Ann Arbor Business to Business
Small Business and the Internet

Touting Routers

November 2000

By Mike Gould

I returned from a recent vacation to find email from 3 different clients awaiting me, all requesting help with setting up multiple computers attached to a cable modem or DSL line. I mentioned this briefly back in April ("Bigger Pipes - The Cable Modem"), but interest is heating up, so let's talk routers.

Multiple Identities
I have had the most experience connecting to cable modems in the home, so I'll concentrate on them here, but the same principles apply to DSL connections. The idea is the same: a bigger pipe from the Internet to your house (or business) provided by either a phone company or your local cable TV service.

The magic wire that connects all these is called Ethernet, and is a special wire with connectors on the end that look like phone plugs on steroids; wider to accommodate 8 wires instead of 4. To take advantage of this, your computer has to have either Ethernet native on the main circuit board (all Macs and some newer PC's), or provided by an add-on card. The problem lies in the way in which our local (Ann Arbor) service, MediaOne (MO), sets up this Ethernet connectivity.

On the Internet, each node (computer) is assigned a unique IP (Internet Protocol) address, which looks like Here, the ones represent addresses broken down by domains and sub-domains. Domains are subsets of the Internet, established by the Secret Sacred Keepers of Mystical Packet Voodoo, and needn't concern us regular folks. The point is that MO allows you one and only one address on the 'net; if you want more than one computer at home to share the connectivity provided by the cable modem, you need a means of sharing that one address.

Why This is Complicated
To make things more interesting, MO assigns you your address dynamically, via a process known as DHCP (Dynamic Host Configuration Protocol). This means that every time you restart your cable modem, you will get a different address. The kicker is that in re-setting your address, your modem looks for a number buried in the bowels of your computer's mother board or Ethernet card, known as the MAC (Media Access Control) number. This is also known as the hardware Ethernet address, and is a number unique to each and every board and card out there. This means that you can't just hook up a hub linking all your computers to the cable modem; the modem wouldn't know how to deal with the multiple MAC numbers. What you need is a "smart" hub whose MAC number you can give to the MO modem, that would then share this number, that would then share the IP address, enabling the computers to talk to the wire that talks to the hub that talks to the Internet that Al Gore built. (A joke, not political commentary).

Whew! Sorry for the alphanumeric soup, but this is complicated. (Do you, the concerned reader, want this level of geekspeak? Write me at the address below telling me to dumb down or smart up these discourses.)

That smart hub is called a router (pronounced "rowter", not "rooter"), and its job is to connect one network (the Local Area Network - LAN - made up of your several computers and hub) to another (the Internet). Strictly speaking, a router doesn't necessarily have multiple outlets (acting as a hub), but most of the ones intended for small office or home use include them.

So here's the sequence: your multiple Macs, PC's, whatever, connect via their Ethernet connections to a hub, which may be built into the router. (If you have a separate hub, it connects to the router via a special cross-over cable). The router then connects to the cable modem (or DSL box), and the cable modem connects you to the Internet.

There are many flavors and brands of routers out there, and the following is an explanation of some of the functions that most of them provide. (Note to serious network wonks out there: yes, this is in many ways a gross over-simplification of what can be some serious heavy lifting of packets, and yes, I should mention Cisco somewhere. I just did.)

NAT-y Dread
Several things are going on within the router, the main one being Network Address Translation or NAT. This sets up your internal network with IP addresses, and then translates these addresses into the one that MO provides. Essentially, all your computers are sharing the address and bandwidth provided by the cable modem. You might suspect that the more computers you add to your LAN, the slower the connection speed: yup. But this isn't that big an issue in a home situation with only 2 or 3 computers, and a speedy cable modem connection. My wife and I share our connection and do a lot of Web surfing simultaneously, and have never noticed much of a problem. I have 4 Macs (one of them wireless via an AirPort broadcaster) and a PC all talking happily to each other and the WWW.

The nice thing about NAT is that it provides a measure of security; anyone hacking into your IP address ends up talking to the router instead of your computer and its files. This is called a Firewall, and while it is not perfect, it provides a lot more security than a regular cable modem connection.

Wires to the Max
To see this all carried out to the extreme, a visit to displays a diagram of my system here at MondoDyne whirled headquarters. The Ethernet stuff is in yellow. The Mac IIci that acts as a hub is going to be replaced soon with a $200 commercial router that I am testing prior to its installation at several of my clients' homes.

One caveat: MediaOne neither condones nor supports the use of routers. I spoke to one of their techs who confirmed that if you have a router and then have a problem with your connection, the problem is yours and not theirs. On the other hand, if you have a router, they won't sniff you out and report you to the Internet police. If you are installing a router, you will have to dig out its MAC number and report it to the MO techs so they can permit the cable modem to talk to your new hardware.

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