Network Router Access Issue

[Ben Scaithe]

I am completely bewildered by a problem I'm currently experiencing with our
network. Many of our PCs are losing connectivity through our ISDN router.
We replaced our aging NT4 Server with a Windows 2003 Server back in October,
and converted most of our Windows NT PCs to Windows XP Pro. All seemed to
be fine until our Netgear ISDN router went out a few weeks later. Our
Internet provider replaced the router with a spare that they had. At first
it wasn't configured correctly, so we had to work with the provider on and
off to get it working.

Later we noticed that some of the PCs, though apparently not all, keep
losing the ability to talk outside the router. They will open an IE window
or check their e-mail, but get nothing but errors. They can ping any
internal IP address, and can ping the router itself, but they cannot ping
the provider's DNS servers, nor any other external IP address. Sometimes
the connectivity will just come back on its own, though more often than not
it will take a reboot of the PC to get it back. Sometimes restarting the
router will also return connectivity, but I'm not sure that it's not
coincidental. As I said, the employees claim that it only happens to
certain particular PCs - most are WinXP, but also one Win2000 station - but
I personally have seen similar behavior occasionally on the other PCs.

I have tried all sorts of things to resolve the issue, and nothing so far
has made the problem go away. We replaced the aging hubs with a brand new
10/100 switch. We've turned on and off DHCP on the router (usually we use
static IPs). I've set the PCs with and without the external DNS server
information recorded in its DNS server list (the Windows 2003 Server itself
is doing DNS forwarding to the externals). We have a Cisco PIX 501
VPN/Firewall box in between the switch and the router, but removing it from
the chain and going to the router directly didn't seem to fix anything. A
couple of people from the provider's office have suggested that it's a
problem with our network infrastructure, but since we kept everything the
same during our system upgrade (IPs, subnet masks, DNS info, etc.), I can't
see how that could be true.

I'm very suspicious of the router. The problem seemed to occur once that
router was replaced. I've worked over and over with the provider
configuring it, but nothing has improved the situation. The provider has
ultimately suggested getting a new ISDN router. Since we can't get any
other broadband connections out here yet, we're stuck with ISDN. As I'm
investigating new ISDN routers, though, I'm concerned that there is
something that's being overlooked. The Internet connection seemed to be
fine immediately after the system upgrade, but could there be anything on
the server or workstations that I'm missing that could explain this odd
behavior?

Thanks!

 

[Hans-Georg Michna]

Later we noticed that some of the PCs, though apparently not all, keep
losing the ability to talk outside the router. They will open an IE window
or check their e-mail, but get nothing but errors. They can ping any
internal IP address, and can ping the router itself, but they cannot ping
the provider's DNS servers, nor any other external IP address. Sometimes
the connectivity will just come back on its own, though more often than not
it will take a reboot of the PC to get it back. Sometimes restarting the
router will also return connectivity, but I'm not sure that it's not
coincidental. As I said, the employees claim that it only happens to
certain particular PCs - most are WinXP, but also one Win2000 station - but
I personally have seen similar behavior occasionally on the other PCs.

Ben,

I cannot pinpoint the cause. I only have a few general
recommendations for a start.

The first thing I would do is to write a log of these events.
When does it happen, to which computer (which operating system),
what was done, what worked?

If you see that all computers are occasionally affected with
equal frequency and regardless of their operating system then
you can most likely deduce that the computers are not at fault.

The other thing to do is to swap the router for a test.

Hans-Georg

 

[William Cooper]

Hi
If you can ping the router then you are going in the right direction. Check
that each machine has the IP address of the router as the default gateway,
or that you are delivering this info in your DHCP server. When it does work
try running tracert to see how you are getting outside. As a rule of thumb,
if you gat ping the gateway and this IP is your default gateway ipconfig
/all then the router is at fault. Check whatever IP / port rules exsist on
the router/gateway.

William