CHAPTER 10

Managing VM Network Interfaces

4 sections · 9 min read · SimpleVM 10.1

This chapter explains how to manage the virtual network interfaces attached to a virtual machine. A virtual network interface is the adapter a VM presents to its guest operating system; it connects the VM to a network source on the SimpleVM host — a virtual network, a host bridge, or another supported source. Interface operations are performed from the VM detail page — the same page used for the VM console, disks, and snapshots — so you can review, attach, change, and remove network connections in the context of the VM that uses them. The most useful habit in this chapter is simple: confirm what an interface is connected to, and what the guest reports, both before and after every change.

Cross-reference: For signing in to the management interface, see Section 6.5, Sign In with Administrative Access. For creating the VM whose interfaces you are managing, see Chapter 8, Creating and Managing Virtual Machines. For the virtual networks an interface can connect to, see Chapter 14, Managing Virtual Networks; for host bridges, see Chapter 15, Managing Host Networking. For disks and snapshots on the same VM detail page, see Chapter 9, Managing VM Disks, and Chapter 11, VM Snapshots.

This chapter at a glance. The sections below follow the network connections of a single virtual machine:

• Review interfaces — read the Network interfaces section to confirm how a VM is connected, what model it presents to the guest, and whether the link is up (Section 10.1).
• Attach to a network — connect a VM to a virtual network or host bridge, or add a second adapter for a separate network role (Section 10.2).
• Change or remove — re-point or reconfigure an adapter, or unplug and remove one deliberately (Section 10.3).
• Verify connectivity — confirm the VM reaches the networks it should, and understand why a displayed IP address may read Unknown (Section 10.4).

10.1 Viewing VM Network Interfaces

Overview

The Network interfaces section of the VM detail page lists every network adapter attached to the VM and how each one is connected. Reading it before you make a change tells you the adapter type, the model presented to the guest, the MAC address, the network source, and whether the link is up — so you know exactly what you are about to modify.

Before you begin

• You are signed in to the SimpleVM management interface with administrative access. See Section 6.5, Sign In with Administrative Access.
• The VM you want to review already exists. See Chapter 8, Creating and Managing Virtual Machines.

Procedure

1. Open Virtual machines from the left-navigation menu.
2. Select the VM you want to review to open its detail page.
3. Scroll to the Network interfaces section.
4. Review each interface's Type, Model type, MAC address, IP address, Source, and State values.

The interface fields report the following:

Verification

• The Network interfaces section lists the VM's adapters.
• Each interface shows the expected Source for the network it should be on.
• An interface that should be connected shows State up.

10.2 Attaching VMs to Virtual Networks

Overview

Attaching a network interface connects a VM to a network source. Use this workflow when a VM needs network access, when you are moving a VM from the default NAT network to a bridged network, or when a VM needs an additional adapter for a separate network role. SimpleVM attaches the adapter and presents it to the guest, but the guest operating system still owns its own address configuration — DHCP or static — once the adapter is connected.

Before you begin

• You know which network the VM should use, and whether it should use DHCP or a static address.
• The target virtual network or host bridge already exists and is active. See Chapter 14, Managing Virtual Networks, for virtual networks, and Chapter 15, Managing Host Networking, for host bridges.
• For bridged networking, the host bridge is configured correctly first.

Procedure

1. Open Virtual machines and select the VM.
2. In the Network interfaces section, select Add network interface.
3. Select the network source — for example, a virtual network or a host bridge.
4. Select the model type if the dialog offers a choice.
5. Select the confirmation button shown by the dialog — for example, Add or Plug.
6. Configure the guest operating system's network settings (DHCP or static) if required.

Verification

• The new interface appears in the Network interfaces section with the expected Source.
• The interface shows State up when it is active.
• The guest receives the expected address from the network's DHCP range, or uses its configured static address.
• The VM can reach the destinations expected for that network. See Section 10.4, Verifying VM Connectivity.

Revert this change

If the interface was added by mistake, unplug and remove it; see Section 10.3, Changing and Removing Interfaces. If you changed the guest operating system's network settings, restore the previous guest configuration as well.

10.3 Changing and Removing Interfaces

Overview

Changing an interface re-points or reconfigures an existing adapter; removing an interface disconnects the VM from a network. Both can interrupt VM connectivity, and some changes — to the source, model type, or MAC address — may require a VM restart before the guest applies them. The safe path is to record the current settings first, make one change at a time, and verify connectivity afterward.

Before you begin

• You have recorded the interface's current Source, Model type, and MAC address, so you can restore them if needed.
• You have confirmed whether the VM can be restarted, in case the change requires it.
• For a removal, you have confirmed that no service depends on the interface.

Procedure

1. Open Virtual machines and select the VM.
2. In the Network interfaces section, identify the interface to change or remove.
3. To change the interface, select Edit and update the source, model type, or other available settings.
4. To disconnect the interface without removing it, select Unplug. To remove it, open the interface's action menu (⋮) and select the remove option.
5. Apply the change, and restart the VM if the dialog or the guest indicates a restart is required.

Verification

• The changed interface shows the new Source or Model type, or the removed interface no longer appears.
• An interface that should remain connected shows State up.
• The VM receives the expected address and reaches the intended destinations. See Section 10.4, Verifying VM Connectivity.
• No unrelated VM lost connectivity as a result of the change.

Revert this change

Return the interface to its recorded Source, Model type, and MAC address. If you unplugged an interface, plug it back in; if you removed one, add it again and reselect the original source; see Section 10.2, Attaching VMs to Virtual Networks. Restore any guest operating system network settings you changed, and restart the VM if the change required it.

Troubleshooting

If the VM has no connectivity after a change, confirm the interface State is up and the Source is the intended network, then confirm the guest's own network service is running and using the right address. An interface that shows up but passes no traffic usually points to a guest-side address or firewall problem rather than the adapter itself. For broader network problems, see Section 25.6, Network Issues.

10.4 Verifying VM Connectivity

Overview

Verifying connectivity confirms that an interface change actually produced working network access. The web console shows the interface state and, when it can, the guest's IP address — but the most reliable confirmation comes from inside the guest. A key point: the IP address column may read Unknown even when the VM is connected and working normally.

Before you begin

• The interface you want to verify is attached and shows State up. See Section 10.1, Viewing VM Network Interfaces.
• You have access to the guest operating system, through the VM console or a remote session. For the console, see Chapter 8, Creating and Managing Virtual Machines.

Procedure

1. In the Network interfaces section, confirm the interface State is up and the Source is the intended network.
2. Note the IP address the console reports, if any, remembering it may read Unknown.
3. Open the guest operating system and confirm its assigned address — for example, with ip address show on a Linux guest, or ipconfig on a Windows guest.
4. From inside the guest, test reachability to the gateway, to a DNS name, and to the specific destination the VM needs to reach.

Verification

• The guest reports an address on the expected network — the DHCP range for the chosen virtual network, or the configured static address.
• The guest can reach its gateway, resolve names, and reach the intended destination.
• The behavior matches the network's design — a NAT-attached VM reaches the outside world through the host, while a bridged VM appears directly on the host's physical network.

Troubleshooting

If the guest has no address, confirm the interface Source is an active network and that the guest's network service is requesting an address; a wrong source or an inactive virtual network is a common cause. If the guest has an address but cannot reach the outside world, check the network's forwarding mode, the host firewall, and DNS. For step-by-step network diagnosis, see Section 25.6, Network Issues; for the virtual networks themselves, see Chapter 14, Managing Virtual Networks.