SUMMARY: Cross platform DHCP

From: Sal Serafino <>
Date: Thu Aug 01 2002 - 11:41:54 EDT
Many thanks to those who replied:  Matthew Mauzy, Michael Connolly, Marcelino 
Mata, Hichael Morton, Dave Miner, and a few anonymous users ;)

The general consensus is that Win9x/NT are more prone to the DHCP release issue 
than is Win2K, but that it does still happen albeit less frequently.  We have 
seen that here.  This problem occurs whether Windows or UNIX DHCP services are 
implemented, so it's *got* to be a problem with the Win client.  Research we did 
here shows that Win9x has a registry setting (go figure!) and that NT has a 
resource kit program that will help.  We found no information on how to fix this 
with Win2K, which only leads us to believe that Microsoft is ignoring the 
problem.  Matthew is running ISC DHCP and has never seen this problem.  Dave 
says that dhcptags in SunOS 5.6 and 5.7 apply only to Solaris and that I should 
shorten the lease, which I agree may be somewhat helpful.  In some DHCP threads 
a few weeks ago it was summarized that Solaris-8's native DHCP is the way to go 
and it better that ISC, so I don't know what to believe.  I think I'll give the 
server an OS upgrade to Solaris-8 (9?) and see how it goes.  Most everyone has 
suggested that users run 'ipconfig /release' when needed, but 

Nobody gave any ideas as to why a client would decline an otherwise good looking 
IP address enough times to suck up a whole network.  I have a feeling that it 
could be a badly configured wireless bridge or worse -- a do it yourself Linux 
installation.  We are looking into that and when we find an answer I'll post.

Thanks again to all.

Sal Serafino
UNIX Administrator
Cold Spring Harbor Laboratory

Original Post:
> Hi all-
> We have a [native] dhcp server running on Solaris 7 for use with DHCP clients 
> running Solaris, IRIX, Linux, Win9x/NT/2K, Mac OS8/9/X and probably some other 
> stuff too including a few Minix experiments.  It serves a lot of config 
> information and has been running for over two and a half years with no major 
> complaints from anyone once we ironed out the kinks.  However, we have two 
> problems with this platform:
> 1 - WinClients don't like to release their IPs on shutdown.  The problem here 
> when a laptop moves to a different subnet so that the old IP is not available 
> and the laptop can't get a new IP in the current subnet.
> I did some research and added a tag per documentation in /etc/dhcp/dhcptags:
> 	258   DHCPRel  -    String      DHCP_Release_On_Shutdown
> And also added a symbol in /var/dhcp/dhcptab:
> 	DHCPRel s       Vendor=MSFT,258,ASCII,1,1
> All clients are configured with a macro that includes :DHCPRel=RELEASE: but it 
> appears to not be working properly.
> 2 - Sometimes, a client will decline a whole pool's worth of addresses in an 
> entire Class-C subnet for no apparent reason.  The IPs offered are not 
> so we think there should be no reason to decline.  Ultimately, most or all of 
> the "free" IPs in any DHCP pool will be tagged as unusable and then nobody can 
> get an IP no matter where they go.
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Received on Thu Aug 1 12:28:23 2002

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