guide to tcp/ip, third edition chapter 1: introducing tcp/ip
TRANSCRIPT
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Guide to TCP/IP, Third Edition
Chapter 1:Introducing TCP/IP
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Introducing TCP/IP 2
Objectives
• Understand TCP/IP’s origins and history
• Explain the process by which TCP/IP standards and other documents, called Requests for Comments (RFCs), are created, debated, and formalized (where appropriate)
• Understand the Open Systems Interconnection network reference model, often used to characterize network protocols and services, and how it relates to TCP/IP’s own internal networking model
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Introducing TCP/IP 3
Objectives
• Define the terms involved and explain how TCP/IP protocols, sockets, and ports are identified
• Understand data encapsulation and how it relates to the four layers of the TCP/IP protocol stack
• Understand and apply the basic practices and principles that underlie network protocol analysis
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Introducing TCP/IP 4
What is TCP/IP?
• Large collection of networking protocols and services
• Two key protocols– Transmission Control Protocol (TCP)
• Reliable delivery of messages
– Internet Protocol (IP)• Manages the routing of network transmissions
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Introducing TCP/IP 5
The Origins and History of TCP/IP
• 1969– Advanced Research Projects Agency (ARPA)
funded research for packet-switched networking– ARPANET
• Network built as a result of this project
• In a packet-switched network– Sender and receiver are identified by unique network
addresses
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Introducing TCP/IP 6
TCP/IP’s Design Goals
• To withstand a potential nuclear strike
• To permit different computer systems to communicate easily
• To interconnect systems across long distances
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Introducing TCP/IP 7
A TCP/IP Chronology
• 1978– Internet Protocol version 4 (IPv4)
• 1983– Defense Communications Agency took over
operation of ARPANET• 1986
– NSF launches high-speed network (NSFNET)• 1987
– Number of hosts on the Internet breaks 10,000
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Introducing TCP/IP 8
A TCP/IP Chronology (continued)
• 1989– Number of hosts on the Internet breaks 100,000
• 1990– Worldwide Web is born at Centre European
Researche Nucleaire (CERN)• 1991
– Commercial Internet Exchange (CIX) is formed• 1992
– Internet Society (ISOC) is chartered
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Introducing TCP/IP 9
A TCP/IP Chronology (continued)
• 1993– InterNIC is chartered
• 1994– Online junk mail begins to proliferate
• 1995– Netscape launches Netscape Navigator
• 1996– Microsoft launches Internet Explorer Web browser
• 1997– 31 million registered domain names
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Introducing TCP/IP 10
A TCP/IP Chronology (continued)
• 2000– Love Letter worm infects over one million PCs
• 2001– Number of hosts on the Internet breaks 150 million– Sircam virus and Code Red worm infect thousands
• 2002– 204 million Internet hosts
• 2003– Public Interest Registry becomes .org registry
operator
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Introducing TCP/IP 11
Who “Owns” TCP/IP?
• TCP/IP – Falls squarely into the public domain– Funded with public monies since its inception– Owned by everybody and nobody
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Introducing TCP/IP 12
Meet the Standards Groups that Manage TCP/IP
• Internet Society (ISOC)
• Internet Architecture Board (IAB)
• Internet Engineering Task Force (IETF)
• Internet Research Task Force (IRTF)
• Internet Societal Discussion Forum (ISDF)
• Internet Corporation for Assigned Names and Numbers (ICANN)
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Introducing TCP/IP 13
TCP/IP Standards and RFCs
• Request For Comments (RFCs)– Provide documentation to understand, implement
and use TCP/IP protocols• Index for all RFCs available at
– www.faqs.org/rfcs/ • RFC 2026
– Describes how a RFC is created
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Introducing TCP/IP 14
OSI Reference Model Overview
• OSI reference model– A network reference model– Formally known as ISO/OSI – Designed to replace TCP/IP– Standard way to explain how networks operate– TCP/IP is the open standard protocol suite of choice
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Introducing TCP/IP 15
Models Break Networking into Layers
• Divide and conquer approach– Separates networking hardware concerns from those
related to networking software
• Key points about networking– Easier to solve problems when broken into series of
smaller problems– Layers operate independently of one another– Changes to one layer need not affect other layers
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Introducing TCP/IP 16
Models Break Networking into Layers (continued)
• Key points about networking– Individual layers work together on pairs of computers– Different expertise is needed at each layer– Network protocols usually map into one or more
layers– TCP/IP is designed around a layered model
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Introducing TCP/IP 18
How Protocol Layers Behave
• Layers– Exist to encapsulate or isolate specific types of
functionality– Provide services to the layer above– Deliver data to or accept data from the layer below
• Protocol Data Units (PDUs) – Include “envelope information” in the form of specific
headers and trailers
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Physical Layer
• Includes the physical transmission medium • Job is to activate, maintain, and deactivate network
connections • Manages communications with the network
medium going down the protocol stack • Handles conversion of outgoing data
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Introducing TCP/IP 20
Data Link Layer
• Situated between the Physical layer and the Network layer in the reference model
• Job is to – Enable reliable transmission of data through the
Physical layer at the sending end – Check reliability at the receiving end
• Manages point-to-point transmission across the networking medium
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Introducing TCP/IP 21
Network Layer
• Handles logical addresses associated with individual machines on a network
• Uses addressing information to – Determine how to send a PDU
• Embodies notion of multiple simultaneous connections between different IP addresses
• Flexible enough to – Recognize and use multiple routes between a
sender and a receiver
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Introducing TCP/IP 22
Transport Layer
• Ensures reliable end-to-end transmission of PDUs• Includes end-to-end error-detection and error-
recovery
• Segmentation – Involves cutting up a big message into a numbered
sequence of chunks, called segments
• PDUs used at the Transport layer are called segments, or data segments
