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Guide To TCP/IP, Second Edition
Chapter 1
Introducing TCP/IP
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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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Objectives (cont.)
• 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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What is TCP/IP?
• Large collection of networking protocols
and services
• Two key protocols
– Transmission Control Protocol (TCP)
• Reliable delivery for messages
– Internet Protocol (IP)
• Manages the routing of network transmissions
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Origins and History
• 1969, Department of Defense (DoD) and
Advanced Research Projects Agency (ARPA)
funded research for packet-switched networking
• The sender and receiver are identified by unique
network addresses
• Do not require all packets to follow the same path
in transit
• The network built as a result of this project is
known as the ARPANET
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TCP/IP’s Design Goals
• Withstand a potential nuclear strike
– Need for packet switching
• Permit different kinds of computer systems
to easily communicate
• Need to interconnect systems across long
distances
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A TCP/IP Chronology
• 1978: Internet Protocol version 4 (IPv4) came into
existence
• 1983: Defense Communications Agency took
over operation of the ARPANET
• 1986: National Science Foundation (NSF)
launches a long-haul, high-speed network, known
as NSFNET
• 1987: Number of hosts on the Internet breaks
10,000
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A TCP/IP Chronology (cont.)
• 1989:
– Number of hosts on the Internet breaks 100,000
– NSFNET backbone upgraded to 1.544 megabits per
second (Mbps)
• 1990:
– McGill University releases the Archie protocol and
service
– Work begins on the Hypertext Transfer Protocol
Worldwide Web is born at Centre European Researche
Nucleaire (CERN)
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A TCP/IP Chronology (cont.)
• 1991:
– Commercial Internet Exchange (CIX) is formed
– Wide Area Information Service (WAIS) protocol and
service allowing Internet searches of multimegabyte
databases
– Gopher (UofM) allows searching of text-based archives
• 1992:
– Internet Society (ISOC) is chartered
– Number of hosts on the Internet breaks one million
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A TCP/IP Chronology (cont.)
• 1992:
– NSFNET backbone upgraded to 44.736 Mbps (T3
speed)
– CERN releases HTTP and Web server technology to the
public
• 1993:
– Internet Network Information Center (InterNIC) is
chartered
– Mosaic, the first high-powered graphical browser
– The U.S.White House goes online at whitehouse.gov
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A TCP/IP Chronology (cont.)
• 1994:
– U.S. Senate and House of Representatives establish
information servers on the Internet
– Online junk mail and shopping malls begin to
proliferate
• 1995:
– Netscape launches Netscape Navigator
– Number of hosts on the Internet breaks five million
• 1996: Microsoft launches Internet Explorer Web
browser
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A TCP/IP Chronology (cont.)
• 1997: Number of registered domain names reaches
31 million
• 2000: Love Letter worm infects over one million
personal computers
• 2001:
– Number of hosts on the Internet breaks 150 million
– Sircam virus and Code Red worm infect thousands of
Web servers and e-mail accounts
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A TCP/IP Chronology (cont.)
• 2002:
– Number of hosts on the Internet breaks 204
million
– The Internet2 backbone utilizes native IP
version 6
• 2003: Public Interest Registry (PIR)
assumes responsibility as .org registry
operator
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Who “Owns” TCP/IP?
• TCP/IP falls squarely into the public
domain
• Funded with public monies since its
inception
• Both everybody and nobody own TCP/IP
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Meet the Standards Groups that Manage
TCP/IP
• Internet Society (ISOC)
• Internet Architecture Board (IAB) – oversight for the architecture of
all Internet protocols and procedures; editorial oversight for RFCs
• Internet Engineering Task Force (IETF) – responsible for
drafting, testing, proposing, and maintaining official Internet Standards
• Internet Research Task Force (IRTF) – responsible for more
forward looking activities of ISOC
• Internet Societal Discussion Forum (ISDF) – explores how the
Internet can be a force for social development and change.
• Internet Corporation for Assigned Names and Numbers
(ICANN) – responsible for managing all Internet domain names, network
addresses, and protocol parameters and behaviors.
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TCP/IP Standards and RFCs
•
•
•
•
Request For Comments (RFC)
www.faqs.org/rfcs
RFC 2026 describes how a RFC is created
RFC status designations
– Proposed Standard, Draft Standard, Internet
Standard, Retired Standard, and Historic
Standard
• Best Current Practice (BCP)
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OSI Reference Model Overview
•
•
•
•
Network reference model
Formally (ISO/OSI )
Designed to replace TCP/IP
OSI model is the standard way to explain
how networks operate
• TCP/IP remains the open standard protocol
suite of choice
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OSI Network Reference Model
• Models break networking into layers
• The OSI network reference model
• How protocol layers behave
–
–
–
–
–
–
–
Physical Layer
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application Layer
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OSI Network Reference Model (cont.)
