[Q]: Filtering based on reverse DNS

["Wayne McDougall" <netfilter@codeworks.gen.nz>]

What I want to achieve is to filter based on a reverse name lookup on a source (and ideally destination) IP on initiating a connection.

Why? Because I'm in a country (island) where communication within the country is very cheap, and communication outside is metered and expensive. So I'd like to be able to apply traffic shaping (quotas and rate limiting) and policing with different polices applying to whether the IP is in my country or outside. I understand that reverse DNS does not always work and I'm quite happy to treat anyone like that as being outside. But if there IP resolve to *.nz I want to treat them differently to everyone else.

I appreciate that this sort of requirement isn't likely to be found in the USA (where I suspect most of y'all are), and I suspect it may not be very common elsewhere (anywhere else?). So I will understand if there isn't much interest or support for this.

My questions are:
1. Is there anything already like this (or could be adapted)?
2. Are there reasons why I shouldn't be doing this at all. I appreciate that there would be a performance hit , and obviously I only want reverse DNS lookups when connections are initiated - I don't mind latency at that point, and obviously I should use a local caching nameserver. But is it all a real mess and I shouldn't go there? Why not?
3. If there is nothing out there, where should I attack this problem if I was going to try and roll my own? A netfilter module, right?


Thank you for your time. I am new to this, so please forgive (and feel free to correct) any inappropriate use of terminology.


Regards

Wayne McDougall