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Two LANs sharing one printer

Last response: in Networking
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March 26, 2011 7:11:51 AM

Hi. Hope someone can help. Not even sure I'm posting to the correct sub-forum.

I have two complete and separate "networks", each with their own internet connections. One is for home use, one is for business use.

(1) Home network has a D-Link cable-modem/router to the ISP. Variable public IP address. NAT'd.
This router is configured "as provided" by the ISP (except for a few port-forwards). DHCP serving is enabled, etc. If possible, I do not wish to change any major router settings.
LAN IP Range: 192.168.0.0/255.255.255.0

(2) Business network has a 2-Wire ADSL-modem/router to a different ISP. Static public IP address. NAT'd.
DHCP serving is handled by a Windows 2003 Server. I am happy to change any router and server settings.
LAN IP Range: 192.168.254.0/255.255.255.0

I have a network printer. It is currently connected to the Home Network (1) and has a static IP address 192.168.0.8, but I wish it to be accessible by PC's on both networks.

My first thought is to simply connect both routers LAN-side via an ethernet cable. However, I can't find a way to add a LAN-LAN static route on the Business Network router (it only has options for WAN-LAN static routes). Do I really need to internetwork the routers via the internet?!?

Help! Although I understand a little about IP addresses, I'm out of my depth when it comes to internetnetworking.

Thanks in advance.

More about : lans sharing printer

March 26, 2011 10:37:20 AM

You have to be careful when creating a LAN to LAN bridge. Because once you do, it becomes possible that users on one network *might* end up on the other network. It’s entirely by chance which DHCP server responds first. And inevitably some of your clients will end up crossing over to the other network and using its subnet, its gateway, etc.

What you need is a gateway, one that provides access to the network w/ the printer for the benefit of the network w/o the printer. Now all your clients remain on their respective networks and only use the gateway for accessing the printer.

You could use another router on the 192.168.254.x subnet.

<-- 192.168.0.x –>(wan)[router](lan)<-- 192.168.254.x -->

So the router grabs a WAN IP address from the 192.168.0.x network’s DHCP server. And you assign a static IP on the LAN side in the 192.168.254.x subnet. Let’s say that’s 192.168.254.254.

Finally, you need to tell the clients of the 192.168.254.x subnet how to find the 192.168.0.x subnet.

route -p add 192.168.0.0 mask 255.255.255.0 192.168.254.254

You can either add this to each client of the 192.168.254.x subnet, or if that subnet’s router support the addition of static routes, add it there so you don’t have to manage individual clients.

Of course, you could use a PC for the gateway instead of a router should you find that more convenient. That PC would need a second network adapter and use ICS to create the actual gateway between the networks.

Whichever way you choose, that’s how you have to do it. Use a gateway, not just connect the two networks LAN to LAN. The latter will only create lots of unwanted problems.

Just to be complete, another approach would be to make the printer available over the Internet and port forward through the 192.168.0.x subnet’s router from the WAN side (iow, use the gateway you already have). But my assumption has been you’d prefer to avoid this and keep it all internal. But if you’re willing, it’s certainly possible to make the printer available remotely like any other network device.
March 26, 2011 11:05:36 AM

Wow! Eibgrad, that's EXTREMELY thorough and helpful. THANK YOU.

I had already considered the last-resort of setting up internet-printing. The down-side of this is that the Home Network, where the printer lives, does not have a static public IP address, so I'd have to try to set up Dynamic-DNS, and I'm not sure the D-Link router supports it.

I have several spare routers, so I will give your suggestion a try. On that basis...

Do I need to set up a static route for the entire 192.168.0.0/255.255.255.0 range, or can I route only the single IP of the printer (192.168.0.8/255.255.255.254 ?

And, will I need to configure a reverse static route (will the printer likely require it)?

Thanks again. I look forward to reciprocating by giving advice on other Sub-Forums where my competencies may assist.
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March 26, 2011 11:24:01 AM

If you'd rather create a route solely to the printer, you certainly can:

route -p add 192.168.0.8 mask 255.255.255.255 192.168.254.254

I just find it easier to cover the entire network in case I want access to other resources later (just less changes to deal with), but do whatever you prefer.

You don't need a reverse route unless the printer needs to *initiate* network requests to the 192.168.254.x subnet (not obvious to me why that would be necessary).

For requests that come in from the 192.168.254.x subnet, the printer will only see the IP address of the gateway itself (let's say that's 192.168.0.10) and return messages to that IP address. The gateway will then map that back to the internal IP address of the original client on the 192.168.254.x subnet. IOW, it just works, no need for additional routing.
March 26, 2011 11:40:50 AM

Neat!

Thanks eibgrad. I'll give it a go during the next couple of days, and report back here.

Best regards,
March 26, 2011 11:43:42 AM

P.S. Almost forgot, be sure to turn OFF the DHCP server on that additional router! Otherwise it could end up being accidentally used by clients of the 192.168.254.x subnet.
March 26, 2011 11:49:25 AM

Good point.

You'll be pleased to hear that (almost) the first thing I do when I receive a new router, is to turn off the DHCP serving!
March 26, 2011 12:58:36 PM

Btw (as if you needed more options, right), you could configure the new router in the reverse, that is, have the WAN face the 192.168.254.x subnet:

<-- 192.168.0.x –>(lan)[router](wan)<-- 192.168.254.x -->

You'd want to make the WAN IP static on the 192.168.254 subnet, so let's say that's 192.168.254.254. You can then use port forwarding behind the WAN to reach the printer. In effect, the port forward becomes your routing mechanism.

The reason I bring it up is because it sounded like you had problems adding static routes to your router. But by facing the WAN to the 192.168.254.x subnet, you avoid having to add static routes at all. Clients of the 192.168.254.x subnet simply address the printer using the 192.168.254.254 IP address. The port forwarding takes care of the rest.

Of course, there are security implications to each configuration. Although since this is all internal, I suspect that's not really an issue.

Anyway, just another possibility. Only you can decide which makes the most sense for your circumstances.
!