11.8.1 AS Path Regular Expression

AS path regular expression can be used for displaying BGP routes and AS path access list. AS path regular expression is based on POSIX 1003.2 regular expressions. Following description is just a subset of POSIX regular expression. User can use full POSIX regular expression. Adding to that special character ’_’ is added for AS path regular expression.

.

Matches any single character.

*

Matches 0 or more occurrences of pattern.

+

Matches 1 or more occurrences of pattern.

?

Match 0 or 1 occurrences of pattern.

^

Matches the beginning of the line.

$

Matches the end of the line.

_

Character _ has special meanings in AS path regular expression. It matches to space and comma , and AS set delimiter { and } and AS confederation delimiter ( and ). And it also matches to the beginning of the line and the end of the line. So _ can be used for AS value boundaries match. show ip bgp regexp _7675_ matches to all of BGP routes which as AS number include 7675.