Transcript Identifying Security Risks

Network Connectivity
1
Basic Networking
• A network is composed of communications
media such as communications cable, used to
link computers, printers, disk storage, CD-ROM
arrays, and network communications equipment
• The basic principle of networking is similar to
connecting telephones for communications
• The hardware components of a computer network
are computers, printers, communications cable,
and internetworking devices such as bridges,
switches, routers, and hubs
2
Telephone and
Computer Networks Compared
3
Basic Networking
• Computer networks also have software components
consisting of client and server network operating
systems
• Windows 95, Windows 98, Windows NT 4.0
Workstation, Windows 2000 Professional, and
Windows XP Professional are examples of client
operating systems
• A client operating system is one that enables a
workstation to run applications, process information
locally, and communicate with other computers and
devices over the network
4
Basic Networking
• A workstation is a computer that has a CPU,
and can run applications locally, or obtain
applications and files from another computer
on the network
• Sometimes the term workstation is confused
with the term terminal
• The difference is that a terminal has no CPU or
local storage for running programs
independently
5
Basic Networking
• A network operating system (NOS) is one that
enables the coordination of network activities
and the sharing of resources – network
communications, shared printing, shared
access to files, and shared access to software,
for example
• A server is a computer running a NOS, which
provides resources, such as shared files and
programs that are accessed by clients
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Reasons for a Network
• Networks were invented for three interrelated
reasons: to share resources, save money, and
increase productivity
• Most important, networks allow organizations to save
money by sharing resources
• Windows NT Server 4.0, Windows 2000 Server, and
Windows .NET Server offer several ways to save
money and time by centralizing software and client
operating system installation through a server
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Sharing Resources in an Office
8
The Development of
Network Operating Systems
• Novell NetWare was one of the first network operating
systems, initially demonstrated in 1982 at the National
Computer Conference as a groundbreaking PC
networking system
• Windows 3.1, released in 1992, was one of the first
Windows-based operating systems with network
capabilities, enabling it to connect to NetWare,
Microsoft, and other networks
• Workgroups (pre-defined groups of member
computers) provide the ability to limit resource
sharing on the basis of group membership
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The Development of
Network Operating Systems
• Windows 95 represents yet another major step into
networking because it expands peer-to-peer networking
and has the ability to connect to more kinds of networks
• Windows XP Home Continues that expansion and comes
with better networking capabilities for home use
• Representing a different Windows operating system track,
Windows NT 3.1 was released just a little later than
Windows 3.1, but Windows NT 3.1 was intended for
industrial strength networking from the beginning
10
The Development of
Network Operating Systems
• In 2000 Microsoft brought two new names for
Windows NT: Windows 2000 Server and Windows
2000 Professional (Workstation)
• Windows 2000 has evolved into two products,
Windows XP and Windows .NET Server, both
containing the core elements of the Windows 2000
kernel
• Both Windows 2000 and Windows XP have built-in
options to configure home and small office networks
11
The Development of
Network Operating Systems
• Besides the NetWare and Windows-based
operating systems, there are several others
designed for networking:
– UNIX
– Banyan Vines
– Pathworks
– LAN Manager
• All are server operating systems that may be in
use on networks, and that run on small to midsized computers
12
The Basics of Network Topologies
• A topology is the design of the network, as if you were
looking at it from above in a helicopter, or following the
path information takes when it goes from one computer to
another
• The star topology is one in which there is a hub in the
middle, with cable segments coming out of the hub in
all directions, as shown in Figure 8-5
• The hub sends the signal onto each segment, which
has a computer at the end
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Star Topology
14
The Basics of Network Topologies
•
A network hub serves as an exchange point for data to be sent
from one user or device to another
•
More common today in place of hubs are switches
•
Switched networks use switches in place of hubs
•
The switch learns what devices are located on each of the
segments attached to it, and only transmits the information on
the segment where the destination device resides
•
Traffic is not transmitted on all segments at once, as happens
on hubs
15
Packets, Frames, and Cells
• Each computer or network device translates data
into individual units, and then places the units
onto the network cable
• Each data unit is called a packet or frame
• These terms are sometimes used
interchangeably, but they are not the same
• Both consist of data and transmission control
information contained in a header that is
appended to the front of the data
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Packets, Frames, and Cells
• The difference is that a packet contains routing
information that can be read by specialized devices that
are able to forward packets to specific networks
• The actual data is placed after the header information,
and followed by a footer or trailer that enables detection
of a transmission error
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Packets, Frames, and Cells
• Older networks transmit at speeds of 2 Mbps 4
Mbps (megabits per second), 10 Mbps, and 16
Mbps
• Newer networks transmit at 100 Mbps to 10
Gbps and faster, or consist of segments that
transmit at 10 Mbps, 100 Mbps, 1 Gbps, or 10
Gbps
• Network backbones, which are segments that
join main networks, typically run at 100 Mbps or
higher
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Packets, Frames, and Cells
• A cell is a data unit designed for high-speed
communications; it has a control header and
