RE: Info on "Can't open display"

["Christopher Landrieu" <landrieu at hotmail dot com>]

>From: "Robert Collins" <robert.collins@itdomain.com.au>
>To: "Christopher Landrieu" <landrieu@hotmail.com>, > -----Original 
>Message-----
> > From: Christopher Landrieu [mailto:landrieu@hotmail.com]
> > To: cygwin-xfree@cygwin.com

> >    - Aventail Connect does not have any affect on non-xfree86
> > local xclients
> > (TeraTermSSH for example).  Therefore, it IS possible to write local
> > xclients that are not impaired by the VPN software.
>
>Do you have any other examples? TeraTermSSH is not an X client. It is an
>SSH client, operates on a single well known port.
>
Actually, it is also behaving as a local xclient when using X Forwarding.  
It tunnels X traffic from the remote machine (DISPLAY=localhost:10.0 on the 
remote host) through the SSH tunnel and redirects it to localhost port 6000 
on the desktop.  In this manner, it is behaving like a local xclient.  It 
doesn't do the actual X Protocol stuff, but it does the TCP/IP stuff and 
gets the X Protocol stuff from the tunnel.

Unfortunately, I don't have any other xclients (other than Cygwin/xfree86) 
to try.  Do you have any recommendations?

> >    - Aventail Connect does not screw up local TCP/IP traffic
> > to server
> > processes running on localhost.  I tested this by running
> > Apache Jakarta's
> > Tomcat 4.0 Beta 1 JSP/Servlet engine on localhost port 8080.
> > This should be
> > equivalent to xfree86 running on localhost at port 6000.  I
> > am able to
> > access JSPs, servlets, and HTML pages at
> > http://localhost:8080 with a local
> > web browser with no problems at all.
>
>Are the requests being made from
>a) an unbound local port,
>b) a local port bound to 127.0.0.1 port ? or
>c) a local port bound to _the ethernet card/modem_ ip address

Aren't all TCP/IP client programs unbound?  They don't choose an individual 
port.  The operating system chooses the client's port.  Thats why the port 
is different each time the client tries to open the connection.  The OS also 
chooses what interface and IP address it should be bound to according to its 
routing table.  Am I wrong here?  Its been a few years since I did much 
socket UNIX programing.  My guess would be that the answer would be "a)" for 
all clients.

>These three things will appear different to Aventail Connect, and it may
>treat them differently.
>This will have bearing on the feasability of changing XFree86 to work
>around your problem.
>Also, for d,e and f the same question applies to the listening server,
>is it bound, unbound and if bound to what address.

My understanding on the server side is that the server can either bind to a 
specific port on a specific interface or it can bind to a specific port on 
all interfaces (loopback, ethernet card, PPP dial-up connection, or what 
have you).  That particular version of Tomcat only allows you to bind all 
interfaces (as opposed to one specific interface).  I would guess that the X 
server does the same, right?  In any case, all servers must bind to a port 
before listening on it, right?  So then e and f are the only posibilities 
for a server application.  In this case Tomcat would be using f and I would 
expect that xfree86 would do the same.

>
> >    - Aventail Connect prevents local xfree86 xclients from
> > displaying on
> > _remote_ X servers.  Yet, no other client TCP/IP programs are
> > affected
> > (telnet, ssh, ftp, etc. - to the same remote host... so
> > networking is fine).
>
>Same two questions as before (local unbound vs local bound 127.0.0.1 vs
>lcoal bound to wire)
>

Same answers (and questions) as before.

> >    - No other applications other than xfree86 xclients are
> > affected by the
> > Aventail Connect software.  Even other cygwin programs, which
> > I expect to
> > use the same networking APIs and features, are _not_ impared
> > by the VPN
> > software.
>
>Thats good to know.
>
> >    - The TCP/IP part of it is working.  I found this by
> > sniffing packets
> > between my win2k machine and a linux box using ethereal.  I ran
> > Cygwin/xfree86's xterm on win2k with the display set to the
> > linux boxes'
> > display (with "xhost +" on the linux box).  I did this with
> > and with out the
> > Aventail Connect config file tweak (so it was successful for
> > one try and
> > failed on the other).  What I found was that the TCP socket
> > is successfully
> > establed in both cases.  But, in the case where the the tweak was not
> > applied (the failed X connect), the win2k machine closed the
> > connection
> > immediately after openning it.  In fact it sent two
> > acknowledgements to the
> > linux boxes' SYN/ACK packet.  The first acknowledgement was
> > simply just an
> > acknowledgement (no other TCP flags set).  The second packet
> > had both ACK
> > and FIN set.  Both packets sent the exact same TCP sequence
> > numbers and
> > acknowledgement numbers (without a "next sequence number").
>
>That sounds to me like Aventail dropping the connection.

What is your reasoning?

> >    - I have experienced no other networking problems with either test
> > machine.
> >
> > Now I at least have a work around for the problem.  However,
> > I still believe
> > that the problem should be fixed and _is_ fixable within
> > Cygwin and/or
> > xfree86.
>
>We cannot work around every vendors bugs :]. True - this may not be an
>Aventail Connect problem but all the indications so far are that it is.
>
><snip logic traing>

But it seems just as likely that it is an Xfree 86 problem as well.  I 
totally agree that other apps' bugs should remain other apps' bugs, but it 
seems like alot of people have been having this same problem... even without 
running VPN software.


I appreciate your comments and questions.

Chris

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