XP clients sometimes ignore DHCPOFFERs
David W. Hankins
David_Hankins at isc.org
Tue Mar 21 16:18:08 UTC 2006
On Tue, Mar 21, 2006 at 10:56:34AM -0500, John Wobus wrote:
> We made the change (xx.xx.xx.255 broadcast addresses
> to 255.255.255.255 broadcast addresses in the routers)
This is actually a very well known problem with Windows DHCP
clients of all versions (that I'm aware of), and the reason
the ISC DHCP software package is so careful to make sure it
forms packets precisely for Windows clients' needs (the BPF
etc hacks). It's also the reference behaviour (rfc2131 is
specific in stating the address MUST be 255.255.255.255),
which makes it more than a little hard to fault them.
I forget sometimes that people don't always use ISC dhcrelay,
so I often don't remember this. It's an incredibly old problem,
dating back to Windows 95 to my earliest memory.
At any rate, a Windows DHCP client may not receive DHCP packets
if they are not being sent to 255.255.255.255. If you're using
Cisco helper-address, I understand you may need to configure the
broadcast address as well.
> P.S. There are excellent explanations of Windows' APIPA
> feature that Googling "APIPA" will turn up.
Supposedly there is now a DHCP option you can use to inform
clients not to consider link-local addressing.
It's an odd duck because it's the only one of its kind that may be
present in DHCPNAK ("you may not have a dynamic lease, but don't
autoconfigure one either").
David W. Hankins "If you don't do it right the first time,
Software Engineer you'll just have to do it again."
Internet Systems Consortium, Inc. -- Jack T. Hankins
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