.
| 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 21.3: BGP4 Special Characters for Regular Expressions (Continued)
Character Operation
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