1 PC accessing two diff subnets?

[David Martin]

Hi, is it possible to have 1 PC with 2 NICs accessing two completely
different subnets at once?

We have a PC with a local LAN connection and we wish to have another NIC
accessing an outside private LAN connection. When I ping an address on the
outside LAN, it doesn't work until I disable my local LAN connection (which
I don't really want to do!).

If I ping a hostname, how does Windows know which NIC to point this request
to? Can you tell Windows to goto a certain NIC when you access a certain
host?

Many thanks,
David

 

[Steve Duff [MVP]]

You can access any number of networks with any number
of NICs just fine (if you want to forward or route traffic
between them it takes a little more work.)

Windows uses the IP address and subnet mask to determine
which adapter to use for particular traffic. You can open a
CMD prompt and enter "route print" to see the current
routing interface table.

Note also -- and this trips a lot of even experienced professionals ---
Windows will only use one "default gateway" at any given time. That is
you can only designate one local address on one of the subnets to
act as gateway router for unknown networks. Otherwise, you
can add manual routes to particular networks for particular
interfaces (using, naturally -- "route add".) You would do this
latter, for example, if the private LAN were not exactly local, but is
reachable via some route on one of the local networks other
than the default gateway router.

I know this is pretty brief -- Post a reply with some specifics of
your configuration if you're still puzzled.

Steve Duff, MCSE
Ergodic Systems, Inc.

 

[David Martin]

Thanks for the reply Steve.

The specific situation here there is a PC on a local LAN, fine. We're adding
another NIC and this NIC points though a router to a private LAN which links
to another company (not local!).

The reason here is just to access one particular host so we want ultimately
to be able to go to IE and go to a URL on the private LAN and any other
traffic routes through the normal local NIC.

You mentioned the route command, so do I just need to add an entry to the
machine that points to the private URLs destination IP address and specifiy
the private LAN NIC details? The private NIC already has a static
IP/GW/SM/WINS in it - this is still fine?

Looking at the route command though, I also don't understand what the
"metric" parameter is all about. I'll look around and see what I can find
about it...

Thanks,
David

 

[Steve Duff [MVP]]

Don't worry about the metric, you shouldn't need it.
(It is used when you have multiple paths to select the "best" one.)

Just add the remote network (subnet and mask), and gateway address
on the local network interface using a "route add", and you should be set. Use "-p" so
it stays around between reboots.

Steve Duff, MCSE
Ergodic Systems, Inc.