Download Chapter 6: Network Communications and Protocols

Chapter 6
Network Communications and Protocols
Contents
1. Protocols
1.1. The Function of Protocols
1.2. Protocols in a Layered Architecture
2. Common Protocol Suites
2.1. Transmission Control Protocol/Internet Protocol (TCP/IP)
2.2. IP Addressing
2.3. Other Protocol Suites
2.4. Implementing and Removing Protocols
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1. Protocols
• Strictly speaking, protocols are the rules and
procedures for communicating
– For two computers to communicate, they must speak
the same language and agree on the rules of
communication
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1.1. The Function of Protocols
• As protocols serve their functions in the OSI model,
they might work at one or many layers
• When a set of protocols works cooperatively, it’s
called a protocol stack or protocol suite
– The most common protocol stack is TCP/IP, the
Internet protocol suite
– IPX/SPX, used in older versions of Novell NetWare,
is disappearing as companies upgrade to newer
versions of NetWare
– Levels of a protocol stack map to their functions in
the OSI model
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1.1.1. Connectionless Versus ConnectionOriented Protocols
• Protocols that use connectionless delivery place
data on the network and assume it will get through
– Connectionless protocols aren’t entirely reliable
– Are fast: little overhead, don’t waste time
establishing/managing/tearing down connections
• Connection-oriented protocols are more reliable
and, consequently, slower
– Two computers establish a connection before data
transfer begins
• In a connection, data is sent in an orderly fashion
– Ensures that all data is received and is accurate, or
that suitable error messages are generated
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1.1.2. Routable Versus Nonroutable Protocols
• The network layer (OSI) is responsible for moving
data across multiple networks
– Routers are responsible for routing process
• Protocol suites that function at Network layer are
routable or routed protocols; otherwise, they are
called nonroutable
– TCP/IP and IPX/SPX are routable protocols
– An older and nearly obsolete protocol, NetBEUI, is a
nonroutable protocol that works well in small
networks, but its performance drops considerably as
a network grows
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1.2. Protocols in a Layered Architecture
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1.2.1. Network Protocols
• Some popular network protocols include:
– Internet Protocol version 4 (IPv4 or simply IP)
• Provides addressing and routing information
– Internetwork Packet Exchange (IPX)
• Novell’s protocol for packet routing and forwarding
• Belongs to the IPX/SPX protocol suite
• Serves many of the same functions as TCP/IP’s IP
– Internet Protocol version 6 (IPv6)
• A new version of IP that’s being implemented on many
current networking devices and operating systems
– Addresses some weaknesses of IPv4
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1.2.2. Transport Protocols
• Transport protocols can be connection-oriented
(reliable) or connectionless (best-effort) delivery
– Transmission Control Protocol (TCP)
• Responsible for reliable data delivery in TCP/IP
– Sequential Packet Exchange (SPX)
• Novell’s connection-oriented protocol used to
guarantee data delivery
– NetBIOS/NetBEUI
• NetBIOS establishes/manages communications
between computers and provides naming services
• NetBEUI provides data transport services for these
communications
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1.2.3. Application Protocols
• Application protocols provide services to client
applications
– Simple Mail Transport Protocol (SMTP) in TCP/IP
– File Transfer Protocol (FTP) in TCP/IP
– Simple Network Management Protocol (SNMP)
• Manages and monitors network devices (TCP/IP)
– NetWare Core Protocol (NCP)
• Novell’s client shells and redirectors
– AppleTalk File Protocol (AFP)
• Apple’s remote file-management protocol
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2. Common Protocol Suites
• Because most protocols contain a combination of
components, these components are usually
bundled as a protocol suite
– TCP/IP
• Dominates the networking arena to the point of
making most of the other suites nearly obsolete
– IPX/SPX
– NetBIOS/NetBEUI
– AppleTalk
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2.1. Transmission Control Protocol/Internet
Protocol (TCP/IP)
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2.1.1. TCP/IP Network Layer Protocols
• Internet Protocol version 4 (IPv4) is a Network
layer protocol that provides source and destination
addressing and routing for the TCP/IP suite
– Connectionless protocol; fast but unreliable
• Internet Control Message Protocol (ICMP) is a
Network layer protocol used to send error and
control messages between systems or devices
– The Ping utility uses ICMP to request a response
from a remote host to verify availability
• Address Resolution Protocol (ARP) resolves
logical (IP) addresses to physical (MAC) addresses
