Download Understand Computer Network V

Understanding Networks
Objectives
• Compare client and network operating
systems
• Learn about local area network
technologies, including Ethernet, Token
Ring, FDDI, and wireless
• Use the OSI model to understand
networking
• Learn how network computers and servers
are addressed
TCP/IP Protocols at Each Layer
• TCP/IP covers the first five layers of the
OSI model, and is included in an operating
system as a group of utilities called the
TCP/IP stack.
• Figure 5-41 shows the four major
groupings of the OSI model as applied to
TCP/IP networks.
Protocols at the Application,
Presentation, and Session Layers
• The first three layers of the OSI model are
handled by the protocol specific to the
application using it and are best treated as a
single group rather than unique layers.
• Web browsers, e-mail, chat rooms, and FTP
software are examples of the applications that
use the Internet.
• The language or protocol each of these
applications uses is listed at the Application,
Presentation, and Session layers.
Protocols at the Transport Layer
• A TCP/IP network has two protocols that
work at the Transport layer; one protocol
guarantees delivery and the other does
not.
• With TCP/IP, the protocol that guarantees
delivery is TCP and the protocol that does
not is UDP (User Datagram Protocol).
• TCP is used for client and server requests
and responses.
Protocols at the Transport Layer
(Continued)
• Because TCP establishes a connection, it
is called a connection-oriented protocol.
• UDP is a protocol that sends data without
caring about whether the data is received.
• It does not establish a connection first;
thus, it is called a connectionless
protocol.
Protocols at the Network Layer
• TCP and UDP communicate with the Network
layer, which is sometimes called the Internet layer.
• Some of the other supporting protocols include
ARP (Address Resolution Protocol),
responsible for locating a host on a LAN; RARP
(Reverse Address Resolution Protocol),
responsible for discovering the Internet address of
a host on a LAN; and ICMP (Internet Control
Message Protocol), responsible for
communicating problems with transmission to
devices that need to know about these problems.
Protocols at the Data Link and
Physical Layers
• PPP (Point-to-Point Protocol) is used
over telephone lines, and allows a
computer to connect to a network using a
modem.
• PPP is the most popular protocol for
managing network transmission from one
modem to another.
MAC Addresses
• MAC addresses function at the lowest
(Data Link) networking level.
• If a host does not know the MAC address
of another host on a local area network, it
uses the operating system to discover the
MAC address.
IP Addresses
• All the protocols of the TCP/IP suite
identify a device on the Internet or an
intranet by its IP address.
• An IP address is 32 bits long, made up of
4 bytes separated by periods.
• Within an IP address, each of the four
numbers separated by periods is called an
octet.
• The first part of an IP address identifies
the network, and the last part identifies the
host.
Classes of IP Addresses
• IP addresses that can be used by companies
and individuals are divided into three classes:
Class A, Class B, and Class C, based on the
number of possible IP addresses in each
network within each class.
• The group of IP addresses assigned to an
organization are unique to all other IP addresses
on the Internet and are available for use on the
Internet.
• The IP addresses available to the Internet are
called public IP addresses.
Private IP Addresses
• Private IP addresses are IP addresses
that are assigned by a network
administrator for use on private intranets
that are isolated from the Internet.
• The RFC 1918 recommends that the
following IP addresses be used for private
networks:
– 10.0.0.0 through 10.255.255.255
– 172.16.0.0 through 172.31.255.255
– 192.168.0.0 through 192. 168. 255.255
Dynamically Assigned IP
Addresses
• Instead of IP addresses permanently being
assigned to computers (called static IP
addresses), an IP address is assigned for
the current session only (called a dynamic
IP address).
• Internet service providers (ISPs) are
organizations through which individuals
and businesses connect to the Internet.
Network Address Translation
• If the hosts on a network using private IP
addresses need to access the Internet, a
problem arises because the private IP
addresses are not allowed on the Internet.
• The solution is to use NAT (Network
Address Translation), which uses a
single public IP address to access the
Internet on behalf of all hosts on the
network using other IP addresses.
Plans for New IP Addresses
• Because of an impending shortage of IP
addresses, as well as some limitations in
the current standards for IP, a new
scheme of IP addresses called the IPv6
(IP version 6) standard is currently being
developed and implemented.
• Current IP addresses using the current
IPv4 (IP version 4) have 32 bits with eight
bits in each of four octets.
Plans for New IP Addresses
(Continued)
• With the new system, each address
segment can have 32 bits, for a total of
128 bits for the entire address.
• A disadvantage of IPv6 is the fact that so
much software used on the Internet would
become outdated because current
software is designed to hold 32-bit IP
addresses and, with the new system, this
number would no longer be sufficient.
Ports
• A port is a number used to address
software or services running on a
computer.
• A host computer might have several
services running on it.
• Each server running on the host is
assigned a port.
• The port is written at the end of the IP
address, separated from the IP address
with a colon—like this: 169.49.209.19.80.
Tying It All Together: How Data
Travels on the Network
• The Web browser wants to make a
request to a Web server, and processes
the request using an API call.
• The API process packages the data using
HTTP format, which includes an HTTP
header, and addresses it to an IP address
and port 80, which is the default port for a
Web server.
• HTTP delivers the package to TCP, giving
the destination IP address and port.
Tying It All Together: How Data
Travels on the Network (Continued)
• TCP guarantees delivery, and attempts to make
a connection to the destination IP address and
port using the three-way handshake.
• With the first attempt that TCP makes to
communicate with the remote host, the first
packet reaches the Network layer and IP uses
ARP to resolve the IP address to a MAC
address.
• When a packet reaches a hub on the Ethernet
LAN, the hub replicates the packet and sends it
to every device to which it is connected.
Tying It All Together: How Data
Travels on the Network (Continued)
• When the IP layer receives a broadcast
packet, it decides if it is appropriate to
respond.
• After it knows the MAC address, it can
send the first packet to make the
connection.
• It prepares the data by attaching a TCP
header in front of the data.
Summary
• The two approaches to managing network
resources are peer-to-peer and client/server.
• Windows 2000 Server and Windows Server
2003 support multiple domain controllers.
• Windows XP has three operating systems:
Windows XP Professional, Windows XP Home
Edition, and Windows XP 64-Bit Edition.
• The most popular network technology used
today is Ethernet; it can be configured either as
a star or bus.
Summary (Continued)
• An IP address can be permanently assigned to a
device (static IP addressing) or a different IP
address can be assigned each time the device
logs on to the network (dynamic IP addressing).
• When a host is configured to used TCP/IP, and
IP address is bound to the MAC address.
• A proxy server uses NAT to substitute its own
public IP address for the private IP address of a
computer on the network that is requesting
Internet access.