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REPUBLIQUE DU CAMEROUNPAIX TRAVAIL - PATRIE
REPUBLIC OF CAMEROONPEACE WORK FATHERLAND
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UNIVERSITE DE DSCHANG THE UNIVERSITY OF DSCHANG- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
INSTITUT UNIVERSITAIRE DE TECHNOLOGIE
FOTSO VICTOR DE BANDJOUN
B.P. 134 Bandjoun (Cameroun)
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AdministrationAdministrationAdministrationAdministration
Systme et RseauxSystme et RseauxSystme et RseauxSystme et Rseaux1111rererere partiepartiepartiepartie
Licence de Technologie
Copyright E. B. TANYI, Mars 2003
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SOMMAIRE:
SOMMAIRE: ...............................................................................................................1
CHAPTER.I:SYSTEM ADMINISTRATION:............................................................ 1
I.1 Notion of system administration: .......................................................................... 1
Fig.1.2: The computer in a complex technological and institutional environnement.. 2
I.2 ROLE OF THE SYSTEM ADMINISTRATOR................................................... 2
I.3 Administering Windows NT Systems:..................................................................3
I.3.1. About Windows NT ......................................................................................3
I.3.2. The windows NT Architecture ...................................................................... 4
I.3.3. implications of the windows NT design........................................................ 6
I.3.4. Windows NT variations :............................................................................... 7
I.3.5. Windows NT administrative tools:................................................................ 7
CHAPTER.II:TRANSMISSION OF INFORMATION:.............................................9
II.1 Introduction: .......................................................................................................... 9
II.2 Addressing, Routing and Multiplexing .................................................................9
I.4 IP ADRESSES................................................................................................. 10
II.3 Sub networks: ...................................................................................................... 16
II.4 Architecture of internet routing:.......................................................................... 18
II.5 The routing table: ................................................................................................ 19
II.6 Resolution of addresses .......................................................................................21
II.7 Protocols, ports and sockets ................................................................................ 21
II.8 Summary: ............................................................................................................ 23
CHAPTER.III:NETWORK SERVICES : .................................................................24
III.1Names and addresses: .........................................................................................24
III.1.1 Tables of machines:..................................................................................... 25
III.1.2 The domain Name service (DNS): .............................................................. 26
III.1.3 the hierarchy of domains ............................................................................. 26
III.1.4 creating domains and sub-domains.............................................................. 27
III.1.5 domain names:............................................................................................. 27
III.1.6 bind, revolver and named: ........................................................................... 27
III.2NIS : Network Information service..................................................................... 28
III.3 Electronic Mail Service................................................................................ 28III.3.1 Simple Mail Transport Protocol............................................................... 29
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III.3.2 Post Office Protocol (POP) ...................................................................... 29
III.3.3 MIME : Multipurpose Internet Mail Extensions ....................................... 31
III.4 Configuration Servers : .................................................................................... 32
III.4.1 RARP: Reverse Address Resolution Protocol............................................ 32
III.4.2 BOOTP : Bootstrap Protocol...................................................................... 33
III.4.3 DHCP: Dynamic Host Configuration Protocol: .........................................34
III.4.4 print servers ................................................................................................ 35
III.4.5 File server ................................................................................................... 35
III.4.6 summary ..................................................................................................... 35
CHAPTER.IVPREPARING INFORMATION FOR CONFIGURATION OF
THE NETWORK:...................................................................................................... 36
IV.1 CONNECTED AND STARD-AOONE NETWORKS:................................ 36IV.2 BASIC INFORMATION:............................................................................... 37
IV.2.1 Obtaining an IP address...............................................................................37
IV.3 ASSIGNING ADDRESSES TO MACHINES:.............................................. 38
IV.4 DEFINING THE NETWORK MASK ........................................................... 38
IV.5 SPECFYING THE BROADCAST ADDRESS.............................................. 41
IV.6 PREPARING THE ROUTING TABLE.......................................................... 41
IV.7 OBTAINING AS AUTONOMOUS SYSTEM NUMBER............................. 42
IV.8 Preparing the domain name service .................................................................42
IV.8.1 Obtaining the domain name......................................................................... 42
IV.8.2 Obtaining a IN-ADDR.ARPA Domain....................................................... 43
IV.8.3 Choosing a machine name:.......................................................................... 43
IV.9 OTHERS SERVICES..................................................................................... 43
IV.9.1 File server........................................................................................................ 43
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CHAPTER.I SYSTEM ADMINISTRATION:
I.1 NOTION OF SYSTEM ADMINISTRATION:
In order to facilitate the use of computer, the modern computer is designed to hide its
technical detail from the ordinary user.
Hardware and software resources in a pyramidal structure which is analogous to
a multi-storey building. The technical details of the machine are hidden I the lower
levels of the structure, while the simple user-oriented aspects of the machine are
placed at the higher levels of the structure.
The concept is illustrated in fig 1.1
FIG1.1 Organization of resources in a modern computer system
For such acomputer to operare in the modern technological and institutional
environnent, expert are required to handle various technical details such as
configuring computers to share resources between many user in a comparater or
unshetion; connecting the computer to the internet; integrating the computer withen
a network; optimising the performance of the computer system and many other tasks.
APPLICATION AND
DATA
COMMUNICATIONSOFTWARE
OPERATING SYSTEMS
HARDWARE
user
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Fig.1.2: The computer in a complex technological and institutional
environnement
The system administrator interacts with the machine at all levesl of the
pyramidal structure. From this perspectitve, system administration is concerned with
the followig skills:
Technical expertise about the hardware and software resources of computer
systems.
Knowledge of networking
Knowledge of the Internet and Internet services.
Diagnosis and solution of operationa problems in computer systems
Interaction with the people who use the computer system in a gwen institution
or cooporation
I.2 ROLEOFTHESYSTEMADMINISTRATOR
Installing and configuring computer systems and networks, updating then and
keeping then running properly ona day-to-day basis.
Reanaging users and user accounts, induding both the computer related aspects
of creating and naintering user account and systems and responding to user requests,
questions and problems.
INTERNET
SystemAdministrator
COMPUTER
Multiple User in
corporations and
Institutions
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Taking case of the periferical dense attached to the various computer systems
(e.g printers, uninterruptable power supplies) as well as adding or removing then as
needed.
Overseeing regular system backups, which can range from performing back-ups
plan to be carried out by others under your supervision.
Ensuring that the systems and networks for which you are resposible are secure
and that valuable or sensitive data is protected from undesidered access.
Monitoring system and network activity in order toquickly detect any problems related to
system security , performance, or general functioning that may arise, and then responding
appropriately to anything you may find.
I.3ADMINISTERING WINDOWS NTSYSTEMS:
Most of the computer networks in Cameroon use the Windows NT. For this reason, it
is necessary to give particular attention to NT systems.
I.3.1. About Windows NT
Windows NT is a 32-bit, microkernel-based, preemptive multitasking operating system
providing compatibility with some programs designed for Windows 3.1 systems and, to a
lesser extent, OS/2 and POSIX-comphart systems.
Its main characteristics include :
A 32-bit operating system. This means that physical memory is addressed using 32-bit
addresses, resulting in a maximum physical address space of 4 GB (2 to 3 GB of which
is available to application programs).
Most modern operating systems use a 32- bit or 64- bit design
Built around a microkernel. The program that serves as the central core of the operating
system is designed to be as small and efficient as possible. Only the most fundamental
and important operating system functions are hardled by the small kernelprogram, most
operating system functions are implemented by semi- independent secondary sub-
systems, all controlled by the micro kernel. Many modern operating system are based
on microkernel architecture.
