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Configuring
the Community Attribute Using UNIX Regular Expressions
When specifying community-ids, you can use UNIX-style regular expressions to specify the
AS number and the member identifier. A regular expression consists
of two components, which you specify in the following format:
- term operator;
term identifies the
string to match.
operator specifies
how the term must match. Table 21 lists the
regular expression operators supported for the community attribute.
You place an operator immediately after term with no intervening space, except for the pipe ( | ) and dash (–) operators, which you place between
two terms, and parentheses, with which you enclose terms. Table 22 shows examples of
how to define community-ids using community
regular expressions. The operator is optional.
Community regular expressions are identical to
the UNIX regular expressions. Both implement the extended (or modern)
regular expressions as defined in POSIX 1003.2.
Community regular expressions evaluate the string
specified in term on a character-by-character
basis. For example, if you specify 1234:5678 as term, the regular expressions see nine discrete characters,
including the colon (:), instead of two sets of numbers (1234 and 5678) separated by a colon.
 |
Note:
Beginning with JUNOS Release 9.1, the range that you can configure
for the AS number has been extended to provide BGP support for 4-byte
AS numbers. For more information about configuring the AS number,
see the JUNOS Routing Protocols Configuration Guide.
|
Table 21: Community
Attribute Regular Expression Operators
|
Operator
|
Match Definition
|
|
{m,n}
|
At least m and at most n repetitions of term. Both m and n must be positive integers, and m must be smaller than n.
|
|
{m}
|
Exactly m repetitions of term. m must be a positive
integer.
|
|
{m,}
|
m or more repetitions of term. m must be a positive
integer.
|
|
*
|
Zero or more repetitions of term. This is equivalent to {0,}.
|
|
+
|
One or more repetitions of term. This is equivalent to {1,}.
|
|
?
|
Zero or one repetition of term. This is equivalent to {0,1}.
|
|
|
|
One of the two terms on either side of the pipe.
|
|
–
|
Between a starting and ending range, inclusive.
|
|
^
|
Character at the beginning of a community attribute regular
expression. We recommend the use of this operator for the clearest
interpretation of your community attribute regular expression. If
you do not use this operator, the regular expression 123:456 could also match a route tagged with 5123:456.
|
|
$
|
Character at the end of a community attribute regular expression.
We recommend the use of this operator for the clearest interpretation
of your community attribute regular expression. If you do not use
this operator, the regular expression 123:456 could also
match a route tagged with 123:4563.
|
|
[ ]
|
Set of characters. One character from the set can match. To
specify the start and end of a range, use a hyphen (-). To
specify a set of characters that do not match, use the caret (^) as the first character after the opening square bracket ([).
|
|
( )
|
Group of terms that are enclosed in parentheses. If enclosed
in quotation marks with no intervening space ("()" ), indicates
a null. Intervening space between the parentheses and the terms is
ignored.
|
|
“ ”
|
Characters (such as space, tab, question mark, and bracket)
that are enclosed within quotation marks in a community attribute
regular expression indicate special characters.
|
Table 22: Examples
of Defining Community Attribute Regular Expressions
|
Community Attribute to Match
|
Regular Expression
|
Sample Matches
|
|
AS number is 56 or 78. Community value is any number.
|
^((56) | (78)):(.*)$
|
56:1000
78:65000
|
|
AS number is 56. Community value is any number that starts with
2.
|
^56:(2.*)$
|
56:2
56:222
56:234
|
|
AS number is any number. Community value is any number that
ends with 5, 7, or 9.
|
^(.*):(.*[579])$
|
1234:5
78:2357
34:65009
|
|
AS number is 56 or 78. Community value is any number that starts
with 2 and ends with 2 through 8.
|
^((56) | (78)):(2.*[2–8])$
|
56:22
56:21197
78:2678
|
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