Best netdev for private comms between VNs?

[Daniel Dawson]

I have a couple of VNs that need to communicate through their own 
network. This network needs to not interact with the Internet or, 
ideally, even with the host. I've tried a few different netdevs:

 * socket with listen/connect options: Works okay. However, if I
   understand correctly, it requires the guest that is listening to be
   started first? What happens if that guest is shut down for a while;
   can the connection be reestablished without also restarting the
   other guest? If not, that's a little too inflexible. Also, I don't
   think it works if more than two guests need to use that virtual
   network; correct me if I'm wrong, but my tests of that failed, with
   a third guest not being able to communicate.
 * socket with mcast option: Works with multiple guests, with no issue
   of order. However, this gets default-routed on the host. I'm not
   sure if packets make it to the gateway, considering the address is
   multicast with (I think?) no IGMP, but I don't think this is ideal.
 * bridge: Works great, though requires a bit of setup on the host, and
   packets obviously have to go through a bridge on the host. Maybe
   this is okay, but I want to explore other options.
 * hubport: This looks like it might be good (more lightweight??), but
   I can't figure out how to actually use it properly, and I couldn't
   find any information about how to do so. Whenever I try this with
   hubid != 0, I get a warning that it's "not connected to host
   network" (which is what I want, if possible), and guests with the
   same hubid can't actually communicate. I suppose that something
   extra is required (say, extra configuration to set up the additional
   hub somehow?), but it's not obvious to me. What am I missing?

TIA for any help/advice you can provide.

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