Add a virtual network

Libvirt virtual networks connect VM interfaces to NAT, isolated networks, or existing host bridges.

NAT and host bridges #

Mode	Connection	Address assignment
NAT	A separate VM subnet. Outbound IPv4 connections use the host’s address. Inbound connections from the LAN are blocked by default.	Libvirt DHCP, if enabled, or static guest addresses.
Host bridge	An existing Linux bridge. A bridge connected to the physical LAN places VMs on that LAN.	The LAN’s DHCP server or static guest addresses. Libvirt does not add DHCP for this mode.
Isolated	VMs communicate with each other and the host, without forwarding to other networks.	Libvirt DHCP, if enabled, or static guest addresses.

Host bridge mode requires a Linux bridge configured on the host first. Selecting this mode does not create the bridge or move a physical interface into it.

Create an IPv4 NAT network #

Open Networks under VMs and select New network.
Enter a Name and select NAT.
Enable Use IPv4 and check the Subnet and Gateway. Use a subnet that does not overlap the LAN, VPN, or other virtual networks.
Enable Enable DHCP server for automatic guest addresses, then check Range start and Range end.
Under DNS, enable the DNS server if needed. With no forwarders entered, queries use the host’s resolvers.
Enable Start now and Start with the host as needed, then select Create network.

For example, if unused on the host and surrounding networks, 192.168.150.0/24 can use gateway 192.168.150.1 and DHCP range 192.168.150.100 through 192.168.150.200.

Register a host bridge #

Select New network and enter a name.
Select Host bridge and choose the existing Bridge.
Set Start now and Start with the host, then select Create network.

This registers the bridge as a named libvirt network. The host’s bridge configuration and the LAN’s address services remain separate.

Connect a VM #

Creating a network does not attach VM interfaces. Select the network when creating a VM or adding a NIC. Start the network before starting a VM that uses it.

Stop or restart a network #

Stopping a NAT or isolated network removes its managed bridge and DHCP, DNS, and firewall rules. Attached VMs lose connectivity on that network. Restart also interrupts traffic.

Stopping a host bridge network does not delete the Linux bridge.