Running FreeBSD / OpenBSD / NetBSD as a virtualised guest on

I’ve been running a mixture of FreeBSD / OpenBSD & NetBSD as guests on a dedicated server at While getting the operating systems installed was fairly seamless, getting networking going was not.

  1. Client are not isolated in a layer 2 domain
  2. DHCPv6 config is broken

Clients not being isolated is not so much a problem itself and is typically what you’d expect if you plugged a bunch of computers into a switch with a single VLAN or unmanaged switched for example; but in a shared environment with untrusted tenants it can cause problems. Broadcast & IPv6 multicast floods aside, one is open to most of the attacks in something like THC-IPv6 due to lack of MLD snooping which would prevent a rogue IPv6 router.

Attacks via IPv6 are not so much of a problem as their use of non-RFC complaint timers settings in their DHCPv6 make it unfeasible to use the offered native IPv6 connectivity as clients will fail to renew leases. Depending on the DHCPv6 client used, the amount of time it takes fail to renew a lease will vary. dhcpcd for example now warns if detects a lease is not compliant with RFC 3315 section 22.4 “Identity Association for Non-temporary Addresses Option”.

Despite having a vast address range in IPv6 and a /48 subnet is allotted free of charge, you’ll need the equal amount of v4 address addresses as the v6 addresses you intend to use at There is a way of using a /48 and allocating addresses yourself but it’s only possible using a version of Proxmox which they provide.

You can save yourself a lot of hassle both with configuration & trying to deal with their support  regarding IPv6 by using a Hurricane Electric tunnel. I actually found connectivity was also faster from Hurricane Electric than using the native connectivity.

For IPv4 connectivity on a guest (assuming you’re renting individual IP addresses & not a /27 prefix), you’ll need to use the default gateway IP address assigned to your host alongside the allotted IP address and a /32 prefix.

Assuming the network details are as follows
Default gateway on host:
Failover IP #1:, assigned to MAC address 00:50:56:00:01:AA
Failover IP #2:, assigned to MAC address 00:50:56:00:02:BB
Failover IP #3:, assigned to MAC address 00:50:56:00:03:CC

The MAC addresses need to be assigned to the tap(4) interface on the host.
If you’re using bhyve and your guest is using the interface tap0, this would be performed using the -s flag to configure the virtual PCI ethernet card, eg -s 1:0,virtio-net,tap0,mac=00:50:56:00:01:AA

It’s then onto configuring each OS to handle a gateway which is in a another subnet for IPv4 connectivity.


In FreeBSD you need to construct a route to reach the default IP address first, before you specify the default IP address, otherwise things will not work. So assuming we’re going to use Failover IP #1, your configuration in /etc/rc.conf would be as follows

static_routes="gateway default"
route_gateway="-host $gateway_ip -interface $gateway_if"
route_default="default $gateway_ip"

Note, the installer at present prevents network installs, you should use a iso image containing the distfiles, bug 206355 has more details.


On NetBSD, configure networking using /etc/netstart.local, entering the commands you’d enter at the console inside the file. Assuming failover IP #2 is going to be used for the NetBSD VM, the following would configure the guest to reach the outside world using, as discussed in the NetBSD Network FAQ

ifconfig vioif0
route add -net -link -cloning -iface vioif0
route add default -ifa


On OpenBSD, configure the networking from the ethernet interfaces configuration file hostname.if(5).

Assuming failover IP #3 is going to be used for the OpenBSD VM, the following will setup networking.


inet NONE
!/sbin/route add -net -netmask -link -cloning -iface vio0
!/sbin/route add default -ifa

It’s also possible to not specify the -cloning flag but a patch is required if you’re running 5.9 release.