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jdaveclark

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Losing network connectivity

For several weeks we've been having a problem at a client site with PC's getting kicked off the network when browsing the network.

What happens is this: A PC will open Windows Explorer, or browse from the search bar using UNC. The hourglass appears, and after several seconds, the NIC goes to "Limited connectivity" with the yellow exclamation. It keeps its IP address, but cannot ping any other host on the network, nor can it be pinged itself.

The machine stays offline for several hours, and then, on its own, rejoins the network without a problem. But, it always happens again.

It's an Active Directory domain, operating at 2012R2 level. The PC's are DHCP-enabled, with IPv6 enabled. Servers are IPv6 enabled. Windows Firewall disabled. Using Webroot Anywhere cloud AV, firewall is enabled. There is a NAP server in place, but as far as I can tell it just has the default policies for VPN clients.

The network, when inherited, had an IPv4 subnet that was non-standard. I renumbered the network to a standard 192 class C, thinking this might help the problem, having read an article about the way IPv6 mishandles IPv6 encapsulation if the IPv4 packet is non-standard addressing. No dice.

I also replaced the LAN switch, which was aged. I've tried setting static IP's on the machines, and disabling NetBIOS over TCP/IP...all to no avail.

Nothing in the event logs...server or workstations....

Wondering if anyone else has seen this behavior...
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BillBondo
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Just a shot but I have seen in my test environments IPv6 cause issues. You could try unchecking from the comp and release/renew/flushdns. HTH
The network, when inherited, had an IPv4 subnet that was non-standard.
What was "nonstandard" C class network address/range, and what is now? How many hosts do you have? Maybe, now after the change, you don't have enough IP addresses for all of your users?
Check how many addresses left free in the DHCP pool.
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jdaveclark

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The previous admin used a public IP range for the internal network, not knowing any better. The internal addresses are now a standard 192.168.x.x/24 range.

Checked the DHCP pool and it's more than large enough. The affected machines get IP addresses, and keep them even when the problem happens. They just lose their connectivity.
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Predrag Jovic
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Good idea...however, the machines on the network appear to be affected randomly. So I'd have to disable it on all computers, and wait to see if the problem stops reappearing.
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This eventually ended up being "resolved" back in October when our area was affected by Hurricane Matthew. The entire network was powered down for a week. When the network equipment was powered back on, the problem no longer happened. Strange but true.