DHCPD and Windows question

[Ken D'Ambrosio]

Hi!  After perusing your e-mail, I have a few things to say, and one idea:
First, to the best of my knowledge, *no* major OS requires a broadcast
response from a DHCP server in response to a request, as per RFC 2131. 
(It does leave some wiggle room, but this is almost certainly for clients
that were having trouble modifying their TCP stacks to implement DHCP
correctly -- HP/UX comes to mind -- and not for modern-day OSes.  (See RFC
2131, near the end of section 2.0, for two pertinent paragraphs.)  I'd be
very interested to see an MS page that says that any current version of
Windows requires a broadcast from the server.

One thing that *does* seem to stand out is the "authoritative" parameter. 
According to the manpage,
  If the server finds the address the  client  is  requesting,  and  that
  address is available to the client, the server will send a DHCPACK.  If
  the address is no longer available, or the client  isn't  permitted  to
  have  it,  the server will send a DHCPNAK.  If the server knows nothing
  about the address, it will remain silent, unless the address is  incor-
  rect  for the network segment to which the client has been attached and
  the server is authoritative for that network segment, in which case the
  server  will  send  a  DHCPNAK  even  though  it doesn't know about the
  address.

My interpretation of this is that the client, already having a lease from
some other network, requests an IP address -- apparently, one "incorrect
for the network segment" (I'm not sure if that means it's for a different
subnet, or conflicts with one of the current addresses), and the server
sends out a DHCPNAK, telling the client to fly a kite.

I'd take out the authoritative bit -- as well as the always-broadcast --
and give it another try.

$.02, YMMV, etc.

-Ken



On Fri, January 29, 2010 7:10 pm, Todd Littlefield wrote:
> Hello,
>
>
> I have a stupid question about how to configure the ISC DHCPD to
> work with Vista/Win7.  At home I have XP and Linux systems running.  They
> all will broadcast out to the network to find the server and request and
> address/lease.
>
> The DHCPD server is configured to hand out the same address, based
> on MAC to all the machines/switches/etc. that are running internally.  The
> problem comes in when someone with a laptop running Vista or Win7 comes
> over.  According to M$ they changed their DHCP client in Vista and 7 to
> rely on broadcasting to get address.
>
> From digging on the network, it seems to be that the broadcast flag
> needs to be enabled on the server side.  Otherwise when clients beacon out
> to get an address, the server doesn't respond to it.  (perhaps the
> incorrect choice of words for the behavior)
>
>
> I've dug through the ISC docs for the daemon.  I thought the
> always-broadcast command would do it...  Unfortunately that is not the
> case.  There didn't seem to be anything in the GNHLUG email archives about
> this problem.
>
> If I disable the daemon on the server and use the one on the router,
> the Windows boxes are happy...  But that makes me unhappy.  I'm at my wits
> end trying to get it figured out.
>
>
> The server in question is running CentOS 5.4 with dhcp-3.0.5-21
> running.  The running config is attached.  I'm sure I there are multiple
> things that could be set up better but it passes parsing and works, at
> least until someone visits.
>
>
> Any and all help is greatly appreciated.  Thanks in advance!
>
>
>
> - Todd
>
>
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