Re: [dtn-users] A problem with dtntunnel

["Zoller, David A. (MSFC-EO60)[HOSC SERVICES CONTRACT]" <[e-mail]>]

Hi Sergey,
I would not even call this a problem. netcat is designed to be extremely flexible and by default the sender keeps its connection open as long as the other end does. On the other hand the receiver by default terminates after receipt of an EOF but there is a switch to keep listening if that is the desired behavior.

With DTN, your sending nc may do its thing while the destination node is not even on line and then an hour later it becomes available and completes the transmission to the receiving nc. In this scenario, the sender would still be "hung up" possibly indefinitely waiting for a terminating signal.

I am not the DTN2 authority, but, I don't see a change to dtntunnel for this as it would assume a specific usage that would probably break someone else's usage (like mine :)).

Best regards,
DZ

David Zoller
COLSA Corporation
Marshall Space Flight Center

From: [e-mail] [mailto:[e-mail]]
Sent: Wednesday, December 05, 2012 2:56 AM
To: Zoller, David A. (MSFC-EO60)[HOSC SERVICES CONTRACT]
Cc: [e-mail]
Subject: Re: [dtn-users] A problem with dtntunnel

Hi David,

Thanks for your help, nc -w1 did the trick. But shouldn't dtntunnel behavior be changed? The receiving dtntunnel could signal the sending dtntunnel, that the listening nc has disconnected, so that the sending dtntunnel close its connection to the sending nc. Or is this solely the problem of nc?
2012/12/5 Zoller, David A. (MSFC-EO60)[HOSC SERVICES CONTRACT] <[e-mail]<mailto:[e-mail]>>
Hi Sergey,
On RHEL 5.7, I am running dtn-2.9.0 plus modifications that should not impact the behavior of dtntunnel.
I just ran your test without the iptables redirect and I see the same behavior.
I believe that the sender exits if you go directly from nc to nc because the receiver exits when it gets an end of file.
You can add a "-w 1" option to the sender nc so that it will timeout and exit after stdin is idle for 1 second.
Best regards,
DZ

David Zoller
COLSA Corporation
HOSC / C107
*Office: [phone]
*EMail: [e-mail]<mailto:[e-mail]>

From: [e-mail]<mailto:[e-mail]> [mailto:[e-mail]<mailto:[e-mail]>] On Behalf Of [e-mail]<mailto:[e-mail]>
Sent: Tuesday, December 04, 2012 11:13 AM
To: [e-mail]<mailto:[e-mail]>
Subject: [dtn-users] A problem with dtntunnel

Hello all!

I am using dtn-2.9.0 on a RHEL 6 based Linux distro and I am having a problem when using netcat (nc) with dtntunnel.
On the sender node I run "cat /etc/passwd | nc receiver_ip". On the receiver node I run "nc -l 9999". With the help
of Iptables port 9999 gets redirected to the port 19999, which is listened by dtntunnel.

The file /etc/passwd is successfully delivered to the receiver and is shown on the screen. After this the receiving nc exists.
No problem here. However, nc on the sender node doesn't exit after it sends the file. It continues to run forever. When I
run nc in the opposite direction, I get the same problem - the sending nc doesn't exit.

My configuration on both nodes is symmetric:
iptables -t nat -A OUTPUT -d $REMOTE_HOST -p tcp --dport 9999 -j DNAT --to $LOCAL_HOST:19999
dtntunnel -T $LOCAL_HOST:19999:$REMOTE_HOST:9999 $REMOTE_NODE/dtntunnel/nc -d
dtntunnel -L --local-eid $LOCAL_NODE/dtntunnel/nc -d

dtnping works ok in both directions.

Please give me any advice.

With best regards,
Sergey Sireskin



--
Kindest Regards

Sergey Sireskin
FGUP CNII EISU