a fixed-length payload
• The payload is that portion of a frame, packet,
or cell that contains the actual data, which
might be a portion of an e-mail message or
word-processing file
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Packets, Frames, and Cells
•
One element of the cell header is path information that enables the
cell to take the route through the network that is most appropriate
to the type of data carried within the cell
20
Packets, Frames, and Cells
• A protocol is a set of formatting guidelines for
network communications, like a language, so that the
information sent by one computer can be accurately
decoded by another
• Protocols also coordinate network communications
so that data is transported in an orderly fashion,
preventing chaos when two or more computers want
to transmit at the same time
• A network may use several different protocols,
depending on the NOS and the types of devices that
are connected
21
Connecting to a Network
• Computers and internetworking devices connect to a
network through a network interface card (NIC)
• A NIC is usually a card that goes into a computer’s
expansion slot, or that is built into a network device
or a computer
• Each NIC has a unique hexadecimal address, called a
device or physical address, which identifies it to the
network
• It is also called the Media Access Control (MAC)
address
22
Devices on a Network
With Unique Physical Addresses
23
Connecting to a Network
• Some NICs also transform data into radio frequency
communications for wireless networks
• The software logic consists of one or more programs
called firmware because it resides in a programmable
chip on the card
• Communication between the operating system and its
NIC, like communication between the operating
system and various input, output, and storage
devices, is controlled by driver software written by the
manufacturer of the device
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Ethernet
• In Ethernet communications, only one station on the
network should transmit at a given moment
• If two or more stations transmit at the same time,
frames collide
• The transmission control method used by Ethernet is
called Carrier Sense Multiple Access with Collision
Detection (CSMA/CD)
• In CSMA/CD, the NICs of computers and devices
check the network communications cable for a carrier
signal that contains an encoded frame
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Ethernet
• If the device’s NIC detects a carrier signal, and
if the NIC decodes its own device address
within the frame, it forwards that packet to its
firmware for further decoding
• If the frame does not contain its device
address, then the NIC does not process the
signal any further
26
Ethernet
• Modern networks that use Ethernet are designed
in a star topology, in which the internetworking
devices simulate a logical bus
• Fast Ethernet (100 mb/s) is becoming
commonplace, and most NICs are currently
designed to handle either 10 or 100 Mbps
communications
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Ethernet
• All versions of Ethernet are compatible with
popular network operating systems such as:
– UNIX
– NetWare
– Windows NT, 2000, XP, and .NET Server
– Windows 3.x
– Windows 95/98/Me
– Mac OS
– Banyan Vines
– Pathworks
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Communications Protocols
• The development of communications protocols
(the protocols that carry data between two
communicating stations, and are encapsulated
in Ethernet or token ring transport protocols)
has been interrelated to the network operating
systems in which they are used
• One of the first widely accepted was the
Internet Packet Exchange (IPX) protocol
developed to enable a NetWare file server to
communicate with its client workstations
29
Communications Protocols
• Researchers implemented and combined two
protocols for use on the Advanced Research
Projects Agency network, ARPANET, which was
the long-distance network that set the
foundation for the Internet
• The ARPANET protocols now used worldwide
over the Internet are Transmission Control
Protocol (TCP) and Internet Protocol (IP)
30
TCP/IP
• TCP/IP is one of the oldest protocols, initially
developed for long-distance networking on
ARPANET, and now used on most networks
• One of the strongest influences on TCP/IP use
has been the growth of the Internet
• UNIX has always used TCP/IP as its main network
communications protocol
• TCP was developed for extremely reliable pointto-point communications between computers on
the same network
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TCP/IP
• TCP/IP is also compatible with the following
operating systems:
– Windows 3.1 and 3.11
– Windows 95/98/Me
– Windows NT 3.0, 3.5, 3.51, and 4.0
– Windows 2000/XP/.NET Server
– Mac OS
– Banyan Vines
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TCP/IP
• Some of the communication functions
performed by TCP are:
– Establishes the communication session between
two computers
– Ensures that data transmissions are accurate
– Encapsulates, transmits, and receives the payload
data
– Closes the communication session between two
computers
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TCP/IP
• The IP portion of TCP/IP is used to make sure that a
frame or packet reaches the intended destination
• IP performs the following complementary functions
with TCP:
– Handles packet addressing
– Handles packet routing
– Fragments packets, as needed, for transport across
different types of networks
– Provides simple packet error detection in conjunction with
the more thorough error detection provided by TCP
34
TCP/IP
• IP addressing uses the dotted decimal notation
that consists of four 8-bit binary numbers
(octets) separated by periods
• There are five IP address classes, Class A
through Class E, each used with a different
type of network
• The address classes reflect the size of the
network, and whether the packet is unicast or
multicast
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TCP/IP
• In the unicast method of transmission, one copy
of each packet is sent to each target destination
• In the multicast method, the recipients are placed
in a group, such as a group of all eight
workstations since they are on the same network
• Classes A through C are intended as unicast
addressing methods, but each class represents a
different network size
• Class A is used for the largest networks
composed of up to 16,777,216 nodes
