Internet and Intranet Fundamentals

Class 5

Session B

Topics

• NNTP

• Mid-Term Review

NNTP

• NNTP = Network News Transfer Protocol– Internet bulletin board system

• 1986– RFC 977 (Kantor & Lapsley)

• “News” means bulletins, information, data, messages from individuals– not news agencies (although this is not

precluded)

NNTP

• Facilitates rapid dissemination of software bug fixes, technical tips, product reviews, discussions, rumors– distribution– inquiry– retrieval– posting

• USENET News System

NNTP

• Model: Centralized storage of postings or news articles– clients / server model

• USENET News

• TCP– Port 119

NNTP

• Info Organized into Newsgroups– hierarchical, like a file directory system

• rec.sports.football.nfl

• Master-Slave Relationship between News Servers– dependent news servers can request that only

certain postings (e.g., since a certain time) are transmitted

– equivalent of caching

NNTPCommands

• ARTICLE <message-id> or [nnn]

Responses: 220 n <a> article retrieved - head and body follow (n = article number, <a> = message-id)221 n <a> article retrieved - head follows222 n <a> article retrieved - body follows223 n <a> article retrieved - request text separately412 no newsgroup has been selected420 no current article has been selected423 no such article number in this group430 no such article found

NNTPCommands

• LIST– lists valid newsgroups

• GROUP ggg– selects a valid newsgroup– response returns first and last article numbers

• LAST– current article pointer set to previous article

• NEXT

NNTPCommands

• NEWSGROUPS date time– list of newsgroups created since date and time

• NEWNEWS newsgroups date time– returns list of articles posted to any one of the

newsgroups specified since date and time

• POST– post article in format specified by RFC 850

NNTPUSENET News-Related Services

• http://www.dejanews.com

• http://www.intellinews.com

Mid-Term Review

• Covers Everything Up Through Class 5

• Selections from Previous Presentations

Open Systems Interconnection Model

• Seven Layers– Application (S/W)– Presentation (S/W)– Session (S/W)– Transport (S/W)– Network (S/W and H/W)– Data Link (F/W and H/W)– Physical (H/W)

OSI Reference Model

Application

Presentation

Session

Network

Transport

Data Link

Physical

Application

Presentation

Session

Network

Transport

Data Link

Physical

Network

Data Link

Physical

OSI Application Layer

• Application and User Interfaces

• File Transfer

• E-Mail

• Database Access

• Program to Program Communication

• http, ftp, gopher, smtp, telnet

OSI Transport Layer

• Host-to-Host Layer

• Error Free End-to-End Connections– virtual connections– doesn’t know about intervening routers

• TCP in TCP/IP

• Often Implemented in Operating System

OSI Network Layer

• Communications Subnet Layer

• Network Routing

• Packets

• Congestion and Flow Control

• Accounting

• IP in TCP/IP

• Typically Implemented as I/O Driver

OSI Data Link Layer

• Breaks Up Input Data from Network Layer and Transmits as Data Frames

• Typically an Interface Card with Firmware– Ethernet card

• Acknowledgement

• Error Handling– Retransmission

• Flow Control

OSI Physical Layer

• Transmits Raw Bits• Includes Communication Channel

– copper wire– fiber– microwave

• Signaling Levels– voltages, timing

• Pin Configurations

DefinitionsClient / Server

• Client– makes request– initiates communication– may have a GUI and human

• but not always

• Server– fulfills request– passively waits for requests– usually multitasking machine

DefinitionsClient / Server

• Fat Clients– full-featured, large applications– use servers as data servers– not much computational power on the server

side

• Thin Clients– small applications– downloaded from the network– relies on computational power of server

DefinitionsClient / Server

• Fat Client Example– Web Browser– Eudora– Visio

• Thin Client– Java Applets– JavaScript Applications inside of HTML Pages– Note dependence on Fat Client (i.e., the

browser)

DefinitionsTCP / IP Berkeley Sockets

• Five Basic Attributes of a Socket Connection– Local Port (chosen by OS on client side)– Local IP Address– Remote Port– Remote IP Address– Protocol (“tcp”, “udp”, etc.)

