August 2000 || Volume 01, Issue 01

Connecting Your DSL to More than One Mac

Historically, Mac users have never been hip to the lingo of networking. Why? Simply because they didn't need to be. AppleTalk is so easy to set up, use, and troubleshoot that you don't need to know a lot of geek-speak to use it. A person could set up an all-Mac network and only need to know how to plug things in and turn on a few Control Panels and Extensions. Those days of ignorance are beginning to fade, what with the introduction of DSL and Cable Modems into homes and businesses. Now you have to know a little more than the average bear, unless you want to hire someone to come in and do it for you. With that in mind I will begin by defining some terms you may encounter, so us Mac folks can understand what's what.

Geek-tionairy

Bridge - A bridge does just what it says it does. What does a real bridge do? It connects two ends of a road over a river, canyon, or another road. Does a bridge care what goes over it? No. It could be cars, trucks, trains, busses, it doesn't matter. These vehicles can go to only one of two places; one side or the other. Here in Portland, Oregon there is a bridge (2 actually) that connects us to Vancouver, Washington. It connects two different states. In the same way, a network device called a bridge connects two different networks. It doesn't care what is going over it, and it is simply a means to get the network traffic from one side to the other. A bridge directs information based on the MAC address of your Ethernet card. Many ISPs offer DSL service with a bridged connection and one static IP address.

PPP/Router - PPP stands for Point-to-Point Protocol. Your modem uses this protocol when you dial into your ISP. It establishes a connection, negotiates the rules for that connection, typically authenticates you to your ISP, and oversees the incoming and outgoing information while you are connected. It connects you (one point) to your ISP (the other point). A router is similar to someone standing at an intersection giving directions as to which way is best to go to reach your destination. It takes information coming in one interface, asks where it is going, and sends it to the best interface. A router can have several interfaces on it. Some ISPs, such as uswest.net offer service with a PPP/Routing connection and a dynamically assigned IP address. Each time your DSL connects out you will get a different IP address. If you have an external CPE (chances are you do if you have a Mac), it will act as a router. It will take traffic coming from the Internet and route it to the computer on your network that requested it. Typically the router (in a DSL scenario) also provides DHCP and NAT services.

PPPoE - This is similar to PPP/Routing. PPPoE stands for Point-to-Point Protocol over Ethernet. In PPP/Routing your router does the authentication and NAT. In PPPoE, client software on your computer does this. ISPs who use this method supply the client software for your computer. One of the more popular clients is MacPoet. PPPoE is almost a hybrid of bridging and PPP/routing. The connection to your CPE is in bridging mode, yet the client on your computer negotiates a PPP connection. In the client software you enter the user name and password given to you by your ISP. You also have to manually set your TCP/IP Control Panel the way your ISP instructs you to. By the way, if you have an AirPort setup and you upgrade to version 1.2 of the AirPort software you will not be able to connect to an ISP using PPPoE, according to Apple.

MAC Address - This one was very confusing the first time I saw it. I'm a Mac user, like you probably are. I thought that this was referring to the address of my Mac, but this term also applies to Windows users. Needless to say my brain was in quite a knot. But the term MAC address does not refer to the address of your Macintosh. MAC stands for Media Access Control. It is information that is burned into the circuitry of your Ethernet card. It is a completely unique address that never changes. If you are curious as to what the MAC address of your Macintosh is, the next time you are connected to the Internet do the following: 1) Open the TCP/IP Control Panel. 2) Go to the File menu and select Get Info. There you will see the hardware address. That is your MAC address. If you have a CPE that is set up as a bridge, the bridge uses the MAC address to route/filter information. A bridge knows the MAC addresses of the equipment attached to it. It knows that if it is getting data whose destination is a MAC address, for something not attached to it, to ignore that data. If the MAC address is for something attached to it, it lets the data through.

DHCP - DHCP stands for Dynamic Host Configuration Protocol. Most Windows networks are based on TCP/IP. That is, each computer on the network has a unique IP address. Networks with Macs are going to this model as well. In addition to running AppleTalk over the Ethernet network, Macs are also being given IP addresses. If you had 10 computers that all needed an IP address, this would be no big deal to handle. You cold easily assign them manually and keep track of them. However, if you had 100 computers and you had to administrate the IP address assignments of these, it would be a lot more work. Enter DHCP. This handy little service typically runs on a server. When a computer comes online it says, "I need an IP address please." The server replies, "OK, here ya go." Basically, it is in charge of giving out IP addresses, keeping track of which ones are being used and which ones are available.

