Foundry Networks AR1202, User Manual

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June 2004 © 2004 Foundry Networks, Inc. 13 - 1
Chapter 13
AS Path Regular Expressions
This appendix provides information about how to use and configure regular expressions for use with BGP4 routing
protocol commands.
Matching AS Paths
An AS path regular expression is a regular expression with the alphabet used as the set of AS numbers defining a
set of AS paths.
Note that according to this definition, AS path regular expressions are implicitly anchored at the beginning and
end.
The following examples provide more information:
AS Path Regular Expressions (regex)
A regex is a character string containing one of the following:
AS Path Terms
A term is one of the following:
690 Matches only the specific AS path “690.”
. *690 .* Matches any AS path containing 690.
690 .* Matches any AS path beginning with 690.
. *690 Matches any AS path ending in 690.
term Matches the given term.
regex1 regex2 Matches a path that is a concatenation of two paths, P1 and P2. P1 matches
regex1 and P2 matches regex2. Note that spaces are ignored in general, but
should be used between two concatenated ASs to distinguish them.
regex1 |regex2 Matches a path that matches regex1 or regex2.
AS Matches the given number, which is any positive 16-bit number from 0-65535
inclusive. Note that valid AS numbers range from one through 65534
inclusive.