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Introducing TCP/IP 23
Session Layer
• Defines mechanisms to – Permit senders and receivers to request that a
conversation start or stop– Keep a conversation going even when traffic may
not otherwise flow between the parties involved
• Checkpoints– Define the last point up to which successful
communications are known to have occurred
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Introducing TCP/IP 24
Presentation Layer
• Handles transforming data from – Generic, network-oriented forms of expression to
more specific, platform-oriented forms of expression
• A redirector or network shell– Special computer facility that resides here
• Can supply special data-handling functions for applications
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Application Layer
• Defines an interface that applications can use to request network services
• Defines a set of access controls over the network
• PDUs– Generically called Application PDUs
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The TCP/IP Networking Model
• Design model that describes TCP/IP differs somewhat from OSI reference model
• Transport layers for both models map together quite well as does the– Network layer from the OSI reference model and the
Internet layer from the TCP/IP model
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TCP/IP Network Access Layer
• Includes Ethernet, token ring, and wireless media devices
• Includes WAN and connection-management protocols
• The IEEE standards for networking apply– Including the IEEE 802 family of standards
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Introducing TCP/IP 29
TCP/IP Network Access Layer Protocols
• PPP– Most important TCP/IP Network Access layer
protocol
• PPPoE (“PPP over Ethernet” )– Widely used on Ethernet networks or those with
Ethernet-like characteristics
• SLIP– Older, simpler serial line protocol that only supports
TCP/IP-based communications
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TCP/IP Internet Layer Functions
• Handle routing between machines across multiple networks
• Three primary tasks– MTU fragmentation– Addressing– Routing
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TCP/IP Internet Layer Protocols
• Internet Protocol (IP)
• Internet Control Message Protocol (ICMP)
• Packet Internetwork Groper (PING)
• Address Resolution Protocol (ARP)
• Reverse ARP (RARP)
• Bootstrap Protocol (BOOTP)
• Routing Information Protocol (RIP)
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TCP/IP Transport Layer Functions
• Functions– Reliable delivery of data from sender to receiver– Fragmentation of outgoing messages and their
reassembly prior to delivery to the Application layer
• Hosts– Devices that operate on the Internet
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TCP/IP Transport Layer Protocols
• Two TCP/IP Transport layer protocols – The transmission Control Protocol (TCP)
• Connection-oriented
– The User Datagram Protocol (UDP)• Connectionless
• UDP– Transmits data in a “best-effort delivery” – Does no follow-up checking on its receipt
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TCP/IP Application Layer
• Also known as the Process layer
• TCP/IP services depend on:– Special “listener process,” called a daemon
• Operates on a server to handle incoming user requests for specific services
– Each TCP/IP service has an associated port address
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TCP/IP Protocols, Services, Sockets, And Ports
• Multiplexing– Combining various sources of outgoing data into a
single output data stream
• Demultiplexing– Breaking up an incoming data stream so separate
portions may be delivered to the correct applications
• Well-known protocols– Assign a series of numbers to represent a sizable
collection of TCP/IP-based network services
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TCP/IP Port Numbers
• TCP/IP application processes – Sometimes called network services – Identified by port numbers
• Source port number – Identifies the process that sent the data
• Destination port number – Identifies the process to receive that data
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TCP/IP Sockets
• Well-known or registered ports– Represent pre-assigned port numbers
• Socket address (or socket)– The combination of a particular IP address and a
dynamically assigned port address
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Data Encapsulation In TCP/IP
• At each layer in the TCP/IP protocol stack– Outgoing data is packaged and identified for delivery
to the layer underneath
• Header– PDU’s own particular opening component – Identifies the protocol in use, the sender and
intended recipient
• Trailer (or packet trailer)– Provides data integrity checks for the payload
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About Protocol Analysis
• Protocol analysis is the process of– Tapping into the network communications system– Capturing packets– Gathering network statistics– Decoding packets
• Popular Windows-based protocol analyzers– Ethereal for Windows (Gerald Combs)– Sniffer Network Analyzer (Network Associates)
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Useful Roles for Protocol Analysis
• Used to troubleshoot network communications• Used to test networks
– Passive– Active
• Gather trends on network performance• Analyzers available for variety of platforms
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Protocol Analyzer Elements
• Promiscuous mode card and driver
• Packet filters
• Trace buffer
• Decodes
• Alarms
• Statistics
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Placing a Protocol Analyzer on a Network
• Protocol analyzer– Captures packets that it can see on the network
• On network connected with hubs– You can place analyzer anywhere on the network
• Options for analyzing switched networks– Hubbing out– Port redirection– Remote Monitoring (RMON)
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Summary
• TCP/IP design goals– To support multiple, packet-switched pathways
through the network – To permit dissimilar computer systems to easily
exchange data– To offer robust, reliable delivery services for both
short- and long-haul communications– To provide comprehensive network access with
global scope
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Summary (continued)
• Initial implementations of TCP/IP – Funded by Advanced Research Projects Agency
• TCP/IP remains in the public domain
• As Standard RFCs go through approval process they begin as Proposed Standard documents
• Best Current Practice (BCP)– An informational (non-standard) RFC
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Summary (continued)
• ISO/OSI network reference model– Breaks networking into seven distinct layers
• TCP/IP uses a variety of encapsulation techniques at its various layers to – Label the type of data contained in the contents, or
payloads, of its PDUs
• Protocol analysis – Network interface inspects all traffic moving across a
segment of network medium