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Now that You're Wired

The Hardware Changes

Regardless of whether the machine on your desk is a Mac, PC, 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 personal computer: 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

There are other differences too. Someone (perhaps you or your department's REACH representative) installed and set up your TCP/IP software and hopefully the ACCC's Network Services Kit. "TCP/IP" is the name commonly given to a "suite of protocols" developed to allow cooperating computers to share resources across a network. In this context, "suite" simply means "set". A "protocol" formally describes a specific type of information exchange. 

TCP and IP are specific protocols in the TCP/IP suite; others that you've heard of 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.

A New Name and Address

With your UIC network 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.)

Every Machine on the UIC Campus Network Must Be Registered

The ACCC's Network group are our network administrators. They're the ones who make sure that each machine has a unique IP address, and they're also the ones who keep our name servers up-to-date with lists of UIC IP addresses and the domain names that correspond to them.

In addition to IP addresses, we also require that you register a domain-style name for your machine. While this might not seem to be necessary, it can be. Some Internet services -- including the U of I human resource department's Nessie system and all other campus resources that require Bluestem authentication -- refuse to serve requests from machines that don't have both a registered IP address and a registered name.

Internet IP Addresses

The IP address is a unique set of four 3-digit numbers, assigned to your machine by its "network administrator", and usually written like (That's tigger's IP address now. Tigger used to have a different IP address. That's one of the problems with IP addresses; they can -- and do -- change.) 

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.)

UIC has two "Class B" Internet addresses: "128.248." and "131.193.". All machines on the west side of campus have IP addresses that begin with 128.248; those on the east side begin with 131.193. We use the third number to indicate the subnet and the fourth to identify your machine. 

Internet Domain-Style Names

Internet domain names are a string of descriptive words, usually up to four, separated (again) by periods. Domain names have a tree structure, listing the name and "address" of the machine in order of increasing generality. 

For many machines, the domain level organization amounts to machine.institution.domain or At UIC, it's generally

Consider, for example, the PC on my desk, (My Mac is For campus-wide machines, like tigger for example, we leave out the department: But 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 (one IP address at a time, that is). We also call tigger 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. The US's top level domain is US, preceeded by the state; the city of Chicago's Web home page is on the machine, for example.

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). 

Domain Name Servers

We've said that domain names are good because they don't change. That's true. But the traffic on the Internet is sent to IP addresses, not domain names, so we need something to translate the domain names that we use to the IP addresses that the Internet uses. That's where Domain Name System (DNS) servers come in; they translate domain names into IP addresses. (Or, to use the proper jargon: Internet domain names are mapped into the numerical IP addresses by a DNS server.)

Name servers are special machines that own tables linking IP addresses to domain names. When networking software on any machine encounters a domain-style name, it contacts a name server that it knows about and asks it to resolves the domain name into the IP address corresponding to that name. Obviously, every name server doesn't know about every name. It does the translation if it can; if it can't, it just passes the request along to the other name servers it knows about. 

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 Server Utilities

Want to talk to the name server yourself? Use the nslookup command. For example, is one of the UIC domain name servers; what's it name? On UNIX, enter: nslookup
You'll find that it's Using your personal computer? Modern operating systems come with nslookup and ping built-in; open a command window and enter the commands.

(Another domain name server is, IP address Did you notice that the third number in the name servers' addresses are different? At UIC, that means that they're on different subnets; that's a useful precaution.) 

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 man nslookup on UNIX.)

Finally, have you ever sat staring at your screen, waiting for a remote computer to answer, wanting to ask "Hey,, are you there?" Well, you can do that, too; enter: ping

The remote machine will acknowledge the ping if it's up and if there's a functional path between it and your machine.

Want to know more about TCP/IP protocols and how the Internet works?

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

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2004-11-16  ACCC documentation
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