IP Addressing

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IP Addressing

• ITNW 2321
• Chapter 2

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Objectives

• By the end of this chapter you should be able to
• Understand IP addressing, anatomy and structures,
  and addresses from a computers point of view
• Recognize and describe the various IP address
  classes from A to E, and explain how theyre
  composed and used
• Understand the nature of IP address limitations,
  and how techniques like Classless Inter-Domain
  Routing and Network Address Translation ease
  those limitations

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Objectives (continued)

• Define the terms subnet and supernet, and apply
  your knowledge of how subnets and supernets work
  to solve specific network design problems
• Understand how public and private Internet
  addresses are assigned, how to obtain them, and
  how to use them properly
• Recognize the importance and value of an IP
  addressing scheme

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IP Addressing Basics

• Computers deal with network addresses as bit
  patterns (Binary Stream)
• IPv4 uses a three-part addressing scheme
• Symbolic
• Example support.dell.com
• Logical numeric
• 172.16.1.10 or 10101100.00100000.00000001.00001010
  
• Physical numeric
• Six-Octet (byte) numeric address, burned into
  firmware (on a chip) by NIC manufacturers

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IP Addressing Basics (continued)

• Address Resolution Protocol (ARP)
• Permits computers to translate numeric IP
  addresses to MAC layer addresses
• ReverseARP (RARP) (used by thin clients)
• Translates MAC layer addresses into numeric IP
  addresses
• Proxy ARP (ProxARP)
• Used in routed networks when the known IP is
  outside the local router segment

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Anatomy of an IP Address

• IP addresses (IPv4)
• Dotted decimal notation for 32 bits (4 Octets)
• Take the form n.n.n.n, where n is guaranteed to
  be between 0 and 255
• Each number is an 8-bit number called an octet
• Duplication is not allowed
• Made up of Network Fields and Host Fields
• IPv6
• Hex 128 bits (16 Octets)
• Network field assigned by vendor to interface
• Host field is the NIC MAC Address

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IP Address Classes

• IP addresses
• Subdivided into five classes Class A to Class E
• For first three classes octets are divided as
  follows
• Class A n. h.h.h
• Class B n.n. h.h
• Class C n.n.n. h
• n network, h host

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IP Address Classes (continued)

• Address Classes D and E are for special uses
• Class D addresses
• Multicast communications
• Class E addresses
• Reserved entirely for experimental use
• IETF

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Class A Addresses

• Class A addresses in binary form
• 0bbbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb
• b can be 1s or 0s
• Reserved for special uses
• Addresses consisting of all 0s and all 1s
• Reserved for private network use
• Address for network 10 (00001010)
• Reserved for loopback testing
• Address 127.n.n.n

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Class B Addresses

• Class B addresses take the following binary form
• 10bbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb
• b can be 1s or 0s
• 214 2
• Maximum number of usable network addresses
• 16,366
• Maximum number of public IP addresses

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Class C Addresses

• Class C addresses take the following binary form
• 110bbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb
• b can be 1s or 0s
• 221 2
• The maximum number of usable network addresses
• Reserved for private use
• 256 Class C addresses, from 192.168.0.0 to
  192.168.255.255

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Address Classes D and E

• Class D addresses
• 1110bbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb
• b can be 1s or 0s
• Multicast addresses
• Class E addresses
• 11110bbb.bbbbbbbb.bbbbbbbb.bbbbbbbb
• b can be 1s or 0s
• Only for experimental purposes by IETF members

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Network, Broadcast, Multicast, Other Special IP
Addresses

• Network address
• Any IP address where all host bits are 0
• Broadcast address
• Address that all hosts on a network must read
• Broadcast traffic
• Seldom forwarded from one physical network to
  another

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Broadcast Packet Structures

• IP broadcast packets have two destination address
  fields
• Data Link layer destination address field
• Destination network address field

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Multicast Packet and Address Structures

• IP gateway
• Router or other device that will forward traffic
  to the hosts physical network
• The Internet Corporation for Assigned Names and
  Numbers (ICANN)
• Allocates multicast addresses on a controlled
  basis

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Vanishing IP Address Space

• Address space saving techniques
• Classless Inter-Domain Routing (CIDR)
• Trade in existing IP network addresses
• RFC 1918
• Reserves three ranges of IP addresses for private
  use
• Network Address Translation (NAT)
• Lets networks use private IP addresses internally
  and maps them to public IP address externally

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Understanding Basic Binary Arithmetic

• Four binary calculations must be mastered
• Converting binary to decimal
• Converting decimal to binary
• Understanding how setting increasing numbers of
  high-order bits to 1 in eight-bit binary numbers
  corresponds to specific decimal numbers
• Understanding how setting increasing low-order
  bits to 1 in eight-bit binary numbers corresponds
  to specific decimal numbers

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Converting Decimal to Binary

• Converting decimal number 125 to binary
• 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

• Count the total number of digits in the number
• Subtract 1 from the total (8 - 1 7)
• Convert to exponential notation, using all the
  digits as multipliers
• 11011011converts as follows
• 11011011 127126025124123022121120
  128640168021 219

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High-Order Bit Patterns

• Binary Decimal
• 10000000 128
• 11000000 192
• 11100000 224
• 11110000 240
• 11111000 248
• 11111100 252
• 11111110 254
• 11111111 255

