[Qemu-devel] user-net -redir working?

[Qemu-devel] user-net -redir working?

[Richard Neill]

Does the user-net redirection for tcp actually work?
I have been unable to make it work at all!

I've tried  several different host machines (all Linux, different 
versions of Qemu from 0.6.1 to 0.7.2), and different guests (Win98 and 
Knoppix). But it doesn't work. Eg:

qemu -cdrom /dev/cdrom -boot d -user-net -redir tcp:2300::2301

In Guest (knoppix):
   netcat -l -p 2301

On Host:

   netcat localhost 2300

   This connection is accepted (Netcat doesn't say connection refused), 
but then no data is ever transferred.


Could someone confirm whether
   a)I am being an idiot
   b) -redir is actually broken
   c) something is extremely weird in my setup.

Thanks for your help,

Richard

Re: [Qemu-devel] user-net -redir working?

[John R. Hogerhuis]

On Sun, 2005-11-20 at 22:45 +0000, Richard Neill wrote:

> qemu -cdrom /dev/cdrom -boot d -user-net -redir tcp:2300::2301
> 
> In Guest (knoppix):
>    netcat -l -p 2301
> 
> On Host:
> 
>    netcat localhost 2300
> 
>    This connection is accepted (Netcat doesn't say connection refused), 
> but then no data is ever transferred.
> 
> 
> Could someone confirm whether
>    a)I am being an idiot

Without more data, I'd vote for (a). It sounds like netcat is behaving
normally to me. Since you are typing this at the prompt, netcat is
dutifully waiting for you to type something to send over the link.

Perhaps if you type something on the client side and hit <ENTER>? Then
see if it shows up on the server side.

If you don't get any output on the server side, a network sniffer
(tcpdump) on both sides of the connection should be illuminating.

Later,

-- John.

Re: [Qemu-devel] user-net -redir working?

[André Braga]

Disabling the Nagle algorithm (i.e., enabling TCP_NODELAY) or typing a
lot of garbage just to fill the buffer with enough data can help,
also.

And IIRC, netcat has a UDP mode as well. I see no reason for this to
happen, but is there any chance it's using UDP by default, and you're
only redirecting TCP?

Good luck!


--
"The user-friendly computer is a red herring. The user-friendliness of
a book just makes it easier to turn pages. There's nothing
user-friendly about learning to read."
-Alan Kay


On 11/21/05, John R. Hogerhuis <jhoger@pobox.com> wrote:
> On Sun, 2005-11-20 at 22:45 +0000, Richard Neill wrote:
> >    This connection is accepted (Netcat doesn't say connection refused),
> > but then no data is ever transferred.
[8<]
> Without more data, I'd vote for (a). It sounds like netcat is behaving
> normally to me. Since you are typing this at the prompt, netcat is
> dutifully waiting for you to type something to send over the link.
>
> Perhaps if you type something on the client side and hit <ENTER>? Then
> see if it shows up on the server side.
>
> If you don't get any output on the server side, a network sniffer
> (tcpdump) on both sides of the connection should be illuminating.
>

[Qemu-devel] user-net -redir working?

[Richard Neill]

[-- Attachment #1: Type: text/plain, Size: 1696 bytes --]


Re: User-net not working:

> Disabling the Nagle algorithm (i.e., enabling TCP_NODELAY) or typing a
> lot of garbage just to fill the buffer with enough data can help,
> also.
> 
> And IIRC, netcat has a UDP mode as well. I see no reason for this to
> happen, but is there any chance it's using UDP by default, and you're
> only redirecting TCP?
> 
> Good luck!

Thanks for your message.

I think that -redir really is broken: I've also been unsuccessful in 
trying to make it work using an FTP server on a Windows guest, and using 
the SSH server on a knoppix guest. Has anyone here ever had success with 
it? It also fails on hosts with 2 different versions of Mandrake.

Anyway, I've taken your suggestion, and run both ends with ethereal. 
Here's what I did:


HOST (Linux);
   qemu -cdrom /dev/cdrom -boot d -user-net -redir tcp:2200::22

GUEST (Knoppix):
   Boot up, then start sshd. Verify that I can indeed do ssh
   root@localhost, and that PermitRootLogin is yes in sshd_config.

    Then, start ethereal (on the "any" interface)


HOST:
   Start ethereal (on the "any" interface")
   ssh -p 2200 root@localhost

  At this point, ssh just stalls. It's obviously waiting for something,
  but not known what. I get no output at all from it.


End of experiment.

ETHEREAL on HOST is showing a series of empty packets:

    SYN
    SYN
    ACK
    FIN
    ACK
    FIN
    ACK
    [repeats]


  ETHEREAL on GUEST is showing a series of empty packets, all of which 
are SYN.

I have no problem in making an outgoing connection from the GUEST to the 
  HOST.


I'm attaching both log files - they are only 2.5 kB

Any ideas? Has anyone succesfully used the user-net -redir option?


Richard

[-- Attachment #2: ethereal.guest.log --]
[-- Type: application/octet-stream, Size: 1506 bytes --]

[-- Attachment #3: ethereal.host.log --]
[-- Type: application/octet-stream, Size: 1064 bytes --]

Re: [Qemu-devel] user-net -redir working?

[Juergen Keil]

> I think that -redir really is broken: I've also been unsuccessful in 
> trying to make it work using an FTP server on a Windows guest, and using 
> the SSH server on a knoppix guest. 

...

> HOST:
>    Start ethereal (on the "any" interface")
>    ssh -p 2200 root@localhost

Try to use the host's real ip address, not the 127.0.0.1 localhost address.

Re: [Qemu-devel] user-net -redir working?

[Ben Taylor]

[-- Attachment #1: Type: text/plain, Size: 1705 bytes --]

Richard Neill <rn214@hermes.cam.ac.uk> wrote:
> 
> Re: User-net not working:
> 
> > Disabling the Nagle algorithm (i.e., enabling TCP_NODELAY) or typing a
> > lot of garbage just to fill the buffer with enough data can help,
> > also.
> > 
> > And IIRC, netcat has a UDP mode as well. I see no reason for this to
> > happen, but is there any chance it's using UDP by default, and you're
> > only redirecting TCP?
> > 
> > Good luck!
> 
> Thanks for your message.
> 
> I think that -redir really is broken: I've also been unsuccessful in 
> trying to make it work using an FTP server on a Windows guest, and using 
> the SSH server on a knoppix guest. Has anyone here ever had success with 
> it? It also fails on hosts with 2 different versions of Mandrake.
> 
> Anyway, I've taken your suggestion, and run both ends with ethereal. 
> Here's what I did:
> 
> 
> HOST (Linux);
>    qemu -cdrom /dev/cdrom -boot d -user-net -redir tcp:2200::22
> 
> GUEST (Knoppix):
>    Boot up, then start sshd. Verify that I can indeed do ssh
>    root@localhost, and that PermitRootLogin is yes in sshd_config.
> 
>     Then, start ethereal (on the "any" interface)
> 
> 
> HOST:
>    Start ethereal (on the "any" interface")
>    ssh -p 2200 root@localhost
> 
>   At this point, ssh just stalls. It's obviously waiting for something,
>   but not known what. I get no output at all from it.


Can you try "ssh -p 2200 root@<my IP address not localhost>

I've run into this several times dealing with the -redir
function, especially since localhost resolves as 127.0.0.1.
On my Solaris host with a linux guest, the packet arriving
showed up as 127.0.0.1, which ended up with the same
behavior as you're describing.


Ben

[-- Attachment #2: ethereal.guest.log --]
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[-- Attachment #3: ethereal.host.log --]
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[-- Attachment #4: reply --]
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