Networking Practicum:
TraceRoute, FTP, Basic HTML
Week 2
LBSC 690
Information Technology
Muddiest Points
•	The math

•	How binary representation affects size

•	System architecture
–	How dual core processors affect overall speed

•	RAID
–	Redundant Array of Inexpensive Disks

•	Things on the slides I don’t mention
Dual-Core System Architecture
Common RAID Configurations
Some Definitions
•	Latency
–	The amount of time it takes data to travel from source to destination

•	Bandwidth
–	The amount of data that can be transmitted in a fixed amount of time
Goals for Today
•	Understand how bits get from here to there

•	Learn to move files to a “Web server”

•	Use those skills to make a Web page
The Internet
•	Global collection of public “IP” networks
–	Private networks are often called “intranets”

•	Independent
–	Each organization maintains its own network

•	Cooperating
–	Internet Protocol (IP) address blocks
–	Domain names
–	World-Wide Web Consortium (W3C)
–	Computer Emergency Response Team (CERT)
A Short History of the Internet
•	1969: Origins in government research 
–	Advanced Research Projects Agency (ARPAnet)
–	Key standards: UDP, TCP, DNS
•	1983: Design adopted by other agencies
–	Created a need for inter-network connections
–	Key standards: IP
•	1991: World-Wide Web added point-and-click
–	Now 571 million Internet “hosts” (August 2008)
–	Key standards: HTTP, URL, HTML, XML
What Changed in 1994?
Overview
Types of Digital Channels
•	“Backbone”
–	Microwave
–	Satellite
–	Fiber
•	“Last mile” wired
–	Telephone modem
–	ADSL
–	Cable modem
–	Fiber

•	“Last mile” wireless
–	Wi-Fi (IEEE 802.11)
–	GSM

Thinking About Speed
Internet  Web
•	Internet: collection of global networks

•	Web: way of managing information exchange

•	There are many other uses for the Internet
–	File transfer (FTP)
–	Email (SMTP, POP, IMAP)
The World-Wide Web

Web Standards
•	HTML
–	How to write and interpret the information

•	URL
–	Where to find it

•	HTTP
–	How to get it

Types of Internet “Nodes”
•	Hosts
–	Computers that use the network to do something

•	Routers
–	Specialized computers that route packets

•	Gateway
–	Routers that connect two networks

•	Firewall
–	Gateways that pass packets selectively
IP Address
•	Every host (and every router) is identified by an “Internet Protocol” (IP) address

•	32 bit number, divided into four “octets”

An Internet Protocol (IP) Address
Dynamic IP Addresses
•	Dynamic Host Configuration Protocol (DHCP)
Hands-on: 
Learn About Your IP Address
•	Find your IP address
–	Select “start” on the taskbar, then “Run”
–	Type in “cmd” and click “OK”
–	Type “ipconfig /all” (and press enter)

•	See who “owns” that address
–	Use http://remote.12dt.com/

•	See where in the world it (probably) is
–	http://www.geobytes.com/ipLocator.htm
Routing Tables
TraceRoute
•	See how packets get from South Africa to you
–	Use http://utl-lnx1.puk.ac.za/cgi-bin/webutil

•	Look at the same data visually
–	http://visualroute.visualware.com/
Domain Name Service (DNS)
•	“Domain names” improve usability
–	Easier to remember than IP addresses
–	Written like a postal address: specific-to-general

•	Each “name server” knows one level of names
–	“Top level” name servers know .edu, .com, .mil, …
–	.edu name server knows umd, umbc, stanford, …
–	.umd.edu name server knows wam, ischool, ttclass, …
–	.wam.umd.edu name server knows rac1, rac2, …
IP Addresses and Domain Names
Uniform Resource Locator (URL)
•	Uniquely identify Web pages

