Transcript Introduction to Networking with narration

Chapter 7 –Security in Networks
Introduction to networks
 Threats against network applications
 Controls against network applications
 Firewalls
 Intrusion detection systems
 Private e-mail

Terminal-Host Systems

Created in the 1960s
• Central host computer does all the
processing
• Terminal is dumb--only a remote screen
and keyboard
• Created in the 1960s, when
microprocessors for terminal intelligence
did not exist
Terminals
Host
PC Networks

The Most Common Platform in
Organizations
• Allows PCs to share resources
• Both Wintel (Windows/Intel) PCs and
Macintoshes
Network
Network

A Network is an Any-to-Any
Communication System
• Can connect any station to any
other
Network
Network

Each Station has a Unique Network
Address
• To connect, only need to know the
receiver’s address
• Like telephone number
DEF
ABC
MNO
“Connect to GHI”
JKL
GHI
LANs and WANs
Networks Have Different
Geographical Scopes
 Local Area Networks (LANs)

• Small Office
• Office Building
• Industrial Park / University Campus

Wide Area Networks (WANs)
• Connect corporate sites or
• Connect corporate sites with sites of
customers and suppliers
Elements of a Simple LAN
Hub or Switch
Wiring
Hub or Switch connects
all stations
Wiring is standard
business telephone wiring
(4 pairs in a bundle)
Elements of a Simple LAN
Client PCs are used by
ordinary managers and
professionals; receive service
Servers provide services
to client PCs
Client PC
Server
Server
Server
Client PC
Elements of a Simple LAN

Client PC
• Begin with stand-alone PC
• Add a network interface card (NIC) to
deal with the network
• Networks have many client PCs

Server
• Most PC nets have multiple servers
Wide Area Networks

WANs Link Sites (Locations)
• Usually sites of the same organization
• Sometimes, sites of different
organizations
Site B
Site A
Site C
WAN
Client/Server Processing

Two Programs
• Client program on client machine
• Server program on server machine
• Work together to do the required
processing
Client Program
Client Machine
Server
Program
Server
Client/Server Processing

Cooperation Through Message
Exchange
• Client program sends Request
message, such as a database
retrieval request
• Server program sends a Response
message to deliver the requested Server
Program
information
or
an
explanation
for
Client Program
failure
Request
Client Machine
Response
Server
Client/Server Processing

Widely Used on the Internet

For instance, webservice
• Client program (browser) sends an
HTTP request asking for a webserver file
• Server program (webserver application
program) sends an HTTP response
message with the requested webpage
HTTP Request Message
HTTP Response Message
Client/Server Processing

On the Internet, a Single Client
Program--the Browser (also known
as the client suite)--Works with Many
Kinds of C/S server applications
• WWW, some E-mail, etc.
E-mail
Server
Browser
Webserver
Standards Organizations and
Architectures

TCP/IP Standards
• Created by the Internet Engineering Task
Force (IETF)
• Named after its two most widely known
standards, TCP and IP


TCP/IP is the architecture, while TCP and IP are
individual standards
However, these are not its only standards, even at
the transport and internet layers
• IETF standards dominate in corporations at
the application, transport, and internet
layers

However, application, transport, and internet
standards from other architectures are still used
Standards Organizations and
Architectures

OSI Standards
• Reference Model of Open Systems
Interconnection
• Created by the International
Telecommunications UnionTelecommunications Standards Sector (ITUT)
• And the International Organization for
Standardization (ISO)
• OSI standards dominate the data link and
physical layers

Other architectures specify the use of OSI
standards at these layers
OSI Reference Model
User / Application program
Layer 7
Application
Layer 6
Presentation
Layer 5
Session
Layer 4
Transport
Layer 3
Network
Layer 2
Data link
Layer 1
Physical
Physical medium
Figure 1.12 OSI Protocol Layers
TCP/IP versus OSI

