Trying to understand relationship between Xinetd and Netcat

Quick question. We have a xinetd entry that calls a script for
service/port x/123. In the script a tunnel is started and then netcat
is called by the following to redirect traffic from port 123 to 3322:
nc localhost 3322

I know that netcat is redirecting traffic to localhost:3322, but how
does IT know to redirect traffic from port 123 to netcat. After this
is started I can see that netcat is started by ps -ef but it only
shows "nc localhost 3322". How does netcat know to listen on port
123. If it didn't know this then it should forward all traffic to
localhost:3322.

Any help is greatly appreciated,
Brian

"cooper" schrieb
> Quick question. We have a xinetd entry that calls a script
> for service/port x/123. In the script a tunnel is started
> and then netcat is called by the following to redirect traffic
> from port 123 to 3322:
> nc localhost 3322
>
> I know that netcat is redirecting traffic to localhost:3322,
> but how does IT know to redirect traffic from port 123 to netcat.
> After this is started I can see that netcat is started by ps -ef
> but it only shows "nc localhost 3322". How does netcat know
> to listen on port 123. If it didn't know this then it should
> forward all traffic to localhost:3322.
>
netcat does not know, inetd(*) does. inetd is a wrapper that listens
on a port and starts a program according to its configuration.
The program that is started reads from stdin and writes to stdout,
it is not aware that the input is coming from / going to the net.

IMHO
Martin

(*) AFAIK xinetd behaves the same way.

On Fri, 14 Dec 2007 11:31:00 -0800, cooper wrote:

> Quick question. We have a xinetd entry that calls a script for
> service/port x/123. In the script a tunnel is started and then netcat
> is called by the following to redirect traffic from port 123 to 3322: nc
> localhost 3322
>
> I know that netcat is redirecting traffic to localhost:3322, but how
> does IT know to redirect traffic from port 123 to netcat. After this is
> started I can see that netcat is started by ps -ef but it only shows "nc
> localhost 3322". How does netcat know to listen on port 123. If it
> didn't know this then it should forward all traffic to localhost:3322.
>
> Any help is greatly appreciated,
> Brian

I'm not sure what your doing exactly... and since you can do port
forwarding ( seems like that is what you are doing ) with xinetd...
I really don't know what your doing...

Anyway... xinetd ( and inetd ) are servers that listen on specified
ports. When a tcp socket connection is made to one of these ports,
they accept the incoming connection and they start a program
( or do something like port forwarding in the case of xinetd )

It's the responsibility of the program to know what to do with the
incoming data and when it sends data, it gets passed to xinetd ( or
inetd ) and back to the client.... something like that.

if you want to do simple port forwarding with xinetd... say that
port 444 is open / available and you want connections to pubic_ip:444
-> private_ip:123 then you'd do something like:

service 444
{
flags = REUSE
socket_type = stream
protocol = tcp
wait = no
user = root
redirect = 192.168.1.1 123
disable = no
}

( this probably won't work as is... but it's something like this.

Not sure what your doing special / different with nc.

jack

--
D.A.M. - Mothers Against Dyslexia

see http://www.jacksnodgrass.com for my contact info.

jack - Grapevine/Richardson