CISCO NETWORKING ACADEMY Chabot College ELEC 99.05 Application Layer Puzzles

CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY

Chabot CollegeChabot College

ELEC 99.05ELEC 99.05 Application Layer PuzzlesApplication Layer Puzzles


PuzzlePuzzle

• When I run a network application, I see results on my screen.

• Where are those events happening?


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”


Application LayerApplication Layer

• Connection types– Make-Break– Session


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


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


telnet Examplestelnet Examples

• telnet://library.uark.edu

• telnet://locis.loc.gov


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.


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”


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”


telnettelnet• In Semester 2, you will use telnet

extensively to connect your PC to routers.


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”.


Fully Qualified Domain NameFully Qualified Domain Name

www.clpccd.cc.ca.us

Host name Domain name Top-LevelDomain name


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


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.


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.


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


Let’s try it!Let’s try it!• Point your browser at:• telnet://library.uark.edu• http://library.uark.edu


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)


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!


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)


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


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.


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.

Documents

CISCO NETWORKING ACADEMY Chabot College ELEC 99.05 Application Layer Puzzles