Updating DNS after DHCP

John john at starfire.mn.org
Thu Jan 15 05:57:56 PST 2004

On Thu, Jan 15, 2004 at 03:30:08PM +0200, Gilad Rom wrote:
> Scott Mitchell wrote:
> > On Tue, Jan 13, 2004 at 01:16:23PM +0100, Ruben de Groot wrote:
> > 
> >>On Mon, Jan 12, 2004 at 11:09:38PM -0600, John typed:
> >>
> >>>I see that some Microsoft systems send out an update to DNS with
> >>>the system name.  I configured my DNS server to accept these updates,
> >>>but now that I'm running FreeBSD on a laptop - how do I do that
> >>>from FreeBSD? I've looked at the dhclient man pages and the named
> >>>man pages and the pages that they refer to and I didn't pick up
> >>>any hints there.
> >>>
> >>>Can anyone give me a clue? (Yeah - I'm clueless...)
> >>
> >>I believe this is done by the nsupdate(8) program.
> > 
> > 
> > You can also have your DHCP server do the updates - which makes sense, as
> > it's the thing handing out the addresses to your client machines.  I have
> > this working reasonably well with isc-dhcpd, for Windows and FreeBSD
> > clients.
> > 
> > You want to read the 'DYNAMIC DNS UPDATES' section of the dhcpd.conf(5)
> > manpage, and whatever docs your DNS server has on this topic.  There are
> > plenty of examples of working configs for isc-dhcpd and bind to be found on
> > the web.
> > 
> > HTH,
> > 
> > 	Scott
> I just set this up today...
> There's actually nothing to be done on the client side.
> The isc-dhcp server takes care of informing BIND that it has handed
> out a new Address.
> You have to add the following line to your dhcpd.conf:
> ddns-update-style ad-hoc;
> and make sure BIND is willing to take it:
> (from /etc/named/named.conf:
> zone "lan" {
>          type master;
>          allow-update {; }; <<--
>          file "s/lan";
> };
> ( is my DHCP server, which is actually
> the same machine which runs BIND)
> after a little while, 'host -l lan' says:
> OREN1.lan has address
> ROIE.lan has address
> Sun.lan has address
> zhacy.lan has address
> ....
> And so forth...
> These are all dynamically-assigned addresses,
> I only have ladon/mail/router.lan defined in the
> zone file.

Thanks, but I'm still missing a piece for my ideal scenario.  This
requires the DCP server to know to whom it is handing out the
address, doesn't it? How would it know that?  Does the DHCP request
include the host name? Or do you have to somehow bind a NIC/MAC
address to a name for isc-dhcp?

Clearly, the BIND configuration is already set up to accept updates,
since the Windows system is successful in doing so.

The Windows dhcp client and the FreeBSD dhcp client are behaving
differently with the same dhcp server configuration (in fact,
time-sharing a WiFi card) - the Windows host can do it, the FreeBSD
system doesn't.  That's why I was looking for a client-side solution.
Consider further the fact that I am sharing a WiFi card between
them, so the host using that NIC address changes.  Depending on my
needs, either of the hosts may be either connected wired or wireless.
They each have their own wired port with it's own NIC, and the
WiFi card bounces between them as needed.

I will look at the isc-dhcp thing and see if it can somehow know
which host it is setting up, and that may be satisfactory, but it
won't be the same mechanism that the Windows system is using.  It
doesn't HAVE to be, but I wanted to make sure people are aware
that there is, apparently, something different going on with the
Windows system than what we can/will/want to do with FreeBSD.

John Lind
john at starfire.MN.ORG

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