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I run a network (I'm just a math teacher) at my school. We get random 10 or so minute periods (I'd guess three a day on average) where the Internet is not accessible from within the LAN. If I go to our sonicwall and do a ping test, I can resolve so it's definitely internal.

We have a Windows 2008 server that handles a small DHCP for cellphones, everything else is static. That is connected to a managed switch with about 15 Cat5e connections and three fiber branches that go to different parts of campus. At each of these parts there is another managed switch that branches out to the LAN.

Our cable Internet comes into one of these locations, goes through the supplied modem and into a Sonicwall. The Sonicwall, as I stated above, stays connected to the Internet when no one on the LAN can see it (plus our VOIP phones keep working and they don't go through the Sonicwall). The only wonky thing I can think of is that I have both the Sonicwall and Windows handing (the same) static IPs to our 16 Chromebook's mac addresses. If I don't do this, the Chromebooks look to the DHCP on Windows for an address. Quite infuriating, you cannot set static IPs at the Chromebooks. But the Internet drops even when those are off, so I discounted that.

I've run wireshark while pinging 8.8.8.8 and watched it go out and come back on, but I have no idea what I am looking for in all that data...

Christopher Moran
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  • The first thing I would try is turning off the DHCP bits of the Sonicwall. You generally don't want to have two DHCP servers on the same LAN, as this can lead to problems. – John Nov 14 '14 at 16:39
  • `"If I go to our sonicwall and do a ping test, I can resolve so it's definitely internal"` What are you pinging? IP? If so, you're saying the same ping to IP fails from the LAN? Or are you only trying FQDN pings from internal? My first thought was a DNS issue, but that depends on your answer to my comment. – TheCleaner Nov 14 '14 at 16:43
  • The Sonicwall does it's own outgoing pings to Google's DNSs, a timeserver and our ISP DNS. If I shut off Sonicwall's DHCP, I lose the static IPs on my Chromebooks. Windows can't seem to handle it alone. They need to be static because of content management. – Christopher Moran Nov 14 '14 at 17:01
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    Man, considering all your other questions, do you think you are fit for the job? Having periods in the network where nothing works may indicate address conflicts, either by accident, or deliberate (if you know what I mean), among many other things. – Marki Nov 14 '14 at 17:21
  • Of course I'm not the best for the job, but it's not my choice and I have to solve it. If I can solve it with help I will. Career input aside. I have checked pretty thoroughly for IP conflicts. When the Internet disappears: Computers on the LAN communicate fine and the firewall communicates with the Internet. – Christopher Moran Nov 14 '14 at 19:13
  • So which machines lose connectivity? All? Just static/ Just dynamic? Next question: from a "dead" machine, can you: ping the sonicwall by IP? ping 8.8.8.8? – Tom Newton Nov 15 '14 at 18:27
  • It's been a while since I've had time to look into this so hopefully @Tom Newton you can continue helping. In answer to your questions. All machines lose connectivity. Static and dynamic. Yes you can ping the sonicwall by IP, I can even log into it to check connectivity to the Internet (the Sonicwall says all is well). No I cannot ping 8.8.8.8 at that time... – Christopher Moran Apr 13 '15 at 20:51
  • It does feel like maybe the other dhcp server is 'winning' occasionally, and your machines get the wrong gateway, but if the static pcs suffer too... Odd. Can you check the gateway when a pc dies? route print on the command line – Tom Newton Apr 13 '15 at 20:59
  • I'm not sure how they'd get the wrong gateway. Both DHCPs should mimic one another... Every system on the network is configured to go to the same gateway (the Sonicwall). Unless I'm misunderstanding the term gateway in this regard. – Christopher Moran Apr 13 '15 at 22:32
  • The DHCP on the Sonicwall is only configured to give out the 16 Chromebook addresses, nothing more. – Christopher Moran Apr 13 '15 at 22:33
  • @TomNewton there was no difference in the route print between a working and non-working connection and the gateway is set correctly. My Sonicwall still pinged multiple sites on the Internet fine. Behind the Sonicwall I could only ping positively within the LAN. – Christopher Moran May 25 '15 at 18:25

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