• The reference model described in ISO
Standard 7498 breaks network
communication into seven layers
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Models Break Networking into Layers
• Divide and conquer approach
– Separate networking hardware concerns from
those related to networking software
• Key points about networking
– Easier to solve problems when broken into layers
– Layers operate independently of one another
– Changes to one layer need not affect other layers
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Models Break Networking into Layers
(cont.)
• Key points about networking (cont.)
–
–
–
–
–
Individual layers work together on pairs of computers
Different expertise is needed at each layer
Layers working together is known as networking
Network protocols usually map into one or more layers
TCP/IP is designed around a layered model
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Seven Layers Of The OSI Model
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How Protocol Layers Behave
• Layers exist to encapsulate or isolate
specific types of functionality
• Layers provide services to the layer above
• Layers deliver data to or accept data from
the layer below
• Protocol Data Units (PDUs)
• PDUs include “envelope information” in the
form of specific headers and trailers
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Physical and Data Link Layers
• Physical Layer
– Includes the physical transmission medium
– Physical and electrical characteristics of the interfaces
– PDUs consist of specific serial patterns of signals
• Data Link Layer
–
–
–
–
Manages point-to-point transmission
Handles sequencing of data from sender to receiver
Data transmission control: called media flow control
PDUs are specific bit patterns and are called frames or
data frames
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Network and Transport Layers
• Network Layer
– Logical addresses associated with individual machines
– Uses logical addressing to determine how to send PDU
traffic to other physical segments
– PDUs are structured data called a packet
• Transport Layer
– Ensure reliable end-to-end transmission of PDUs
– Includes end-to-end error-detection and error-recovery
– PDUs are structured numbered sequence data called
segments or data segments
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Sessions and Presentation Layers
• Sessions
– Conversations are set up, maintained, and then
terminated
– Includes mechanisms to maintain reliable ongoing
conversations called checkpoints
– PDUs at this level are Session PDUs, or SPDUs
• Presentation
– Manages how data is presented to the network and to a
specific machine/application
– PDUs are generically called Presentation PDUs
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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 are generically called Application
PDUs
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OSI and TCP/IP Models
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TCP/IP Network Access Layer
• Includes Ethernet, token ring, and wireless media
• Includes WAN and connection-management
protocols
• Include the IEEE 802 family of standards
–
–
–
–
802.1 Internetworking
802.2 Media Access Control
802.3 CSMA/CD
802.5 Token Ring
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TCP/IP Network Access Layer Protocols
•
•
•
•
High-level Data Link Control (HDLC)
Frame Relay
Asynchronous Transfer Mode (ATM)
PPP and SLIP
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TCP/IP Internet Layer Functions
• Handle routing between machines across
multiple networks
• 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)
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
• Protocols
– Transmission Control Protocol (TCP)
• Connection oriented
– User Datagram Protocol (UDP)
• Connectionless
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TCP/IP Application Layer
• Function
– Interfaces with applications or processes on a
host machine
• Protocol and Services
– File Transfer Protocol (FTP)
– Telnet
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TCP/IP Protocols, Services, Sockets, And Ports
• TCP/IP protocol numbers
– Protocol numbers are used to identify distinct protocols,
and those protocols use port numbers
• TCP/IP port numbers
– TCP/IP application are identified by port numbers
– The source or destination port number identifies the
process that sent or receives, respectively, the data
• TCP/IP sockets
– Dynamically assigned port address is called a socket
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TCP/IP Protocol Numbers
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Data Encapsulation In TCP/IP
• Outgoing data is packaged and identified for
delivery to the layer underneath
• Incoming data has its encapsulating information
from the underlying layer stripped off before it’s
delivered to its upper-layer
• Each PDU has an opening component, called a
header, and closing component called a trailer
• Data portion of the PDU is known as 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
• Protocol analyzers can also transmit packets
– A task for testing a network or device
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Roles for Protocol Analysis
• Used to troubleshoot network
communications
• Used to test networks
– Passive
– Active
• Gather trends on network performance
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Protocol Analyzer Elements
•
•
•
•
•
•
Promiscuous mode card and driver
Packet filters
Trace buffer
Decodes
Alarms
Statistics
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Network Analyzer Process
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Decodes
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Statistics
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Placing a Protocol Analyzer on a Network
• Hubbing out
– Placing a hub between a device of interest and the
switch, and connecting the analyzer to the hub
• Port redirection
– Switches can be configured to redirect (to copy) the
packets traveling through one port to another port
• Remote monitoring (RMON)
– Collect traffic data at a remote switch and send the data
to a management device
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Analyzer Placement Example
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Chapter Summary
• TCP/IP was designed with the following goals in
mind
– (1) To support multiple, packet-switched pathways
through the network so that transmissions can survive
all conceivable failures
– (2) To permit dissimilar computer systems to easily
exchange data
– (3) To offer robust, reliable delivery services for both
short- and long-haul communications
– (4) To provide comprehensive network access with
global scope
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Chapter Summary (cont.)
