[wplug] ip forwarding on ubuntu

[Larry Daberko]

I know you can set up interfaces in bridging mode in OpenBSD, but I've 
never tried it in Ubuntu.

Quick and dirty google search:
http://ubuntuforums.org/archive/index.php/t-403316.html

LBD

Vance Kochenderfer wrote:
> Tom Fetherston wrote:
>   
>> Rather than introducing a hub and monitor things that way, I've
>> purchased a expresscard gigabit ethernet module.
>>     
>
>   
>> 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.
>>     
>
> Using a hub is really preferable, as it is the least invasive way
> to do what you want (well, OK, I suppose the *least* invasive way
> would be to use some sort of inductive tap to read the data from
> the cable itself, but that's kind of overboard...).  You may find
> that sticking a router in between the two devices changes the
> behavior you're trying to examine, for the better or for the
> worse!
>
>   
>> The last sentence brings me to my first question, just how do I set up
>> ip forwarding under Linux?
>>     
>
> I'm not very knowledgeable with setting up routing, but this may
> get you started.  You have two interfaces on your laptop, eth0 and
> eth1.  Say that eth0 is connected to the network at large and eth1
> is connected (only) to the Dicom machine, which has IP address
> 10.10.10.10.  I think you would set up the routes like so:
>   # route add default dev eth0
>   # route add -host 10.10.10.10 dev eth1
>
> You'll need to make sure that at least the iptables FORWARD table
> is not set up to reject or drop packets.  I'm not sure if the
> Dicom machine will be able to get a DHCP lease at this point, so
> make sure it has obtained an IP address before disconnecting it
> from the main network and plugging it into the laptop.
>
> Hopefully someone else can chime in as I'm fairly lost at this
> point and not sure if any other steps are required.
>
>   
>> 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?
>>     
>
> You should be able to set up a rule in the iptables OUTPUT table
> to prevent packets having one of the laptop's IP addresses as the
> source address from leaving the laptop.
>
> Vance Kochenderfer        |  "Get me out of these ropes and into a
> vkochend at nyx.net          |   good belt of Scotch"    -Nick Danger
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