VM Network Access: Can Your Host be Reached?

TL;DR

Yes, a host can usually be accessed when using a VM on a network, but it depends on your network setup and how you’ve configured the VM. This guide explains common scenarios and solutions.

Understanding Network Modes

Virtual Machines (VMs) connect to networks in different ways. The most common modes are:

• Bridged Networking: The VM gets its own IP address on your network, just like any other device.
• NAT (Network Address Translation): The VM shares the host’s IP address and connects to the internet through it.
• Host-Only Networking: The VM can only communicate with the host machine and other VMs on the same host-only network.

Scenario 1: Bridged Networking

If your VM is using bridged networking, accessing it from another device on your network is straightforward.

1. Find the VM’s IP Address: Inside the VM, open a terminal and use the following commands (depending on your operating system):
   • Linux:

     ip addr show

   • Windows:

     ipconfig

2. Ping the VM: From another device on your network, open a command prompt or terminal and ping the VM’s IP address:

   ping [VM's IP Address]

3. Access Services: If you have services running on the VM (e.g., a web server), access them using the VM’s IP address in your browser or other applications.

Scenario 2: NAT Networking

With NAT, the VM is hidden behind the host’s IP address. Direct access isn’t possible without port forwarding.

1. Port Forwarding: Configure your virtualisation software (e.g., VirtualBox, VMware) to forward specific ports from the host to the VM.
   • In VirtualBox, go to Settings > Network > Advanced > Port Forwarding. Add a rule that forwards the desired port on the host to the corresponding port on the VM’s IP address.
   • In VMware Workstation, edit the virtual machine settings and navigate to Network Adapter > NAT > Port Forwarding. Add a new forwarding entry.
2. Access Services: Access services on the VM using the host’s IP address and the forwarded port (e.g., http://[Host's IP Address]:8080 if you forwarded port 8080).

Scenario 3: Host-Only Networking

In this mode, the VM is isolated from your main network.

1. Access from Host: The host machine can usually access the VM directly using a special IP address assigned by the virtualisation software. Check your virtualisation software documentation for details.
2. No External Access: Devices on your external network cannot directly access the VM without additional configuration (e.g., setting up routing or bridging).

Firewall Considerations

Ensure that firewalls on both the host and the VM are not blocking incoming connections to the services you want to access.

• Host Firewall: Check your host’s firewall settings (e.g., Windows Defender Firewall, ufw on Linux) and allow traffic on the necessary ports.
• VM Firewall: Similarly, check the VM’s firewall settings and ensure it allows incoming connections.

Troubleshooting

• Check IP Addresses: Double-check that you’re using the correct IP addresses for both the host and the VM.
• Network Connectivity: Verify basic network connectivity between devices (e.g., pinging the gateway).
• Virtualisation Software Logs: Examine the logs of your virtualisation software for any error messages.