Now that You're Wired...

Regardless of whether the machine on your desk is a Mac, IBM-compatible, or something else, there are changes when you get hooked up to the net. There are physical differences -- you have an additional card in your PC, an ethernet card, and there's a wire connected to the ethernet card on one end and a "B-jack" on the other. (That's the other jack, beside your phone jack.)

• The Software Changes
• A New Name and Address
• The ADN Network group are our network administrators:
• Internet IP Addresses
• Internet Domain-Style Names
• Domain Name Servers
• Name Server Utilities
• Want to know more about TCP/IP protocols and how the Internet works?

TCP and IP are specific protocols in the TCP/IP suite; others that you've heard of -- and will probably use -- are TELNET, for logging into remote computers, and FTP and TFTP for file transfer. TCP and IP are "lower-level" protocols; the task-oriented protocols like TELNET and FTP depend on TCP and IP to actually move information along the network.

With your ADN-ii connection, your desktop machine gets a new name and a new address -- an Internet domain-style name and an IP address. (Actually, there's another "address"; your ethernet card's MAC address, given to it by its manufacturer. MAC addresses do have a few uses, but not for anything that most people need to be concerned about.)

The first two numbers, "128.248." (and also "131.193."), belong to UIC; we use the third number to indicate the subnet. (See Of Wires and Routers.) The fourth identifies your machine.

Each of the four fields in an IP address can range from 0 to 255. Sounds like a lot of IP addresses, doesn't it? But we can't put more than 20 or 30 machines on a subnet if we want to keep things moving... Is it any wonder that the Internet is running out of IP addresses? (But don't worry, they're working on extending them.)

For many machines, the domain level organization amounts to machine.institution.domain or machine.network.institution.domain. At UIC, it's generally machine.department.uic.edu. Consider, for example, the PC on my desk, judys.cc.uic.edu. For campus-wide machines, like tigger for example, we leave out the department: tigger.uic.edu. But tigger.cc.uic.edu works too; that's one of the nice things about domain names -- a single machine may have any number of them, whereas (generally speaking) it can only have one Internet IP address -- at a time, that is. So we also call tigger www.uic.edu when it's acting as our campus's World Wide Web server. This is good because it's easy to remember, and it's also good because we can move the server and the name to another machine without having to tell people about it. In fact, we'd only have to update a name server or two.

Many top level domains have specific domain names which all institutions in their domains take; for example, AU for Australia, CA for Canada, and JP for Japan. Alternatively, when an individual institution that is not already part of an organized domain joins the Internet, it chooses one of the following as their top level domain name: EDU (for education), GOV (for government), COM (for commercial), NET (for network), MIL (for military), or, if all else fails, ORG (for organization).

Since IP addresses can change, common sense recommends that you use a machine's domain-style name rather than its IP address when contacting it. However, you might want to try using the IP address (after first trying the name), if it seems that the name server is down.

Name servers know a lot more about the machines they recognize than just their name and IP address. For details, see the online help for the nslookup command. (Enter help nslookup on CMS, man nslookup on UNIX.)

Finally, have you ever sat staring at your screen, waiting for a remote computer to answer, wanting to ask "Hey, tigger.uic.edu, are you there?" Well, you can do that, too; enter: ping tigger.cc.uic.edu
The remote machine will acknowledge the ping if it's up and if there's a functional path between it and your machine. Ping is part of the TCP/IP suite; so you should be able to enter the command from your PC.

Comments are appreciated; send them to
Judith Grobe Sachs, judygs@uic.edu

There's a very readable description of TCP/IP and how it's used to carry information through networks on Inform; use the search keyword tcp/ip. The article starts out very simply, but does eventually get to almost all anyone would ever want to know. It's the "Introduction to the Internet Protocols," written in 1987, by Charles L. Hedrick of Rutgers University. It's worth reading.