Ports
•	Well-known ports
–	22 Secure Shell (for SSH and SFTP)
–	25 Simple Mail Transfer Protocol (SMTP)
–	53 Domain Name System (DNS)
–	68 Dynamic Host Configuration Protocol (DHCP)
–	80 Hypertext Transfer Protocol (HTTP)
–	143 Internet Message Access Protocol (IMAP)
–	554 Real-Time Streaming Protolol (RTSP)
•	Registered Ports
–	8080 HTTP server run by ordinary users
•	Ephemeral Ports
Port Mapping
•	Internet Service providers lease one IP address
–	But home networks may contain many machines

•	Network Address Translation (NAT)
–	Each internal machine gets a private IP address 
–	Ports on internal machines are mapped both ways

•	Port forwarding
–	Permits public server to run in the local network
Paths
•	Specify location of files on a hard drive
•	Folder metaphor
–	Hierarchically nested directories

–	Absolute vs. relative paths
Hands On:
The Directory Tree
•	First, use Windows Explorer to visually explore the directory tree

•	Now launch a “shell” with Start->Run->cmd
–	“c:” takes you to Drive C
–	“dir” lists the present “directory”
–	“cd WINDOWS” takes you “down” to the WINDOWS directory
–	cd .. takes you “up” in the tree
The TCP/IP “Protocol Stack”
•	Link layer moves bits 
–	Ethernet, cable modem, DSL
•	Network layer moves packets
–	IP 
•	Transport layer provides services to applications
–	UDP, TCP 
•	Application layer uses those services
–	DNS, SFTP, SSH, …
TCP/IP layer architecture
Transmission Control Protocol (TCP)
•	Built on the network-layer version of UDP

•	Guarantees delivery all data
–	Retransmits missing data

•	Guarantees data will be delivered in order
–	“Buffers” subsequent packets if necessary

•	No guarantee of delivery time
–	Long delays may occur without warning
User Datagram Protocol (UDP)
•	The Internet’s basic transport service
–	Sends every packet immediately
–	Passes received packets to the application

•	No delivery guarantee
–	Collisions can result in packet loss

•	Example: sending clicks on web browser
UDP/IP Protocol Stack
HyperText Transfer Protocol (HTTP)
•	Send request 
GET /path/file.html HTTP/1.0 
From: someuser@jmarshall.com 
User-Agent: HTTPTool/1.0 

•	Server response
HTTP/1.0 200 OK 
Date: Fri, 31 Dec 1999 23:59:59 GMT 
Content-Type: text/html 
Content-Length: 1354 
<html><body> <h1>Happy New Millennium!</h1> �c </body> </html> 
File Transfer Program (FTP)
•	Used to move files between machines
–	Upload (put) moves from client to server
–	Download (get) moves files from server to client

•	Both visual and command line interfaces available

•	Normally requires an account on the server
–	Userid “anonymous” provides public access

Hands On:
Graphical Secure FTP
•	SFTP to “terpconnect.umd.edu”

•	Change directory to “/pub/USERID”

•	Upload or download files

•	You can see these files at:
http://www.wam.umd.edu/~USERID/
Hands On:
Unsecure Command Line FTP
Start->Run->cmd
“ftp umiacs.umd.edu”
Login in as user “anonymous”
Download a file
•	“cd pub/gina/lbsc690/”
•	“binary”
•	“get hwOne.ppt”
Exit
•	“quit”
Network Abuse
•	Flooding
–	Excessive activity, intended to prevent valid activity

•	Worms
–	Like a virus, but self-propagating

•	Sniffing
–	Monitoring network traffic (e.g., for passwords)
Encryption
•	Secret-key systems (e.g., DES)
–	Use the same key to encrypt and decrypt

•	Public-key systems (e.g., PGP)
–	Public key: open, for encryption
–	Private key: secret, for decryption

•	Digital signatures
–	Encrypt with private key, decrypt with public key
Encrypted Standards
•	Secure Shell (SSH)
–	Replaces Telnet
•	Secure FTP (SFTP)/Secure Copy (SCP)
–	Replaces FTP
•	Secure HTTP (HTTPS)
–	Used for financial and other private data
•	Wired Equivalent Protocol (WEP)
–	Used on wireless networks
•	Virtual Private Network (VPN)
–	Not really a “standard”
Virtual Private Networks
HyperText Markup Language (HTML)
•	Simple document structure language for Web