• Each Connection Has Own 5-tuple

DefinitionsTCP / IP Berkeley Sockets

• Server Listens on (Well-Known) Port

• Clients Attempts Make a Connection

• Server Accepts the Connection

• Server Receives Request from Client

• Server Interprets Request– performs some action

• Sends Response to Client

• Shuts Down the Connection

Internet ProtoclsTCP/IP Overview

• TCP / IP = Transmission Control Protocol / Internet Protocol

• Early 1970s– ARPANET

• Distributed with UC Berkeley UNIX in Early 1980s

• Public Domain, Non-Proprietary, Open Source

Internet ProtocolsLayers

• Five Layer Model– Application– Transport (TCP / UDP)

• contains some Session features

– Network (IP)• actually there are three sublayers

– internet (IP)– convergence– subnet

– Data Link and Physical

Internet ProtocolsLayers

• Packet Switching– datagrams

• Nodes– hosts

• end-user machines• clients or servers

– routers• connecting different networks• a router is also a host of sorts

Internet ProtocolsLayers

• Connection-Oriented– TCP– reliable two-way, byte stream protocol

• Connectionless– UDP = User Datagram Protocol

• also known as the “Unreliable Datagram Protocol”

Internet ProtocolsTCP

• Reliable, Bidirectional Byte Stream– like a UNIX pipe

• End-to-End Reliability

• Bandwidth Optimization (flow control)

• Ports– source– destination

Internet ProtocolsUDP

• User Datagram Protocol

• Ports (like TCP)

• Length, Checksum, Data– no sequencing or acknowledgment structure– error handling left to applications protocol

• DNS uses UDP

Internet ProtocolsDNS

• Domain Name System

• Distributed– database scattered across thousands of

nameservers

• Top-Level Domains– root domain: .– net, edu, com, org, mil, and country codes (jp)

• FQDN: Fully Qualified Domain Name

TCP / IP

• ICMP = Internet Control Message Protocol– routers generate most ICMP traffic– most common types

• destination unreachable: can’t find routing table entry

• routing redirect: better route exists

• time expired: ttl = 0; traceroute uses this

• echo request / echo reply: ping uses this

TCP / IPRouting Architecture

• Autonomous Systems (AS)– collection of routers under single administration– use same routing protocol

• Interior Gateway Protocol (IGP)

• keeps routers informed of interior routes

– AS-to-AS connection uses a different protocol• Exterior Gateway Protocol

• policy routing, transit traffic, local traffic (originating within)

TCP / IPRouting Architecture

• Routing Protocols

• Reachability Protocols– whether path exists

• EGPs and BGPs (Border Gateway Protocol)

• Distance Vector Protocol– distance metric to remote network

• RIP = Routing Information Protocol– broadcast exchange of routing information

– uses UDP

• OSPF = Open Shortest Path First

Internet ArchitectureOverview

• A Network of Networks– internetworking

• The Big Picture– http://navigators.com/internet_architecture.html

ISPs

• Points of Presence (POPs)

• Dial-Up and Dedicated Network Connections– variety of underlying technologies– PPP (Point-to-Point Protocol)

• modems

– ISDN (Integrated Services Digital Network)– Frame Relay, Dedicated T-1– ADSL and Cable Modems

Regional Networks

• BARRNet: Northern Central California (CA)

• CERFnet: Western US and International

• CICnet: Midwest US (MN, WI, IA, IN, IL, MI, OH)

• MIDnet: Mid-US (NE, OK, AR, MO, IA, KS, SD)

• NEARNET: Northeastern US (ME, NH, VT, CT, RI, MA)

• NYSERNet: Northeastern US (NY...)

