Network OK but no Internet

[Mobius]

On this Windows 7 Professional machine the system works perfectly well on
our small office LAN.
We can do all network tasks as moving files and process documents over the
network.
But this machine, from time to time, cannot get on the Internet, served over
our network from a DSL.
Other computers don't have any problems.
But this one says that there is network access but no Internet.
All network related tasks can continue.
Just that IE and Firefox as well as Outlook report no connection.
The issue resolves itself within a few minutes.
Keeps appearing and disappearing at random.
System checked for malaware. DSL router rebooted, network switch rebooted -
all no go. No un-necessary or suspiscious services running.
System rebooted several times - no go.
Network device drivers uninstalled and reinstalled fresh.
Somewhat perplexing.
Regards and TIA.
Mobius
--------

 

[Big Steel]

On this Windows 7 Professional machine the system works perfectly well on
our small office LAN.
We can do all network tasks as moving files and process documents over the
network.
But this machine, from time to time, cannot get on the Internet, served over
our network from a DSL.
Other computers don't have any problems.
But this one says that there is network access but no Internet.
All network related tasks can continue.
Just that IE and Firefox as well as Outlook report no connection.
The issue resolves itself within a few minutes.
Keeps appearing and disappearing at random.
System checked for malaware. DSL router rebooted, network switch rebooted -
all no go. No un-necessary or suspiscious services running.
System rebooted several times - no go.
Network device drivers uninstalled and reinstalled fresh.
Somewhat perplexing.

Do an IPconfig /all at the command prompt on the machine. If the
machine has an IP that starts with 169., then the machine doesn't
have an IP from the DHCP server on the router, which will allow the
machine to access the Internet. The 169 means the O/S assigned the
169 IP because it timeout in trying to obtain an IP from the DHCP
server on the LAN. The machine can access other machines on the LAN
with the 169 IP, but it will not be able to access the Internet,
because it's not using an IP assigned by the DHCP server on the LAN.
The router has the DHCP server.

The NIC in the computer may be going bad, the cable between the
router's LAN port and the NIC could be going bad, or it could be the
router's LAN port the cable is plugged into could be going bad too,
causing the computer to loose the DHCP IP.

Those are other things you can look at and you can try switching
things out to see if the problem follows.

 

[Char Jackson]

Do an IPconfig /all at the command prompt on the machine. If the
machine has an IP that starts with 169., then the machine doesn't
have an IP from the DHCP server on the router, which will allow the
machine to access the Internet. The 169 means the O/S assigned the
169 IP because it timeout in trying to obtain an IP from the DHCP
server on the LAN. The machine can access other machines on the LAN
with the 169 IP, but it will not be able to access the Internet,
because it's not using an IP assigned by the DHCP server on the LAN.
The router has the DHCP server.

One correction - if the troublesome PC has a 169 IP and the other LAN
PC's don't, they won't be able to communicate with each other.

But in this case he/she says that the computer normally works fine and
then doesn't for a few minutes. That behavior doesn't really indicate
a DHCP problem, especially since the other PCs are OK. I like your
advice below:

The NIC in the computer may be going bad, the cable between the
router's LAN port and the NIC could be going bad, or it could be the
router's LAN port the cable is plugged into could be going bad too,
causing the computer to loose the DHCP IP.

Those are other things you can look at and you can try switching
things out to see if the problem follows.

I like to do a series of continuous pings to get a view of the network
connectivity, or lack of. I open multiple Command Prompt windows and
do a ping to another PC on the LAN, to the router's LAN IP, to the
cable modem, to the first ISP hop (the ISP's gateway IP), to the DNS
server, etc. Probably not all at once, but a few, as needed, to help
me see where connectivity exists and where it ends.

 

[Mobius]

Do an IPconfig /all at the command prompt on the machine. If the machine
has an IP that starts with 169., then the machine doesn't have an IP from
the DHCP server on the router, which will allow the machine to access the
Internet. The 169 means the O/S assigned the 169 IP because it timeout in
trying to obtain an IP from the DHCP server on the LAN. The machine can
access other machines on the LAN with the 169 IP, but it will not be able
to access the Internet, because it's not using an IP assigned by the DHCP
server on the LAN. The router has the DHCP server.

The NIC in the computer may be going bad, the cable between the router's
LAN port and the NIC could be going bad, or it could be the router's LAN
port the cable is plugged into could be going bad too, causing the
computer to loose the DHCP IP.

Those are other things you can look at and you can try switching things
out to see if the problem follows.

