[OpenAFS] rxtcp, rxutcp

[Jim Rees]

  Unfortunately, switching to tcp will not solve your NAT problems.
  NATs drop their mappings from internal addr/port to external port
  equally for both both udp and tcp.

I don't believe that's true for most nats.  The one I use at home has a one
day timeout for tcp, and 60 seconds for udp.  Linksys firewall/routers have
a two hour tcp timeout, and much shorter udp (I don't know the exact
number).  I suspect most commercial nats are similar.  I've seen timeouts as
short as 30 seconds for udp.

There is apparently a protocol called something like "nat upnp" that some
gnutella clients use to set up service mappings on nat boxes.  Last time I
looked at it, I thought using it for afs would be killing a flea with a
sledgehammer, but maybe we should look into it.