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IP, ICMP, and ARP in Action
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2.1.2. TCP/IP Transport Layer Protocols
• Transmission Control Protocol (TCP) is the
primary Internet transport protocol
– Connection oriented using a three-way handshake
– Message fragmentation and reassembly
– Uses acknowledgements to ensure that all data was
received and to provide flow control
• User Datagram Protocol (UDP) is connectionless
– Generally faster, although less reliable, than TCP
• Doesn’t segment data or resequence packets
• Doesn’t use acknowledgements for reliability
• Used by NFS and DNS
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2.1.3. TCP/IP Application Layer Protocols
• Domain Name System (DNS)
– Session layer name-to-address resolution protocol
• Hypertext Transport Protocol (HTTP)
– To transfer Web pages from Web server to browser
• File Transfer Protocol (FTP)
– For file transfer and directory and file manipulation
• Telnet
– Remote terminal emulation; operates at layers 7-5
• Simple Mail Transport Protocol (SMTP)
– Operates at layers 7-5; provides messaging services
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2.2. IP Addressing
• Logical addresses are 32 bits (4 bytes) long
– Each byte is represented as an octet (decimal
number from 0 to 255)
– Usually represented in dotted decimal notation
• E.g., 172.24.208.192
– Address has two parts: network and host ID
• E.g. 172.24.208.192 (172.24.0.0 and 208.192)
– Categorized into ranges referred to as classes
• Class system provides basis for determining which
part of address is the network and which is the host ID
• The first octet of an address denotes its class
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• Classes
– Class A: first octet between 1-126
• 16,777,214 hosts per network address
– Class B: first octet between 128-191
• 65,534 hosts per network address
– Class C: first octet between 192-223
• 254 hosts per network address
– Class D: first octet between 224-239
• Reserved for multicasting
– Class E: first octet between 240-255
• Reserved for experimental use
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• 127.0.0.0 network is called the loopback address
– localhost always corresponds to address 127.0.0.1
• IETF reserved addresses for private networks
–
–
–
–
–
–
Class A addresses beginning with 10
Class B addresses from 172.16 to 172.31
Class C addresses from 192.168.0 to 192.168.255
These addresses can’t be routed across the Internet
To access the Internet, NAT is needed
IPv6 eliminates need for private addressing;
provides a 128-bit address (vs. IPv4’s 32 bits)
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2.2.1. Classless Interdomain Routing (CIDR)
• Addressing by class has been superseded by a
more flexible addressing method
– Classless Interdomain Routing (CIDR)
– The network and host demarcation can be made
with any number of bits from beginning of address
– E.g., a Class C address’s network section is 24 bits
• Using CIDR, an address registry can assign an
address with a network section of 26 bits
– 192.203.187.0/26
– Subnetting divides network address in two or more
subnetwork addresses (with fewer host IDs for each)
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2.2.2. Why Subnet?
• Subnetting
– Makes more efficient use of available IP addresses
– Enables dividing networks into logical groups
– Can make network communication more efficient
• Broadcast frames are sent to all computers on the
same IP network
– Hubs and switches forward broadcast frames;
routers do not
– Broadcast domain: extent to which a broadcast
frame is forwarded without going through a router
– Subnetting reduces broadcast traffic
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2.2.3. Subnet Masks
• Subnet mask determines which part of address
denotes network portion and which denotes host
– 32-bit number
– A binary 1 signifies that the corresponding bit in the
IP address belongs to the network portion; a 0
signifies that bit in address belongs to host portion
– Default subnet mask uses a 255 in each octet in
address that corresponds to the network portion
• Class A: 255.0.0.0
• Class B: 255.255.0.0
• Class C: 255.255.255.0
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2.2.4. Some Simple Binary Arithmetic
• Four kinds of binary calculations:
– Converting between binary and decimal
– Converting between decimal and binary
– Understanding how setting high-order bits to the
value of 1 in 8-bit binary numbers corresponds to
specific decimal numbers
– Recognizing the decimal values for numbers that
correspond to low-order bits when set to 1
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Converting Decimal to Binary
• 125 is converted to binary as follows:
–
–
–
–
–
–
–
125 divided by 2 equals 62, remainder 1
62 divided by 2 equals 31, remainder 0
31 divided by 2 equals 15, remainder 1
15 divided by 2 equals 7, remainder 1
7 divided by 2 equals 3, remainder 1
3 divided by 2 equals 1, remainder 1
1 divided by 2 equals 0, remainder 1
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Converting Binary to Decimal
•
To convert 11010011 to decimal:
