[OpenAFS] rxtcp, rxutcp

[Jeffrey Altman]

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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.   If the internal peer is not
sending data often enough to the external peer, the mapping will be
dropped and the connection will be broken.

If you are seeing a failure to transmit and receive udp packets
through a device it may very well be due to firewall rules that
block UDP.  However, that is not a NAT issue.

The NAT issues for AFS are caused by the assumption in many of the
RPCs that the port numbers are fixed at their standard values.
Unfortunately, due to NATs this is not true and the file servers
have traditionally not done a good job of following clients when
their addr/port values change.  There has been significant effort
placed into 1.4.1 to make mobile clients work.  Mobile clients
encompass both the clients behind NATs and those that move from address
to address intentionally.

Jeffrey Altman


Adam Megacz wrote:
> Wow, NATs have been giving me a spectacular headache lately.  Turning
> on TCP support on the KDC resolved all the issues with kinit, but
> long-term I'm starting to realize that I just can't rely on UDP as the
> only connectivity method... support out there is just too lousy.
> There's a real need for a "fallback" connectivity method that works
> behind even the lamest NATs (without regard for performance).
> 
> I checked out the rxtcp branch, and I'd like to give it a try, but I
> couldn't exactly find any documentation.  Any pointers on how to try
> it out?  I realize it's not ready for prime time yet.  If I just
> compile it up and install it does it listen for both rxudp and rxtcp
> connections?  How does the client decide which to use when initiating
> a connection?
> 
> Lastly, has anybody considered running the raw "rxudp" protocol with
> TCP headers wrapped around it ("Unreliable TCP" or "rxutcp")?  Nearly
> ever NAT I've seen is stateless aside from connection mappings; as
> long as you send the proper SYN/ACK/SYN+ACK handshake to set up a
> mapping the NAT doesn't care what the packets you send after that look
> like (as long as they have TCP headers).  Specifically, you can throw
> TCP's ack/retransmission algorithm right out the window -- just ignore
> it completely.  I think a bunch of the P2P filesharing programs do this.
> 
> Seems like this would be a really easy hack to get through NATs until
> we have an officially supported rxtcp.  Anybody see any immediate
> barriers to this working?
> 
>   - a
> 

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