F

rrrrrrrrr

rrrrrrrrr

Pebbles loves the idea. She builds and connects the new hubs in the lab, just to prove the concept. It works! She makes the (now shorter) cables, installs the hubs and cables, and is ready to test. She goes to a few representative PCs and tests, and it all works! The first network has now been deployed.

Wanting to surprise Poppa Fred, Pebbles writes a memo to everyone in the company, telling them how to use the soon-to-be-famous Fred Transfer Program to transfer files. Along with the memo, she puts a list of names of people and the four-digit network address to be used to send files to each PC. She puts the memos in everyone's mail slot and waits for the excitement to start.

Amazingly, it all works. The users are happy. Fred treats Pebbles and Bam Bam to a nice dinner—at home, cooked by Wilma, but a good meal nonetheless.

Pebbles thinks she did it—created the world's first computer network, with no problems— until a few weeks pass. "I can't send files to Fred anymore!" exclaims Barney Rubble. "Ever since Fred got that new computer, he's too busy to go bowling, and now I can't even send him files telling him how much we need him back on the bowling team!" Then it hits Pebbles—Fred had just gotten a new PC and a new networking card. Fred's network address had changed. Or what happens if the card fails and it has to be replaced? The address changes.

About that time, Wilma comes in to say hi. "I love that new network thing you built. Betty and I can type each other notes, put them in a file, and send them anytime. It's almost like working on the same floor!" she says. "But I really don't remember the numbers so well. Couldn't you make that FTP thing work with names instead of addresses?"

In a fit of inspiration, Pebbles sees the answer to the first problem in the solution to her mom's problem. "I'll change FTP to use names instead of addresses. I'll make everyone tell me what name they want to use—maybe Barney Rubble will use BarneyR, and Barney Fife will use BarneyF, for instance. I'll change FTP to accept names as well as numbers. Then I'll tell FTP to look in a table that I will put on each PC that correlates the names to the numeric addresses. That way, if I ever need to replace a LAN card, all I have to do is update the list of names and addresses and put a copy on everyone's PC, and no one will know that anything has changed!" Table 1-2 lists Pebbles first name table.

Table 8-1 Pebble's First Name/Address Table

Person's Name

Computer Name

Network Address

Fred Flintstone

Fred

0001

Wilma Flintstone

Wilma

0002

Barney Rubble

BarneyR

0011

Betty Rubble

Betty

0012

Barney Fife

BarneyF

0022

Pebbles Flintstone

Netguru

0030

Bam Bam Rubble

Electrical-guy

0040

Pebbles tries out the new FTP program and name/address table in the lab, and it works. She deploys the new FTP software, puts the name table on everyone's PC, sends another memo— and now she can accommodate changes easily by separating the physical details, such as addresses on the networking cards, from what the end users need to know.

Like all good network engineers, Pebbles thought through the design and tested in a lab before deploying the network. For the problems she did not anticipate, she found a reasonable solution to get around the problem.

So ends the obviously contrived imaginary first computer network. What purpose did this silly example really serve? First, you have now been forced to think about some basic design issues that confronted the people who created the networking tools that you will be learning about for the CCNA exams. Although the example with Pebbles might have been fun, the problems that she faced are the same problems faced—and solved—by the people who created the original networking protocols and products.

The other big benefit to this story, particularly for those of you brand new to networking, is that you already know some of the more important concepts in networking:

Ethernet networks use cards inside each computer.

The cards have unique addresses, similar to Pebble's networking cards.

Ethernet cables connect PCs to Ethernet hubs—hubs that repeat each received signal out all other ports.

The cabling is typically run in a star configuration—in other words, all cables run from a cubicle to a wiring (not broom!) closet.

Applications such as the contrived Fred Transfer Program or the real-life File Transfer Protocol (FTP) ask the underlying hardware to transfer the contents of files. Users can use names—for instance, you might surf a web site called www.myfavoritewebsite.org—but the name gets translated into the correct address.

Now on to the real chapters, with real protocols and devices, with topics that you could see on the CCNA INTRO exam.

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