Comments on: Howto perform UDP tunneling through SSH connection

By: Jovan Janevski

Jovan Janevski — Wed, 23 Nov 2011 18:41:54 +0000

Agreed, after first DNS query has been questioned and answered nc stops listening on udp port 53.
If I try to add -k then nc would show error help menu.
If I add -w 1 and put it in bash with a while loop I get around 1 DNS query per second which is not good enough.

By: Krypton

Krypton — Tue, 08 Nov 2011 14:46:55 +0000

Has anybody had any luck getting this working with SNMP?

This method looks like its could potentially work but the sting:

nc -l -p 22222 /tmp/fifo

Appears to be too static? Any ideas how to make this address dynamic in such a setup?

By: iBro

iBro — Sat, 03 Sep 2011 20:34:08 +0000

If you only use it occasionally, you can just pipe it through ssh like this:

sudo nc -l -u -p 53 < dnsfifo | ssh user@server.net "/usr/bin/nc -u dns.server.address 53" > dnsfifo

By: iplparm

iplparm — Fri, 11 Mar 2011 20:53:07 +0000

Doesn’t work for me either.

By: nima0102

nima0102 — Sat, 22 Jan 2011 15:54:09 +0000

Hi
First of all thanks for good tricks.
In our scenario I have to forward my traffic on local machine to remote switch for checking snmp object,it’s means forward traffic for port 161.
Only my debian machine has connection to our switches,so I want to check snmp on switches from my local machine.with your scenario I did not have any luck.
My you explain “nc -l -u -p 53 < /tmp/fifo".what does this command do?

Thanks in advance

By: Kevin

Kevin — Thu, 16 Sep 2010 20:04:21 +0000

There is an option to keep listening after the first connection. From the man page:
-k Forces nc to stay listening for another connection after its current connection is completed. It is an
error to use this option without the -l option.

By: SF

SF — Fri, 27 Aug 2010 12:39:08 +0000

I was able to achieve slightly better results with nc.openbsd (although this is not perfect, too).

By: SF

SF — Fri, 27 Aug 2010 11:59:56 +0000

Evr, Jan: it looks that nc is able to handle only 1 connection. If you use netstat you should be able to see that after accepting the first connection the UDP socket is not listening anymore.

So I would say that either this howto is for some other (than ours) nc version, or it is a piece of crap.

By: chris

chris — Mon, 10 May 2010 13:43:36 +0000

the above didn’t show as it should..

basically I was saying that if I split the first “nc” command shown into 2 commands it works but when you put the whole line in I get a usage error

By: chris

chris — Mon, 10 May 2010 13:41:49 +0000

This doesn’t work for me

when I enter the line “nc -l -p 22222 /tmp/fifo”

I get “usage: nc [-46DdhklnrStUuvzC] [-i interval] [-p source_port]
[-s source_ip_address] [-T ToS] [-w timeout] [-X proxy_version]
[-x proxy_address[:port]] [hostname] [port[s]]”

However when I enter the commands seperately like
nc -l -p 22222 /tmp/fifo

neither give me the “usage” error that I get when I put them together with a pipe inbetween.

By: Jan

Jan — Fri, 16 Oct 2009 13:50:57 +0000

I see the same behaviour as describes above by Evr:

I am packing SNMP (UDP) into TCP and unpack on the other side. (I do not use the SSH tunnel, rather I connect directly to the servers port 22222)
The first request is answered correctly, subsequent run into timeouts

By: croco

croco — Mon, 03 Aug 2009 07:46:29 +0000

This howto is simple-minded amazing! I will try to connect an extern teamspeak server with this method. I must check this because i’m behind a great firewall.

By: evr

evr — Fri, 26 Jun 2009 14:30:33 +0000

This is a quiet smart & simple method, but i have a problem : the first DNS request works, but all the next attempts encounter timeouts.
Have you any idea of the origin of the trouble ?
Thanks,