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TCP/IP
• Class A networks are identified by a value
between 1 and 126 in the first position of the
dotted decimal address
• The network ID is the first eight bits, and the host
ID is the last 24 bits
• Class B is a unicast addressing format for
medium-sized networks composed of up to
65,536 nodes, and it is identified by the first octet
of bits ranging from decimal 128 to 191
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TCP/IP
• The first two octets are the network ID, and the
last two are the host ID
• Class C addresses are used for unicast network
communications on small networks of 256 nodes
or less
• The first octet translates to a decimal value in the
range of 192 to 223, and the network ID is
contained in the first 24 bits, while the host ID is
contained in the last eight bits
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TCP/IP
• Class D addresses do not reflect the network size, only
that the communication is a multicast
• Unlike Classes A through C, the four octets are used to
specify a group of nodes to receive the multicast, which
consists of those nodes that are multicast subscription
members
• Class D addresses are in the range from 224.0.0.0 to
239.255.255.255
• A fifth address type, Class E, is used for
experimentation, and addresses range from 240 to 255 in
the first octet
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TCP/IP
• Computers and devices that use IP addressing
actually have two addresses: a physical address and
an IP address
• The use of two addresses provides better insurance
that a packet will reach the right destination, while
expending the fewest network resources
• TCP/IP works with a range of associated protocols
that make this a powerful combination for networks of
all sizes and types
40
AppleTalk
• AppleTalk is a network communications protocol used
between Macintosh computers
• It is designed primarily as a peer-to-peer protocol, rather
than for combined peer-to-peer and client-to-server
communications
• As a peer-to-peer protocol, AppleTalk establishes equal
communications between networked Macintosh computers,
without the need for a server
• AppleTalk performs three essential services: remote access
to files over a network, network print services, and access
to computers running MS-DOS or Windows operating
systems
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Peer-to-Peer Networking
Using AppleTalk and No Server
42
Implementing Communications
Protocols in an Operating System
• Most computer operating systems are designed
to support one or more communications
protocols
• In general, there are two steps involved in setting
up a communications protocol in an operating
system
• The first is to install the protocol software that is
written for that operating system
• Step two is to bind the protocol with the NIC
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Implementing Communications
Protocols in an Operating System
• Binding the protocol
enables the NIC to
format data for that
protocol, and identify
the most efficient
methods for
transporting it within
Ethernet or token ring
• When two or more
protocols are used,
binding also enables
the NIC to set a priority
for which protocol to
process first
44
Implementing Communications
Protocols in an Operating System
• The Mac OS up through version 9.x provides
one of the easiest methods for setting up
communications protocols
• In the Mac OS, you use a Control Panel to
designate a port for network communications
associated with the NIC
• In Mac OS X, setting up network
communications is also simplified, but with
more options than in Mac OS 9.x
45
Implementing Communications
Protocols in an Operating System
• Through the Mac OS X Network panel, you can
fully configure your Mac to use TCP/IP and
TCP/IP network services, including the following:
– Manual configuration of IP address and subnet mask
– Automatic configuration of the IP address using DHCP
– Identification of the nearest router by IP address
– Identification of Domain Name Service (DNS) servers by
IP address
– Identification of search domains by IP address
46
Implementing Communications
Protocols in an Operating System
• Most UNIX systems have TCP/IP networking
support built in, and some of these
automatically run a network configuration
program when you first boot the computer with
an installed NIC
• For some versions of UNIX, including Red Hat
Linux, you must configure a loopback device,
which is used to provide your computer with an
internal IP address, even when it is not
connected to the network
47
Implementing Communications
Protocols in an Operating System
• Communications
protocols are set
up in Windows
95/98/Me and
Windows NT 4.0
through the
Network icon in
the Control
Panel
48
Integrating Different Operating
Systems on the Same Network
• The key to implementing multiple operating systems
on one network is to select a transport protocol and
communications protocols that are supported in all of
the operating systems that must be connected
• Ethernet is particularly well suited to a network that
has different operating systems
• In situations where TCP/IP is not supported by all
operating systems, then multiple protocols can be
configured, such as a combination of AppleTalk,
TCP/IP, and IPX/SPX
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Routers
• Routers are used to join networks, either locally
or remotely
• Routers are designed to look at routing
information in packets before forwarding those
packets to another network
• Routers also make excellent firewalls because
networks connected to a router can be divided
into subnets as a way to control incoming and
outgoing traffic to each subnet
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Local and Wide Area Networks
• A local area network (LAN) is one in which the service area
is relatively small, such as a network in an office area, or
one spread through a floor in a building
• A wide area network (WAN) is one that offers networking
services over a long distance, such as between cities,
states, or countries
• There are several interrelated elements that can be used to
determine the intersection of a LAN with a WAN
• One element is that the network topology may change
between the two, such as a LAN that uses a ring topology
and a WAN that uses a star
• Another factor is a change in cable type
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