Dynamic DNS

[Simon Hobson]

Pascal offredo wrote:

>I'd like the hostname to be unresolvable when the machine is not up.

You cannot do that reliably.

IFF you are using an address from a dynamic pool, AND your client 
releases it's lease on shutdown, THEN it will mostly work. But bear 
in mind that depending on your DNS setup, the client may still be 
resolvable for a short time after it shuts down via slave or caching 
servers.

But if the client does not shut down cleanly, or does not release 
it's lease on shutdown then the DNS will still not be updated until 
the lease expires.

Why is it so essential that the client is not resolvable when shut down ?

As a thought, you could run a DNS server on the client, with a small 
zone (child of your main zone) containing only an A record for 
itself. In the main zone, make the 'public' name of the client a 
CNAME to the name in this child zone. When the client is down, 
queries for it's name will fail because the target of the CNAME can 
not be resolved. You will also needs to arrange that the A record 
does not get cached by the other servers.

It will still result in a delay when other attempt to connect to the 
service, but they will get a name not found error instead of just a 
connection timeout.

Simon

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