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Network interfaces

Declare a MicroVM's virtual network interfaces like this in its NixOS configuration:

{
  microvm.interfaces = [ {
    type = "tap";

    # interface name on the host
    id = "vm-a1";

    # Ethernet address of the MicroVM's interface, not the host's
    #
    # Locally administered have one of 2/6/A/E in the second nibble.
    mac = "02:00:00:00:00:01";
  } ];
}

type = "user"

User-mode networking is only provided by qemu and kvmtool, providing outgoing connectivity to your MicroVM without any further setup.

As kvmtool seems to lack a built-in DHCP server, additional static IP configuration is necessary inside the MicroVM.

type = "tap"

Use a virtual tuntap Ethernet interface. Its name is the value of id.

Some Hypervisors may be able to automatically create these interfaces when running as root, which we advise against. Instead, create the interfaces before starting a MicroVM:

sudo ip tuntap add $IFACE_NAME mode tap user $USER

Note: add multi_queue to this command line if the VM is configured with more than one CPU core.

When running MicroVMs through the host module, the tap network interfaces are created through a systemd service dependency.

Extend the generated script in the guest configuration like this:

microvm.binScripts.tap-up = lib.mkAfter ''
  ${lib.getExe' pkgs.iproute2 "ip"} link set dev 'vm-ixp-as11201p' master 'ixp-peering'
'';

type = "macvtap"

MACVTAP interfaces attach to a host's physical network interface, joining the same Ethernet segment with a separate MAC address.

Before running a MicroVM interactively from a package, do the following steps manually:

# Parent interface:
LINK=eth0
# MACVTAP interface, as specified under microvm.interfaces.*.id:
ID=microvm1
# Create the interface
sudo ip l add link $LINK name $ID type macvtap mode bridge
# Obtain the interface index number
IFINDEX=$(cat /sys/class/net/$ID/ifindex)
# Grant yourself permission
sudo chown $USER /dev/tap$IFINDEX

When running MicroVMs through the host module, the macvtap network interfaces are created through a systemd service dependency. Per interface with type = "macvtap", a link attribute with the parent interface, and mode attribute for the MACVTAP filtering mode must be specified.

type = "bridge"

This mode lets qemu create a tap interface and attach it to a bridge.

The qemu-bridge-helper binary needs to be setup with the proper permissions. See the host module for that. qemu will be run without -sandbox on in order for this contraption to work.