regex to match as_path regex

While working on input validation for my soon-to-be-released looking glass app Hyperglass, I had to find a way to validate regex with regex. Google searches returned nothing of relevance, so I built it myself. I figured this might be useful for others in the future:

Supported lookup patterns

Expression Match
_65000$ Originated by AS65000
^65000\ Received from AS65000
_65000_ Via AS65000
_65000_65001_ Via AS65000 and AS65001
_65000(_.+_)65001$ Anything from AS65001 that passed through AS65000

AS_PATH regex pattern for asplain


AS_PATH regex pattern for asdot



If using these patterns with Python as I am, you’ll want to make sure you use the raw string literal flag, e.g. r"pattern". For example:

re_bgp_aspath_default = r"^(\^|^\_)(\d+\_|\d+\$|\d+\(\_\.\+\_\))+$"

This will ensure that Python doesn’t interpret the regex escape characters as Python recape characters, and returns the raw string.