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Chapter 6
Networking Protocols
Introduction
• Look at:
– Protocol Basics(6.1)
– A Brief Protocol Prospectus(6.2)
– Transmission Control Protocol/Internet
Protocol (TCP/IP)(6.3)
– TCP/IP Network Access Layer
Protocols(6.4)
Introduction
• Look at:
– TCP/IP Internet Layer Protocols(6.5)
– TCP/IP Transport Layer Protocols(6.6)
– TCP/IP Application Layer Protocols(6.7)
Protocol Basics
• A protocol is a set of rules and conventions
that determines how computers exchange
information over a network medium
• A wide variety of communication protocols
exist, and many of them rely on others for
operation
• Groups of related protocols are often called
stacks or protocol stacks
A Brief Protocol Prospectus
• Data packets can be sent over the medium
using any one of a number of protocols
• Protocols can be either standard or
proprietary
• A standard protocol is one where users can
purchase equipment from any manufacturer
because it is programmed to communicate
universally
A Brief Protocol Prospectus
• A proprietary protocol is usually protected by
patents or other legal stipulation
• Proprietary protocols include
– XNS
– NetBIOS
– IPX/SPX
– AppleTalk
– DECNet
A Brief Protocol Prospectus
• XNS stands for the Xerox Network
Systems
• This is a suite of protocols created by
Xerox in the late 1970s and early 1980s
for use in Ethernet networks
• XNS is used in very few new networks
today
A Brief Protocol Prospectus
• The Network Basic Input/Output
System (NetBIOS) interface was
developed in 1983 for IBM
• The intention was to allow applications
on different computers to communicate
within a local area network
• NetBIOS was not designed for large
networks
A Brief Protocol Prospectus
• In the early 1980s, Novell introduced its own
network protocol stack called Internetwork
Packet Exchange/Sequenced Packet
Exchange (IPX/SPX)
• This stack was based on the XNS network
protocol family
• IPX is the Network layer protocol
• SPX is the Transport layer protocol
A Brief Protocol Prospectus
• AppleTalk is Macintosh’s networking protocol
• It is designed to be a flexible, simple, and
inexpensive network means for connecting
computers, peripherals, and servers
• Newer versions of Macintosh operating
systems use TCP/IP and SMB as default
protocols rather than AppleTalk
• AppleTalk is a protocol and LocalTalk is a
media type
A Brief Protocol Prospectus
• DECnet is a proprietary network protocol
designed by Digital Equipment Corporation
• Currently two versions of DECnet are in use:
– DECnet Phase IV which is based on the
Phase IV Digital Network Architecture
(DNA)
– DECnet/OSI also called DECnet Phase V
is a layered model
Transmission Control
Protocol/Internet Protocol
• TCP/IP is considered the language of the
Internet
• It is the most widely used protocol today
• It is a suite, or stack, of small, specialized
protocols
• Because of its routing ability, TCP/IP has
become the protocol of choice for many
LANs, as well as the basis for the Internet,
making it the standard
Transmission Control
Protocol/Internet Protocol
• In the early 1970s, the Department of
Defense funded ARPA to design a new set of
computer communication protocols that
would allow multiple networks to be
interconnected in a flexible and dynamic way
• The protocol developed was originally called
Network Control Protocol
• This success led to the implementation of the
two main Internet protocols
• These are Transmission Control Protocol and
Internet Protocol (TCP/IP)
Transmission Control
Protocol/Internet Protocol
• TCP/IP’s implementation of the OSI
model makes functionality simpler
• It maps the same seven layers of
the OSI model to a four-layer
TCP/IP model instead
• The TCP/IP model focuses more on
delivering interconnectivity than on
functional layers
Transmission Control
Protocol/Internet Protocol
• Since TCP/IP is the language of the Internet,
you may also hear this model referred to as
the Internet reference model
• The Layers are:
– Network Access
– Internet
– Transport
– Application
TCP/IP Network Access Layer
Protocols
• The Network Access layer is the lowest
layer in the model
• It Maps to Layers 1 (Physical) and 2
(Data Link) of the OSI model
• It is responsible for the delivery of
datagrams by creating a frame for the
network type and then sending the data
to the wire
TCP/IP Network Access Layer
Protocols
• This layer contains the protocols that are
used to deliver data to computers and