Lowest Four Layers are Comparable
in Functionality
TCP/IP
OSI
Application
Application
Presentation
Session
Transport
Network
Data Link
Transport
Internet
Data Link (use
OSI)
Physical (use
OSI)
Physical
Internet Standards

Accessing the WWW from Home
App
HTTP
App
Trans
TCP
Trans
Int
IP
Int
IP
Int
DL
PPP
DL
?
DL
Phy
Modem
Phy
?
Phy
User PC
Router
Webserver
Indirect Communication

Application programs on
different machines cannot
communicate directly
• They are on different machines!
Browser
HTTP Request
Web App
Trans
Trans
Int
Int
DL
DL
Phy
Phy
User PC
Webserver
Layer Cooperation on the
Source Host

Application layer process passes
HTTP-request to transport layer
process
Application
HTTP Request
Transport
Internet
Data Link
User PC
Physical
Layer Cooperation on the
Source Host

Transport layer makes TCP
segments
• HTTP message is the data field
• Adds TCP header fields shown earlier
• Transport process “encapsulates”
HTTP request within a TCP segment
TCP Segment
HTTP Request
Data
Field
TCP-H
TCP
Header
Layer Cooperation on the Source Host

Transport layer process passes the
TCP segment down to the internet
layer process
Application
Transport
TCP segment
Internet
Data Link
User PC
Physical
Layer Cooperation on the Source Host

The internet layer process passes the
IP packet to the data link layer
process
• Internet layer messages are called
packets
Application
Transport
Internet
IP packet
Data Link
User PC
Physical
Layer Cooperation on the Source Host

The data link layer process passes the
PPP frame to the physical layer
process, which delivers it to the
physical layer process on the first
router, one bit at a time (no message
at the physical layer)
Application
Transport
Internet
Data Link
User PC
PPP frame
Physical (10110 …)
To first
router
Layer Cooperation on the Source Host

Recap: Adding Headers and Trailers:
Application
HTTP msg
Transport
HTTP msg
TCP-H
Internet
HTTP msg
TCP-H IP-H
HTTP msg
TCP-H IP-H PPP-H
Data Link
User PC
PPP-T
Physical
Protocols

A protocol is a standard for
communication between peer
processes, that is, processes at the
same layer, but on different machines
• TCP, IP, and PPP all have “protocol” as
their final “P;” they are all protocols
• TCP (Transmission Control Protocol) is
the protocol governing communication
between transport layer processes on
two hosts
Message
Trans
TCP
Trans
Domain Name System (DNS)

Only IP addresses are official
• e.g., 128.171.17.13
• These are 32-bit binary numbers
• Only they fit into the 32-bit
destination and source address fields
of the IP headers
IP Packet
32-bit Source and Destination Addresses (110011...)
Domain Name System (DNS)

Users typically only know host names
• e.g., voyager.cba.hawaii.edu
• More easily remembered, but
• Will not fit into the address fields of an
IP packet
IP Packet
NO
voyager.cba.hawaii.edu
Internet and Data Link Layer Addresses

Each host and router on a subnet
needs a data link layer address to
specify its address on the subnet
• This address appears in the data link
layer frame sent on a subnet
• For instance, 48-bit 802.3 MAC layer
frame addresses for LANs
Subnet DA
DL Frame for Subnet
Addresses

Each host and router also needs an
IP address at the internet layer to
designate its position in the overall
Internet
Subnet
128.171.17.13
Subnet
Subnet
IPv6

Current version of the Internet Protocol is
Version 4 (v4)
• Earlier versions were not implemented

The next version will be Version 6 (v6)
• No v5 was implemented
• Informally called IPng (Next Generation)

IPv6 is Already Defined
• Continuing improvements in v4 may delay its
adoption
IPv6

IPv6 will raise the size of the internet
address from 32 bits to 128 bits
• Now running out of IP addresses
• Will solve the problem
• But current work-arounds are delaying
the need for IPv6 addresses