Preemptive multitasking. The operating system is responsible for deciding which
process gets to run at any given time and when one process must pause in order to let a
different one run. This is contrary to the scheduling method use by both Windows and
MacOS. Cooperative multitasking, such as in Windows, gives a running process
complete control of the system until it voluntarily gives up control. It is designed for a
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singleuser environment such as a Pc, where switching between tasks occurs as the
user desires.
Multiple excution mode. Windows NT provides two different modes under which
processes may execute : user mode and kernel mode. Kernel mode execution allows
complete access to every system resource and all of memory and is limited to the
operating system itself. In contrast, processes executing in user mode can obtain access
to system resources only by making request to the operating system. In this way, the
portions of memory used by the operating system are protected and can only be access
by processes running in kernel mode.
Compatibility with some DOS, Windows 3.1, OS/2 and POSIX programs. Windows
NT provides subsystems for running many 16-bits DOS and Windows programs and
OS/2 programs. The operating system also complies with the posix 1 standard, whichincludes the POSIX application program interface, so POSIX program can be ported
more easily to Windows NT.
The NT acronym is translated as New Technology but what is realy new about
Windows NT is an implementation of real operating system functionality combined with a
well-designed user interface.
I.3.2. The windows NT Architecture
Fig 1.3 illustrates the structure of the Windows NT operating system. It is separated
into two sectors. The upper section contains components which run in user mode and the
lower section contains components which run in kernel mode. The heart of the Windows
NT system consist of the modules running in kernel mode. The kernel mode is sometimes
referred to as executive services or NT executive .
Most interactions with the computer hardware take place via the hardware abstraction
layer(HAL) although some device drivers also directly access the hardware. Isolating
hardware access into a separate module allows most of the windows NT operating system
to remain independent of any particular computer architecture, thereby simplifying its
ability to support multiple computer platforms and multiprocessor systems.
The core of the system is the micro kernel which overseas the workings of all of the other
modules and handles communication between them and the HAL. The other components
of the kernel each have a single specific area of responsibility :
The I/O manager controls most input and output operations.
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The object manager creates, modifies, and deletes system objects : data structure
corresponding to a specific instance of resource (for example a file, a process, or a
port).
WIN16
WOW
NTVDM
WIN32 Subsystem
Security
Subsystem
Login
Procedure
OS/2Subsystem
TrueBlue
Net Use
Xwing
Word 7
rm
POSIXSubsystem
hardware
I/OManager
Cache Mgr
FileSystem
Drivers
Network
DriversDevic8
Drivers
Object Security Process Local Virtualmanager Reference Manager Procedure Memory
Manager Call Manager
Facility
Graphics
Subsystem
Window
Manager
GraphicsDevice
interface
Graphics
Device
Drivers
MicroKernel
Hardware Abstraction Layer
Fig 1.3 The Windows NT Architecture.
User Mode
Kernel Mode
SYSTEM SERVICES
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The process manager create and Narages system processes. However, process
scheling is handled by the MecroKenel.
The local procedure call Facilitty is responsible for commuinicating between
distinct process (interprocess communication)
The virtual memory Manager hangles the allocation and use of the system menory.
The graphics subsystem provides services required for interfactingto graphical
displays. This componemnt became part of the windows NT Kernel with version 4.
(Previoushy, et was part of the win32 subsystem )
I.3.3. implications of the windows NT design
The client server approachpervades the entire windows NT environment , from the
operating system itself to the simpllest tool that it provides.You will need to be
aware of this fact as you learn about administerig Windows NT systems. These are
its most important implications:
Under windowsNT, distinct computer systems are viewed as single-user
systems. Only one user maybe logged in to any user a given systems CPU resources.
Interactively. Many administrative tools are similarly dasigived with single system
assumphoon. There are ways to revedy this deficiency.
The voelular design of windows NT also applees to the administrative and user
facilities that at provides. They tend to be compartment alised into a large number
%tools with limited scopes ef action.
The design model aims at run missing the role of the system administrator.
Once installation and initial configuration is complete, ordinary applications and the
operating system are expected to function according the designs pre-defined
procedures.
Priority is given to the graphical user interface (GUI) this vears that the
primary system administration tools are all GUI-Based . While there era command
line utilities that perform the same function, many administrative tools have 20
command-line equivalent. This makes automatines. System management tasks much
more complex.
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I.3.4. Windows NT variations :
Windows NT is sold in two formats: a server version and a workstation version
wokstation are designed to be can optionally share their resoueces with orther
systems servers are designed to provide resources and services to a collection of
systems ( worktations and possibly other servers) linked togerther by a local area
network They can proviide computing rsources and facilities (e.g database services )
disk space, access to printers ,networking-related services (eg hostname resolution).
Windows NT groups computers into collections known as domains each overseen
by a special server system- the primary domain controllers (also servers)
The same Kernel is used for both versions of the windows NT product. It is
configured.
Differently for the two environments . the important differences are:
The maximum number of processus in a multiprocessor system supported is two
for the workstation version is and 32 for the server .
The workstation version is is limited to 10 simultaneous client (file sharing),
printing, some Internet and web related services.
The server version includes some additional software: several administrative
tools for mane ging domains, the internet information server , various networking
name service faculties, and others.
Some of the subsystems in the server version provide advanced features not
available in the workstation version:
For example fault-tolerant file system and remote booting capabilities for diskless
workstations.
Some parameters related to system performances are set differently in the two
products.
The workstation version costs substantially less than the server version
I.3.5. Windows NT administrative tools:
Windows NT provides four classes of administrative tools:
Control panel applets
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These utilities are accessed via start - >settings control panel or from the
control panel or from the control panel under my computer
Administrative wizards
On server systems, these programs provide automated, step-by-step procedures
for performing common administrative tasks such as adding new user and setting
permissions on files and directories. They are accessed via the
start- > programs- >administrative tools (common)- > administrative wizards
they can also be accessed via the winger command.
Graphical administrative tools
The tools are found on the
Start -> programs -> Administrative tools each is designed to, message a
specify(command) system or domain component or subs tem Command the tools
Some of the functionality in the preceding classes is n duplicated in windows
NT commands may be extend directly into the start -> run .dialog box or via
a command window (you can user one by specifying (you can user one by specifying
command start -> Run))
The derailed administrative tools in each category will be presented in a later
chapter of this course.
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CHAPTER.II TRANSMISSION OF INFORMATION:
II.1 INTRODUCTION:
in this chapter, we explore ways in which information is transmitted through
the different layers of the TCP/IP Internet protocols and the systems connected to the
network. We shall also explore the structure of Internet addresses and how such a
structure enables information to be routed, through the Internet, to their final
destination. We shall also show how the rules of addressing are defined locally to
create subnets. We shall equally present protocol numbers and how these entities are
used to transmit information to applications. These details will enable students to
understand the specific implementation and configuration of networks.
II.2 ADDRESSING,ROUTING AND MULTIPLEXING
to transit information between two machines connected to the Internet, it is necessary
for the information to be transferred across the network to the required machine and
inside the machine to the required process. TCP/IP uses three systems to achieve
this:
Addressing
IP addresses which identify all machines in a unique way and enable information to
be sent to destination.
Routing
The mechanism for transferring information to an intermediate network.
Multiplexing
The protocols and post numbers which enable information to be transmitted to a
required program or process.
To illustrate these concepts, consider the national network show in fig 2.1.