• SURAnet: Southeastern US (WV, VA, SC, NC, TN, KY, LA, MS, AL, GA, FL, Washington, D.C., MD, DE)

• Westnet: Western US (AZ, CO, ID, NM, UT, WY)

NAPs and MAEs

• NAP = Network Access Point– originally NFS

• MAE = Metropolitan Area Exchange– MCI Worldcom has a service mark on this– Tier-1

• MAE-East (D.C.) and MAE-West (San Jose)

– Tier-2• LA, Chicago, Dallas, Houston, New York

– Giant LAN switch (FDDI)

DNS

• Function of DNS?

• Function of central registry and what does it hold.

• Why aren’t we drowning in DNS requests?

• What is a “root domain”, a “fully qualified domain name”.

TopicsRegulation

• Documentation– RFCs and STD

• Organizations– ISOC (IAB, IESG)– IETF– W3C– InterNic

• IAB Standards Process

DocumentationRFCs

• RFC = Request for Comments– series of notes– ARPANET 1969– anyone can write an RFC– two paths

• as Internet Draft• through IETF• through RFC Editor

– http://www.rfc-editor.org/

Organizational Hierarchy

ISOC

IESG

IETF

IAB

Working Group Working Group Working Group

Areas

OrganizationsIETF

• IETF = Internet Engineering Task Force– technical worker bees

• Applications Area

• General Area

• Internet Area

• Operations and Management Area

• Routing Area

• Security Area

• Transport Area

• User Services Area

IAB Standards Process

• Informational

• Experimental

• Proposed Standard

• Draft Standard

• Internet Standard

HTTPOverview

• HyperText Transfer Protocol

• Applications Layer Protocol– Generic Protocol

• gateway to SMTP, NNTP, FTP, Gopher, WAIS

• Uses TCP Port 80 (by default)– presumes reliable transport

HTTPOverview

• Language of the World Wide Web

• Provides Open-Ended Set of Methods– indicating purpose of request

• Builds on URI, URL, URN disciplines

HTTPOverview

• URI = Uniform Resource Identifier– identifies points of content– mechanism used to access resource – specific computer housing the resource – specific name of resource on computer– formatted strings which indicate characteristics

of a resource

HTTPOverview

• URL = Uniform Resource Locator– a particular form of URI– Web page address

• URN = Uniform Resource Name– institutional persistence– identifies agency responsible for a definition,

for example, but not the location

HTTP/1.0

• Shortcomings of HTTP/1.0– weak on proxies, caching, persistent

connections, and virtual hosts– proliferation of imposters:

• incompletely implemented applications

– stateless• new connection for each request/response exchange

How HTTP WorksRequest/Response Protocol

• Response from server contains …– status line

• message protocol version

• success or error code

– MIME-like message• server info

• entity meta-information

• possible entity body content

How HTTP WorksRequest/Response Protocol

• More Sophisticated Interactions– proxies

• forwarding agent

– gateways• receiving agent

– tunnels• relay point between two connections• firewalls• non-caching

How HTTP Works Media Types

• Type / Subtype– followed by 0 or more optional parameters

delimited on the left by “;”• parameter are of form attribute=value

– Content-type: text/html– Content-type: text/plain (default)– Content-Type: multipart/mixed;

boundary=gc0p4Jq0M2Yt08jU534c0p

• Assigned by IANA

HTTP

• Authentication– .htaccess files

• Secure Sockets Layer (SSL)– https– RSA Encryption

• public key / private key

– not really part of HTTP

HTML

• Main Tags– <html> </html> starts HTML stream– <head> </head> delimits HEAD of document– <title> </title> title that appears at top of

browser frame– <body> </body> delimits document BODY– <a href=“…URL…”>Text</a> creates a

hyperlink– <img src=“…”> inserts an image into a file

Misc.

• What is an application server, when would you use it, when would you not use one?

• What are html “cookies”, what problem do they solve?

• What is the difference between a Get and a Post request?

• How is an https page secured?