Best way to access two networks from one PC

May 28, 2010 at 11:27:43
Hi there,
I have the following problem and would appreciate any suggestions on the best way to solve it.

There are two LANs, both in the same building. The first is company-wide. My office has one PC that accesses a server on that LAN to get some realtime information from another part of the building. The PC has a static IP on that network. Contacting that one other server on the LAN is the only thing I need to on this LAN.

The second LAN is the one within our office itself. It's a very simple setup with an Apple Airport router and a couple computers attached. It also gives these computers access to the internet.

What I would like to do is maintain the PC's access to the first LAN, but also give it access to our office LAN and the internet. In other words, I want to connect the PC to both networks at once.

What's the best way? Is it possible without buying a second NIC for the PC? Is there a way to connect the router in the office to both networks at once, and connect the PC to that? It is fine if the other computers on my office LAN also have access to the company LAN, but they must keep their internet access.

Thanks in advance for any help you can offer!

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May 28, 2010 at 11:45:33
Who setup your network? DId they do this because of security to prevent the other LAN from being connected to the Internet?

If security is not an issue then yes all you need is a simple router to connect the LANs. You want the Internet accesable LAN to be connected to External (WAN) side of the router and you will want to give it a static IPs for each LAN on appropriate router connection. Don't forget to setup a Reservation in your DHCP servers.

If the router has IP Filtering then you will need to setup port forwarding for ICMP and what ever else you need to get through. You may just op to for "Allow Any" to turn off the Firewall. If you do that make sure you do not allow DHCP through or you will get into DHCP wars between the servers depending on the TTL.

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May 28, 2010 at 12:15:57
the pc with the static ip, does it have a gateway entry?

Putting a second nic this pc should be cheaper than putting in a router. but you need to answer the question to determine if this is a viable course of action.

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May 28, 2010 at 12:45:56
Thanks for the replies!

Security is not really a concern, because the office internet connection is highly firewalled by company (basically allows no incoming traffic). I think I get what you are saying, but just for the sake of concreteness, let's say the following (no these are not the real IPs, but I guess it doesn't matter since they're local anyway):
office LAN: router connected to internet via ethernet jack to company's main connection. Internet IP of router is static. Router acts as DHCP server on LAN with address Connected computers have IPs in the range
company LAN: wired throughout building. Gateway address is and possible IPs are PC on this LAN has IP, and server we talk to has IP
You're saying I should:
1) Get new router. Connect WAN port to office LAN. Reserve it a static IP (e.g. on office LAN's router. Turn off DHCP on new router.
2) Connect new router to company LAN via LAN port on new router? But what do I tell the new router its IP is at this point or
3) Connect PC to new router. What IP should it have?
4) Use PC to contact company LAN server at, and office LAN computers at Connect to internet IPs/domains as normal.

The PC with the static IP has an IP (what I called above), subnet mask, and gateway (what I called entry in the internet config.

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May 28, 2010 at 12:47:29
One other question:

Do I really need a second router, or can I just plug the company LAN connection into a LAN port on the office router and configure it appropriately?

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May 28, 2010 at 12:59:29
Put a 2nd nic in the pc.
Take the gateway entry off the company lan nic. It is not needed.
Connect the 2nd nic to the office router.

You can now access the office lan and internet via the 2nd nic.
You can access the company reattime data on the 1st nic
No router required.

BTW the router discussed above would be to connect the office and company lans together at which point it does not matter which the realtimedata pc is connected to.
Do note that the office lan and the company lan need to be in different subnets.

btw if you put a router between the two networks this will result in two gateway entries which isn't allowed. You would need to drop your local internet access and go thru the main company's lan to the internet.

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May 28, 2010 at 14:27:39
>btw if you put a router between the two networks this will result
>in two gateway entries which isn't allowed. You would need to >
>drop your local internet access and go thru the main company's >lan to the internet.

This is kind of what I figured intuitively, but my networking kungfu wasn't strong enough to know for sure.
Thanks again for the help - it seems like the easiest thing is to shell out a couple bucks for another NIC and be done with it. Much appreciated!

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