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The network in fig 2.1is an intranet of a company. There are many networks
within the intranet and a connection point to the internet. The system administrator
has the responsibility of managing this Ethernet network from the computer centre.
The machine sales is a workstation. The machine gate is a gateway. The shaded
line in the middle of the diagram represents the Ethernet network of the computer
centre. The circle is the local network which interconnects the different computers
of the company.
In this chapter, we shall consider the meanings of the different numbers and how
they are used to transmit the datagrams.
IP ADRESSES
The internet protocol transmits information between machines in the form of
datagrams. Each datagram is sent to the address specified in the address fields of the
destination machine (fifth word of the datagram heading). This address is a standard
172.16.12.3
Gate
172.16.1.5
Internet
nternet172.16.1.
172.16.12.3
Personnel
172.16.1.5
172.16.12.0
Sales
172.16.12.2
Accounts
172.16.12.2
Fig 2.1 National Network
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IP address coded in 32 bits and containing network and a unique machine within the
network .
An IP address contains a machine part and a network part but the format of
these two parts is not the same in all addresses.
IP addresses are identified in two ways: the class of the address or the address
mask CIDR (Classless Inter Domain Routing).
ADDRESS CLASSES:
There are three classes A,B,C.
Class A: first bit of IP address is 0. the 7 bits which follow identify the
network and the last 24 bits identify the machine. There are less than 128 classes of
type A but each class can contains millions of computers.Class B: first two bit are 10. the first two bits identify the class, the next 14 bits
identify the network and the last 16 bits identify the machine. There are thousands of
class addresses and each of these classes can contains thousands of machines.
Feuille 5-6:
Class c the first three bits are 110. the first three bits identify the class,
the next 21 bits identify the network and the last 8 bits identify the machine. There
are millions of class C addresses but each class can only contain a maximum of 254
machines.
Multicast address - of the first four bits are 1110, it is a multicast address. These
addresses are sometimes referred to class D, but they refer to a group of computers
which share a given program, ( a videoconference program for example) in contrast
to a network of computers.
Reserved Address - of the first four bits are 1111, the address is reversed. These
addresses are sometimes referred to as class E, but they dont refer to physical
networks. No number has yet been assigned to these addresses .
IP addresses are often written in decimal form with 4 decimal numbers, each
between
255 (one octet of information). Since the bits which identify the address are located
in the same byte with the bits which identify the network, we can combine them into
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a single block and present IP addresses as incorporating bytes which address the
network and bytes which
address the machine. From this viewpoint, if the numerical value of the first byte is:
Less than 128, the address is class A . the first byte is the address of the network.
The last three bytes are the address of the machine.
Between 128 and 191, the address isclass B . the first two bytes are the address of
the network, while the last 2 bytes are the address of the machine.
Between 192 and 223, the address is class C. the first three bytes address the
network and the last byte addresses the machine.
Between 223 and 233, the address is multicast. These is no part reserved for the
network. The whole address identifies a group of machines.
Greater than 239, the address is reserved. We can ignore these classes.
An example of a class A address is 10.104.0.19
An example of a class B address is 172.16.12.1
An example of a class C address is 192.168.16.1
The IP address which provides a universal addressing system across all the
networks of the Internet is one of the major strengths of the TCP/IP protocols.
However, the structure of these addresses contains a weakness. The designers of TCP
did not foresee the large scale of the networks, which now form part of the Internet.
Networks were initially used only in very big organization. The designers of TCP/IP
could not imagine the idea of a powerful UNIX system in every office. At that time
32bit addresses were adequate. They were divided into classes to reduce the cost of
processing them through the routers, even if this division into classes severely
reduced the number of machines, which can be addressed. For example, a network
witch one-class B address requires fewer routers than a similar network witch six
classes C addresses because the router only uses a single route for all the addresses.
However the network certainly doesnt have up to 64.000 computers, so a large part
of the address space reserved for such company will never be used.
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172.16.26.32 * 255.255.255.224 U 1500
195.4.0.0 129.6.26.62 255.255.0.0 UG 1500
Loop back * 255.0.0.0 U 3584
Default 129.6.26.62 * UG 1500
It is very cumbersome to write addresses and their masks. A more concise
notation has been developed for CIDR addresses. Instead of specifying a machine as
having the address 172.16.26.32 and the mask as 255.255.224.0 we can write172.16.26.32/19. The number 19 refers to the number of bits of the address part of
the IP address. The RFC 1878 grieves a list of the 32 values of CIDR Prfixes. CIDR
is a temporary solution. The long term solution is to replace the existing addressing
system with a new system. In this connection, IETF( Internet Engineering Task
Force) has created a new version of IP addresses. Such a large address space makes it
possible to use a hierarchical address structure which reduces the number of routers.
Other advantages of Ipv6 include:
Enhancement of security in the protocol.
Simplification of headings, which have a fixed size.
New technique for managing the options in the heading.
Ipv6 will take a few years to be implemented In the mean time, the present
generation of TCP/IP will be adequate for all communication within the Internet.
Before ending this discussion on IP addresses, the following points should be noted:
Not all network addresses are usable. Addresses with the first byte greater than
223 cannot be used as machine addresses. Similarly the address zones 0.0.0.0/8 and
127.0.0.0/8 are reserved for specific purposes.
The network 0 represents the default route and network 127 corresponds to the
simplify the routing information that IP has to manage.
The loop back simplifies internet applications by enabling a local machine to be
considered by the software in the same way as distant machines. These special
addresses are used during the configuration of a machine.
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In all network, machine numbers 0 and 255 are reserved. An IP address with all the
bits of the machine part set to 0 identifies the network itself. For example 10.0.0.0
refers to network 10 and 176.10.0.0 refers to network 176.10 these addresses are
used in routing tables to refers to networks. An IP address with all the bits of the
machine part=1, corresponds to a broadcast address. A broadcast address is used for
simultaneous communication with all the machines of the network. The broadcast
address of network 176.16 is 172.16.255.255. A data gram sent to this address will
be sent to all the machines of the network.
IP addresses are often referred to as machine addresses. This is misleading.
Network addresses are assigned to the interfaces of the gateway gate in fig 2.1 has
two addresses: one for each network card. The gateway of other peripheral devices
connected to the network are the same as the address of the network to which thesedevices are connected. For example sales addresses gate as 172.16.12.1 while
external machines communicate with gate using the address 10.104.0.19.
Three types of ways of using addresses coexist. Independent machines are directly
reached through a machine address called unicast. A unicast packet is sent to a
specific machine. Groups of machines can be contacted using a multicast
address(224.0.0.9 for example). Routers, which are located between the source and
destination, recognise the special addresses and route copies of packets to every
member of a multicast group.
IP uses the network part of an address to route the data gram between networks.
The complete address, including the address of the machine is used to send the data
gram reaches its destination.
II.3 SUB NETWORKS:
A network can be partitioned into sub-networks to decentralise the
administrartion of the network. For example , the network of the principal network.
For example a network of the university oe dschang can be organised in such a way
that every faculty has a sub-network which can be managed locally by one person
under the supersion of the principal network administrator.
Form outside the network,all the sub-network have the same network address
as the parent network , but locally each sub-network has a separate network address.
A sub-network is defined by charging the masic of IP address. For example ,
consider a nework with address 172.16.0.0/16. The mask of the sub-network
associated with this network 255.255.255.0 . The most frequencetly used subnet
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mask extends the network post of the IP address by one byte (255.255.255.0) . All
the bits of the first three bytes are 1. Only the bites of the last byte are 0. the first two
bytes define the initial network, the third byte defines the subnet , and the fourth
byte defines the machines connewsted to the sub-network.
