monitoring for multiple origin AS’s

Posted by Andree Toonk - October 20, 2008 -, regular expressions - No Comments
The majority of the emails I receive with feedback and questions are things which can be solved with a regex. Today I would like to go over 1 common example: How do I monitor prefixes that originate from multiple origin AS's Some people mailed me with a feature request for the ability to specify multiple ASNs that are allowed to originate a specific prefix. The good news is that is already possible, the bad news is that it wasn't documented. So how do you allow for multiple origin AS's? Normally you have to add a source AS when adding a new prefix. This than would be the only AS allowed as origin AS for that particular prefix. However if you use originAS 0 (zero) this field will be ignored.  If you than also leave the transit AS field empty and just use the regex field you have achieved what you wanted to. So the trick is to use originAS 0 (a wildcard) and catch everything else in a regular expression. A typical regex would look like this:
This regex allows your prefix to be originated from either AS10, AS20 or AS30. In all other cases BGPmon would generate an alarm and notify you.  I also updated the FAQ with this information.

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