X forwarding

X forwarding

Post by Louis L » Sat, 14 Oct 2000 04:00:00



Hi,

Consider I have two machines, machine A which is on the network and
machine B which is a laptop using DHCP (also on the network).  Under
machine A, if I do a "ping B", it will not resolve.  Therefor, if I do
the following from A:

ssh B -f xterm

I get the following error:

xterm Xt error: Can't open display: B:10.0

How do I resolve this problem (besides setting up a DNS server on B)?

Thanx,

 
 
 

X forwarding

Post by Richard E. Silverm » Sat, 14 Oct 2000 04:00:00


    Louis> Consider I have two machines, machine A which is on the network
    Louis> and machine B which is a laptop using DHCP (also on the
    Louis> network).  Under machine A, if I do a "ping B", it will not
    Louis> resolve.  Therefor, if I do the following from A:

    Louis> ssh B -f xterm

If the name B is not usable on A, then how does this work?  Have you made
"B" an alias for the laptop's IP address in your SSH client config file?

    Louis> I get the following error:

    Louis> xterm Xt error: Can't open display: B:10.0

That's not the reason for this error.  xterm is running on B, not A.  If
it's naming problem, that implies that the name "B" does not resolve on B,
either.  But it may not be a naming problem; it could be X authentication,
or perhaps X forwarding wasn't even negotiated.  Run the connection with
"ssh -v ..." to get more information.

    Louis> How do I resolve this problem (besides setting up a DNS server
    Louis> on B)?

First, you find out what the real problem is.  You would not set up a DNS
server on B in any event; that doesn't make any sense.

--
  Richard Silverman


 
 
 

X forwarding

Post by Louis L » Sat, 14 Oct 2000 04:00:00



> If the name B is not usable on A, then how does this work?  Have you made
> "B" an alias for the laptop's IP address in your SSH client config file?

The name is does not resolve due to the dhcp I am using does not send the
host name to the dhcp server (this is another problem I need to resolve).
The reason that I did not put the alias in SSH client config was the ip
changes everytime so I don't want to modify it every time I obtain an ip
address.

Quote:

> That's not the reason for this error.  xterm is running on B, not A.  If
> it's naming problem, that implies that the name "B" does not resolve on B,
> either.  But it may not be a naming problem; it could be X authentication,
> or perhaps X forwarding wasn't even negotiated.  Run the connection with
> "ssh -v ..." to get more information.

You are right.. its not the resolving problem, here's the debug info and I
don't see any X
forwarding negotiation .

ssh -v godzilla -f xterm
SSH Version OpenSSH_2.2.0p1, protocol versions 1.5/2.0.
Compiled with SSL (0x0090581f).
debug: Seeding random number generator
debug: ssh_connect: getuid 1043 geteuid 0 anon 0
debug: Connecting to godzilla [10.1.0.38] port 22.
debug: Seeding random number generator
debug: Allocated local port 954.
debug: Connection established.
debug: Remote protocol version 1.5, remote software version 1.2.27
debug: Local version string SSH-1.5-OpenSSH_2.2.0p1
debug: Waiting for server public key.
debug: Received server public key (768 bits) and host key (1024 bits).
debug: Host 'godzilla' is known and matches the RSA host key.
debug: Seeding random number generator
debug: Encryption type: 3des
debug: Sent encrypted session key.
debug: Installing crc compensation attack detector.
debug: Received encrypted confirmation.
debug: Trying rhosts or /etc/hosts.equiv with RSA host authentication.
debug: Remote: Ignoring wild host/user names in /home/louis/.rhosts.
debug: Remote: Rhosts/hosts.equiv authentication refused: client user
'louis', server user
 'louis', client host '10.1.9.8'.
debug: Server refused our rhosts authentication or host key.

debug: Server refused our key.
debug: Doing password authentication.

/etc/ssh% debug: Sending command: xterm
debug: Entering interactive session.
debug: Sending eof.
xterm Xt error: Can't open display:
debug: Transferred: stdin 0, stdout 37, stderr 0 bytes in 0.4 seconds
debug: Bytes per second: stdin 0.0, stdout 100.0, stderr 0.0
debug: Exit status 1

Any idea?

 
 
 

X forwarding

Post by Etienne Detroi » Sun, 22 Oct 2000 04:00:00



> Hi,

> Consider I have two machines, machine A which is on the network and
> machine B which is a laptop using DHCP (also on the network).  Under
> machine A, if I do a "ping B", it will not resolve.  Therefor, if I do
> the following from A:

> ssh B -f xterm

> I get the following error:

> xterm Xt error: Can't open display: B:10.0

> How do I resolve this problem (besides setting up a DNS server on B)?

Add B to /etc/hosts:

ip.address.for.B        B

Turn on files in nsswitch.conf

hosts:  files dns

 
 
 

1. what is the difference between "local forwarding" and "remote forwarding"???

I an a newbie of SSh.
I just confused with "local forwarding"(ssh -L) and "remote forwarding"
(-R).

Say, I can use ssh -L 2323:ssh-server:23 ssh-server, so i can telnet to
my local host via port 2323, and it tunnels to the ssh-server. It seems
like this command will create a port-listening process at my local
mychine, and forwards data from this port 2323 to the ssh port. At the
ssh server side, data will be forwarded to the port 23, the reponse
from the ssh server will also be forwarded back to my local port 2323.
So in this scenario, i cannot find it is necessary to use "remote
forwarding" because i can already connect to the ssh server in a
secured tunnel.

In which case should I use "remote forwarding"?

thanks.

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