NAT - NAT is Network Address Translation. This can be a great thing or it can really be a drag, depending on what you are doing over the Internet. I will use USWest's use of the Cisco 675 as an example. When you are running the 675 in PPP/Routing mode it gets a real IP address from USWest. It then acts as a DHCP server for the computers attached to it. By default it will give the first computer it sees an address of 10.0.0.2. This is not a real IP address, which is to say that it isn't recognized out on the Internet (geek speak is that it is a non-routable address). In other words, someone out on the Internet could not connect to the address of 10.0.0.2. It has been set aside for people to use on their own internal networks. The 675 will give the next computer 10.0.0.3, and so on down the line. Because it is a non-routable address, the 675 must translate these addresses for use on the Internet. Let's say that your 675 was given an address of 204.147.80.5 by USWest (that happens to be one of their DNS servers and is used for purposes of illustration only). Your computer, which is 10.0.02, tells your 675 that you want to go to www.macosjournal.com. The 675 then sends the request out to www.macosjournal.com, gets the information back, and forwards it on to 10.0.0.2. It translates the internal and external addresses, one to the other. The good side of this is that since your computer has a "fake" Internet address no one can get to it and mess with it. The bad side is that some services on the Internet require that you have a routable IP address to use them. ICQ is an example of this. In order to use those services you have to create a NAT Table in the 675's settings that specifically maps the 675's IP address to your internal address and the ports that the service uses. Describing how to do that is beyond the scope of this article. But essentially that is what NAT does.

IP Address - IP stands for Internet Protocol. When a computer is connected to the Internet it has a unique IP address so that when you send out requests and information comes back to you, it will know exactly where to go. If you want to see your IP address while connected to the Internet you can go to the TCP/IP Control Panel and view it there. There are two kinds of IP addresses; static and dynamic. A static IP is an address that never changes. It has been assigned to you/your connection. A dynamic IP is an address that changes every time you connect to the Internet. When using a modem to dial in, you will most likely get a different IP each time you connect in. The same can be true of DSL, depending on how your ISP is set up.

Ports - In the world of the Internet, ports aren't physical like a printer or a modem port. They are numeric/logical. Services on the Internet use specific ports. HTTP uses port 80, newsgroups use port 119, mail servers use ports 25 and 110 to send and receive mail. If a port is blocked, you obviously can't get through it. Hardware that is set up for NAT does not always have the ports open that you want to use.

TCP/IP - Transmission Control Protocol/Internet Protocol. This is actually a collection of protocols that the Internet is based on. FTP and SMTP are some examples of this collection. TCP/IP is what allows your computer to communicate with the Internet and vice versa.

Hook it up!

This is going to be a very generic description of how to network your DSL to your Macs. Why? Because there are so many ISPs and ways of delivering the service, that there is no way I could map them all out. Nevertheless, this should give you an idea of what to do.

1) Buy a hub. You should be able to go to any computer store and purchase a 10BaseT hub for around $30-40. However, if you plan on doing more than sharing the DSL connection (say file/printer sharing or gaming) and your Macs have 10/100BaseT cards in them, then you would be better off spending the money for a 10/100BaseT hub. Hubs aren't platform specific so you don't need to look for one that says "Mac OS Compatible." If you find one that does, it doesn't really mean anything. Make sure that the hub has an uplink port on it.

2) If your CPE performs DHCP/NAT functionality then you can skip this step. If not, read on. You will need a software package that allows you to share the one IP address that your ISP has assigned to you. An example of this is the IPNetRouter from Sustainable Softworks. Another example is NetBarrier from Intego. If your Mac has limited resources or is slower/older and you know that more software will bog your Mac down, there are some hardware solutions you can buy. Netgear makes a router/hub (which means you could skip #1 above) that will do DHCP/NAT for your network to share your IP address for cable modems and DSL. Netopia has a similar solution.

3) Your CPE should have come with a crossover cable. This looks like a standard Ethernet patch cable but it is wired a little bit differently. Just so you know, crossover cables are designed to connect two Ethernet devices directly without the use of a hub. Take this crossover cable and connect one end to your CPE and the other end to the uplink port on your hub. NOTE: The uplink ports on some hubs are switchable. In other words, the port can be used as a standard Ethernet port, or it can be used as an uplink. If there is a switch for it on the hub make sure that it is set to uplink.

4) Finally, connect your Macs to the hub with standard Ethernet patch cables, which you can also get at your local computer store. Set the TCP/IP settings according to your ISPs recommendations, or the settings described in the manuals you received with the software/hardware package you decided to go with. Try a web browser and see what happens.

Surf Away!

Don't Forget? Corby has supplements for all of his columns on his personal page. You'll find the relevant links within each month's Shop Talk!

If all went well with my very generic suggestions above, all of your Macs should be surfing like The Big Kahuna on a storm surge (what do I know about surfing, I'm just a Mac head!). If all did not go well and you are stuck on the beach come on over to this page for some more detailed instructions on how to configure your setup. That is where most of the geek-tionairy terms will come in handy. I even go into a little AirPort action.

As always feel free to send your questions, comments, and snide remarks to corby@macosjournal.com. Surf's up big doggy!

Corby Stephens - corby@macosjournal.com
Corby's Page