# [SOLVED] All computers on network lose connectivity, but router seems ok!



## JVRacing (Jan 4, 2012)

Hi there.

I manage the network for a fairly small non-profit, and I've run into a problem I can't figure out.

We've got 12 computers, plus 4 network printers all connected to a SYSWAN dual WAN router.
Newegg.com - SYSWAN SW24 VPN Dual WAN VPN Load Balancer 10/100Mbps 2 x 10/100Mbps WAN Ports 4 x 10/100Mbps LAN Ports

The dual internet is Time Warner Business Class Cable and Verizon Business DSL. Between the router and the 16-odd network devices are several switches (Netgear and Linksys).

We are starting to get an intermittent problem where all devices lose their connectivity. I tried swapping out the router for our old SnapGear, but the problem remained. I also tried swapping out the first switch that connects to the router, which most other devices go through, and the connectivity did not return with a different switch in place.

The crazy thing is that the one computer plugged directly into the router would continue to work, as long as that was the ONLY thing plugged into the router. When I linked up to the main 16-port switch (or the alternate switch that I had swapped in to try and replace that one), then even the computer plugged directly into the router would lose its connectivity. It's like there's some device (or switch?) on the network that paralyzed the connection to every device simply by being plugged in.

I finally was able to get everything working again by powering down all network devices and bringing them back up. I had hoped this was the end of the problem, perhaps caused by static buildup and/or having things plugged in and powered on for months and years at a time.

Unfortunately it happened again today, after 4 days of proper functioning. I power cycled the cable/DSL equipment and the router, and as before that didn't help. So I went straight to powering everything off and when they came back up everything worked again.

So I have no idea what's going on, or how to fix it! It seems like it could basically be any device on the network causing the problem, but I don't know what could cause a complete network failure like this, simply by having the offending device plugged in to the network?

Any suggestions of where to start, or how to determine the problem device? It's particularly difficult since it's an intermittent problem, and when it happens the entire office kind of grinds to a halt, so I can't do a lot of trial and error at the time of failure.

Would it be wise to replace all of my network hardware (switches and/or router)? Is that too drastic? Some of the switches are maybe 5+ years old. What kind of lifespan should I expect from these things? Help!

Thank you so much in advance.


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## Wand3r3r (Sep 17, 2010)

*Re: All computers on network lose connectivity, but router seems ok!*

connect the pc to the router - its working
add the switch to the router with nothing connected to the switch - still working?
connect one pc at time to the switch [no other switches!] - still working?
connect one switch at a time to the main switch - still working?

where this fails will give us a clue where to look.


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## Signify (Jan 6, 2012)

*Re: All computers on network lose connectivity, but router seems ok!*

When this happens do all devices just lose connectivity to Internet and the router or can you for example ping between two PCs?
The symptoms sound like it could be a device connected to the network that with the same ip as the router. If that device normally is silent it wont interfere with the traffic to and from Internet. If it starts talking and answering arp requests for the routers IP all traffic destined to Internet would end up at the device to the conflicting IP.

As Wand3r3r suggested. Go through his troubleshooting list connecting one device at a time but also consider checking the ip address of all devices in the network so noone conflicts with the routers ip address


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## TheCyberMan (Jun 25, 2011)

*Re: All computers on network lose connectivity, but router seems ok!*

Try cloning the mac address of the first pc connected ever to connect to the router to the router do you understand?


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## JVRacing (Jan 4, 2012)

*Re: All computers on network lose connectivity, but router seems ok!*



Signify said:


> When this happens do all devices just lose connectivity to Internet and the router or can you for example ping between two PCs?
> The symptoms sound like it could be a device connected to the network that with the same ip as the router. If that device normally is silent it wont interfere with the traffic to and from Internet. If it starts talking and answering arp requests for the routers IP all traffic destined to Internet would end up at the device to the conflicting IP.
> 
> As Wand3r3r suggested. Go through his troubleshooting list connecting one device at a time but also consider checking the ip address of all devices in the network so noone conflicts with the routers ip address


They lose all connectivity period, as far as I can tell. I didn't try pinging from one PC to another, but I did try accessing one PC from another through Explorer.

I don't know how another device could have 192.168.1.1 as its IP address, since there is only one router on the network and it seems like nothing except a router would try and use that IP. But I could check into that. Is there an easy way to find the IP of every device without going around to each and inspecting their configration?

Thanks for the suggestions.


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## JVRacing (Jan 4, 2012)

*Re: All computers on network lose connectivity, but router seems ok!*



TheCyberMan said:


> Try cloning the mac address of the first pc connected ever to connect to the router to the router do you understand?


Unfortunately I don't totally understand, no. I am somewhat aware of the option in routers that let you clone the MAC address of a PC. Is that what you mean?

And what do you mean by "the first pc connected ever to connect to the router"? You mean EVER? Or you mean the first one when I boot up the router? Because I don't know if the first PC ever to connect to that router even exists anymore, or if I would know where it is. 

Thanks for helping!


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## Wand3r3r (Sep 17, 2010)

*Re: All computers on network lose connectivity, but router seems ok!*

JVRacing it would appear you have a hardware issue.
I gave you the steps to troubleshoot that. Have you done so?

Since internet has been working there is no need to be cloning workstation mac address to the router.

Question is which piece of equipment is failing.

If you don't want to isolate it like I said then next time you have a failure don't reboot anything. first see if the pc connected to the routers has internet. Then go to the first downstream switch and see if the pc connected to it has internet. So on and so forth until you have a failure.


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## JVRacing (Jan 4, 2012)

*Re: All computers on network lose connectivity, but router seems ok!*



Wand3r3r said:


> JVRacing it would appear you have a hardware issue.
> I gave you the steps to troubleshoot that. Have you done so?
> 
> Since internet has been working there is no need to be cloning workstation mac address to the router.
> ...


Wand3r3r, thank you for your help. I have not been able to follow the steps you gave because this intermittent problem has not yet reoccurred. And yes, the procedure you outlined sounds like the most logical way to isolate the problem.


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## Signify (Jan 6, 2012)

*Re: All computers on network lose connectivity, but router seems ok!*

JVRacing,
Do you have people with laptops coming and going at the office? That could be a source of the problem. Also check for anything that might be switched of at the moment. From the sound of it it's not a large net so it should not be hard to find everything connected.


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## JVRacing (Jan 4, 2012)

*Re: All computers on network lose connectivity, but router seems ok!*

Thank you Signify and others for your help and suggestions.

We decided to just go ahead and purchase a new router and switches. So far that appears to be a good decision.

One amazing thing was that before, doing a tracert to our hosted exchange server, there would be 19 hops. Now, with the new router, there are 12. I can't fathom how the old router could have been adding 7 extra hops, but that seems to be what happened because the 12 is the way it should be. (I know this because connecting through the same ISP at my home a few miles away had always been just 12 hops.)

Anyway, everything is operating faster, and hopefully the problem will be gone now with new network hardware. Thanks again everyone!


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## TheCyberMan (Jun 25, 2011)

*Re: All computers on network lose connectivity, but router seems ok!*

You are welcome i'll mark this as solved.


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## Signify (Jan 6, 2012)

Very odd about the router hops. Nice to hear you seem to got it sorted.
There's nothing like shiny new hardware to play with. Hope it got loads of flash LEDs


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