Many sub-network administrators prefer byte-oriented masks becaused they are
easy to understand when expressed in decimal format. However, this approach is 17
limited and does not enable the full power of this system to be utilised . the mask of a
subnet is bit-oriented . We can divide 172.16.0.0/16 into 16 sub-nets using the mask
255.255.240.0, for example 172.16.0.0./20. The 4 most significatnt bits of the third
byte era the address of the subnet. The 12 renaining bits (4 bits of the third byte and
8 bits s of the 4th
byte) are the address of the machine . This creates 16 subnets each
with more then 4000 machine address. The table below shaws the subnet address andthe machines produces by applying the subnet masks
Network address First Class Last Class
172.16.0. 0 172.16. 0.1 172.16. 15.254
172.16. 16.0 172.16. 16.1 172.16. 31.254
172.16. 32.0 172.16. 32.1 172.16. 47.254
172.16. 48.0 172.16. 48.1 172.16. 63.254
172.16. 64.0 172.16. 64.1 172.16. 79.254
172.16. 80.0 172.16. 80.1 172.16. 95.254
172.16. 96.0 172.16. 96.1 172.16. 111.254
172.16. 112.0 172.16. 112.1 172.16. 127.254
172.16. 128.0 172.16. 128.1 172.16. 143.254
172.16. 144.0 172.16. 144.1 172.16. 159.254
172.16. 160.0 172.16. 160.1 172.16. 175.254
172.16. 176.0 172.16. 176.1 172.16. 191.254
172.16. 192.0 172.16. 192.1 172.16. 207.254
172.16. 0.208 172.16. 208.1 172.16. 223.254
172.16.224.0 172.16. 224.1 172.16. 229.254
172.16.240.0 172.16. 240.1 172.16. 254.254
Tables of the kind are already pre-calculated and avalable in RFC 1878.
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Organisations have been discouraged from creating sub-nets from class c addresses,
since, this will further reduce the number of machines (a class c address holds less
than 255 machines), The mask 255.255.255.192 divides a class C address into 4
subnets of 64 machines. The problem is that subsnet addresses with all OS or all 1'S
are not usable, wich leaves only subnets. Futhermore, since machine adresses with all
O'S or all 1'S are not usable these two subnets can only have 62 machines each this
reduces the adress space of a class C adress from 254 to 124. the fear of creating
subnets from a class c address is not longer justified. Initially, RFC stated that
network addresses containing all zeros or all ones could not be used. However, RFC
1812, (Requirements for IP version 4 routers) announces that theses subnets are legal
and can be processed by all roiuters. Some old routers do not allow the use of these
network adresses, updating the router sofware or harware enables these adresses tobe used in total security.
Class c subnets are ued when small networks are necessary for equipement
such as servers of terminals and router controllers. In some cases, a subnet can be
used to create a link between two routers. In this case, only 2 machines adressed are
requiered, on for each router the mask 255.255.255.252 applied to a class C address
creates 64 subnets each containing 64 machines. In some special cases, this approch
can be justify.
II.4 ARCHITECTURE OF INTERNET ROUTING:
The initial of the internet was based on a hierarchy gateways centred on the
APARNET. In this structure, routing information about all network was sent to the
central gateways. the central gateways processed and interchanged information using
GGP(Gateway to gateway Protocol). The processed routing information was then
sent to external gateways.Routing information was centralised by the central
gateways.
The centalised approch didnot facilitate the expansion of the internet. A new
model was developped, based on the set of equal and automatous gateways called
routing domains.These gateways interchange information 20 using the BGP (Border
Gateway Protocol). This is a decentralised system. Every gatew
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NFS created the RA(Routing Arbiter) servers. A server is the placed at each
NAP(Network Access Point) . The server gives access to database, the
RADB(Router Arbiter database). Internet service providers can intorogatethis
database to validate the information supplied by an automatous system, the RADB is
only a port of the IRR(Internet Routing Registrery).
Creating an efficient routing architecture remains a major ambition of the
Internet. however this evolves, routing information will be used by IP to take the
necessary routing decisions.
II.5 THE ROUTING TABLE:
Gateways route data betwen networks, but all the periphecal devices,
machines and gateways withen network must make deciseons about routing. For
many machines the deciseons are simple:
- Of the destination machine is part of the local network, the data is sent to the
destination machine.
-
Of destination machine is part of a distant network, the data is sent to a local
gateway
After having detrminated the destination network, IP searches for network in the
routing table. the packets routing table. the table can be constructed by the the
network administrator or by the routing protocols. You can display the contents of
the routing table by using netstat -nr. The option -r tells netstat to display the routing
table while the option -n displays the information in numeric form. On a solaris
sytem, the following fields are displayed by the netstat command:
Destnation= network or machine at the destination
Gateway= gateway ta rech final destination
Flags:
U: the route is activated and operationnal
h: a specific route to a particular machine
G: the route uses a gateway
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D : this route has been added dynamically after an ICMP message(a
redirected message ) Ref=the number of times that the route has been referenced to
establish a connection.
Use = number of packets transmitted by this route
Interface = the rase of the network interface used by this route
Consider a n example
% netstat nr
routing table:
Destination Gateway Flags Ref Use Interface
127.0.0.1 127.0.01 UH 1 298 1o 0Default 172.16.12.1 UG 2 50360
172.16.12.0 172.16.12.2 U 40 111379 1e 0
172.16.2.0 172.16.12.3 UG 4 1179
172.16.1.0 172.16.12.3 UG 10 1113
172.16.3.0 172.16.12.3 UG 2 1379
172.16.4.0 172.16.12.3 UG 4 1119
The first entry in the routing table corresponds to the loopback route for the
localmachine. You can deduce from this example that the machine sales is directly
connected to network 172.16.12.0 since no external gateway is specifiied for ths
network. That is to say that the entry 172.16.12.0 doesnot contoun the option G.
consequently, sales is directly connected to this network.
All the gateways in a routing table are found on networks which are directly
connected te the local system. In the abore example, the gateway addresses always
start wich 172.16.12 because this in the only network to which sales is connected.
The routung problem is further illustrated by fig2.3. the IP layer of each machine and
gateway connected to our imaginary network is replaced by a piece of the routing
table, shouring the destination networks and the gateways used in reaching them.
When a machine (172.16.12.2) sends data to another machine (172.16.1.2), it first
determines that 172.16.1.2 is the official address of the local network and applies the
mask of the subnet(the network 172.16.0.0 is divided into subnets and use the mask
255.255.255.0). After applying this mask, IP knows that the address of the
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destination network is 172.16.1.0 the routing table of the source machine shows that
data for address 172.16.1.0 must be sent to gateway 172.16.12.3. This gateway can
then send data by using its network interface 172.16.1.5. Note that 172.16.12.1 is the
gateway for both 172.16.12.2 and 172.16.12.3. But since 172.16.1.2 cannot reach the
network 172.16.12.0 directly, it uses another route.
II.6 RESOLUTION OF ADDRESSES
An IP address directs datagrams to a physical network but when data crosses the
network it must be in a format consistent with the protocols of the physical layer.
The physical layer doesnt understand IP addresses. The IP address must be
translated to a machine address, which is very often the ethernet address. The
address resolution protocol(ARP) does the conversion.
The command arp displays the arp table.
% arp sales
sales(172.16.12.2 at 8:0:20:0:e:c8)
the gestion a of the arp command displays aU the contents of the arp table.(arp -a ).
