Web Servers and URLs

Web Servers and URLs

And Domain Names

WWW vs. Internet

World Wide Web• An application layer built

using the Internet• Refers mostly to protocols

and content– http– ftp– Email: pop, imail, etc.

• Anything accessible via a URL.

Internet• Existed before the WWW• Refers mostly to physical

network, i.e., hardware, computers, etc.

• Network of Network concept

• Unique features– TCP/IP protocol– Packet Switching

MAC Address vs. IP Address

• On a network, a device has a unique manufactures address.

• Via TCP/IP an IP Address is “mapped” to specific MAC addresses, specific device.

• The IP Address is like an extended zip code (12211-1462) that helps “find” a device on the Internet.

IP Address vs. URL

• IP Address can only specify a device.• A URL (uniform resource locator) specifies a

device, an application protocol, and the file location of a resource.

• http://www.cs.siena.edu/facilities/map.jpg

Protocol Server Name

Sub-domain

Domain Name TDL

Folder Path

File Name

Important WWW protocols

• File Transfer Protocol (FTP): Early file sharing• Telnet: Early remote access• POP, SMTP, IMAP, MIME: Electronic Mail• Modern Protocols: – Gnutella– Bit Torrent

• Hypertext Transfer Protocol (http)– Secure http (encrypted http)

Client-Server model of WWW

• Client: Web Browser, i.e., Firefox

• Client connects to Server

• Requests a web page• Uses a URL to make the

request.• Sends request over the

Internet.

• Server: Web Server, i.e., Apache.

• Daemon process (constantly running) listens for web page requests.

• Responds by sending web page (or resource) over the Internet.

Web Servers

• Apache – Made by an open source foundation, i.e, it’s free! 50% of the web servers in the world.

• Microsoft IIS – 34% market share• Google GWS – 5%• Sun Java System – Once great…now hardly

used.

Anatomy of a Web Server (http host)

• Can be any computer. Apache can run on a PS3.• Computer needs Internet connectivity and a

static IP address – http://193.68.103.43– It helps to have a domain name, but it’s not

necessary• RAM and multiple processors are important.• FYI: Getting a static IP address is the big cost ($50/month

minimum). Most ISPs don’t give you a static IP address for nothing.

Domain Names and DNS

• Domain Name System (DNS) refers to the hierarchical system of servers that help give the WWW names instead of just IP addresses.

• Essentially, it’s a globally distributed lookup table• Look up the domain name and system tells you

the IP address.

–siena.edu 66.163.8.30–rpi.edu 71.124.69.58

DNS Rational

• IP Address can change– If you change your Internet service provider– Move to a different location– Expand your local area network

• Domain names do not have to change, just update the DNS servers.

• More importantly, Domain names are easier to remember and significant!

Who maintain the DNS

• ICANN: International Corporation for Assigned Names and Numbers– Non-profit, international, public company founded

in 1998 to make sure the Internet works globally.• Internet Service Providers (AT&T, Time

Warner, Sprint, AOL, etc.)• Organizations with Local Area Networks

(Siena, NYState Government, MapInfo, etc.)

Domain Name Registration

• Used to be centralized, non-profit– Only had to pay administrative fee– ICANN couldn’t handle the volume

• Domain Name Registration is now Commercialized:– Company (like GoDaddy) becomes a registrar by applying to

ICANN.• Once Registrars are approved by ICANN

– They can charge a fee for domain name registration and do the paperwork for you

– Thus, ICANN only has to deal with a few thousand registrars, rather than millions of customers.

Notable Registrars

• Network Solutions– One of the first. In the early days, ICANN

exclusively outsourced operations to Network Solutions, but then realized it should be an open market.

• GoDaddy• Yahoo• Verio• Aplus

What comes first, domain name or web server?

Like asking, “What came first, the chicken or the egg?”

Early days (pre-2000)• Setup a web server, test it

via its IP address and then register a domain name.

• Then, update your local DNS, or

• Ask your Internet Service provider to update their DNS.

Typical Process (post-2000)• Register a domain with a

certified Registrar.• Purchase web hosting

service.• Ask your hosting service to

add your domain to their DNS.

DNS Hierarchy

Siena

twtelecom

edu

nysernetcentic

St. RoseRPIStanford UAlbany

comnetTop Level Domain (TDL) DNS… coordinated by ICANN

cs

Web Hosting Revolution

• Very few organization maintain their own web server?

• Why?• What are the alternatives?

Web Hosting Options

Virtual Hosts ($5-50/month)

• A single computer can run multiple instances of web server software

• Many websites can be hosted off of one computer with one IP address.

Dedicated Host($50-???/month)

• You get your own computer

• And IP Address• Usually, rack-mounted

in a server farm with thousands of other computers.

One Web Server, Many Domains

DNS Server

Web Serverwww. siena-space.org

www.cs.siena.edu

www.sos.siena.edu

66.168.3.102

public_html

sos cs siena-space.org

Web Server can be configured to resolve domain name to specific folder.

Sometimes called mapping or binding

Domain Names, TDLs and URLs

http://www.cs.siena.edu/~ebreimer/courses/csis-401-s09/index.html

Server Details

• public_html (or www) folder– The folder that contains publically readable web

pages (and other public files)• cgi-bin folder– Common gateway interface binaries– The folder that contains custom scripts and

applications– Not really used anymore– Toda, scripts often go right in the public_html folder.

Server Error files

• 404.html– If a file can’t be found, you can have this web page

load by default• 401.html– If a file can’t be access (no privilege)

• http://en.wikipedia.org/wiki/List_of_HTTP_status_codes

Default page for folders

• http://www.siena.edu/people/faculty/

• If a URL points to a folder, you can have a page load by default.

• index.html or default.html will load if a specific page is not specified.

• Server can be configured so that a folder listing will be returned if there is no index or default page.

How websites used to be organized

• Early Days: Folder Hierarchy– http

://www.cs.siena.edu/~ebreimer/courses/csis-401-s09/labs/

– With index page and Up, Down, and Next links• http://www.w3.org/TR/html401/

• Today: Menus– Static (~ebreimer)– Dynamic (www.cs.siena.edu)

HTML Frames

• If we have time.• Bad idea taken to the next level.

Dynamic Menus and Content

• Let the web server do the work.– Part of TBLs original framework.

• URL can point to a script/program.• Web server can run the script and output the

results• Result is usually – A Web Page– Part of a Web Page (like the main menu)