devices on the network
• These include Serial Line Interface Protocol
(SLIP) and Point-to-Point Protocol (PPP)
• These are communication protocols for serial
data transmission by which IP packets can be
sent over a modem
TCP/IP Network Access Layer
Protocols
• Other protocols that are used at this layer
include a means to relate different types of
addresses to each other:
– the Address Resolution Protocol (ARP)
– the Reverse Address Resolution Protocol
(RARP)
• This layer defines the logical network layout
so routers can determine where to forward
packets
TCP/IP Internet Layer Protocols
• The layer above the Network Access
layer is called the Internet layer
• It manages the routing of packets that
are to be forwarded on to different
networks
• It relies on routable protocols for
delivery
TCP/IP Internet Layer Protocols
• The Internet Protocol (IP) is responsible for
making data packets routable
• It is a forwarding protocol that uses routing
tables that are created by routing protocols
• It is a simple, connectionless internetworking
protocol
• The basis of IP is how it uses routing tables to
make decisions about routing an IP packet
TCP/IP Internet Layer Protocols
• Every host on the network needs
an IP address
• TCP/IP uses a 32-bit Layer 3 address in
the format xxx.xxx.xxx.xxx to identify the
network and the host compute
• Each set of xxx is called an octet
TCP/IP Internet Layer Protocols
• There are five classes of IP addresses
their corresponding numbers are:
– Class A: Has a first octet number between
1 and 126 and can support a network with
16,777,216 hosts.
– Class B: Has a first octet number between
128 and 191 and can support 65,536 hosts
TCP/IP Internet Layer Protocols
• There are five classes of IP addresses
their corresponding numbers are:
– Class C: Has a first octet number between
192 and 223 and can support 254 hosts
per network
– Class D: Begins at 224 and ends at 239.
This address class is reserved for sending
multicast messages
TCP/IP Internet Layer Protocols
• A There are five classes of IP
addresses their corresponding numbers
are:
– Class E: Begins with 240 and ends at 255.
This address class is reserved for
experimental use
– The IP address 127.0.0.1 is used as the
loopback address
TCP/IP Internet Layer Protocols
• A datagram is the packet format defined by IP
• Datagrams are packets that consist of a
header, data, and a trailer
• The header contains information that the
network needs to route the datagram
• Trailers typically contain a checksum value,
which is used to ensure that the data is not
modified in transit
TCP/IP Internet Layer Protocols
• IP delivers the datagram by checking
the destination address in the header
• When IP checks the destination address
in the header, if it is the address of a
host on the local network, the datagram
is delivered directly to the destination
• If it is not on the local network, the
datagram is passed on for delivery
TCP/IP Internet Layer Protocols
• Each router that a datagram passes through
is considered a hop
• A system transmits IP datagrams as fast as it
can generate them
• IP has two features that can affect throughput
– the IP Time to Live (TTL)
– IP Fragmentation
TCP/IP Internet Layer Protocols
• By interconnecting multiple switches with
redundant paths, you overcome problems
with faulty cables or port failures
• Another less well-known side effect of a loop
is the corruption of the forwarding tables on
all the switches
• It would take very little time before Layer 2
broadcast loops completely destroy the
functionality of a network
TCP/IP Internet Layer Protocols
• The Spanning Tree Protocol (STP) prevents
bridging loops by identifying a preferred path
through a series of looped bridges
• Administrators can provide redundancy and
fault-tolerance by wiring a loop, and then
using STP turn off ports that would cause
loops to occur
• If a primary link fails, STP will reactivate the
back-up port allowing normal operation of the
network to continue
TCP/IP Internet Layer Protocols
• The TTL field is actually the number of
hops the datagram has made
• IP places a limit on how long a
datagram may live in the network
• Specifications for higher-layer protocols
usually assume that the maximum time
a datagram can live in the network is
only two minutes
TCP/IP Internet Layer Protocols
• Each type of network has a maximum
transmission unit (MTU), which is the largest
packet it can transfer
• A datagram received from one network may
