Chapter 6 Network Communications and Protocols

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Oct 27, 2013 (4 years and 14 days ago)

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Chapter 6
Network Communications and Protocols
Guide to Networking Essentials, Fifth Edition
2
Objectives

Explain the function of protocols in a
network

Describe common protocol suites
Guide to Networking Essentials, Fifth Edition
3
Protocols

Strictly speaking,
protocols
are the rules
and procedures for communicating

For two computers to communicate, they must
speak the same language and agree on the
rules of communication
Guide to Networking Essentials, Fifth Edition
4
The Function of Protocols

As protocols serve their functions in the OSI
model, they might work at one or many layers

When a set of protocols works cooperatively, it’s
called a
protocol stack
or protocol suite

The most common protocol stack is
TCP/IP
, the Internet
protocol suite

IPX/SPX, used in older versions of Novell NetWare, is
disappearing as companies upgrade to newer versions
of NetWare

Levels of a protocol stack map to their functions in the
OSI model
Guide to Networking Essentials, Fifth Edition
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Connectionless Versus Connection
-
Oriented Protocols

Protocols that use
connectionless
delivery place
data on the network and assume it will get through

Connectionless protocols aren’t entirely reliable

Are fast: little overhead, don’t waste time
establishing/managing/tearing down connections

Connection
-
oriented
protocols are more reliable
and, consequently, slower

Two computers establish a connection before data
transfer begins

In a connection, data is sent in an orderly fashion

Ensures that all data is received and is accurate, or that
suitable error messages are generated
Guide to Networking Essentials, Fifth Edition
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Routable Versus Nonroutable Protocols

The network layer (OSI) is responsible for
moving data across multiple networks

Routers are responsible for routing process

Protocol suites that function at Network
layer are
routable
or routed protocols;
otherwise, they are called
nonroutable

TCP/IP and IPX/SPX are routable protocols

An older and nearly obsolete protocol, NetBEUI,
is a nonroutable protocol that works well in
small networks, but its performance drops
considerably as a network grows
Guide to Networking Essentials, Fifth Edition
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Protocols in a Layered Architecture
Guide to Networking Essentials, Fifth Edition
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Protocols in a Layered Architecture
Guide to Networking Essentials, Fifth Edition
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Network Protocols

Some popular network protocols include:

Internet Protocol version 4 (IPv4 or simply IP)

Provides addressing and routing information

Internetwork Packet Exchange (IPX)

Novell’s protocol for packet routing and forwarding

Belongs to the IPX/SPX protocol suite

Serves many of the same functions as TCP/IP’s IP

Internet Protocol version 6 (IPv6)

A new version of IP that’s being implemented on
many current networking devices and operating
systems

Addresses some weaknesses of IPv4
Guide to Networking Essentials, Fifth Edition
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Transport Protocols

Transport protocols
can be connection
-
oriented (reliable) or connectionless (best
-
effort)
delivery

Transmission Control Protocol (TCP)

Responsible for reliable data delivery in TCP/IP

Sequential Packet Exchange (SPX)

Novell’s connection
-
oriented protocol used to guarantee data
delivery

NetBIOS/NetBEUI

NetBIOS establishes/manages communications between
computers and provides naming services

NetBEUI provides data transport services for these
communications
Guide to Networking Essentials, Fifth Edition
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Application Protocols

Application protocols
provide services to client
applications

Simple Mail Transport Protocol (SMTP) in TCP/IP

File Transfer Protocol (FTP) in TCP/IP

Simple Network Management Protocol (SNMP)

Manages and monitors network devices (TCP/IP)

NetWare Core Protocol (NCP)

Novell’s client shells and redirectors

AppleTalk File Protocol (AFP)

Apple’s remote file
-
management protocol
Guide to Networking Essentials, Fifth Edition
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Common Protocol Suites

Because most protocols contain a
combination of components, these
components are usually bundled as a
protocol suite

TCP/IP

Dominates the networking arena to the point of
making most of the other suites nearly obsolete

IPX/SPX

NetBIOS/NetBEUI

AppleTalk
Guide to Networking Essentials, Fifth Edition
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Transmission Control Protocol/Internet Protocol (TCP/IP)
Guide to Networking Essentials, Fifth Edition
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TCP/IP Network Layer Protocols

Internet Protocol version 4 (IPv4)
is a Network
layer protocol that provides source and destination
addressing and routing for the TCP/IP suite

Connectionless protocol; fast but unreliable

Internet Control Message Protocol (ICMP)
is a
Network layer protocol used to send error and
control messages between systems or devices

The Ping utility uses ICMP to request a response from a
remote host to verify availability

