Re: DHCP in a Windows 2000 domain - udhcpc

[Ajit Warrier <unixajit yahoo com>]

Hi Rick,

As far as I can make out from what you say, the DHCP
server will issue the hostname to the DHCP client and
if the DNS is Dynamic and properly configured, this
hostname should get registered with it. I know that
when a Windows client gets its information from the
DHCP server, it is properly entered into the DNS
server as well, so we can assume that the DHCP and the
DDNS are properly set up.

This means that the hostname that the DHCP server
issues to the DHCP client should get registered in the
DNS server as well whether that is the name the client
requested for or not. Ok, so far?

Well, I am getting an IP from the DHCP server but the
hostname entry on the DHCP server is blank and there
is no entry for this IP in the DNS server. When I do
"hostname" on the DHCP client, it returns the hostname
that I have set, of course and it does _not_ resolve
it to the IP (which is expected since this name has
not registered with the DNS).

I guess what I asking for boils down to this -
1. How can I find out what name is being issued to the
DHCP client?
2. Can I change the hostname to the one that has been
issued to the DHCP client, automatically, as soon as
the client finds out what its hostname is?

Thanks.

Ajit

--- Rick Stevens <rstevens vitalstream com> wrote:
> Ajit Warrier wrote:
> > --- Rick Stevens <rstevens vitalstream com> wrote:
> > 
> >>Ajit Warrier wrote:
> >>
> >>>I am the administrator of the Windows DHCP server
> >>
> >>and
> >>
> >>>it was already set as you have described. It
> still
> >>>doesn't work. As in, I get an IP all right but my
> >>>hostname does not get registered. Thanks for the
> >>>interest anyway.
> >>>
> >>>A friend has suggested that something called
> >>
> >>udhcpc
> >>
> >>>could do this. I am searching for it. If it is of
> >>
> >>any
> >>
> >>>use, I will post to the list. Of course, if some
> >>
> >>one
> >>
> >>>knows about this, please let me know.
> >>
> >>Never heard of that one.  Are you sure the DHCP
> >>server is sending you a
> >>hostname?  It will only be able to update DNS with
> a
> > 
> > 
> > ********************
> > I think the way it works in W2K is that the W2k
> client
> > asks for an IP and once it has received it, the
> DHCP
> > server registers the client hostname and IP with
> the
> > DNS server, I dont know if the DHCP server sends
> the
> > hostname to the client but it sure sends it to the
> DNS
> > server. Is there a way I can find out?
> 
> That's the way it works in _any_ DHCP environment
> (well, it's supposed
> to work that way).  The DHCP server gives an
> address, gateway, hostname,
> and DNS server info to the client, it then does a
> DDNS update to the
> DNS server inserting the appropriate A and PTR
> records into DNS.  The
> client should NEVER have to do that.  If it does,
> then there's a severe
> screwup in the design of the network servers.
> 
> The client _can_ ask for a specific hostname to be
> given, but there's
> no rule that says the DHCP server has to abide by
> that request. On the
> other hand, the client is required to live by what
> the DHCP server says.
> It can alias the hostname in its /etc/hosts file,
> but basically what
> the DHCP server says, goes.
> 
> > But doesn't the hostname of the client go from the
> > client to the DHCP server rather than from the
> DHCP
> > server to the client?
> 
> No.  As I said above, the client can _ask_ for a
> specific host name, but
> the DHCP server does NOT have to honor that request.
>  The hostname that
> the server _does_ give is what will be inserted into
> DNS (if DDNS is
> enabled).
> 
> If the server honors the client request, the name
> returned in the DHCP
> lease will be what the client asked for.  If the
> server does NOT honor
> the request, the name will be whatever the server
> deems appropriate and
> the client will have to deal with that fact.
> 
> If the hostname is important (e.g. print queues, X),
> one can create a
> post-lease script that picks up the IP address and
> adds a record to the
> /etc/hosts file to "alias" the hostname they want to
> the IP address they
> got.  As far as DNS is concerned, the alias doesn't
> exist (there's no
> CNAME record), so the outside world will only know
> the client by the
> name the DHCP server gave it, but your print queues
> and X-windows stuff
> will work properly since the hostname will resolve
> to the current IP
> address via the hosts file.
> 
> You can alternately insert a /etc/hosts line that
> equates 127.0.0.1 to
> your desired host name and things will always work
> locally regardless of
> what DHCP does to you.  In that case, make sure you
> set up your DHCP
> client to NOT set the hostname to that given by the
> DHCP server (dhcpcd
> does NOT set the hostname by default, the "-H"
> option turns that on).
> 
> As a side note, the client should NEVER be able to
> insert its hostname
> into DDNS--that is reserved for the DHCP server.  If
> a client can do an
> insertion, then the security of the DDNS system is
> SEVERELY compromised.
>
----------------------------------------------------------------------
> - Rick Stevens, Senior Systems Engineer    
> rstevens vitalstream com -
> - VitalStream, Inc.                      
> http://www.vitalstream.com -
> -                                                   
>                 -
> -      "Doctor!  My brain hurts!"  "It will have to
> come out!"       -
>
----------------------------------------------------------------------
> 
> 
> 
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