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We have just moved into a new office and have been given our 'internet connection' in the following form:

  • One Ethernet cable in the corner of the room
  • An IP address with subnet mask 255.255.255.0

We have several computers, and are wanting to set up a simple LAN, all with internet access.

Given that our 'wan' cable is an RJ45 Ethernet cable, is it possible to use a normal home router, and plug in all the computers alongside the 'internet' cable into the router's switch ports?

The switch would need to have machines on a different IP subnet than the one we have been assigned, because we have only been granted one IP address. We must somehow use NAT to get everyone online at once.

Can a normal router handle this?

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Edited: this question has nothing to do with "multiple subnets." All of your LAN computers will be on the same RFC1918 network, e.g. 192.168.1.0/24. –  Skyhawk May 29 '12 at 1:24

5 Answers 5

Most consumer routers have a WAN port, and will automatically do NAT for outgoing traffic. You should be able to plug the Internet cable into the WAN part, and then configure the router appropriately (it will use DHCP by default, if you need to assign a static address you'll need to configure that). Then configure the router's DHCP server for handing out addresses to LAN clients, and plug the computers into the LAN ports.

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I wouldn't really recommend a "Home" router. At the very least, get yourself something like a Netgear FVS318 (a new one, mind you, not an old one). They're quite good for a half-dozen computers set up in branch-office configuration.

It will likely serve you quite well unless you're planning on doing some high-performance stuff that you haven't mentioned above. With something like the FVS I mentioned, there's no particular reason to further subnet your office location as everything will be behind a LAN.

If you happen to have $300-$400 and you're working with some network-savvy people, you can't really beat a Cisco ASA5505 with a 10 user license either.

Of course, all these configuration suggestions will change when IPv6 comes to town.

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For situations such as the OP is talking about a "Home" router is far more than adequate. This is what the very vast majority of small businesses around the world use and few ever run into the limitations of such a device. –  John Gardeniers May 29 '12 at 0:50
    
agreed, home router with ddwrt is the way to go –  SpacemanSpiff May 29 '12 at 0:55
    
Most home routers are far more capable than the FVS318. Unless this business is using an archaic, T1-class internet connection, an FVS318 is likely to actually limit available bandwidth: the FVS318 supports 12Mbps WAN speed at best; in the USA, providers like Comcast/Verizon/Frontier routinely provision 25, 35, and 50Mbps connections even for very small businesses. I don't necessarily agree that a home router is the way to go, but a Netgear FVS318, on the market since 2002, is unequivocally the wrong choice in 2012. –  Skyhawk May 29 '12 at 1:20
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True, but 10 years of dealing with this equipment has shown me that most home routers aren't nearly as reliable. I've never had a Netgear barf up its NVRAM settings unlike several generations of Linksys, Motorola, and ActionTec units. And I've never had a high-bandwidth connection crash a Netgear. And the only Linksys DDWRT unit I've ever worked with was a total cluster right out of the box. And we are pulling 20Mbit/s through the Netgear that I'm stuck with. That said, I am stuck with Netgear, and would be getting Cisco if I could afford it which is why I posted that. –  Magellan May 29 '12 at 2:44
    
@MilesErickson - I don't know which FVS you've been using but we had one serving a 20Mb link. It had other issues which is why we don't have it any more, but link speed was not one of them. –  Mark Henderson May 29 '12 at 2:59

There are literally hundreds of products that will meet your requirements. Most Consumer Off The Shelf (COTS) or Small Office / Home Office (SOHO) include a "WAN" port for your external connection and "LAN" ports for your networked machines and will of course do NAT between them.

I recommend that you purchase a dedicated firewall/router and a dedicated switch instead of an integrated all-in-one COTS device for a few reasons. By using different devices you gain functional separation which is almost always a good thing. You increase the flexibility of your network design because you can upgrade or replace one or other without having to replace both, it will simplify troubleshooting and in my experience I have found that many COTS devices are very unreliable. You will find that the business definition of downtime is very different form the home network definition of downtime.

Features I like to look for in a SOHO or small business router would be:

  • NAT
  • Layer-3/4 filtering
    • (with the ability of write custom rules or exceptions)
  • the ability to write static routes
  • Port Forwarding
  • DHCP and DNS services
  • a rudimentary way to monitor your network traffic
  • remote logging
  • vendor or a local re-seller support
  • a decent warranty

VLAN tagging and VPN support are also real nice to have and you might find need of them in the future but they are by no means necessary.

Take a look at this question for features you might want to look at in a networking switch: What should I pay attention to when I'm buying a network switch?

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Pretty much any router you buy, consumer or otherwise (I assume this is consumer? Kinda off topic, but whatever), will be able to do what you need, which is NAT and some LAN subnet other than the one that's been given to you.

There are two situations to be careful of. First, if the WAN connection uses a non-routable address (such as RFC1918 addresses: 10.0.0.0/8, 192.168.0.0/16, or 172.16.0.0/12), forwarding of ports requires that you forward them to your router from the router before it, as well as forwarding them in your router. Secondly, if neither your router nor whatever it is connecting to on the WAN side supports auto-MDI-X (most do now), you will need to use a crossover cable.

You can pick whatever subnet you want, really. Technically it can even be the same as the WAN subnet, but this tends to make troubleshooting messy and renders your hosts unable to access hosts on the same network as the router's WAN interface. You can pick whatever you want from the above three... you could do something like 192.168.212.0/24, or 172.16.0.0/24, or whatever really.

I wouldn't bother with anything that costs more than $150 unless by a small number of PCs you mean more than 10. Also, the subnet mask on the WAN side doesn't really matter for this... enterprise-grade connections often come with a /30 allocation (point to point link, "255.255.255.252").

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If you are on a budget, I can advice purchasing a somewhat older model from ebay. As I understand, you need a wired connection so the wi-fi speed/capability is not if the essence. Going for aftermarket firmware is also a good move, assuming you have the time and compatible hardware. Go through OpenWRT's list of supported devices. There you can get a good idea about what hardware to search for on ebay. You would also get technical specifications on all of them.

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