Guide to Networking Essentials Fifth Edition

1
Guide to Networking EssentialsFifth Edition

• Chapter 6
• Network Communications and Protocols

2
Objectives

• Explain the function of protocols in a network
• Describe common protocol suites

3
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

4
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, its
  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

5
Connectionless Versus Connection-Oriented
Protocols

• Protocols that use connectionless delivery place
  data on the network and assume it will get
  through
• Connectionless protocols arent entirely reliable
• Are fast little overhead, dont 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

6
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

7
Protocols in a Layered Architecture
8
Protocols in a Layered Architecture (continued)
9
Network Protocols

• Some popular network protocols include
• Internet Protocol version 4 (IPv4 or simply IP)
• Provides addressing and routing information
• Internetwork Packet Exchange (IPX)
• Novells protocol for packet routing and
  forwarding
• Belongs to the IPX/SPX protocol suite
• Serves many of the same functions as TCP/IPs IP
• Internet Protocol version 6 (IPv6)
• A new version of IP thats being implemented on
  many current networking devices and operating
  systems
• Addresses some weaknesses of IPv4

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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)
• Novells 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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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)
• Novells client shells and redirectors
• AppleTalk File Protocol (AFP)
• Apples remote file-management protocol

12
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

13
Transmission Control Protocol/Internet Protocol
(TCP/IP)
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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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IP, ICMP, and ARP in Action (continued)
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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
• Doesnt segment data or resequence packets
• Doesnt use acknowledgements for reliability
• Used by NFS and DNS

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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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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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IP Addressing (continued)

• 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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IP Addressing (continued)

• 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 cant be routed across the
  Internet
• To access the Internet, NAT is needed
• IPv6 eliminates need for private addressing
  provides a 128-bit address (vs. IPv4s 32 bits)

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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 addresss 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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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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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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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
• Count the total number of digits in the number
  (8)
• Subtract one from the total (8 - 1 7)
• That number (7) is the power of 2 to associate
  with the highest exponent for two in the number
• Convert to exponential notation, using all the
  digits as multipliers
• 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
• Decide how many subnets you need
• 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
• Borrow bits from the top of the host portion of
  the address down
• Ensure that you have enough host bits available
  to assign to computers on each subnet (2n-2)

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Calculating a Subnet Mask (continued)
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Calculating a Subnet Mask (continued)
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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 tables size on Internet
  routers
• This reduction in routing table size increases
  the speed and efficiency of Internet routers

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Network Address Translation (NAT)
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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)

36
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 20012600002ed3340ab
• Shorthand notation 20012602ed3340ab
• If one of the 16-bit numbers doesnt 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 hosts NIC

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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
  suites 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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NetBIOS and NetBEUI
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IPX/SPX
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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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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