CHAPTER 14

Managing Virtual Networks

8 sections · 12 min read · SimpleVM 10.1

This chapter explains how to manage SimpleVM virtual networks — the network paths the SimpleVM host provides to virtual machines. A virtual network sits between a VM’s network interface and the host networking stack, and it determines how a VM reaches other VMs, the host, and the outside world. In the management interface, virtual networks live on the Networks page, reached from Virtual machines — not from the host Networking page. The distinction matters: a virtual network governs how VMs connect, while host networking governs the host’s own physical and bridge interfaces. SimpleVM ships with one virtual network — the default NAT network — that is ready to use immediately, and most deployments need nothing more. The habit this chapter encourages is the one that keeps any network change safe: know a network’s addressing and forwarding, and which VMs depend on it, before you change it.

Cross-reference: For signing in to the management interface, see Section 6.5, Sign In with Administrative Access. For attaching a VM’s interface to a network, see Section 10.2, Attaching VMs to Virtual Networks; for choosing a network while creating a VM, see Section 8.6, Configuring Virtual Networks. For the host’s own interfaces, bridges, DNS, and hostname, see Chapter 15, Managing Host Networking. For how the firewall treats VM network traffic, see Chapter 16, Firewall and Security Settings.

This chapter at a glance. The sections below move from the network that already exists to the networks you create:

• Understand virtual networks — what a virtual network is and where it sits relative to VM interfaces and host networking (Section 14.1).
• Use the default NAT network — the ready-to-use network that suits most VMs (Section 14.2).
• Manage addressing — DHCP ranges (Section 14.3) and static host entries that reserve an address for a VM (Section 14.4).
• Create and edit networks — add a separate network for a lab or workload, and change one safely (Sections 14.5 and 14.6).
• Connect VMs — point a VM at the right network (Section 14.7).
• Best practices — keep virtual networking simple and predictable (Section 14.8).

14.1 Virtual Network Overview

Overview

A virtual network is a network path SimpleVM provides to one or more virtual machines. It sits between the VM network interface and the host networking stack. Depending on its forwarding mode, a VM can use it for outbound access to external networks, for communication with other VMs on the same network, or for isolated traffic that never leaves the host.

In the SimpleVM management interface, virtual networks are managed on the Networks page, reached from Virtual machines (breadcrumb Virtual machines > Networks, URL /machines#/networks). This is a different place from the host Networking page, and the difference is the point: a virtual network controls how VMs connect; host networking controls the host’s own interfaces.

14.2 Default NAT Network

Overview

SimpleVM includes one virtual network out of the box, named default. It uses NAT forwarding, which lets VMs reach external networks through the host while staying behind it from the upstream network’s point of view. The default network is the right starting point for most new VMs because it needs no changes to the physical switch, VLANs, or upstream router — it suits operating system installation, testing, patching, and general outbound access. Its confirmed values are below.

Before you begin

• You are signed in to the SimpleVM management interface with administrative access. See Section 6.5, Sign In with Administrative Access.

Procedure

1. Open Virtual machines from the left-navigation menu.
2. Select Networks to open the Networks page.
3. Locate the default network in the list.
4. Select the expander (⌄) on the default row to expand it.
5. Review the General, IPv4 address, and DHCP Settings sections.

Verification

• The Networks list shows the default network with Device virbr0.
• The State shows active.
• The Forwarding mode shows NAT.
• Autostart shows Run when host boots enabled, so the network returns after a host reboot.

14.3 DHCP Ranges

Overview

A DHCP range is the set of addresses a virtual network can assign automatically to the VMs attached to it. When a guest is configured to obtain its address automatically, it requests one from the DHCP service of its virtual network. On the default network the range is 192.168.122.2 – 192.168.122.254 within 192.168.122.1/24.

Before you begin

• You are signed in with administrative access. See Section 6.5, Sign In with Administrative Access.
• You know which VMs use the network whose range you are reviewing.

Procedure

1. Open Virtual machines > Networks.
2. Expand the virtual network you want to review, such as default.
3. Under DHCP Settings, read the Range value.
4. Confirm the range does not overlap with addresses you assign statically inside guests on the same network.

Administrator verification from the host

Current leases and the live network configuration can be confirmed from the web terminal or an SSH session — useful when a guest is not receiving the address you expect. The web terminal opens as the signed-in administrative user (svmadmin), not root, so prefix commands that need elevated privileges with sudo.

14.4 Static Host Entries

Overview

A static host entry reserves a specific IP address for a VM while the guest stays on DHCP. It associates the VM interface’s MAC address with a chosen address inside the network’s range, so the VM consistently receives that address without static configuration inside the guest. The default network has no static host entries by default; the Networks page exposes an add entry control under Static host entries.

Before you begin

• Identify the VM that needs a reserved address.
• Record the MAC address of the VM network interface. See Section 10.1, Viewing VM Network Interfaces.
• Choose an address within the network’s range that is not already in use.
• Plan a brief maintenance window if the VM is running and connectivity matters.

Procedure

1. Open Virtual machines > Networks.
2. Expand the virtual network the VM uses.
3. Under Static host entries, select add entry.
4. Enter the VM interface MAC address and the IP address to reserve.
5. Save the entry using the dialog’s confirmation button.
6. Renew the guest’s DHCP lease or restart its network connection if it does not pick up the reserved address automatically.

Verification

• The entry appears under Static host entries for the network.
• The VM receives the reserved address after renewing its lease or restarting its network connection.
• The reserved address is not assigned to any other VM — confirm with virsh net-dhcp-leases default from the host.

