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I have a bit of a weird issue. I have a HyperV server (192.168.0.3) that hosts all my VM's in my network and, up until today, I have had no issues with it.

Now for some reason the PC that is hosting the VM's can not communicate outside of its own subnet....

All other machines on the subnet have no issues, and all the VM's function fine.

There is a central router that handles all my cross subnet routing and internet routing (192.168.*.10 on all subnets). Both the router and the HyperV machine work on the same switch.

My VM's run on both my workstation VLAN/SUBNET (192.168.0.0/24) and on a VM only subnets (192.168.100.0/24 192.168.101/24)

There has been no power or internet loss at the location that hosts the server hardware, the HyperV server simply stopped communicating with anything outside the 192.168.0.0/24 subnet.

A tracert to my RAS server stops at the router (192.168.0.10) and goes no further, all pings to and from any other subnets just time out.

ROUTE PRINT

Network Destination        Netmask          Gateway       Interface  Metric
          0.0.0.0          0.0.0.0     192.168.0.10      192.168.0.3    261
        127.0.0.0        255.0.0.0         On-link         127.0.0.1    306
        127.0.0.1  255.255.255.255         On-link         127.0.0.1    306
  127.255.255.255  255.255.255.255         On-link         127.0.0.1    306
      192.168.0.0    255.255.255.0         On-link       192.168.0.3    261
      192.168.0.3  255.255.255.255         On-link       192.168.0.3    261
    192.168.0.255  255.255.255.255         On-link       192.168.0.3    261
        224.0.0.0        240.0.0.0         On-link         127.0.0.1    306
        224.0.0.0        240.0.0.0         On-link       192.168.0.3    261
  255.255.255.255  255.255.255.255         On-link         127.0.0.1    306
  255.255.255.255  255.255.255.255         On-link       192.168.0.3    261

Persistent Routes:
  Network Address          Netmask  Gateway Address  Metric
          0.0.0.0          0.0.0.0     192.168.0.10  Default

LOGS FROM ROUTER

Mar 16 15:28:08 EXGA-FIREWALL-001 kernel: IPv4: martian source 192.168.0.3 from 0.0.0.0, on dev eth0
Mar 16 15:28:08 EXGA-FIREWALL-001 kernel: ll header: 00000000: 01 00 5e 00 00 01 e0 b9 e5 99 40 5e 08 00        ..^.......@^..
  • broadcom Nics? Try disabling VMQ. Hyper-V+Broadcom can result in weird network problems. serverfault.com/search?q=vmq+hyper-v+broadcom Also make sure you have updated firmware and drivers. – Zoredache Mar 15 '17 at 23:37
  • Unfortunately they are INTEL Nics, never had an issue with them in the past, maybe had it running for 3+ years now – Hampkade Mar 15 '17 at 23:40
  • Please provide a route print output from the server. I suspect a bad 0.0.0.0 route – yagmoth555 Mar 16 '17 at 1:34
  • I added the route print to the question – Hampkade Mar 16 '17 at 2:21
  • A tracert to my RAS server stops at the router (192.168.0.10) and goes no further, all pings to and from any other subnets just time out.... ummm, so have you looked at the logs in that router, have you power cycled that router? Don't overlook the obvious and eliminate the simple problems from being the cause too. Get the issue with the PC that is hosting the VM's resolved and the rest should be resolved too I assume but check the router, it's logs, etc. Bypass that router and see what happens, just start following the hops man, troubleshooting 101. – Pimp Juice IT Mar 16 '17 at 4:44
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Sounds like a DHCP lease may have expired - verify that your VM host (the Hyper-V system) is using either a Static IP, or a Reserved DHCP IP (which ensures it gets the same IP every time it renews lease).

If there are any other DHCP servers on the network besides your router, make sure they're disabled or isolated - you don't want your systems pulling addresses from them and causing overlaps or orphaned systems. Since you're using three class C subnets, you'll need to make sure they can all route to/from each other properly, and that systems in one subnet aren't getting IP's from one of the other subnets (keep your scopes separated)

Lastly, check your routing tables. If the routes to world+dog got corrupted, then you are likely routing requests outside your local network to an IP that simply isn't connected to your network, which would cause the behavior you're seeing. Check your gateway IP's and subnet masks as well.

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  • The server runs on a static IP address, gateway is correct and so is the subnet mask, the routing tables appear to be absolutely fine. – Hampkade Mar 15 '17 at 23:13
  • OK, so next you need to give the router the critical once-over. Firewall rules, forwarding, ARP cache... shoot, I'd just bounce it and then see how things behave once it's restarted. – George Erhard Mar 17 '17 at 15:43
  • I have restarted the server and router, cleaned the ARP and NAT tables on both, triple checked the firewall rules and made sure both router and server had the latest updates. Still no success in getting it working. – Hampkade Mar 18 '17 at 4:13
  • OK. Let's break this down logically. You've got three subnets, two just for your VM's, and one for your hypervisor and your VM's together. Because the hypervisor's NIC is used as a virtual switch for the VM's, it's basically both a NIC and a passthru. How are these three nets connected, via the router? Or does the hypervisor communicate to the VM's within its own local subnet? I'm trying to think about how these talk to each other, and how traffic flows from one to the next. – George Erhard Mar 20 '17 at 20:29
  • All the traffic from the HyperV Server goes out and in on one port on a switch, and then any traffic that needs to be routed across the subnets goes to my firewall/gateway – Hampkade Mar 20 '17 at 22:44

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