Address Resolution Protocol (ARP)
resolves
logical (IP) addresses to physical (MAC)
addresses
Guide to Networking Essentials, Fifth Edition
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IP, ICMP, and ARP in Action
Guide to Networking Essentials, Fifth Edition
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IP, ICMP, and ARP in Action
Guide to Networking Essentials, Fifth Edition
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TCP/IP Transport Layer Protocols

Transmission Control Protocol (TCP)
is the
primary Internet transport protocol

Connection oriented using a three
-
way handshake

Message fragmentation and reassembly

Uses acknowledgements to ensure that all data was
received and to provide flow control

User Datagram Protocol (UDP)
is
connectionless

Generally faster, although less reliable, than TCP

Doesn’t segment data or resequence packets

Doesn’t use acknowledgements for reliability

Used by NFS and DNS
Guide to Networking Essentials, Fifth Edition
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TCP/IP Application Layer Protocols

Domain Name System (DNS)

Session layer name
-
to
-
address resolution protocol

Hypertext Transport Protocol (HTTP)

To transfer Web pages from Web server to browser

File Transfer Protocol (FTP)

For file transfer and directory and file manipulation

Telnet

Remote terminal emulation; operates at layers 7
-
5

Simple Mail Transport Protocol (SMTP)

Operates at layers 7
-
5; provides messaging services
Guide to Networking Essentials, Fifth Edition
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IP Addressing

Logical addresses are 32 bits (4 bytes) long

Each byte is represented as an
octet
(decimal number
from 0 to 255)

Usually represented in
dotted decimal
notation

E.g., 172.24.208.192

Address has two parts: network and host ID

E.g. 172.24.208.192 (172.24.0.0 and 208.192)

Categorized into ranges referred to as classes

Class system provides basis for determining which part of
address is the network and which is the host ID

The first octet of an address denotes its class
Guide to Networking Essentials, Fifth Edition
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IP Addressing (continued)

Classes

Class A: first octet between 1
-
126

16,777,214 hosts per network address

Class B: first octet between 128
-
191

65,534 hosts per network address

Class C: first octet between 192
-
223

254 hosts per network address

Class D: first octet between 224
-
239

Reserved for multicasting

Class E: first octet between 240
-
255

Reserved for experimental use
Guide to Networking Essentials, Fifth Edition
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IP Addressing (continued)

127.0.0.0 network is called the
loopback address

localhost
always corresponds to address 127.0.0.1

IETF reserved addresses for private networks

Class A addresses beginning with 10

Class B addresses from 172.16 to 172.31

Class C addresses from 192.168.0 to 192.168.255

These addresses can’t be routed across the Internet

To access the Internet, NAT is needed

IPv6 eliminates need for private addressing; provides a
128
-
bit address (vs. IPv4’s 32 bits)
Guide to Networking Essentials, Fifth Edition
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Classless Interdomain Routing (CIDR)

Addressing by class has been superseded by a
more flexible addressing method

Classless Interdomain Routing (CIDR)

The network and host demarcation can be made with
any number of bits from beginning of address

E.g., a Class C address’s network section is 24 bits

Using CIDR, an address registry can assign an address with a
network section of 26 bits

192.203.187.0/26

Subnetting
divides network address in two or more
subnetwork addresses (with fewer host IDs for each)
Guide to Networking Essentials, Fifth Edition
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Why Subnet?

Subnetting

Makes more efficient use of available IP addresses

Enables dividing networks into logical groups

Can make network communication more efficient

Broadcast frames are sent to all computers on the
same IP network

Hubs and switches forward broadcast frames; routers
do not

Broadcast domain:
extent to which a broadcast frame
is forwarded without going through a router

Subnetting reduces broadcast traffic
Guide to Networking Essentials, Fifth Edition
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Subnet Masks

Subnet mask
determines which part of address
denotes network portion and which denotes host

32
-
bit number

A binary 1 signifies that the corresponding bit in the IP
address belongs to the network portion; a 0 signifies
that bit in address belongs to host portion

Default subnet mask uses a 255 in each octet in
address that corresponds to the network portion

Class A: 255.0.0.0

Class B: 255.255.0.0

Class C: 255.255.255.0
Guide to Networking Essentials, Fifth Edition
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Some Simple Binary Arithmetic

Four kinds of binary calculations:

Converting between binary and decimal

Converting between decimal and binary

Understanding how setting high
-
order bits to the
value of 1 in 8
-
bit binary numbers corresponds
to specific decimal numbers

Recognizing the decimal values for numbers
that correspond to low
-
order bits when set to 1
Guide to Networking Essentials, Fifth Edition
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Converting Decimal to Binary

125 is converted to binary as follows:

125 divided by 2 equals 62, remainder 1

62 divided by 2 equals 31, remainder 0

31 divided by 2 equals 15, remainder 1

15 divided by 2 equals 7, remainder 1

7 divided by 2 equals 3, remainder 1

3 divided by 2 equals 1, remainder 1

1 divided by 2 equals 0, remainder 1
Guide to Networking Essentials, Fifth Edition
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Converting Binary to Decimal

