Hosts/Guests cannot access each other (ping: Destination Host Unreachable) but have internet access

Question

Hi,

I have a WS 2019 as a host and two VMs running on the hyper-v, one ubuntu and one windows 7. The host has a network bridge set up, which contains a number of ethernet interfaces (one of which connects to a router that links to the internet) and a virtual switch from hyper-v. The two VMs are connected to this virtual switch (in hyper-v manager, this is set up as an internal switch).

Now the problem is that, although both VMs have external network access (internet), and all other machines on the network can connect with these VMs, the host cannot communicate with either VM. If I ping from the host to either VM or ping from either VM to the host, it reports Destination Host Unreachable. Note that DNS works fine but they cannot access each other even using the IP address. Weirdly, this setup had been working perfectly in the past but only very recently stopped working. I really don't know what has happened.

Troubleshooting steps performed include: restarting the host, restarting the guests, resetting the network bridge, removing the virtual switch from the bridge and adding it back, deleting the virtual switch and creating another one, disabling the virtual switch and re-enabling it, renewing DHCP lease, and restarting the router. I feel I have run out of ideas. Any help/idea is really appreciated!

Edit 1: I tried to arp -a in the Ubuntu VM and found that the MAC address of the host is "incomplete". arp -a in the Windows 7 VM gives no record of the host, and arp -a in the host gives no record of either of the VMs.

Answer 1

Hi ,

In Hyper-V, we always don't recommend to bridge the Virtual Switch adapter with physical network adapters in the host. The correct way to implement networking in Hyper-V for VM communication and internet is to create an external Virtual Switch.

If you want to virtual machines to be isolated behind a single shared IP address on the host, then you can create a NAT virtual switch. NAT Virtual Switch allows virtual machines to have an internal network and have internet access.

As picture below:

For how to configure a NAT Virtual Switch with Hyper-V, you can refer to the following article:

Using a NAT Virtual Switch with Hyper-V

Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.

Best Regards,

Candy

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Answer 2

The firewall profile in use may be blocking.

reason why I used an internal virtual switch instead of an external one is that I have this network bridge --seems that when the physical NIC is already assigned to the Bridge, an external virtual switch binding to this NIC cannot be created

Something here may help.
https://www.altaro.com/hyper-v/simple-guide-hyper-v-networking/

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Answer 3

I'll assume by "network bridge" you mean a teaming? An internal vSwitch would not allow direct access to the internet. As to ping; you may need to allow ICMP Echo Request (ICMPv4-In) on the firewall profile in use. For trouble shooting might try without the teaming to remove that complication.

When you create a new external vSwitch the internet protocols are removed from the adapter and the Hyper-V Extensible Switch protocol is added turning that physical port into a multi-port virtual switch. Connect your VMs to this vSwitch and use each VM's vEthernet to configure the addressing in the exact same manner as if it were a physical NIC

https://blogs.technet.microsoft.com/jhoward/2008/06/17/hyper-v-what-are-the-uses-for-different-types-of-virtual-networks/

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