DNS versus NAT ?

[Ronald F. Guilmette]

In message <C8EB50CF-E021-4E32-9762-E65D0673B91A at samplonius.org>, 
Tom Samplonius <tom at samplonius.org> wrote:

>...
>> But much or most DNS is performed via connectionless UDP datagrams, so I
>> am at a loss to understand or even imagine how two or more instances of,
>> say, Unbound... or Bind for that matter... could successfully co-exist,
>> on a single home network, together, behind a single typical SOHO router.
>...
>
>UDP packets have source and destination port numbers, just like TCP.  So
>even though UDP is connectionless, the state can be tracked in the NAT
>table by the source-destination port numbers just like TCP.

Thank you, but this does not answer my question.

Please allow me to restate it again.

Assume there exist two instances of, say, Unbound, running on two machines,
both behind the same single SOHO router which is doing NAT for the local
network.

If they both send outbound DNS queries at about the same time, and both
happen to select the exact same outbound port number to do so, say for
example UDP port 53, then when the two DNS response packets come back
to the NAT router, how will it know which of the two machines it should
send each of those two DNS response packets to?

For the outbound DNS query packets, does the router re-jigger the orginal
source port numbers so that they will (hopefully) not conflict and so that
the DNS response packets, when they arrive, can be directed appropriately
to one machine or the other?

And if that is the case, then will my SOHO router catch fire if and when
I elect to send out through it a set of 65536 or more separate DNS queries,
all in rapid succession?

(That last question might sound silly but it isn't.  I do a lot of research
relating to DNS, and the scenario described is actually not at all far
fetched in my case.)


Regards,
rfg