guide to tcp/ip, second edition1 chapter 1 introducing tcp/ip

Guide To TCP/IP, Second Edition 1

Guide To TCP/IP, Second Edition

Chapter 1

Introducing TCP/IP


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


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


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


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


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


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


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)



• 1991: – Commercial Internet Exchange (CIX) is formed

– Wide Area Information Service (WAIS) protocol and service allowing Internet searches of multimegabyte databases

– Gopher allows searching of text-based archives

• 1992: – Internet Society (ISOC) is chartered

– Number of hosts on the Internet breaks one million



• 1992: – NSFNET backbone upgraded to 44.736 Mbps

– 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



• 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


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


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)


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)


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


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


OSI Network Reference Model (cont.)

• The reference model described in ISO Standard 7498 breaks network communication into seven layers


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


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


Seven Layers Of The OSI Model


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


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


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


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


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


OSI and TCP/IP Models


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


TCP/IP Network Access Layer Protocols

• High-level Data Link Control (HDLC)

• Frame Relay

• Asynchronous Transfer Mode (ATM)

• PPP and SLIP


TCP/IP Internet Layer Functions

• Handle routing between machines across multiple networks

• MTU fragmentation

• Addressing

• Routing


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)


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


TCP/IP Application Layer

• Function– Interfaces with applications or processes on a

host machine

• Protocol and Services– File Transfer Protocol (FTP) – Telnet


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


TCP/IP Protocol Numbers


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


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


Roles for Protocol Analysis

• Used to troubleshoot network communications

• Used to test networks

• Gather trends on network performance


Protocol Analyzer Elements

• Promiscuous mode card and driver

• Packet filters

• Trace buffer

• Decodes

• Alarms

• Statistics


Network Analyzer Process


Decodes


Statistics


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


Analyzer Placement Example


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


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



• 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



• 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”)



• Another popular type of RFC is an informational (non-standard) 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



• 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



• 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



• TCP/IP also uses numbering techniques to identify well-known 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



• 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)



• 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

guide to tcp/ip, second edition1 chapter 1 introducing tcp/ip

Documents

tcpip slide

tcpip chronology

tcpip protocols

tcpip standards

tcpip protocol stack

second mbps

arpanet slide

internet protocol version