1 network pc unable to connect to internet.

[Dianne]

I have a home network with 4 computers, all running
Windows XP home, which has been working fine for the last
6 months. Two days ago my son was in the middle of a game
(offline) and a message popped up saying he'd been
disconnected from the internet. He clicked work offline
and continued playing. Now if I run the wizard it sets
him up with a different ip address (169.xxx instead of
192.xxx) and a different subnet mask (255.255.0.0 instead
of 255.255.255.0). If I manually configure his settings
(ipaddress, subnet mask, gateway and DNS server), then he
can access the other computers on the network and they
can access his files, but he cannot connect to the
internet. I have a cable connection through my pc and the
other 2 pcs on the network can still connect. I have
tried pluggin his cable into a different socket on the
switch, and all of the lights on the switch are on for
whichever socket he is using.
My most urgent question is why his pc cannot connect to
the internet, but I am also curious as to why the wizard
now sets him up with a different subnet mask and address.
When it isn't manually set, I can release his ip address,
but when I try to renew, I get a message saying it is
trying to connect through something that isn't a socket.
MSN says he may be behind a firewall and IE simply
doesn't connect.
Thanks in advance for any assistance.

 

[David Dickinson]

The address block 169.254.xxx.xxx is reserved for "automatic private IP
addresses". Windows XP assigns numbers in this block to a NIC when the
machine is set up for DHCP but it can't find a DHCP server. The machine
assigns the interface an IP address, but it is one that by design cannot be
used to access a network. See

Plug and Play Networking with Microsoft Automatic Private IP Addressing
http://msdn.microsoft.com/library/en-us/dniph/html/pnpip.asp

From the way it sounds, you are using Internet Connection Sharing on your
machine and your machine has two network cards. Thus your machine is
providing the DHCP service to the LAN (as well as NAT). Correct?

On your son's machine, reset the TCP/IP protocol to obtain both an IP
address and DNS server addresses automatically. Disable the firewall on
that connection if it's enabled. Right-click on the connection in Network
Connections and select "Repair". What happens?

Were you doing anything on on the gateway (your machine) when he lost the
connection? What firewall are you using on the gateway? Look in the event
log on both machines for events that occurred at the time he lost his
connection and let us know if you find anything.

David Dickinson
eis at softhome dot net