• Initial implementations of TCP/IP were funded under the
auspices of the ARPA and Department of Defense
• Until the late 1980s, the ARPANET remained largely in
government hands and supported by government funding
• TCP/IP remains in the public domain as an open and
collaborative set of standards and best practices
• The documents that govern TCP/IP standards and practices
are called RFCs, and the process of their creation,
development, and approval involves representatives from
government, industry, research, and academia
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Chapter Summary (cont.)
• The standards creation and management processes
fall within the IETF, and final approval of Internet
standards rests in its parent organization, the IAB
• Although the process of creating such standards is
rightfully called “rough consensus ,” this process
works well enough to define literally hundreds of
protocols and services used every day on the
Internet
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Chapter Summary (cont.)
• As Standard RFCs go through the approval process, they
begin life as Proposed Standard documents
• After discussion and debate, and demonstration that two or
more separate reference implementations can successfully
interoperate, RFCs can become Draft Standards
• After further discussion and revisions, and approval from
the parent working group within the IETF, the Draft is
turned over to the IAB for final approval
• When the Draft is approved, it becomes a Standard RFC
(sometimes called an “Internet Standard”)
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Chapter Summary (cont.)
• Another popular type of RFC is an informational (nonstandard) RFC called a Best Current Practice, or BCP
• Although these documents do not have the force of a
Standard RFC, they do provide useful information that
represents best approaches to designing, configuring,
implementing, or maintaining TCP/IP-based networks and
related services
• For those reasons, BCPs are highly regarded and can be
useful tools for network administrators seeking to make the
most out of their TCP/IP networks
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Chapter Summary (cont.)
• In general, networking is a big, complex problem that is
most easily solved if broken up into a series of smaller,
less-complex, and interrelated problems
• The ISO/OSI network reference model breaks networking
into seven distinct layers that allow issues related to
hardware, media, and signaling to be separated from issues
related to software and services
• Likewise, this model permits activities in software to be
distinguished on the basis of machine-to-machine
communications
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Chapter Summary (cont.)
• This communication involves handling information
delivery from any sender to any receiver, moving large
amounts of data across the network, and handling various
issues related to ongoing communications, data formats,
and application interfaces for network access
• TCP/IP uses an older, simpler, four-layer model that lumps
the latter three issues into a single application/services
layer, but is otherwise very much like the ISO/OSI
reference model
• 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
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Chapter Summary (cont.)
• TCP/IP also uses numbering techniques to identify wellknown protocols at the lower layers (protocol numbers)
and to support ready access to well-known applications
and services at upper layers (well-known ports)
• When a client makes a request to a server that requires an
ongoing exchange of information, a listening process on
the server creates a temporary connection that combines a
computer’s numeric IP address with a specific port address
for the process involved (called a socket address)
• This ensures that the right process on the right computer
may be accessed on both sending and receiving machines
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Chapter Summary (cont.)
• Protocol analysis is a process whereby a network interface
is used to inspect all traffic moving across a segment of
network medium
• Protocol analyzers are software programs that can manage
this task and can capture not only “healthy” (properly
formed) traffic, but also erroneous or ill-formed traffic
• This lets protocol analyzers characterize network traffic on
a descriptive basis (the protocols used, the active station
addresses, the conversations, and the parties involved), and
on a statistical basis (percentage of errors, percentage of
traffic per protocol, peak loads, low loads, average loads,
and so forth)
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Chapter Summary (cont.)
• Much of the remaining text depends on putting the
topical and theoretical discussions about TCP/IP
protocols together with the traces and decodes
(formatted contents of packets) to see how theory
and practice fit together
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