[wplug] ip forwarding on ubuntu

[Tom Fetherston]

 From some advice to help in my troubleshooting a Dicom network transfer 
problem, I've got ubuntu and Wireshark installed on a laptop I plan to 
take with me so I can look at the actual network activity to try and pin 
down what is messing up the customers medical image transfer problems.  
Rather than introducing a hub and monitor things that way, I've 
purchased a expresscard gigabit ethernet module.  According to what I've 
read this should let me monitor the activity between the Dicom pc in the 
x-ray fluro suite and the PACS server in the most transparent fashion.  
Just plug the PACS side of the cable to one port on the laptop and run a 
cable from the second port to the Dicom pc, and then enble ip forwarding 
between the two cards.

The last sentence brings me to my first question, just how do I set up 
ip forwarding under Linux?

I'm also wondering about services running on the laptop polluting the 
monitoring of the traffic, this ubuntu is the server edition, set up to 
run some dicom network services on start, do I have to kill a bunch of 
things, or start in a particular way in order to keep ubuntu from 
sending its own traffic out?

Another question, (less important, I already  have a work around), 
starting Wireshark from the Application menu runs the program in a state 
that does not let it see any of the available interfaces, i.e. the 
ethernet cards, however, starting it via sudo from a terminal does make 
the interfaces available, although it warns about the insecurity of 
running as root, so the question is; is there a better way to do this?

Tom