dns in dhcp
dhcp1 at thehobsons.co.uk
Fri Apr 24 13:22:37 UTC 2009
>option domain-name "sitestar.net";
>option domain-name-servers 150.161.x.y,150.161.q.z;
>option time-offset -18000; #EST
>How does the DNS information in the parameter option
>domain-name-servers. The machine switches between dns informed?
Hmm, I'm guessing that your question is :
How does the guest use the list of servers supplied ? Does it switch
between them ?
The answer is that it's entirely up to the client what it does and
you should NOT do anything that relies on a particular client
behaviour as that is inviting strange and difficult to diagnose
problems in the future.
To give an example, some (all ? most ?) versions of Windows have a
feature whereby they will query the configured name servers in order
until they get an answer. Some people thought this was a useful
feature and configured an internal server to only serve internal
addresses - on the basis that the client would query that, and if it
didn't get an answer it would go to the next outside nameserver. They
figured that this was easier than setting up a properly configured
"split horizon" DNS configuration.
Trouble is, if the internal server goes down, it stops responding,
and the clients shifts it's address to the bottom of the list (ie
query it last) - permanently ! I imagine it was "difficult"
diagnosing why some (but not all) clients had suddenly stopped
querying the internal nameserver and could no longer access any
Other clients might query servers at random, query all servers, keep
statistics on which responds fastest and use that in preference, or
any other behaviour they want. So it's important that all servers you
specify should return exactly the same records in response to any
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