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)
