Basic Networking

Networking Basics

A network of networks that communicate using shared protocols
A network is loosely defined as several computers that can directly communicate with each other, under single management
A protocol (p. 25-28) is an agreed-upon standard for doing something
Point-to-Point Protocol (PP) is a protocol for doing TCP/IP over phone lines
Post Office Protocol (POP) is a protocol for downloading mail from servers

RE-INVENT THE INTERNET

Suppose it’s 1968 and you’re in charge of a project to make two computers talk to each other. How would you go about doing it? What are the basic things that must be there?

Networking Basics

Two computers, a piece of wire, and a software protocol

What kind of wire? What do the electrical signals mean?

What if the operating systems of the computers are different?

How do you know what data is meant for what machine?

What if someone on another network wants to use different

Wiring types?

TCP/IP

TCP/IP is a basic protocol for communications between computers

Ethernet is a standard for communicating across specific types of wires

TCP/IP runs on top of many physical mediums, from Ethernet to phone lines to FDDI to token ring

If your web browser uses TCP/IP for communications, you don’t have to worry about what type of wiring you have

Other protocols

TCP/IP is one of several high level protocols. There are others:

AppleTalk

DECnet

SNA (IBM mainframe)

OSI (Open Systems Interconnect, an international standards group that cratered)

TCP/IP is far and away the biggest in the marketplace

Communicating with TCP/IP

Every computer in a TCP/IP network has a unique number assigned to it

If you want to communicate with a computer, you have to refer to it by number

PC1

131.120.7.1

PC2

131.120.7.5

PC3

131.120.7.17

Domain Name Service (DNS)

DNS is a utility that allows humans to refer to computers by name instead of number

A server machine keeps track of the number-to-name translation and answers queries from machines on the network

PC 1

131.120.7.1

hume.nps.navy.mil

PC2

131.120.7.5

locke.nps.navy.mil

PC3

131.120.7.17

smith.nps.navy.mil

PC4

131.120.7.42

dns.nps.navy.mil

DNS

DNS lookups happen all the time; any time you refer to a machine by name, this translation has to happen

This leads to a common failure mode: the DNS server is down or can’t be reached, so the translation can’t happen.

Watching DNS Work

On NT an Unix machines you can see DNS working with “nslookup”

Web-based at http://dns411.com/

> nslookup www.apple.com

Server: otter.mbay.net

Address: 206.40.79.2

Non-authoritative answer:

Name: www.apple.com

Address: 17.254.0.91

Domain Names

The name of a computer gives you a clue about what type of organization it belongs to:

www.apple.com (.com means commercial)

www.nps.navy.mil (.mil is US military)

uunet.net (.net is an internet service provider)

mit.edu (.edu is degree-granting educational)

web3d.org (.org is non-commercial organization)

www.whitehouse.gov (.gov is government)

Other nations have their own top level domain

uk, au, tk, tw, jp

Whois

What if someone wanted to create a new website with the name “microsoft.com”?

You have to register a domain name; two people can’t have the same domain name

A central database is maintained of who owns what domain name

Whois tells you information about who registered the domain name

Whois http://dns411.com/

Registrant:

Apple Computer, Inc. (APPLE-DOM)

1 Infinite Loop

Cupertino, CA 95014

Domain Name: APPLE.COM

Record last updated on 05-May-98.

Record created on 19-Feb-87.

Database last updated on 10-Jul-99 09:14:52 EDT.

Domain servers in listed order:

NSERVER.APPLE.COM 17.254.0.50

NSERVER2.APPLE.COM 17.254.0.59

NSERVER.EURO.APPLE.COM 194.151.19.41

NSERVER.ASIA.APPLE.COM 203.120.14.5

Domain Names

You can buy your own domain name for $70.

Go to www.internic.net, check to make sure it’s not taken already, sign up, send ‘em a check. Need to coordinate with your ISP if you want to actually use it

Domain Name Ownership

“ownership” of domain names is hazy; trademark and other laws collide here

A classic strategy is “domain name squatting”--someone buys up likely domain names in expectation of selling them later or to make a point

mcdonalds.com, dole96.org, Bush domain names, flowers.com, etc

The domain name system is being transitioned to a more free market system with more than one seller and a few new top level domain names

New top level names proposed are

firm, shop, web, arts, rec, info, nom

Overview

Protocols let computers communicate

TCP/IP is one example of a protocol

Protocols can be layered so that changing one does not break other software

DNS translates names to IP numbers, and vice versa