Transcript Chapter Five

Business Data Communications
Chapter Five
Network, Transport, and
Application Layer Services
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
Chapter Five
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Primary Learning Objectives
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Understand the function of the application,
transport, and network layers
Explain IP classes and address formats
Convert binary to decimal and decimal to binary
Define subnetting
Describe subnet masking
Understand IP addressing guidelines
Define supernetting
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Application, Transport, and
Network Layers
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The application layer is the highest level layer in
the TCP/IP model
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This layer performs the functions of the application,
presentation, and session layers in the OSI model
The transport and network layers are the midlevel layers in the TCP/IP model
Each of these three layers has special functions
and responsibilities
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Application, Transport, and
Network Layers
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Network Layer
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Sits above the data link and below the transport layers
At its core is IP – Internetworking Protocol:
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IP’s key function is the transmittal of data packets
IP has four assistants:
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Address Resolution Protocol
Reverse Address Resolution Protocol
Internet Control Message Protocol
Internet Group Message Protocol
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Network Layer
Structure
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Network Layer
Services
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Address Resolution Protocol - ARP:
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To enable communication in a TCP/IP network, two key
pieces of information are required: a device’s logical IP
address, and its physical MAC address
If a sending device knows the MAC address of a
receiving device but not that device’s IP address, the
sender’s network layer services broadcasts an ARP
request
ARP may find the requested information in the sender’s
own memory or the memory of another local host, or
have a router send out a request to other networks
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Address Resolution Protocol
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Network Layer
Services
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Reverse Address Resolution Protocol – RARP:
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The opposite of ARP
Sender knows the MAC address, but not the IP address
RRAP is used mostly when a host device first boots up,
and by diskless devices
Diskless devices:
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Know their MAC, but not their IP address
Can improve security, as they have no storage
Can help prevent virus spread
Can be cost effective
May not be popular with users
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Network Layer
Services
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Internet Control Message Protocol – ICMP:
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IP has no error reporting or error correction controls
ICMP supports IP by providing error reporting and
query management
ICMP can report five error types:
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Destination unreachable
Source quench
Time exceeded
Parameter error
Redirection
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Network Layer
Services
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Over a TCP/IP network two types of communication
can occur: Unicasting and Multicasting
Internet Group Message Protocol – IGMP:
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Used primarily when multicasting is required:
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Multicasting occurs when a sender wants to send to
multiple receivers
A multicast address can be used only as a destination, not
as a source
Multicast routers maintain lists of multicast addresses for
groups of hosts
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Network Layer
Services
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Network Layer
Services
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Network Layer
Services
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Internet Group Message Protocol – IGMP:
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Supports two message types:
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Reporting
Query
Reporting messages are sent from a host to a router
Query messages are sent from a router to a host
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Transport Layer
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Has two key protocols: TCP and UDP
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TCP is connection oriented and is called a reliable data
stream – more overhead than UDP, but offers
guarantees
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Transmission Control Protocol
User Datagram Protocol
Here, “reliable” refers to a sender and receiver’s
agreeing to establish a communication
UDP is connectionless and is a non-reliable delivery
service – more efficient, but no guarantee of delivery
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Sender and receiver do not have to agree to establish a
communication
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Transmission Control Protocol
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User Datagram Protocol
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Application Layer
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Fulfills the function of the application, presentation,
and session layers of the OSI model
Provides user connectivity to the network
Supports a variety of protocols, including:
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Telnet
FTP
SMTP
SNMP
HTTP
For application layer services, a client and/or server
process has a specific, logical meaning
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Application Layer - FTP
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Application Layer - SMTP
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IP Address Classes
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Logical IP network layer addresses fall into a
categorization called classes
IP address classes are categorized from A to E
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D and E are reserved and not commercially available
As these addresses are logical, they can be modified
Addressing schemes have to be developed by network
administrators for the entire enterprise
TCP/IP logical addresses have both a binary and a
decimal equivalent
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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IP Address Classes
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IP Address Classes
00000001
00000011
0+0+0+0+0+0+0+1
0+0+0+0+0+0+2+1
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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IP Address Classes
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IP Address Classes
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Subnetting
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IP addresses are often subdivided, creating “subnets”
Subnetting allows a business to take a single allocated
network IP address and create, internally, multiple
subnets from that address
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Subnetting
An enterprise
will often need
more than one
logical network
IP address.
