>>>>> "Ulrich" == Ulrich Wisser <liste@xxxxxxxxxxxx> writes:
Ulrich> I want to setup several dns servers. Each of them should
Ulrich> be in the network of a different ISP. How can I make sure
Ulrich> that the nearest dns is used by the other dns servers in
Ulrich> the respective net?
You can't: you have no control or influence over how the rest of the
world's name servers are configured. However what you seem to want to
achieve happens automatically with BIND. It measures the round trip
time to each name server for some zone and then generally uses the one
that has the lowest RTT. So as a general rule, BIND favours the
closest name server, for some definition of close. BIND also uses this
info to avoid querying unresponsive servers. The RTT measurements get
done continuously so BIND can accommodate name servers which go away
or come back.
Ulrich> Maybe you could point me to some good reading about
Ulrich> optimal dns deployment?
Define "optimal". For most environments, all you need to do is just
put name servers close to the clients that make the most questions: eg
web proxies, mail and web servers, etc. This tends to only matter when
there are high query rates, say from a server farm in a big corporate
network. The other key consideration is avoiding single points of
failure like putting all your name servers behind the one router or in
the one computer room. The CAIDA people have been analysing DNS
traffic to the root and TLD servers. They'll have some info on
placement of name servers, though the detail is not likely to be
relevant to you. See http://www.caida.org.
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