--On 21 July 2008 13:28:38 +0200 Laurent Zimmerli <laurentz@student.ethz.ch> wrote:

I'm making use of the riswhois service and would like to cache queries locally. However, I am not sure whether I can do it the way I want to. My idea is to store the ASN an the corresponding route of each query I execute. Before performing another query I would then check whether I already stored the ASN of a route which contains the IP for which I want to find the AS. Can I do that? Or is then the following case possible: I store an AS an its route -- say ASx, 123.0.0.0/8 -- whose IP range includes another one -- say ASy, 123.100.0.0/16. When I store ASx first and then query an IP of ASy, I will assign ASx to this IP instead of ASy. Is such a case possible? Or is there even another problem with my caching approach?

Yes, overlapping prefixes originating from different autonomous systems do exist in the wild. The problem I see is that when you find a matching prefix in your cache from one particular AS you would return that (or what's the point of the cache) and won't know whether there is a more specific (longer) prefix originating from a different AS which a query to riswhois would return. I can't really see a way around this problem except to use a local copy of the RIS RIB dumps in the same way that riswhois does. James