secnet: "IP"-over-DNS transport

[Ian Jackson]

FYI I am working on a series which will allow secnet to use DNS as a
transport mechanism.  That is:
 * secnet will be able to be a stunt DNS server (obv. it will
   need an IP address to which it can bind to :53, appropriate
   delegations)
 * secnet will be able to be a stunt DNS client

So far so good.  These are new "comm"s.  On clients you'd configure a
comm list including (a) the normal udp comm (b) the stunt dns client
comm.  The server would have both comms and the clients would be
recorded as mobile.

I think that part of this will have to be a way to tell secnet to
switch into and out of this mode.  That is, I will have to invent a
control socket interface.  Thinking about this, I propose to invent a
new kind of closure to which everything can register itself.  The
control socket would be AF_UNIX line-based commands, suitable for
nc.openbsd or dedicated clients.  

At the moment I imagine the only command would be "site such-and-such,
switch to comm index N" or "all sites, switch to comm index N".

Opinions welcome.

Ian.