Automatic TCP/IP Addressing Without a DHCP Server problem

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John Smith

According to Microsoft Knowledgebase article 220874, Windows will
automatically assign an IP address in the range of 169.254.0.0 -
169.254.255.255 when a DHCP server is not present.

With 802.11x wireless networking, it is possible for the connection between
a client and the wireless router to be temporarily lost due to a variety of
causes - a 2.4Ghz cordless phone is too close to the client or router, a
microwave is turned on (they also operate at 2.4Ghz), a large motor is
starting up nearby, a neighbor turns on his wireless router on the same
channel yours operates on and his signal strength is higher, etc....

If the connection to your router is lost for more than some small (unknown)
period of time, the DHCP assigned IP address from your router (typically
192.168.x.x) gets clobbered by the Windows automatic Transmission Control
Protocol/Internet Protocol addressing system (see the KB article for
details).

If that happens, your machine then automatically gets assigned a 169.254.x.x
IP address instead and is then *typically* unable to reconnect to your local
wireless network without rebooting. Upon rebooting you'd get new DHCP
assigned 192.168.x.x address from your wireless router (assuming that it
wasn't the router that was having problems).

It is possible to edit the registry to turn off the Windows automatic
Transmission Control Protocol/Internet Protocol addressing system. Does
anyone here know what happens if you turn this off, ie. will your computer
continue to hold on to the original DHCP 192.168.x.x address in the hopes
that the connection betwen the client and router is re-established?

I have seen this problem happen with D-Link DI-624 / DWL-G650 wireless G
routers and PC cards. D-Link is suggesting that the problem is a software
conflict with ZoneAlarm, but I have not seen evidence of this problem when
using SMC 2804WBR router and SMC 2835W PC card and ZoneAlarm is enabled.

Thanks for any tips.
 
Under RFC's 2131 and 2132, DHCP clients try to renew there lease when it has
reached 50% of the lease period with the DHCP server that it received it's
TCP/IP resources from. At 87.5% into the lease period it trys to contact any
DHCP server. If the client reaches the end of the lease it will stop using
the TCP/IP resources it received.
What you might consider is extending the lease period on the DHCP server
to maybe 5 days. And configure a script for the clients with ipconfig
/renew , put a shortcut on there desktops and name it ReConnect to
Internet. That way they will not have to restart there computer.
 
Thanks for the thoughts.

My lease period in the router settings is currently set to 7 days but the
problem occurs (I think) because when the 802.11x link drops for a short
time (seconds to minutes) due to interference or some other cause (maybe no
beacon from the wireless router) Windows itself times the lease out and
substitutes an autoconfigured ip address in the 169.254.x.x range.

Once Windows 2000 sets the ip to a 169.254.x.x there is no way I've found
short of rebooting the machine to release that ip address and allow the DHCP
server to attempt to reassign a usable ip address. Eeven ipconfig /release
and ipconfig /renew fail to work. This behaviour seems to be by design once
the ip address has been set to 169.254.x.x.

This problem seems to be wireless related because another machine connected
to the same D-link router via a Cat5e cable does not lose the 192.168.x.x
address at the same time as my wireless laptop does.
 
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