To convert 11010011 to decimal:
1.
Count the total number of digits in the number
(8)
2.
Subtract one from the total (8
-
1 = 7)
3.
That number (7) is the power of 2 to associate
with the highest exponent for two in the
number
4.
Convert to exponential notation, using all the
digits as multipliers
5.
11010011, therefore, converts to:
Guide to Networking Essentials, Fifth Edition
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High
-
Order Bit Patterns
Guide to Networking Essentials, Fifth Edition
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Low
-
Order Bit Patterns
Guide to Networking Essentials, Fifth Edition
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Calculating a Subnet Mask

To decide how to build a subnet mask:
1.
Decide how many subnets you need
2.
Decide how many bits you need to meet or
exceed the number of required subnets

Use the formula 2
n
, with
n
representing the number
of bits you must add to the starting subnet mask
3.
Borrow bits from the top of the host portion of
the address down
4.
Ensure that you have enough host bits
available to assign to computers on each
subnet (2
n
-
2)
Guide to Networking Essentials, Fifth Edition
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Calculating a Subnet Mask
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Calculating a Subnet Mask
Guide to Networking Essentials, Fifth Edition
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Calculating Supernets

Supernetting
“borrows” bits from network portion
of an IP address to “lend” those bits to host portion

Permits consecutive IP network addresses to be
combined and viewed in a single logical network

Combining two or more small networks into one
larger network is only one reason to supernet

Supernetting can combine multiple routing table entries
into a single entry, which can drastically decrease the
table’s size on Internet routers

This reduction in routing table size increases the speed
and efficiency of Internet routers
Guide to Networking Essentials, Fifth Edition
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Network Address Translation (NAT)
Guide to Networking Essentials, Fifth Edition
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Dynamic Host Configuration Protocol (DHCP)

Detailed configuration of devices, keeping track of
assigned addresses and to which machine they
were assigned, etc., is difficult in large networks

DHCP
was developed to make this process easier

DHCP server must be configured with a block of
available IP addresses and their subnet masks

Clients must be configured to use DHCP

Broadcast request message is sent on boot

Client leases the address the server assigns to it

If no answer is received, in an
APIPA
-
enabled OS,
the computer
assigns itself an address (169.254.x.x)
Guide to Networking Essentials, Fifth Edition
36
Internet Protocol Version 6 (IPv6)

IPv6
solves several IPv4 problems

Limiting 32
-
bit address space

An IPv6 address is 128 bits long

Lack of built
-
in security

IPSec provides authentication and encryption

A sometimes complicated setup

IPv6 is autoconfiguring (stateless or stateful)

Lack of built
-
in QoS

QoS headers in IPv6 packets can identify packets
that require special or priority handling, making
applications such as streaming audio and video
much easier to implement
Guide to Networking Essentials, Fifth Edition
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IPv6 Addresses

IPv6 addresses are specified in hexadecimal
format in 16
-
bit sections separated by a colon

Longhand notation: 2001:260:0:0:0:2ed3:340:ab

Shorthand notation: 2001:260::2ed3:340:ab

If one of the 16
-
bit numbers doesn’t require four hexadecimal
digits, the leading 0s are omitted

Addresses have a three
-
part addressing hierarchy

A public topology (first three 16
-
bit sections)

A site topology (next 16 bits)

An interface identifier (last 64 bits)

Derived from the MAC address on the host’s NIC
Guide to Networking Essentials, Fifth Edition
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Other Protocol Suites

Other protocol suites are sometimes used
on older networks, where the need to
change to TCP/IP is not warranted, or in
environments suited to the suite’s features

NetBIOS/NetBEUI

Used primarily on older Windows networks

IPX/SPX

Designed for use on NetWare networks

AppleTalk

Used almost exclusively on Macintosh networks
Guide to Networking Essentials, Fifth Edition
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NetBIOS and NetBEUI
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IPX/SPX
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AppleTalk

Although the AppleTalk standard defines physical
transport in Apple Macintosh networks, it also
establishes a suite of protocols those computers
use to communicate

Apple created AppleTalk Phase II to allow
connectivity outside the Macintosh world

AppleTalk divides computers into zones

Allow a network administrator to logically group
computers and other resources that have frequent
communication, in a manner similar to subnetting
Guide to Networking Essentials, Fifth Edition
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Implementing and Removing Protocols
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Summary

Many protocols are available for network
communications, each with its
strengths/weaknesses

The TCP/IP protocol suite dominates network
communication in part due to its use on the
Internet

IP addressing involves several concepts,
including address classes, subnetting, and
supernetting

IPv6 will eventually replace IPv4 because it offers
several advantages: 128
-
bit address space,
autoconfiguration, built
-
in security, and QoS