DNS question, null MX records

Joe Abley jabley at hopcount.ca
Wed Dec 16 18:08:56 CST 2009


On 2009-12-17, at 00:02, Douglas Otis wrote:

> To avoid server access and hitting roots:
> 
> host-1.example.com. IN A 192.0.2.0
> ...
> host-10.example.com. IN A 192.0.2.9
> 
> example.com. 	IN MX 0 host-1.example.com.
> ...
> example.com. 	IN MX 90 host-10.example.com.

This will still cause DNS requests to be sent towards 192.0.2.0 and 192.0.2.9, and they may not be dropped at the first router depending on local conditions. There are implications of state in the local resolver.

Choosing MX RDATA with a name that is known not to exist ideally will only exercise the local cache for the non-existent name, since it will perhaps not be the first such query and the non-existence will already be cached.

SINK.ARPA doesn't exist today. The document I referred to only exists to enforce that non-existence in the future; operationally you could install MX records towards SINK.ARPA today and get the desired effect, regardless of the state of the document.


Joe



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