II.7 PROTOCOLS, PORTS AND SOCKETS
As data crosses the layers of TCP/IP, a mechanism is required to ensure that the
data is sent to the right protocols in the transport and Internet layers. The data is
Application
Transport
Destination gateway
172.16.1.0172.16.12.0
default
172.16.12.3172.16.12.2
172.16.12.1
Network
172.16.12.2
Application
Transport
Destination gateway
172.16.1.0default
172.16.1.2172.16.1.5
Network
172.16.1.2
Destination gateway
172.16.1.0
172.16.12.0
default
172.16.1.5
172.16.12.3
172.16.12.1
Network
172.16.12.3 172.16.1.5
172.16.12.0 172.16.1.0
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transmitted in a multiplexed form and must be demultiplexed before being sent to the
various applications. IP uses protocol numbers to identify the appropriate transport
protocols and the transport use port numbers to identify the applications.
Protocol numbers
The protocol number is a byte situated on the third word of heading of the
datagram. It identifies the protocol, in the layer below, to which the datagram must
be sent.
In a Unix system, protocol numbers are defined in the file /etc /protocols file.
# Internet (IP) protocols
ip 0 IP # Internet Protocolicmp 1 ICMP # Internet Control Message Protocol
ggp 3 GGP # Gateway Gateway Protocol
tcp 6 TCP # Transmission Control Protocol
egp 8 EGP # Exterior Gateway Protocol
pup 12 PUP Parc Universal Protocol
udp 17 UDP User Datagram Protocol
hmp 20 HMP Host Monitoring protocol
Port Numbers
Port numbers are stored in the file /etc/services. An example of the contents
of this file:
tcpmux 1/tcp
echo 7/tcp
echo 7/udp
discard 9/tcp
discard 9/udp
systat 11/tcp
daytime 13/tcp
daytime 13/udp
netstat 15/tcp
chargen 19/tcp
chargen 19/udp
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ftp-data 20/tcp
ftp 21/tcp
telnet 23/tcp
smtp 25/tcp
Inspite of its size, the file /etc/services does not contain the post numbers of
all applications, for example, it RPC (Remote Procedure Call).
Sockets
These are dynamically assigned port numbers. It is a mechanism which allows
multiple users to access the save application
II.8 SUMMARY:
This chapter has explained how information is transmitted through the Internet,
from an application in a local machine to another application in a distant machine
TCP/IP uses a unique address to identify each machine, which is connected to the
Internet. It uses protocol and port number to identify protocols and application,
which are required to process the data as it moves from the source to the destination.
Routing tables enable datagrams to be directed through the maze of gateways, to
their final destination. Rioting tables always contain a default route.
Once data reaches the destination network, the IP address is converted to a machine
address (Ethernet address) by the ARP (address Resolution Protocol) to transfer the
data to the machine.
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CHAPTER.III NETWORK SERVICES :
Some network services supply services which are very essential to client
machines. Unlike Internetaplications, these services are not directly accessible touses, but are used by machines which are connected to network to simplify their
installation,configuration and operation.
The functions perfomed by thse servers are varied:
- domain name server to convert Ipaddress to macine names.
- Configuration servers which simplify the instalklation of TCO/ip and
the installation of machines mail service.
- Electronic mail service
- File servers
- Print servers
Tcp/IP servers chould not be configurated with file servers on a Micro-computer. All
unix machines connected to a network can be servers and clients at the same rank
(peer ). The network does not depend on one or more servers.
III.1 NAMES AND ADDRESSES:
Jon Postel ,in his refence document RFC 791, Internet Protocol , defines
names addresses and routes as follows:
A name indites what we looking for .
An address indicate where it is found.
A route indicated how to access it.
Every machine (network interface) connected to a TCP/IP network has a unique
IP . A name (hostname) can be assigned to any machine or equipment which has an
IP address.Names are machine oriented. Names and user-oriented. In most cases
machines names and ip addresses can be used interchangably. For example, a user
who wishes to connect to the machine with IP address 172.16.12.2 can type to telnet
172.16.12.2 Or To telnet calls .htec.com . Whether the command is issued with a
name or IP address, the network connected is always with te IP address before
making the connection. There are two methds used in tranlating names to addresses.
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The oldest method is based of machines. A more recent method is based on a
dDistributed DataBase of names and address. This is the DNS (Domain Name
Service)
III.1.1 Tables of machines:
A table of machines is the text file which associtaed names of machines to ip
adresses. on many UNIX systems, this file corresponds to /etc/hosts.
This file on the machine "sales" could contain the following entries:
172.16.12.2 sales.htec.com sales
127.0.0.1 localhost
172.16.12.4 accounts.htec.com accounts
172.16.12.3 gate.htec.com gate loghost172.16.12.3 personnnal.htec.com pacane
172.16.1.2 research.htec.com research
The name of machine 172.16.12.2 is "sales.htec.com"the alias of machine is
"sales
the second entry of the file assigns the address 127.0.0.1 to the machine localhost.
Address 127 of a class A address is reserved for the loopback network. Machine
address 127.0.0.0 is a special address of a local machine. This is a mechanism which
enables the machine to communicate with itself as well as with distant machines.
Although machine tables have been replaced by DNS, it is still widely used for many
reasons:
Most systems have a short table containing only the names of the most iportant
machines of the local network. this table is used when DNS is not functioning, for
eaxample during booting of a machine. Even if we use DNS it is advisable to create a
short /etc/hosts file containing the entries of the machine, the localt host, the
gateways and the servers of the network.
Sites which use NIS use the table of machines as input to the database of NIS
machines
Small networks which are not connected to the internet use sometimes use machine
tables. If the network only has a few machines do not communicate with via TCP/IP
with distant machines then it is sufficient to use machine tables.
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The machine tables have been superpected by the DNS for two reasons : lack of a
capacity for extension and automatic update. tables which were manually updated
could not be communicated to all the machines withen the internet.
III.1.2The domain Name service (DNS):
The DNS overcomes all the deficiencies of the system of machine tables:
- it is easily extendable
- all new information about a machine is automatically transmitted to every part of
the network
DNS is a decentralised database. Of a DNS server receives a request about a
domain which it doesnt know about, it transmits the request to a server which has
authority over that domain. When the distant sever responds, the local server keepsthe information (in a cache) for future use. The next time the local server receives a
request about the domain, it uses the information in the cache to respond directly.
In addition to replacing machine tables, DNS also replaces an older system of
name service. The older system is also called name service. Both servers are found
in file /etc/service. The old version uses port number 42 for the UDP protocol and it
has the name nameserver or name. The newer version uses port number 53 for
UDP and has the name domain. The presence of these two systems in the same file
is a potential source of configuration for many uses.
III.1.3 the hierarchy of domains
The DNS is a hierarchical system, organised like an inverted tree. The roots of
the tree are the domains of the highest level. Some of these domains are
.com
.edu
.gov
.net
.int
.org
several proposals have been made to increase the number of top-level domains. One
proposal is to create more organisations to manage domains. At the moment, only
InterNIC manages all domains. The most important domain .com already has so
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many sub-domains that it will soon be difficult to manage the databases containing
this domain. At the present, the registration of domain costs 50 dollar per annum.
Some domains which have been proposed include:
firm(businesses and enterprises)
store ( enterprises selling articles)
web ( organisations specialised in the web)
info ( services pronding information).
III.1.4creating domains and sub-domains
The NIC (network information center) is the competent authority for
allocation of domains. If you need to create a domain below one of the highest-level
domains you must apply to NIC. Once the authorisation is granted, you can createother domains(sub-domains) below your domain.