1. Count the total number of digits in the number (8)
2. Subtract one from the total (8 - 1 = 7)
3. That number (7) is the power of 2 to associate with
the highest exponent for two in the number
4. Convert to exponential notation, using all the digits
as multipliers
5. 11010011, therefore, converts to:
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High-Order Bit Patterns
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Low-Order Bit Patterns
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Calculating a Subnet Mask
•
To decide how to build a subnet mask:
1. Decide how many subnets you need
2. Decide how many bits you need to meet or exceed
the number of required subnets
•
Use the formula 2n, with n representing the number
of bits you must add to the starting subnet mask
3. Borrow bits from the top of the host portion of the
address down
4. Ensure that you have enough host bits available to
assign to computers on each subnet (2n-2)
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Calculating Supernets
• Supernetting “borrows” bits from network portion
of an IP address to “lend” those bits to host portion
– Permits consecutive IP network addresses to be
combined and viewed in a single logical network
• Combining two or more small networks into one
larger network is only one reason to supernet
– Supernetting can combine multiple routing table
entries into a single entry, which can drastically
decrease the table’s size on Internet routers
– This reduction in routing table size increases the
speed and efficiency of Internet routers
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2.2.5. Network Address Translation (NAT)
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2.2.6. Dynamic Host Configuration Protocol
(DHCP)
• Detailed configuration of devices, keeping track of
assigned addresses and to which machine they
were assigned, etc., is difficult in large networks
– DHCP was developed to make this process easier
– DHCP server must be configured with a block of
available IP addresses and their subnet masks
– Clients must be configured to use DHCP
• Broadcast request message is sent on boot
– Client leases the address the server assigns to it
– If no answer is received, in an APIPA-enabled OS, the
computer assigns itself an address (169.254.x.x)
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2.2.7. Internet Protocol Version 6 (IPv6)
• IPv6 solves several IPv4 problems
– Limiting 32-bit address space
• An IPv6 address is 128 bits long
– Lack of built-in security
• IPSec provides authentication and encryption
– A sometimes complicated setup
• IPv6 is autoconfiguring (stateless or stateful)
– Lack of built-in QoS
• QoS headers in IPv6 packets can identify packets that
require special or priority handling, making
applications such as streaming audio and video much
easier to implement
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IPv6 Addresses
• IPv6 addresses are specified in hexadecimal
format in 16-bit sections separated by a colon
– Longhand notation: 2001:260:0:0:0:2ed3:340:ab
– Shorthand notation: 2001:260::2ed3:340:ab
• If one of the 16-bit numbers doesn’t require four
hexadecimal digits, the leading 0s are omitted
– Addresses have a three-part addressing hierarchy
• A public topology (first three 16-bit sections)
• A site topology (next 16 bits)
• An interface identifier (last 64 bits)
– Derived from the MAC address on the host’s NIC
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2.3. Other Protocol Suites
• Other protocol suites are sometimes used on older
networks, where the need to change to TCP/IP is
not warranted, or in environments suited to the
suite’s features
– NetBIOS/NetBEUI
• Used primarily on older Windows networks
– IPX/SPX
• Designed for use on NetWare networks
– AppleTalk
• Used almost exclusively on Macintosh networks
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2.3.1. NetBIOS and NetBEUI
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2.3.2. IPX/SPX
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2.3.3. AppleTalk
• Although the AppleTalk standard defines physical
transport in Apple Macintosh networks, it also
establishes a suite of protocols those computers
use to communicate
• Apple created AppleTalk Phase II to allow
connectivity outside the Macintosh world
• AppleTalk divides computers into zones
– Allow a network administrator to logically group
computers and other resources that have frequent
communication, in a manner similar to subnetting
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2.4. Implementing and Removing Protocols
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Summary
• Many protocols are available for network
communications, each with its strengths/weaknesses
• The TCP/IP protocol suite dominates network
communication in part due to its use on the Internet
• IP addressing involves several concepts, including
address classes, subnetting, and supernetting
• IPv6 will eventually replace IPv4 because it offers
several advantages: 128-bit address space,
autoconfiguration, built-in security, and QoS
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