•	Advantages
–	Adapts easily to different display capabilities
–	Widely available display software (browsers)

•	Disadvantages
–	Does not directly control layout
“Hello World” HTML
Hands On:
Learning HTML From Examples
•	Use Internet Explorer to find a page you like
–	http://www.glue.umd.edu/~oard 

•	On the “Page” menu select “View Source” (in IE7)
–	Opens a notepad window with the source

•	Compare HTML source with the Web page
–	 Observe how each effect is achieved
Hands On: “Adopt” a Web Page
•	Modify the HTML source using notepad
–	For example, change the page to yours

•	Save the HTML source on your “M:” drive
–	In the “File” menu, select “Save As”
–	Select “All Files” and name it “test.html”

•	FTP it to your ../pub directory on terpconnect

•	View it
–	http://www.wam.umd.edu/~(yourlogin)/test.html 
Tips
•	Edit files on your own machine
–	Upload when you’re happy
•	Save early, save often, just save!
•	Reload browser to see changes
•	File naming
–	Don’t use spaces
–	Punctuation matters
HTML Document Structure
•	“Tags” mark structure
–	<html>a document</html>
–	<ol>an ordered list</ol>
–	<i>something in italics</i>
•	Tag name in angle brackets <>
–	Not case sensitive
•	Open/Close pairs
–	Close tag is sometimes optional (if unambiguous)
Logical Structure Tags
•	Head 
–	Title

•	Body
–	Headers: <h1> <h2> <h3> <h4> <h5> 
–	Lists: <ol>, <ul> (can be nested)
–	Paragraphs:<p>
–	Definitions: <dt><dd>
–	Tables: <table> <tr> <td> </td> </tr> </table>
–	Role: <cite>, <address>, <strong>, …
Physical Structure Tags
•	Font
–	Typeface: <font face=“Arial”></font>
–	Size: <font size=“+1”></font>
–	Color: <font color=“990000”></font>
•	http://webmonkey.wired.com/webmonkey/reference/color_codes/Emphasis
–	Bold: <b></b>
–	Italics: <i></i>
(Hyper)Links
Hypertext “Anchors”
•	Internal anchors: somewhere on the same page
–	<a href=“#students”> Students</a>
•	Links to: <a name=“students”>Student Information</a>

•	External anchors: to another page 
–	<a href=“http://www.clis.umd.edu”>CLIS</a>
–	<a href=“http://www.clis.umd.edu#students”>CLIS students</a>

•	URL may be complete, or relative to current page
–	<a href=“video/week2.rm”>2</a>

•	File name part of URL is case sensitive (on Unix servers)
–	Protocol and domain name are not case sensitive
Images
•	<img src=“URL”> or <img src=“path/file”> 
–	<img src=“http://www.clis.umd.edu/IMAGES/head.gif”>
–	SRC: can be url or path/file
–	ALT: a text string
–	ALIGN: position of the image
–	WIDTH and HEIGHT: size of the image
•	Can use as anchor:	
–	 <a href=URL><img src=URL2></a>
•	Example: 
–	http://www.umiacs.umd.edu/~daqingd/Image-Alignment.html
Tables
Table Example
<table align=“center”>
<caption align=“right”>The caption</caption>    
	< tr align=“LEFT”>
		<th> Header1 </th>
		<th> Header2</th>
	</tr>
	<tr><td>first row, first item </td>
            <td>first row, second item</td></tr>
	< tr><td>second row, first item</td>
            <td>second row, second item</td></tr>
</table>
See also: http://www.umiacs.umd.edu/~daqingd/Simple-Table.html
Before You Go
	On a sheet of paper, answer the following (ungraded) question (no names, please):

	What was the muddiest point in today’s class?