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Hi JY and Chris,

  I remember that, at some point (if I remember correctly) you have been 
interested in the possibility of communicating with an xrootd server 
through ssh tunnels. Since this was one of the latest commits, if you 
want to give a try to it, it's there (in the head).
  Basically it's an implementation of the SOCKS4 protocol in XrdClient. 
What follows is an example of how to use it.

I suppose that I want to access the file

root://kanolb-a.slac.stanford.edu//store/SP/R14/000993/run4/14.4.0c/SP_000993_002423.02E.root

into my laptop in Padova. We know that the kanga cluster at slac is not 
accessible from outside (at least not from here). Here is a trivial 
example of how to do it using a SOCKS4 ssh tunnel and xrdcp.

Step 1: Tunnel localhost-->noric02 mapping the local port 8080 through 
SOCKS4

fabrizio@dhcp-61 15:20:32 ~>ssh -D 8080 [log in to unmask]

Step 2: in another window...

fabrizio@dhcp-61>xrdcp -d 2 -DISocks4Port 8080 -DSSocks4Server 127.0.0.1 
root://kanolb-a.slac.stanford.edu//store/SP/R14/000993/run4/14.4.0c/SP_000993_002423.02E.root 
  ~fabrizio/

and the copy should be ok.
... if you want to shut it up, remove the "-d 2" parameter.
Well, from Europe you will note that the data xfer rate is very low. 
This will hopefully change in December, when we finish implementing the 
multistream stuff.

Please note that the parameter Socks4Server does not understand names 
yet, but IP addresses only.
Another thing that made me crazy. Typically the ssh-tunnelled port (8080 
in the example) is only available from localhost. To override this and 
make it visible also from other hosts, you have to use the "-g" switch 
(for older ssh) or specify */8080 (in the more recent releases of ssh).

Any comment?
Fabrizio