For example, if the network in chapter 2 is in company dealing with high technology,
we can apply to NIC for a domain name HTEC and create sub-domain sales,
accounts, personnel and several others.
III.1.5 domain names:
A domain name reflects the hierarchy of the domains. The name starts with the
most specific domain(machine name) and ends with the most generic domain. An
example is sales.htec.com.
III.1.6 bind, revolver and named:
The DNS, implemented on most unit system is based on the program
bind(Berkeley Internet Name Domain). The program is organised in two parts: a
resolver and a name server.
The resolver is the program which creates requests. It asks questions. The name
server is the process which processes the request to answer the question asked by the
resolver.
Bind is executed in the form of a process call named.
Name servers are classified according to their configuration. The are three
categories:
Primary server
This is the server which has all the information about a domain. This server is a
file created by the system administrator. There should only be one primary server for
each domain.
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Secondary server
Tecondary server transfer all the database about a domain from the primary
server. The file containing the database of the primary server is called the Zone file.
Copying this file to a secondary server is called transferring the zone file. A
secondary server ensures that it contains up-to-date information about domain by
transferring the zone file periodically. Secondary server also have authority over
their domain.
Cache servers
This server store the response obtained from other servers and use the
information when necessary.
When you add a new machine to the network, you modify the database of the
primary server. The modified Information is atomically transmitted to other serversby complete transfer of the zone files or by response caches.
III.2 NIS:NETWORK INFORMATION SERVICE
NIS is a system of databases of administration developed by sun Microsystems. It
provides centralised control and automatic dissemination of important system
administration files. NIS can be used at the same time as the DNS.
NIS provides information about the local network. It is not designed to be used
globally on the Internet.
III.3 ELECTRONIC MAIL SERVICE
electronic mail is the most widely used Internet Service. The service uses many
protocols, the most important of which include:
- SMP (Simple Mail Transfer Protocol)
- POP (Post Office Protocol)
- MIME ( Multipurpose Internet Mail Extersions)
Another protocol, IMAP (Interactive Mail Access Protocol) has been designed to
replace POP. IMAP is described in RFC 1176 has functionalities such as the search
are not found in POP.
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III.3.1 Simple Mail Transport Protocol
SMTP is the protocol which transports electronic mail across the internet and across
your local network. It is described in RFC 821 . it functions by connecting to TCP.
The standard port number assigned to SMTP is 25. some of the simplest commands
of SMTP are shown below.
Command Syntaxe Function
Hello HELO < sender
machine>
Identify SMTP
From MAIL from:
Sender address
Recipient RCPT TO : < recipientaddress>
Destination address
Data DATA Beginning of message
Reset RSET Cancel message
Verify VRFY Verification of name of
user
Expand EXPN Expand mailing list
Help HELP Demand on line helpQuit QUIT End of SMTP session
SMTP is so simple that you can use it directly by sending a telnet command to port
25 :
% telnet gate.htec.com 25
connected to gate.htec.com
helo sales.htec.com
mail from: < Daniel@sales.htec.com>
The system is facily simple. A TCP connection is opered, the connecting
system is identified, and a dialog ensues unite the message is transmitted.
SMTP provides a system of direct transmission between the sender and recipient
machines. This is unusual, most electronic mail protocols use a save-and-resend
system in which the mail is saved and resent. This is the case with UUCP and X.400
which transmit messages to their destination step by step.
III.3.2Post Office Protocol (POP)
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Two versions of POP are widely user POP2 and POP3. POP2 is defined in
RFC 937 and POP3 is defined in RFC 1725.
Version 2 of this protocol uses port number 109 while
Version 3 uses port number number 110.
The two protocols are incompatible and have different commands, but they
perform the login name and password of the user are correct and the move the users
mail from the server to the local mail reader.
POP2 and POP3 commands can also be issued from a telnet.
POP2 commands are shown below.
Commands Syntaxes Functions
Folder
Read
Retrieve
Save
Delete
Failed
Quit
FOLD destination
file
READ [n]
RETR
ACKS
ACKD
NACK
QUIT
Destination file for e-mail
Read e-mail, starting with
the message [n]
Recuperation of message
Save message and quit
Delete message and quit
Quit without saving
End of session
POP3 commands are completely different.
Commands Functions
USER
(username)
PASS
Account name of the user
Password
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(password)
STAT
RETR n
DELE n
LAST
RSET
QUIT
Number of messages and size of messages which have not
been read
Recuperate the message n
Delete n
Give the name of the last message accessed
Cancel the suppression of all messages. The first message
becomes the active message.
End of session
III.3.3MIME : Multipurpose Internet Mail Extensions
MIME extends the definition of the contents of electronic mail. The structure
of a message which is transmitted by SMTP is defined in RFC822. (Standard for the
format of ARPA Internet text Messages). This document defines standard headings
which must be included in the e-mail.
MIME extends RFC822 in two directions:
Type of Data RFC822 specifies that only ASCII text coded in 7 bits can be
used while this is sufficient for the English language, it is insufficient for other
languages which have a more extensive character set
Complexity of messages RFC822 gives no details about the body of the
message. It only concentrates on the headings.
MIME addresses these short-comings by defining coding techniques for transmitting
various types of messages and a structure which allows the body of the message to
contain several different objects. RFC1521 defines seven types of objects which can
be included in an E-mail:
Text
Application (binary data)
Image ( graphical images)
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Vido
Audio
Multiport (data containing several independent sections)
Message (encapsulated message such as file extension)
III.4 CONFIGURATION SERVERS :
The powerful features which make TCP/IP flexible and practical also tend to
increase its complexity. TCP/IP is not easy to configure. It is necessary to supply
information about machines, addresses, and routing. It is designed to be independent
of any hardware or network technology. Configuration servers enable the network
administrator to control the configuration of TCP/IP from a central machine. Thefrees the user from the more obscure part of the configuration.
There are three configuration protocols:
o RARP
o BOOTP
o DHCP
o
RARP: Reverse Address Resolution Protocol
RARP is defined in RFC903. It is a protocol which converts the physical
address. It is the reverse of ARP (Address Resolution Protocol). The user sends a
broadcast by using the the broadcast services of the network.
The packet sent to all the machines of the machines of the network contains the
physical address of the client and requests whether any system within the network
know the IP address associated with the physical address. The RARP server responds
with a packet containing the IP address. The client knows its physical address since it
is included in the Ethernet card. For example, the super-user can type: # ifconfig leo
To respond to a RARP request, the server must transform the machine name
foud in /etc/ethers to an IP address. This is done using DNS or BY consulting the file
/etc/hosts.
An example of the contents of /etc/ethers:
2: 60:8c:48:84:49 apollo
0:0:c0:a1:5e:10 plato
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0:80:c7:aa:a8:04 aristotte
an example of the contents of /etc/hosts
Apollo 172.16.3.10
Plato 172.16.3.16
Aristote 172.16.3.4
BOOTP : Bootstrap Protocol
this protocol is define in RFC 951and RFC 1532. it is an alternative to RARP. When
BOOTP is used, RARP is no longer necessary. However, BOOTP is a more
comprehensive protocol than RARP. It supplies more configuration information.
