Internet Applications Lynn Bashaw Manager, Network Engineering

Applications DNS Telnet FTP WWW News

Internet Architecture

Private Peering Public Peering

Internet Architecture

Domain Name Service Machines talk in numbers; Humans can’t remember numbers Map names to numbers – =

Domain Name Service Enter destination in browser

Domain Name Service DNS Resolver DNS Server

Domain Name Service DNS Resolver DNS Server Root Name Server

Domain Name Service DNS Server Root Name Server DNS Server

Domain Name Service DNS Resolver DNS Server

Domain Name Service DNS Resolver DNS Server

Domain Name Service

Telnet

Telnet Client Telnet Server Initially Support NVT NVT - Network Virtual Terminal

Telnet Telnet Client Telnet Server Negotiate Terminal Options

File Transfer Protocol Provides a service for applications that want to move files between networked computers It does NOT define the user interface What you know as FTP is really an application designed to provide a friendly interface to the FTP application. Primary function of FTP is to reduce or remove incompatabilities between the handling of files on different operating systems Uses a set of defined network standard commands

File Transfer Protocol FTP Client FTP Application FTP Server IP Network User “double clicks” on a folder on “Formus” List MAC OS ls SunOS Formus

File Transfer Protocol FTP Client FTP Application FTP Server MAC OS SunOS Control Data Port 21 Port 20

World Wide Web Originated at European Particle Physics Laboratory (CERN) Hypertext system modified for use on the Internet Hypertext is a another method of organization unlike a traditional hierarchial tree Three key specifications of a WWW implementation are; –URL (Universal Resource Locator) –HTTP (HyperText Transfer Protocol) –HTML (HyperText Mark-up Language)

Universal Resource Locator Intended to be a method of identifying a specific resource on a specific host protocol://server/directory/filname http: ftp: telnet: Host Indicator carl.org /pub/carlweb/pa ges index.html jobs.html

HyperText Transfer Protocol Client Server TCP

HyperText Transfer Protocol Client Server Request Chain

HyperText Transfer Protocol Client Server Response Chain

WWW Browser WWW Browser WWW Server WWW Server User requests a resource

WWW Browser WWW Browser WWW Server WWW Server Browser (Client) requests resource from server

WWW Browser WWW Browser WWW Server WWW Server Server provides the resource

WWW Browser WWW Browser WWW Server WWW Server 1. Browser decodes document to present final document to user 2. Browser determines it needs additional resources to complete the document

WWW Browser WWW Browser WWW Server WWW Server Browser (Client) requests resources from server

WWW Browser WWW Browser WWW Server WWW Server Server provides the resources

WWW Browser WWW Browser WWW Server WWW Server Browser finishes decoding the document and presents to the user

Electronic Mail Most popular form of traffic on the Internet Two protocols of interest –Simple Mail Transfer Protocol –Post Office Protocol Originator does not discard mail until target acknowledges receipt

Electronic Mail System User Interface User Interface Outgoing Mail Spool Area Outgoing Mail Spool Area Mailboxes for Incoming Mail Mailboxes for Incoming Mail SMTP Client SMTP Client SMTP Server SMTP Server User Reads Mail User Sends Mail TCP Connection

Electronic Mail System User Interface User Interface Outgoing Mail Spool Area Outgoing Mail Spool Area Mailboxes for Incoming Mail Mailboxes for Incoming Mail SMTP Client SMTP Client SMTP Server SMTP Server User Reads Mail User Sends Mail TCP Connection Alias Expansion & Fowarding Alias Expansion & Fowarding Alias Database

Electronic Mail System Outgoing Mail Spool Area Outgoing Mail Spool Area Mailboxes for Incoming Mail Mailboxes for Incoming Mail SMTP Client SMTP Client SMTP Server SMTP Server TCP Connection Alias Expansion & Fowarding Alias Expansion & Fowarding Alias Database POP Server POP Server Outgoing Mail Spool Area Outgoing Mail Spool Area Mailboxes for Incoming Mail Mailboxes for Incoming Mail POP Client POP Client Alias Expansion & Fowarding Alias Expansion & Fowarding Alias Database Mgmt & Editing Application TCP Connection SMTP Client SMTP Client SMTP Relay SMTP Relay

Addressing account host

Example Internet denver.carl.org lynn.carl.org whitehouse.gov bigguy.whitehouse.gov lbashaw

Example Internet denver.carl.org lynn.carl.org whitehouse.gov bigguy.whitehouse.gov lbashaw Composes message from to

Example Internet denver.carl.org lynn.carl.org whitehouse.gov bigguy.whitehouse.gov lbashaw Completed message is sent to spooler on PC spool

