How do you network two buildings together that are half a mile apart when each building has a 20 station 100 BaseT LAN with a 24-port switch?

Answer 1

The easiest way (and reliable but not cheapest) is to rent a T1 line have it run between the buildings. If that's not an option then I would look into a wireless point-to-point solution. Some of the higher powered antennas available today can reach 16 or so miles, which would more than suit your needs. Another option is using a laser connection, but this requires line-of-sight between the buildings.

Wireless directional high-gain antennae would be cost-effective. T1 lines run $1k/mo or so.

DSL or Cablemodem at each end and VPN can also be cost-effective, but probably much slower than Wireless.

The fastest method practical to connect two points a reasonable distance apart is to use fibre optic cable. Many industrial parks have their buildings connected with fibre cables, and it can be very simple to connect a 100Base-F bridge to both ends of that cable. This would get you high performance, very reliable connectivity with no monthly charge.

Cable and DSL are poor solutions, because they tend to severely limit "upload" speeds, and, frankly, are unreliable in anything other than business-class service levels, which are drastically (x5 or more) expensive than consumer versions. A T1 service can be expensive, but not always. T1 service between two buildings will actually require (2) T1 links, as the links go from each building to the telco Central Office. T1 service is usually priced by distance from the CO. You would not have to pay ISP service on top of that, so $300/month per T1 is not an unreasonable expectation for much of the US. Besides these options, there is also a microwave transmitter, which, while modestly expensive, can work through significantly poorer weather than WiFi, and has no re-occurring costs.

Overall, the easiest way to do it is via the wireless solution mentioned above: you will need an special-purpose antenna (which are easily available) to attach to a standard Wireless Router (actually, you need to read the documentation, and make sure that Router can act in Bridge Mode). The antenna will have to be attached to the outside of the building, and the cable between the antenna and the Router should not be excessively long (a couple of meters or so, in the best case).

Finally, if both buildings' networks already have internet access, you can buy a VPN solution, to create a virtual network connection between the two buildings. You will most likely want a small hardware VPN device on each end of the connection, which will cost a few hundreds of dollars each.

Talk to a local Computer Consultant (not your local computer store, but a business specializing in computer consulting, not retail sales) for more options and pricing.