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Low-Order Bit Patterns

• Binary Decimal Exponent
• 00000001 1 21 - 1
• 00000011 3 22 - 1
• 00000111 7 23 - 1
• 00001111 15 24 - 1
• 00011111 31 25 - 1
• 00111111 63 26 - 1
• 01111111 127 27 - 1
• 11111111 255 28 - 1

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IP Networks, Subnets, Masks

• Subnet mask
• Special bit pattern that blocks off the
  network portion of an IP address with an all-ones
  pattern
• Default masks for Classes A, B, and C
• Class Layout Default Mask
• Class A n h.h.h 255.0.0.0
• Class B n.n h.h 255.255.0.0
• Class C n.n.n h 255.255.255.0

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IP Subnets and Supernets

• Subnetting
• Stealing (borrowing) bits from the host portion
  to further subdivide the network portion of an
  address
• Supernetting
• Stealing bits from network portion
• Using them to create a single, larger contiguous
  address space for host addresses

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Calculating Subnet Masks

• Types of subnet masking techniques
• Constant-length subnet masking (CLSM)
• Variable-length subnet masking (VLSM)
• In a VLSM addressing scheme
• Different subnets may have different extended
  network prefixes

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Designing a Constant-Length Subnet Mask

• Decide how many subnets are needed
• Add 2 to number of subnets needed then jump to
  the nearest higher power of two
• Reserve bits of host portions address from the
  top down
• Be sure that there are enough host addresses left
  over on each subnet to be usable
• If using RIP
• Use the formula 2b 2 to calculate the number of
  usable subnets from a mask

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Designing a Variable-Length Subnet Mask

• Analyze requirements for individual subnets
• Aggregate requirements by their relationships to
  the nearest power of two
• Use subnets that require largest number of
  devices
• To decide the minimum size of the subnet mask
• Aggregate subnets that require fewer of hosts
• Define VLSM scheme that
• Provides the necessary number of subnets of each
  size to fit its intended use best

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Calculating Supernets

• Supernets
• Steal bits from network portion of an IP
  address to lend those bits to the host
• Permit multiple IP network addresses to be
  combined
• Allow an entire group of hosts to be reached
  through a single router address

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Classless Inter-Domain Routing

• Limitations
• Network addresses must be contiguous
• When address aggregation occurs
• CIDR address blocks work best when they come in
  sets that are greater than 1 and equal to some
  lower-order bit pattern that corresponds to all
  1s
• Addresses commonly applied to Class C addresses
• To use a CIDR address on any network
• Routers in routing domain must understand CIDR
  notation

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Public Versus Private IP Addresses

• Private IP addresses ranges
• May be in the form of IP network addresses
• Address masquerading
• May be performed by boundary devices that include
  proxy server capabilities
• Private IP address limitation
• Some IP services require a secure end-to-end
  connection

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Public Versus Private IP Addresses (continued)

• Public IP addresses
• Remain important for identifying all servers or
  services that must be accessible to the Internet
• Most organizations need public IP addresses only
  for two classes of equipment
• Devices that permit organizations to attach
  networks to the Internet
• Servers designed to be accessible to the Internet

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Managing Access To IP Address Information

• Reverse proxying
• Permits the proxy server to front for servers
  inside the boundary
• Important service that proxy server provides
• Manages what source addresses appear in outbound
  packets that pass through it

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Obtaining Public IP Addresses

• Public IP addresses
• Issued by ISPs
• IP renumbering
• Switching addresses on every machine that uses
  address from old ISP to unique address obtained
  from new ISP
• ICANN
• Manages all IP-related addresses, protocol
  numbers, and well-known port addresses
• Assigns MAC layer addresses for use in network
  interfaces

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IP Addressing Schemes

• IP addressing scheme constraints
• Number of physical locations
• Number of network devices at each location
• Amount of broadcast traffic at each location
• Availability of IP addresses
• Delay caused by routing from one network to
  another

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The Network Space

• Application Specific Integrated Circuits (ASICs)
• Hardware used by switches to make decisions
• Layer-3 switch
• Implements the layer-3 logic from the software
  into its own ASICs
• Allows you to partition a large network into many
  smaller subnets with almost no loss of performance

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The Host Space

• Reasons for using binary boundaries
• You may want to implement layer-3 switching to
  reduce the broadcast traffic
• One day you will want to classify your traffic to
  apply Quality of Service (QoS) or policies of
  some sort
• Can be applied to firewall rules

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Summary

• By now you should be able to answer questions
  regarding
• IP addresses
• Provide foundation for identifying individual
  network interfaces on TCP/IP networks
• IP addresses
• Come in five classes named through E
• Understanding binary arithmetic
• Essential to knowing how to deal with IP
  addresses

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Summary (continued)

• Classless Inter-Domain Routing (CIDR)
• Permits network-host boundary to fall away from
  octet boundaries
• Subnetting
• Permits additional bits to be taken from the host
  portion of a network
• Address masquerading and address substitution
• Techniques used to hide internal network IP
  addresses from outside view

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Summary (continued)

• Within the Class A, B, and C IP address ranges
• IETF has reserved private IP addresses or address
  ranges
• Internet Corporation For Assigned Names and
  Numbers (ICANN)
• Ultimate authority for obtaining public IP
  addresses

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Questions???
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