The client sends a broadcast containing a single packet called BOOTREQUESTwhich must specify the physical address of the client. The client sends the broadcast
using the address 255.255.255.255 which is a special address called reduced
broadcast address. The client waits for the reply of the server. If after a reasonable
delay, there is no response, the client sends the packet BOOTREPLY.BOOTP which
uses two official port numbers. The UDP port number 67 is used for the server and
number 68 is used for the client. This is unusual. Most protocols use a standard port
number for the client, to ensire that each pair of client-server port numbers identifies
a unique connection for the exchange of information.
However, a BOOTP client is always ready to send a broadcast. The client
may not even know its IP address. Even of the client generates a part for the
BOOTREQUEST packet the response of the server addressed to the part and the IP
address of the client will not be read by a client which does not know its IP address.
This is why BOOTP send the response to all the machines using a specific part
number. A broadcast send to UDP part 68 is read by all the machines, ever a
machines which does not know its IP address. The machine determines whether it is
the recipient of this message by comparing the physical address included in the
message with its own address.
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Static addresses assigned by DHCP to BooTP clients.
Dynamic addresses assigned to all DHCP clients.
print servers
A print server enables printers to be shared by all the users of a network. It has
several advantages:
It requires fewer printer.
Reduced maintenance cost.
Accessed to special printers(color and high-speed printers are very expensive).
The are two ways of sharing printers. One way is to use the file-sharing facilities of the
network. One other approach is to use the unix command LPR and print server lpd.
File server
File sharing is different from the transfer of files. A client can read a file saved in
a remote server, modify it, and save the modified file on the server without
transferring the file across the network. The user accesses files stored on a distant
server as if the files were stored locally.
File sharing was not part of TCP/IP protocols. It was added to manage machines
without hard disks. There are 3 protocols for file sharing: RFS(remote File System),
AFS(Andrew File System) and NFS(Network File System). NFS is the most widelyused system.
summary
TCP provides a variety of services which simplify the installation, configuration
and use of the network. These services include Domain Name Service(DNS); e-mail
services provided by protocols such as SMTP, POP and MIME; server configuration
service provided by protocols such as RARP,BOOTP and DHCP; pointer-sharing
facilities; and file-sharing facilities.
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CHAPTER.IV PREPARING INFORMATION FOR
CONFIGURATION OF THE NETWORK:
Before configuring the TCP/IP layer of a machine the system Administrator
must have various types of Information:
Address of the default Gateway if the machine dialogs with other TCP/IP machines
which are not part of the local network.
Domain name server
to transform machine names into IP addresses
Subnet Mask
To communicate correctly, all the machines of the network must use thee samesubnet mask.
Broadcast address
To avoid broadcasting problems, the broadcast address of all the computers in a
network must be the same.
If you create a new TCP/IP network, you must take number of important
decisions. Will the network be connected to Internet? If so, what type of connection
will be made? how will the address of network be chosen? How will the domain
name be registered? How will the machine name be chosen?
IV.1 4.1CONNECTEDANDSTARD-AOONENETWORKS:
a connected network is directly linked to the Internet has complete access to all other
network which are connected to the Internet.
A stard-alone network is not directly connected to the internet and can only access
the internet intermittently. An example of such is a TCP/IP network which accesses
the external world through a gateway of America Online (AOL). The users of the
network can send electronic mail to machines using commands such as RLOGIN.
A large number of machines are not connected to the Internet. TCP/IP is used to
communicate with the different networks of a organisation. When such corporate
networks use TCP/IP applications, especially the web, for their internal
communication, these network are referred to as Intranets. One of the most
fundamental reasons for not connecting to the Internet is the security.
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Before deciding on the type of connection, a compromise must be made between cost
of connection and advantages derived from the connection.
i. Many companies only use e-mail or the web to give information about their
products. Full Internet access is not necessary in such cases. In such aces, it is
sufficient to connect a server to an internet service provider.
ii. Some organisations such as Universities and research institutions consider Internet
access as an absolute necessity.
iii. You can have the two types of connection
A private network install behind a firewall and a small connected network which
supplies information to external clients and a proxy(mandatory server ) to internal
users.
IV.2 4.2BASICINFORMATION:The interface between TCP/IP and the physical network requires an IP address,
and may eventually require a broadcast address and subnet mask.
IV.2.1 Obtaining an IP address
if the network is connected to the Internet, the IP address of every machine must be
unique in the whole Internet. Of the network is not connected, the address of a
machine only needs to be unique locally choose addresses from those proposed in
RFC 1918, address allocation for private networks. the address of these networks
are :
- Class A , 10.0.0.0 ( prefix 10/ 8 and a 24 bits address)
- Class B, from 172.31.0.0. (Prefix 172.16/ 12 and a 20 bit address)
- Class C, from 192.168.0.0 to 192.168.255.0 (prefix 192.168/16 and 16 bit
address)
To connect a network to the Internet, it is necessary to have the addresses of official
networks. These can be obtained from Internet service providers, or from CAMTEL
(in the context of Cameroon). Of the problem is not solved at the rational level, a
request is addressed to InterNIC through an application form obtained from the
address.
ftp://rs.internic.net/templates/internet-number-template.txt of you choose from RFC
1918, it is possible to connect to the Internet without having to assign new addresses
to the machines. This requires a NAT(Network Address Translation) or a proxy
server. The NAT is available in the of an additional element or software on some
routers and firewalls.
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Ethernet network, referred to as maximal deameter, is 2500 metres. Of you have to
cover very long distances, you can use routers to link several Ethernet cables. Each
cable must not a separate Ethernet network.
ii) Interconnection of different network technologies. IP router can be
used to connect incompatible
Network technologies. Fig 4.1 illustrates the principle. A token ring network
172.16.1.0 is connected to two Ethernet networks 172.16.6.0 and 172.16.12.0
172.16.6.0
A
B
C
D172.16.9.0 172.16.1.0172.16.3.0
172.16.12.0
E
Internet
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Fig. 4.1 Routing and Subnet work
iii) Filtering of traffic
Local traffic remains in the subnet work. Only traffic destined for other networks
crosses the gateway.
Organisational considerations include:
i) Simplifying network administration by delegating the management ofaddresses, maintenance and other responsibilities to other people.
ii) Conformity with the structure of an organisation. An organisation may require
its departments to be independent in the way they manage their networks.
iii) Isolating Internet traffic. Some organisations require their local traffic to be
isolated in a network is only accessible internally.
iv) Anticipating potential problems.
A part of the network may be used for research and experimental activities which
may make that part of the network unstable. In such cases, it is better to convert that
part of the network into a subnet work
After partitioning the network into subnets, the network administrator defines the
subnet mask. For example, our imaginary network has the mask 255.255.255.0. 8
bits are used to identify the subnet work, which creates 256 subnets. The network
administrator decides that this mask allows many subnets to be created and that each
subnet has enough machines (253 machines for each subnet).
Once the mask has been defined, it must be communicated to all the machines. There
are two ways to do this : manually by configuring the network interface and or
automatically by using routing protocols. Older routing protocols cannot store the
masks in their routing tables. Never routing protocols and operating systems are
designed to solve this problem. Masks of variable length can even be used. There are
referred to as VLSM
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(Variable length subnet Mask). Fro example, the network 192.168.5.0/24 can be
divided into three subnet containing110, 50 and 60 machines be using subnet masks
255.255.255.128 is applies on the big subnet while the two smalls networks use the
mask 255.255.255.128.
IV.5 SPECFYING THE BROADCAST ADDRESS
The standard broascast address is obtained by setting all the bits of the machine part
of the address to 1. The network 172.16.12.0 has the broadcast address
172.16.12.255.
