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In my office we use two different lan’s and they both are connected to two different adsl-ISP’s. But there is only one network printer in the house.
How can I connect these lan’s secure, so I can print from both networks on this printer?
On both networks I use IpCop as DHCP and firewall.

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Create a point-to-point VPN and connect the two offices together. If you don't want to share all traffic/devices between the two LANs, just make a simple firewall rule to deny all traffic except the traffic necessary to print to that one device.

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If you have firewalls in place behind each DSL Modem and they support a DMZ network you can potentially put the two firewalls in the same DMZ, put static routes for the private lans on each firewall and setup specific rules to allow traffic between the two LANs.

The basic principle is generic but how to do it will be completely dependent on what you are using for firewalls.

For Example:

Lan 1: 192.168.0.X Lan 2: 192.168.1.X

Network Printer:

DMZ Interface Firewall 1: DMZ Interface Firewall 2:

Set Route on Firewall 1: gateway Set Route on Firewall 2: gateway

The way rules are defined will be dependent on the firewall, but you would want something on Firewall 1 saying that the DMZ/Lan2 are allowed to talk to

Regarding IPCop:
Since you are using a PC based firewall you probably right now only have to NICs right now, the Red (Internet) and Green (LAN). You need to add a third NIC to each firewall box and set it up as the Orange (DMZ) interface.

Haven't used IPCop before but have used other Linux PC based firewalls and the quick glance at IPCop's documentation looks like you should be fine to do the above described.

As for the physical link, you can either use a crossover patch cable between the two firewall DMZ interfaces since you are only putting the two devices on the DMZ network or you can connect them using a third network switch if you want to have other devices in the DMZ.

You could actually put the printer in the DMZ network if you so wish, it would make the routes simpler as both firewalls would naturally know how to find the DMZ network. With the printer inside of one of the private LANs you have to tell the one firewall to talk to the other to get to that private network.

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This looks very helpfull. Does it mean that I can connect the two switches/hubs by linking them with a simple utp cable? On both networks I use IpCop as DHCP and firewall. Thanks, Adrian – Adrian Feb 1 '10 at 21:13
No, if you connect the two switches together they will be physically one network and your DHCP will get into a big fight. – ManiacZX Feb 2 '10 at 2:27

You could also enable IPP (Internet Printing) on the device and publish it to the web, for the other site to get to.

Of course, it has to have that as an option. Since you didn't say if it's served up by a server, network device, or has networking built-in, and didn't specify what the make and model of the hypothetical print-serving devices is, I can't tell you how to do that.

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