Example Internet denver.carl.org lynn.carl.org whitehouse.gov bigguy.whitehouse.gov lbashaw At predefined interval SMTP client logs on to SMTP Host and following successful login establishes a TCP session with mail server spool

Example Internet denver.carl.org lynn.carl.org whitehouse.gov bigguy.whitehouse.gov lbashaw SMTP client transfers all waiting mail in mail spool to mail server spool

Example Internet denver.carl.org lynn.carl.org whitehouse.gov bigguy.whitehouse.gov lbashawspool Mail from bigguy.whitehouse.gov is processed and sent to mail spool to await pick-up

Example Internet denver.carl.org lynn.carl.org whitehouse.gov bigguy.whitehouse.gov lbashawspool SMTP client checks spool and notes message from to

Example Internet denver.carl.org lynn.carl.org whitehouse.gov bigguy.whitehouse.gov lbashawspool SMTP client requests IP address of carl.org from DNS resolver

Example Internet denver.carl.org lynn.carl.org whitehouse.gov bigguy.whitehouse.gov lbashawspool DNS resolver requests IP address of carl.org from domain name server

Example Internet denver.carl.org lynn.carl.org whitehouse.gov bigguy.whitehouse.gov lbashawspool Domain Name Server determines that IP address of carl.org is

Example Internet denver.carl.org lynn.carl.org whitehouse.gov bigguy.whitehouse.gov lbashawspool SMTP client establishes a TCP session to port 25 (SMTP Server)

Example Internet denver.carl.org lynn.carl.org whitehouse.gov bigguy.whitehouse.gov lbashawspool SMTP client transfers message from whitehouse.gov to SMTP Server on denver.carl.org

Example Internet denver.carl.org lynn.carl.org whitehouse.gov bigguy.whitehouse.gov lbashawspool SMTP server acknowledges receipt of message to SMTP client on whitehouse.gov

Example Internet denver.carl.org lynn.carl.org whitehouse.gov bigguy.whitehouse.gov lbashaw SMTP server puts message from president in mailbox for account lbashaw SMTP client discards message and tears down TCP connection

Example Internet denver.carl.org lynn.carl.org whitehouse.gov bigguy.whitehouse.gov lbashaw POP client in lynn.carl.org logs on to denver.carl.org and upon successful login establishes a TCP session with the POP server on denver.carl.org SMTP client discards message and tears down TCP connection

Example Internet denver.carl.org lynn.carl.org whitehouse.gov bigguy.whitehouse.gov lbashaw POP client uses POP to download all mail messages from mailbox for account lbashaw on denver.carl.org to mailbox on lynn.carl.org. Upon successful receipt POP client acknowledges receipt and POP server deletes messages from mailbox on denver.carl.org SMTP client discards message and tears down TCP connection

Example Internet denver.carl.org lynn.carl.org whitehouse.gov bigguy.whitehouse.gov lbashaw I read my message from the President SMTP client discards message and tears down TCP connection

List Server Outgoing Mail Spool Area Outgoing Mail Spool Area Mailboxes for Incoming Mail Mailboxes for Incoming Mail SMTP Client SMTP Client SMTP Server SMTP Server TCP Connection Alias Expansion & Fowarding Alias Expansion & Fowarding Alias Database Administration Program Administration Program Relay Program Relay Program

List Server Outgoing Mail Spool Area Outgoing Mail Spool Area Mailboxes for Incoming Mail Mailboxes for Incoming Mail SMTP Client SMTP Client SMTP Server SMTP Server TCP Connection Alias Expansion & Fowarding Alias Expansion & Fowarding Alias Database Administration Program Administration Program Relay Program Relay Program Digest Program Digest Program

Usenet News Usenet News is a distributed computer conferencing system Conferences in Usenet News are called newsgroups, and messages are called articles Each server can download as much as it wants of what is available on any of the adjacent servers "Pouring water" principle of Usenet News distribution

Usenet News

References Internet RFC/STD/FYI/BCP Archives – –Repository of Internet Specifications STD 13 - Domain Name System STD 8 - TELNET Protocol Specification STD 9 - File Transfer Protocol (FTP)

References RFC Hypertext Transfer Protocol -- HTTP/1.1 STD 10 - Simple Mail Transfer Protocol STD 53 - Post Office Protocol - Ver. 3 RFC Network News Transfer Protocol

References FYI 4 - FYI on Questions and Answers Answers to Commonly asked "New Internet User" Questions FYI 7 - FYI on Questions and Answers Answers to Commonly asked "Experienced Internet User" Questions FYI 34 - Users' Security Handbook