Using 2 or more Network Cards

[Skippy]

Say I have 2 Network cards in my computer, both with different IP address's and both connected to the same hub.

I would like using LV to setup a connection from one NIC to the other going through the hub.

The problem I’m having is with the "TCP OPEN CONNECTION" command, it doesn’t require a local address and therefore seems to have free reign to choose the IP address it would like to use.

So having setup a LISTENER on one address, the TCP Link is opened from that same address and therefore cuts out the hub.


Can this type of link be achieved with LV?

[EdDickens]

Try using the 'TCP Create Listener' instead. This will allow you to specify an IP address for the listener.

Ed

[Skippy]

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@Ed Dickens wrote:
Try using the 'TCP Create Listener' instead. This will allow you to specify an IP address for the listener.

Ed

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That's the thing, i can setup a listener on a particuler address but I cannot find a way of saying "now you (meaning the other NIC with a diffrent IP) go and connect to the listener I've just made.

[altenbach]

The interface used for the outgoing connections (TCP open) is determined based on the destination IP and the routing tables. Fortunately, I don't think you have much control over this. 🙂

Have you tried some serious editing of the routing tables? If it is even possible, it won't be pretty.

[Skippy]

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@altenbach wrote:
The interface used for the outgoing connections (TCP open) is determined based on the destination IP and the routing tables. Fortunately, I don't think you have much control over this. 🙂

Have you tried some serious editing of the routing tables? If it is even possible, it won't be pretty.

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Cheers mate, routing tables sounds like the strongest lead i have so far. Do you have any idea of how i would go about messing with them? I don't even know where to find them.

[chrisger]

hi

i think the routing-thing is worth a try. under win\system32 theres a "route.exe" which allows you to edit the table. execute it on a cmd-line and read the info. you should be able to execute within your vi with SysExec.vi or create a batch and call that with SysExec.vi (maybe there's even a dll, but i don't know).

good luck and let us know
chris

[Ben]

It has been more than 15 years since I looked into the details so things may have changed.

My concern is that the TCP/IP stack will recognize that the source and destination addresses are on this machine and by-pass the network completely.

I would recomend the following.

1) Isolate your hub such that your machine is the only machine on the hub. This way you can watch the activity lights to ensure that the packets are really making it to the wire.
2) Concider unique sub-nets for each NIC.

Trying to help,

Ben

[altenbach]

Since routing tables are based on "subnets", the two NICs need to be on seperate subnets, this also means that you need to replace your hub with a router.

I agree with Ben that the OS is probably smart enough not to send anything on the wire if the destination is local.

Somehow, this seems like an useless task. What are you trying to achieve exactly? Sniff the traffic on the hub?
A better idea would probably be to use a second machine as an external loopback proxy, maybe this can be coded in LabVIEW?

[Skippy]

Thanks for the advice guys, I'll try a few of the thing's you've suggested and let you know how I get on.

What I am trying to achieve is to make LV send a file through a hub using just the one computer. So in short I just want it to exercise a hub.

[chrisger]

hi

how about DataSocket or OPC-Demo Server with the IPs in the URL?

best regards
chris