All IP addresses here are 192.168.0.x
Also, during the times when this particular PC "loses" the Internet, it does
not lose network connectivity. As already said.
We had also tried relocating the PC itself to another room to check whether
the cabling is at fault. But the behavior continued.
We also checked the web-accesses admin panel of the DSL router - it can see
all PCs - including this particular one - at all times.
We checked Event Viewer - strangely it does not show any "loss" of Internet
or network connectivity or anything related at any time.
The self-diagnostic utility of the onboard Intel NIC shows the device has no
problems.
We will do ping and traceroute tests later.
The mystery continues.......

 

[Big Steel]

One correction - if the troublesome PC has a 169 IP and the other LAN
PC's don't, they won't be able to communicate with each other.

That's not correct. The 169 IP assigned to a machine will allow the
machine to see other machines on the LAN, when one of my machines got
the 169 IP. That's how it worked on my network.

The OP is indicating that the problem machine can see the other
machines on the LAN. So either the machine has DHCP IP or it's using
the 169 IP to do it. The machine could be using a 0 IP too, and it
has no connectivity to the LAN or WAN.

 

[Big Steel]

All IP addresses here are 192.168.0.x
Also, during the times when this particular PC "loses" the Internet, it does
not lose network connectivity. As already said.

Yeah, it can loose Internet connectivity, because it has lost the IP
the router has assigned to it due to some type of issue that is
causing the machine to loose the IP.

If the machine has the 169 IP for a short period of time, it will
still see the other machines on the LAN, but it can't access the
Internet, because it's not using an IP on the router anymore. Then
the machine can acquire the IP from the router again and access the
Internet. You wouldn't necessarily see this happening if checking
what IP the machine has, because it may be happening too fast.

We had also tried relocating the PC itself to another room to check whether
the cabling is at fault. But the behavior continued.

You can assign a static IP on the router to the computer's NIC
instead of letting the DHCP server on the router dynamically assign
the IP, to see if the problem follows.

I worked in a IT shop where the machines were running XP, Vista, and
Win 7. The Vista and Win 7 machines keep loosing Internet
connectivity while the XP machines did not loose the Internet
connectivity. I say the machines were having problems with the DHCP
server on the LAN, they were loosing the DHCP IP. I didn't check it.
I left the organization, which was only a couple of months ago. I'll
bet they are still having the issues.

 

[Big Steel]

Guess you better tighten it up then if it's *loose*.

Yawn

You can crawl back to your hole.

 

[Big Steel]

Loose and fancy free, eh?

Yawn

Crawl back to your hole....

 

[Big Steel]

On Mon, 10 Jan 2011 19:03:47 +0100, Alias

<snipped your babble I didn't read it>

Yawn....

See ya I wouldn't want to be ya.

Bye

 

[Char Jackson]

That's not correct. The 169 IP assigned to a machine will allow the
machine to see other machines on the LAN, when one of my machines got
the 169 IP. That's how it worked on my network.

The OP is indicating that the problem machine can see the other
machines on the LAN. So either the machine has DHCP IP or it's using
the 169 IP to do it. The machine could be using a 0 IP too, and it
has no connectivity to the LAN or WAN.

I might be doing something wrong. I have 5 PC's that I tested with,
two with Win 7 and 3 with XP. When I force any one of them to acquire
a 169.254.* (APIPA) address, that PC becomes isolated from the other
PCs and from the Internet. If two or more PCs are forced to acquire
169.254.* IP's, those PCs can see each other but they can no longer
see the other PCs on the LAN, nor can they access the Internet.

Since that makes perfect sense to me, (after all, my normal
192.168.*/24 subnet is completely different from the 169.254.*/16
subnet), I'm not sure what I'm doing wrong or why my results are
different from yours. Any ideas?

 

[Big Steel]

I might be doing something wrong. I have 5 PC's that I tested with,
two with Win 7 and 3 with XP. When I force any one of them to acquire
a 169.254.* (APIPA) address, that PC becomes isolated from the other
PCs and from the Internet. If two or more PCs are forced to acquire
169.254.* IP's, those PCs can see each other but they can no longer
see the other PCs on the LAN, nor can they access the Internet.

Since that makes perfect sense to me, (after all, my normal
192.168.*/24 subnet is completely different from the 169.254.*/16
subnet), I'm not sure what I'm doing wrong or why my results are
different from yours. Any ideas?

I was using a wireless router at the time with machines on the wire
and wireless. You may be correct. I do recall the machine with the
169 IP was accessing the other machines. But that was over six years
ago. So I suspect that you are right.