be too large to be transmitted in a single
packet on another network
• It may be necessary to divide the datagram
into smaller pieces
• This division process is called fragmentation
TCP/IP Internet Layer Protocols
• Internet Control Message Protocol (ICMP) is
part of the Internet layer and uses IP
datagram delivery to send its messages
• ICMP uses the basic support of IP as if it was
higher-level protocol, but it is actually an
integrated part of IP
• ICMP is a protocol meant to be used as an
aid for other protocols
• It is used to test for connectivity and search
for configuration errors in a network
TCP/IP Internet Layer Protocols
• PING uses the ICMP echo function
• A small packet containing an ICMP echo
message is sent through the network to a
particular IP address
• The computer that sent the packet then waits
for a return packet
• If the connections are good and the target
computer is up, the echo message return
packet will be received
TCP/IP Internet Layer Protocols
• PING is one of the most useful network tools
available because it tests the most basic
function of an IP network
• Traceroute was originally developed for the
Unix operating system but is used for many
operating systems and most routers
• It is used to track the path a packet takes to
get to its destination
• It measures how long it takes to travel
through each hop to get to its target
TCP/IP Internet Layer Protocols
• Traceroute uses an ICMP echo request
packet to find the path
• Besides assisting in troubleshooting
functions such as PING and Traceroute,
ICMP capabilities include:
– Announcing network errors
– Congestion
– Timeout notification
TCP/IP Transport Layer Protocols
• The protocol layer above the Internet
layer is the Transport layer
• It is responsible for providing end-to-end
data integrity
• It also provides a reliable
communication service so that an
extended two-way conversation may
take place
TCP/IP Transport Layer Protocols
• This layer accepts and returns
information to be transmitted as a
stream of characters
• It uses open and close commands to
initiate and terminate the connection
• It consists of two protocols:
– Transmission Control Protocol (TCP)
– User Datagram Protocol (UDP)
TCP/IP Transport Layer Protocols
• TCP provides connection-oriented data
transmission
• It can support multiple data streams
• It provides for flow and error control
• It uses sequence numbers and
acknowledgements to guarantee
delivery
TCP/IP Transport Layer Protocols
• Sockets make up a TCP connection
• The two most typical network
applications that use TCP are:
– File Transfer Protocol (FTP)
– Telnet
• Telnet uses port 23
• FTP uses port 21
TCP/IP Transport Layer Protocols
• UDP does not provide either
sequencing or acknowledgements
• It is a connectionless protocol
• It is used a lot in telephony traffic and
the Remote Procedure Call (RPC)
• The major difference between TCP and
UDP is reliability
TCP/IP Application Layer
Protocols
• The top layer in the Internet reference
model is the Application layer
• This is how applications and certain
services access the network
• It provides the services that applications
use to communicate over the network
• It serves as a service provider for
workstations and applications.
TCP/IP Application Layer
Protocols
• The most widely known and
implemented TCP/IP Application layer
services are:
– File Transfer Protocol (FTP) which allows
files to be uploaded and downloaded on
port 21
– Telnet which uses terminal emulation for
access to remote hosts using port 23
TCP/IP Application Layer
Protocols
• The most widely known and
implemented TCP/IP Application layer
services are:
– Simple Mail Transfer Protocol (SMTP)
which supports basic message delivery
services between mail servers on port 25
– HyperText Transfer Protocol (HTTP) which
is a low-overhead Web browser service
protocol that uses port 80
TCP/IP Application Layer
Protocols
• The most widely known and
implemented TCP/IP Application layer
services are:
– Simple Network Management Protocol
(SNMP) which uses UDP port 161 to
collect information from network devices.
– Network News Transfer Protocol (NNTP):
handles distribution and posting of news
articles using port 119
TCP/IP Application Layer
Protocols
• The most widely known and
implemented TCP/IP Application
layer services are:
– Dynamic Host Configuration Protocol
(DHCP) allows for automatic IP addressing
– Domain Name Service (DNS) uses UDP
port 53 for resolving domain names to IP
addresses