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In an office I've got a network connection with 5 external IPs and a Linksys router (I'm not 100% percent sure of the model). I need 4 of those 5 IPs to be routed to a server, and the fifth to be shared between the other computers at the office.

This can probably be done using a switch in front of the router. Connect the server and the router to the switch, and let the router handle the rest of the network.

Is there a way to configure the router to route the 4 IPs to the server, and create an internal network the the other computers at the same time?

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2 Answers 2

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This depends on the featureset of the Linksys router, since there are literally hundreds of models, but what you are looking for is running PAT alongside static NAT. Your router may have such a feature listed as static routing.

It is definitely possible, and very common in organizations, but most SOHO routers do not support such a feature.

You could also probably get away with using a setup such as:

Modem ----> Switch ----> Multiple SOHO Routers

And assign an external IP to each of the routers, then branch the server off of them into multiple NICs. Not ideal, but it would work.

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I'm not 100% sure of the model of the router, but I understand it's a good one. Can you give me an example of what the configuration would look like (or maybe a link to a tutorial?) –  Adrian Mester Mar 4 '11 at 22:09
    
Sure. Ideally you could use the Linksys RV016 which has multiple WAN ports for this purpose: cisco.com/en/US/products/ps9924/index.html or You can configure your server with an internal IP and create static routes from the WAN IP's (assuming your device supports them): fold-server.sourceforge.net/images/… –  John T Mar 4 '11 at 22:14
    
If you have a small spare box, pfSense can also do the trick: pfsense.com as well as some third-party router firmware. –  John T Mar 4 '11 at 22:17

It is unlikely the Linksys router will have this capability natively. I may allow you to bridge one of the LAN ports to the WAN port. This would allow you to connect the server to the Internet through the router. This would likely be an unsecured connection with no firewall between the server and the Internet.

If you can install DD-Wrt or OpenWRT on the router it is will likely be easier to do what you want. This will enable you to do a NAT solution or bridging solution using a firewall tool like Shorewall-lite.

You may find it simpler to use an old PC and install a couple of extra ethernet ports. You could then install Linux or FreeBSD and build an appropriate firewall.

The Shorewall documentation on One to One NAT may be of help in understanding the NAT solution.

The bridging solution would involve bridging one or more LAN ports to the WAN port. If all 4 addresses need to go to the server, then you only need to bridge the one port to which the server is connected. Firewalling a bridge is more difficult. Set the Shorewall documentation on Shorewall-perl and Brided Firewalls.

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