Revert this change

• Open Virtual machines > Networks and expand the affected network.
• Locate the static host entry and remove it.
• Renew the guest’s DHCP lease or restart its network connection so it returns to a pool-assigned address.

14.5 Creating Virtual Networks

Overview

Create an additional virtual network when you need to separate VMs from the default network — for example, an isolated lab network, a network with a different DHCP range, or a network dedicated to a group of workloads. Keep the design simple; add separation only when a clear requirement calls for it.

Before you begin

• Decide the purpose of the new network.
• Choose a name that clearly describes the workload or environment, such as lab-net or test-net.
• Choose an IPv4 subnet and DHCP range that do not overlap with existing virtual networks, host networks, or the physical LAN.
• Decide whether the network should start automatically when the host boots.
• If the network must reach the physical LAN directly, review host bridge requirements in Chapter 15, Managing Host Networking, first — a NAT virtual network will not do this.

Procedure

1. Open Virtual machines > Networks.
2. Select Create virtual network.
3. Enter a network name.
4. Select the forwarding mode for the network’s purpose — for example, NAT for outbound access or isolated for host-only traffic.
5. Enter the IPv4 address, netmask, and DHCP range.
6. Choose whether the network starts automatically when the host boots.
7. Review the settings, then select the create/confirm button.

Verification

• The new network appears in the Networks list.
• Its State shows active if it was started during creation.
• It shows the expected forwarding mode and DHCP range.
• A test VM attached to it receives an address from the expected range — confirm with virsh net-list --all and virsh net-info <network> from the host.

Revert this change

• Disconnect or shut down any VMs using the network.
• Open Virtual machines > Networks and open the network’s row menu (⋮).
• Select Deactivate if the network is active.
• Delete the network.
• Confirm no VM still references it.

14.6 Editing Virtual Networks

Overview

Editing a virtual network can change how attached VMs receive addresses and communicate, so treat edits as production-impacting whenever VMs depend on the network. Some properties — autostart and activation state — are low-risk; others — the address range or forwarding mode — affect every attached VM.

Before you begin

• Record the current values you intend to change, so you can restore them.
• Confirm which VMs use the network and whether they can tolerate a brief interruption.
• Plan a maintenance window for any addressing or forwarding change.

Procedure

1. Open Virtual machines > Networks and expand the network you want to edit.
2. Review its state, DHCP range, and static host entries before changing anything.
3. Use the available controls to change autostart, static host entries, or activation state.
4. For an addressing or forwarding change, apply it in a maintenance window and renew or restart affected VM connections afterward.

Verification

• The changed value shows correctly in the network details.
• Attached VMs still show a connected interface and the expected address.
• No unrelated VM lost connectivity.

Revert this change

Return the changed value to its previous setting. If you did not record it, reconstruct it from host backups, screenshots, or administrative notes. If you deleted a network that was still in use, recreate it with the same name, subnet, DHCP range, and forwarding mode, then reconnect the affected VMs; see Section 14.5, Creating Virtual Networks, and Section 14.7, Connecting VMs to Virtual Networks.

14.7 Connecting VMs to Virtual Networks

Overview

A VM uses a virtual network through a VM network interface. You can connect a VM to the default network, move it to another virtual network, or add a second interface for a separate network role. The interface-level workflow lives on the VM detail page and is covered in full in Chapter 10, Managing VM Network Interfaces; this section frames it from the network’s side and points you there.

Before you begin

• Confirm the target virtual network exists and is active.
• Confirm whether the VM can be restarted, in case the interface change requires it.
• Have the interface workflow ready; see Section 10.2, Attaching VMs to Virtual Networks.

Procedure

1. Open Virtual machines and select the VM.
2. Scroll to the Network interfaces section.
3. Select Add network interface for a new interface, or edit an existing one to move it to another network.
4. Choose the target virtual network as the interface source.
5. Keep the default interface model unless a guest operating system or support requirement calls for another.
6. Save with the dialog’s confirmation button.
7. Restart the VM if the interface change requires it.

Verification

• The VM network interface shows the target network as its Source.
• The VM receives an address from the expected DHCP range, unless it is statically configured inside the guest.
• The VM reaches the destinations expected for the network’s mode. For full interface verification, see Section 10.4, Verifying VM Connectivity.

Revert this change

• Open the VM detail page and edit the network interface.
• Change the source back to the previous virtual network, or remove the added interface. See Section 10.3, Changing and Removing Interfaces.
• Restart or reconnect the interface if required, and confirm the VM returns to its previous address and connectivity.

14.8 Virtual Network Best Practices

Overview

Virtual networks should make VM connectivity easier to understand, not harder. Separate workloads only when separation serves a clear purpose.

Recommended practices

• Use the default NAT network for first-time VMs, operating system installation, and basic outbound access.
• Create separate virtual networks for lab, test, or isolated workloads that should not share a VM-side network.
• Use names that describe the purpose of the network.
• Avoid overlapping subnets across virtual networks, host networks, VPNs, and the physical LAN.
• Record DHCP ranges and static host entries before changing them.
• Enable autostart for networks that production VMs require after a host reboot.
• Treat bridged production networking as a host task; plan it from Chapter 15, Managing Host Networking, rather than as a simple virtual-network edit.
• Make addressing and forwarding changes in a maintenance window when production connectivity could be affected.

Troubleshooting quick checks

Command-line checks for support

Use these from the web terminal or an SSH session when the web console does not show enough detail, or when collecting information for support. The web terminal opens as the signed-in administrative user (svmadmin), not root, so prefix commands that need elevated privileges with sudo.