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CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
Chabot CollegeChabot College
ELEC 99.05ELEC 99.05 Application Layer PuzzlesApplication Layer Puzzles
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
PuzzlePuzzle
• When I run a network application, I see results on my screen.
• Where are those events happening?
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
Application LayerApplication Layer
• Host relationships:– Client
• typically a user PC• the source of a transaction
– Server• a shared host on the network• the destination of the transaction
• Network applications usually are “client-server”
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
Application LayerApplication Layer
• Connection types– Make-Break– Session
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
Make-Break ConnectionsMake-Break Connections
• Typically involve a single file transfer.• Examples
– HTTP• HyperText Transfer Protocol
• web file
• TCP port 80
– SMTP• Simple Mail Transfer Protocol
• E-mail file
• TCP port 25
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
Session ConnectionsSession Connections
• Maintained until “session” is closed.• Examples
– telnet• terminal emulation
• passes keystrokes from client to server
• TCP port 23
– FTP• File Tranfer Protocol• manages transfer of many files
• TCP port 21
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
telnet Examplestelnet Examples
• telnet://library.uark.edu
• telnet://locis.loc.gov
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
Running telnet (DOS)Running telnet (DOS)
• At the DOS Prompt, type
>telnet hostname
or
>telnet Ipaddress• Try it! Demo
Telnet to library.uark.edu• Be sure to choose “Q” to logoff when
done.
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
Running telnet (Windows)Running telnet (Windows)• Start | Programs | Accessories | Communications |
Hyperterminal• Double-click Hypertrm.exe• Enter a name for this connection• At the bottom of the next dialog box, for “Connect Using”, select
TCP/IP (winsock)• Add the destination host name or IP address• (Notice the port number in this dialog)• Try it! Demo
Telnet to library.uark.edu• Be sure to choose “Q” to logoff when done.• When asked if you wish to save the session, say “No”
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
Running telnet (browser)Running telnet (browser)• Browsers use helper applications to provide certain
functions.• By default, Internet Explorer launches Hyperterm
when it encounters a URL that specifies the telnet protocol
• Try it! Demo
• Point your browser at telnet://library.uark.edu
• Be sure to choose “Q” to logoff when done.• When asked if you wish to save the session, say “No”
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
telnettelnet• In Semester 2, you will use telnet
extensively to connect your PC to routers.
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
DNS PuzzlerDNS Puzzler• In the following URL,
what does “WWW” refer to?• http://www.clpccd.cc.ca.us
• Answer:
It is the hostname (computer name) portion of a “fully qualified domain name”
It does not specify the protocol HTTP (web)!
This computer just happens to be named “www”.
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
Fully Qualified Domain NameFully Qualified Domain Name
www.clpccd.cc.ca.us
Host name Domain name Top-LevelDomain name
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
Let’s try it!Let’s try it!• Point your browser at:• http://209.129.156.3• http://www.clpccd.cc.ca.us• http://www• http://porter.clpccd.cc.ca.us• http://porter
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
Let’s try it!Let’s try it!• For the host at 209.129.156.3, Chabot’s
DNS servers list
• porter as the host name
• www as a name alias (a canonical name)
• We will study the structure of DNS tables in Semester 2.
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
DNS PuzzlerDNS Puzzler• Why is Chabot-Las Positas assigned a
domain name of clpccd.cc.ca.us ?
• Why aren’t we clpccd.edu ?
• Answer:
RFC 1480
• A recent change permits community colleges to move to the .edu top-level domain.
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
Browser URLBrowser URL• Universal Resource Locator
• Example:
http://www.cisco.com
• Browser uses the text before :// to select protocol and port number.
protocol hostname domain top-leveldomain
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
Let’s try it!Let’s try it!• Point your browser at:• telnet://library.uark.edu• http://library.uark.edu
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
Browser URLBrowser URL• Universal Resource Locator• Example:
http://www.cisco.com• If protocol:// is omitted, then the
protocol is not specified.• In that case, the browser tries to “guess”
the protocol from the hostname:– hostname www defaults to http (port 80)– hostname ftp defaults to ftp (port 21)
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
HTTP PuzzlerHTTP Puzzler• When you view a web page, where is it?
• Answer:
On your PC!
• Let’s look at the contents ofC:\windows\temporary internet files demo
• Note that one web page may be made up of many files of various types.
• Note that one web page may contain files loaded from several servers!
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
E-mail PuzzlerE-mail Puzzler• When you view your E-mail, where is it
stored?
• Answer
It depends on the protocol!– Post Office Protocol (POP)– Web mail (e.g. yahoo mail)
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
E-mail ClientsE-mail Clients• POP Clients
– E-mail is transferred from the mail server to your PC– Port 110– Client examples” Eudora, Outlook Express, Netscape– Most ISPs offer POP E-mail
• Web mail clients– E-mail remains on the server for viewing by any browser in the
world.– Port 80– Browser is the client.– Offered by Yahoo, Hotmail, GroupWise Web Access
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
POP E-mailPOP E-mail
SMTP Server/POP Server
POP (110) POP (110)SMTP (25)
SMTP Server/POP Server
E-mail is delivered to client PC.Once delivered, it can only be accessed at that PC.
E-mail passes through the post officeserver but does not remain there.
CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY
Web E-mailWeb E-mail
SMTP Server/HTTP Server
HTTP (80) HTTP (80)SMTP (25)
SMTP Server/HTTP Server
E-mail is delivered to the Web mail
server and remains there.
Web E-mail can be viewed from any web browser.
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