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Subnetting
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IP addressing also requires a subnet mask
The purpose of the subnet mask is to filter out the
network and host portions of an IP address
Each class, A, B, and C, has a standard, default
subnet mask
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Subnet Masks
Class
Subnet Mask
in Decimal
Subnet Mask
in Binary
A
255.0.0.0
11111111.00000000.00000000.00000000
B
255.255.0.0
11111111.11111111.00000000.00000000
C
255.255.255.0
11111111.11111111.11111111.00000000
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Subnet Masks
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The same subnet mask must be used throughout the
entire enterprise
If a business chooses to modify its allocated network
IP address for subnetting, the standard subnet mask
for that address must also be modified
In subnetting, bits are borrowed from the host portion
of an IP address, based on the number of network
identifiers required
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Subnetting and
Subnet Masks
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The number of network identifiers possible from
borrowing host bits is shown by formula
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Two to the power of the number of high order bits
borrowed, then minus two, gives the number of new
network identifiers available
(22 – 2) = number of usable network addresses
Two is subtracted because two network addresses, all
zeros or all ones, are reserved for special use
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Subnetting and
Subnet Masks
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Assume you have one allocated network IP address
Also assume you need five network identifiers:
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If two high-order bits were borrowed, the result would
be: 22 – 2 = 2 additional network addresses available.
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Not enough bits were borrowed
If three high-order bits were borrowed, the result would
be: 23 – 2 = 6 additional network addresses available.
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Enough bits were borrowed
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Subnetting and
Subnet Masks
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Given a single Class B, IP address: 156.101.0.0
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The default subnet mask would be: 255.255.0.0
We want five network IP addresses, not one
We borrow three high-order bits from the host portion of
the IP address
It is critical to remember that high-order bits are
borrowed, and they have corresponding decimal values
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Subnetting and
Subnet Masks
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Subnetting and
Subnet Masks
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With three high-order bits borrowed, the following bit
patterns are possible:
Original IP address: 156.101.00
In the table, 000 and 111 are not
allowed, leaving the values in
between
New Network Addresses Possible:
156.101.32.0
156.101.64.0
156.101.96.0
156.101.128.0
156.101.160.0
156.101.128.0
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Subnetting and
Subnet Masks
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An IP address is compared to the subnet mask in a
process called ANDing
ANDing performs a bit-by-bit comparison of a given IP
address and the submit mask
This bit-by-bit comparison reveals the true network
and host values from a given IP address
ANDing enables a sender to determine if a receiver is
on the same or another logical network
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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IP Addressing
Guidelines
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Choose an addressing scheme that accommodates
future growth
Verify that each host within a LAN has a unique
address
Ensure that each network within an enterprise has a
unique address
Do not assign restricted addresses
Use ranges of host addresses to identify specific types
of devices
Keep documentation current, accurate, accessible
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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IP Addressing – Possible Guidelines
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Supernetting
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Subnetting borrows bits from the host to create more
networks
Supernetting borrows bits from the network to create
more hosts
Supernetting might be an option for a business
holding several Class C addresses
Supernetting requires that the addresses being
supernetted be contiguous
Supernetting is a function of Classless Inter-Domain
Routing, or CIDR
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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In Summary
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The application, transport, and network layers provide
high- and middle-layer services
Addressing is a critical component of an enterprise’s
data communications structure
Most organizations use subnetting
Subnetting generally requires modification of standard
subnet masking
IP addressing schemes should be well thought out
and documented
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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