Some version of UNIX use incorrect broadcast addresses. UNIX BSD 4.2 uses a
broadcast address in which all the bits of the machine part are 0 and it is no possible
to change this. This problem does not exist in BSD 4.3 and more recent versions.Some other systems position the broadcastaddress adt the using value. Of you have
such a system, you must change the address.
IV.6 PREPARINGTHEROUTINGTABLE
There are two way to construct the routing table:
i) Static routing by a routing table prepared by the work administrator. This
approach is used when the number of gateway is limited.
ii) Dynamic routing using routing protocols. This approach is used when there are
many gatewaysin a network or when more than one gateway can reach a specific
destination .
The following considerations are a useful guide to preparing routing table:
i) Of the network has no gateway to other networks, no configuration of routing is
requered.
ii) Of the network has single gateway, dont use protocol software. Define the
single gateway as the default route.
iii) Of the network has internal gateways to sub-networks and a single gateway to
the external world, you can configure each subnet statically and make the external
gateway the default route or use a routing protocol.
iv) Of the network has many external gateways, then it is essential to use a routing
protocol.
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Fig 4.1 Show a network which is sub-divided into subnets interlinked by five gateway
A, B, C, D and E. A central subnet(172.16.1.0) interconnects 5 others subnets. One
of the subnet contain a gateway to the external world. The network administrator can
choose to configure 172.16.1.0 by a routing protocol. The same approach may be
applie on 172.16.1.0. Dynamic routing is appropriate for these subnets because they
contain several gateways. Without dynamic routing, the network administrator will
have to update the routing table each time a new subnetwork is added to the system.
On the other hand, the network administrator will probably choose to configure the
other subnetworks(172.16.3.0, 172.16.6.0, 172.16.9.0) narually. All of thse subnets
have only one gateway each to reach other destinations. All subnet added to the
system are accessible through the same gateway.
IN fig4.1, the local network is connected to an external network and this imposes theuse of the BGP(Border Gateway Protocol) as the routing protocol. This forces the
gateway E to use BGP to exchange routes whith other external networks.
IV.7 OBTAINING AS AUTONOMOUS SYSTEM NUMBER
BGP imposes a unique identification number on gateways. However , mask
system do not need suck a unique identification 0. Only networks with multiple
connections to several service provides reachy require this option.
IV.8 PREPARING THE DOMAIN NAME SERVICE
To configure a machine, the user of a network must know the domain name, the
name of this machine and and the name and address of the domain name server. This
information is provided by the network administrator.
IV.8.1Obtaining the domain name
The domain name can be obtained from the offucial Internet Organisation in
your country (CAMTEL) or by sending a request to the address.
FTP;// rs.internic.net/templete/domain-templete.txt
You must pre-select a domain name and have a domain name server which works
before sending a request to INTERNIC. The commands whois verifies that this name
is not already used. The command nslookup is also useful for such verification. Once
you are sure that the domain name is avalable, run the primary server and use
nslookup to verify that the server responds to querirs about it. The application form
for a domain name, obtained from the address given above, shoild be completed and
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sent by mail to hostmaster@internic.net . A registration fec of 100 dollars is paid, to
reduce the number of domain names from people who donot really need them .
To register the domain name, you are asked to supply the names and IP addresses of
your primlary and secondary servers. The servers must be operationel and corrected
to the Internet. The secondary server must be situated on a different physical network
from the primary server.
IV.8.2Obtaining a IN-ADDR.ARPA Domain
The in-addr.arpa domain is an inverse domlain which converts domain names, you
must equally apply for an in-addr.arpa doamin.
IV.8.3Choosing a machine name:
Once you have a domain name, you must assign machine names within this
domain. The network administrator has the freedom to assign names, but the
following guidelines should be followed:
i. Use simple and short names
ii. Chooses machines names base on a theme.For example the name of stars, planets,
scientists.
iii. Dont use the name of projects, personal names, abreviations or technical terms.
The only thing which is really obligatory about the name of a machine is that it
should be unique within the domain
IV.9 OTHERS SERVICES
The applications are used in most network:
File servers, printer servers, and mail servers. Users must be provided with the
information which enables them to configure these servers correctly.
IV.9.1 4-9-1 File server
At the very least, a user must know the name of the machines containing the file
server. The command showmount can then be used to know which file system are
imported by the the machines. For example, a file server may contain a UNIX
manual. The users must be informed that trhey should not install these pages on their
local disks and they must be shown how to use the manual.
Print Servers
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Whether printers are share using lp, lpd or NFS, the information required to
configure the client machines to access the printers is the same:
The name of the machine and the ip address of the print server as well as the name of
the printer.
Preparing the electronic Mail system
TCP/IP provides the necessary tools to create a reliable and flexible electronic mail
system. Mail servers are a tool for improving the reliability of the mail service. The
mail servers receives all the mail sent to the computers of a network. It facilitates
distant connections and the use of the protocols POP and IMAP. This enablers users
to read their mail.
Informing the users
All the configurations informations assembled during the preparation of the networkmust be communicated to the user. There are several ways of communicating such
information. NIS,NFS and configuration servers are possibilities. NIS support
databases which have a lot of information about the configuration of networks. NFS
can alowconfiguration files to be sent from a server to the client machine.
Configuration servers such as DHCP and BOOTP can supply all the parameters
which allow a TCP/IP system to be configured properly.
An example of preparation for network configuration
It is often necessary for the network administrator to create a document which
communicates configuration information to users. Such a document is presented
below for the workstation sales, in the national network of chapter 2.
Machine name
Sales
Ip address
172.16.12.2
Subnet mask
255.255.255.0
default gateway
172.16.12.1 (gate.htec.com)
broadcast address
172.16.12.255
domain name
htec.com
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Name servers
172.16.12.1 (gate.htec.com)
172.16.6.8 (stocks.factory.htec.com)
routing protocol
RIP: Routing Information Protocol
Mail server
172.16.12.1 (gate.htec.com)
relay of electronic mail
172.16.12.1 (gate.htec.com)
print server
172.16.12.3 (personnel.htec.com)
NFS server172.16.1.2 (research.htec.com)
A similar document prepared for gate is presented below:
Machine name
Gate (172.16.12.1)
Gway(10.104.0.19)
Ip address
172.16.12.1
10.104.0.19
Subnet mask
255.255.255.0
default mask (10.104.0.19)
domain name
htec.com
Domain name servers
172.16.12.1 (gate.htec.com)
172.16.6.8 (stock.factory.htec.com)
Routing protocols
RIP: Routing information protocol (172.16.12.1)
BGP: Border Gateway Protocol (10.104.0.19)
Print server
172.16.12.3 (personnel.htec.com)
NFS server
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172.16.1.2 (research.htec.com)
Note that the machine Gate has two network cards. All gateways have more than 1
network card and each card has to be configured separately. Each card has an address
and may have a separate name, a subnet mask and a routing protocol.
Netconfig
When installing LINUX, you are asked a series of questions. When asked if you
want to configure the network, answer yes to start netconfig. This program can be
strated by the super-user, from the command line.
The first two questions asked by netconfig concern the name of the machine and the
domain name. In the third place, you are asked if the machine will be configured to
use only loopback.
Answer no if the machine is connected to the internet or any part of a network.Only machines which use TCP/IP on machines which are not connected to a
network have to type no in response to this question.
Suummary
Preparatory to the configuration of a network, the network administration prepares
basic information which enables users to configure their machines correctly. This
information is varied and includes machines names, IP addresses, routing
information, domain names and servers such as print, file and e-mail. The
information is compiled into a document which is communicated to every user.