IP Addressing And Related Topics

1
Guide To TCP/IP, Second Edition

• Chapter 2
• IP Addressing And Related Topics

2
Topics

• IP addressing
• IP address classes from A to E
• The disappearing IP address space
• Classless Inter-Domain Routing
• Network Address Translation
• Subnet and supernets
• public and private IP addresses
• Designing IP addressing schemes

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IP Addressing Basics

• Computer network addresses are bit patterns
• IP provides humans with a three-level addressing
  scheme
• Symbolic Example support.dell.com
• Logical numeric Example 172.16.1.10
• Physical numeric Consists of a 6-byte MAC address

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IP Addressing Basics (cont.)

• Data Link Sublayers Layers
• Media Access Control (MAC)
• Logical Link Control (LLC) sublayer
• At the Data Link layer MAC addresses are used to
  transfer frames between NICs on the same physical
  network
• At the Network layer IP addresses in the packet
  header are used to forward messages to there
  ultimate destination

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Anatomy Of An IP Address

• Dotted decimal notation can be used to represent
  a binary IP address
• IP Addresses take the form n.n.n.n, where n is
  between 0 and 255
• An IP address is made up of four 8-bit numbers,
  each called an octet

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IP Address Classes

• IP addresses are subdivided into five classes, A,
  B, C, D, E
• First three classes of addresses divide the
  addresses as follows
• Class A n. h.h.h
• Class B n.n. h.h
• Class C n.n.n. h
• n Network, h Hosts

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IP Address Classes (cont.)

• Class D addresses are used for multicast
  communications
• Class E addresses are reserved entirely for
  experimental use

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More About Class A Addresses

• Expressed in binary form, Class A addresses
  always take the following binary form
• 0bbbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb
• b 1 or 0
• 00000000 thru 01111111 for first octet
• Addresses consisting of all 0s and all 1s, for
  the variable b, are reserved for special uses
• Network ID and Broadcast Address
• 127.n.n.n is reserved for loopback testing

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Class A Address Facts And Figures
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More About Class B Addresses

• Class B addresses always take the following
  binary form
• 10bbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb
• b 1 or 0
• 10000000 thru 10111111 for first octet
• Addresses consisting of all 0s and all 1s, for
  the variable b, are reserved for special uses
• Network ID and Broadcast Address

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Class B Address Facts And Figures
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More About Class C Addresses

• Class C addresses always take the following
  binary form
• 110bbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb
• b 1 or 0
• 11000000 thru 11011111 for first octet
• Addresses consisting of all 0s and all 1s, for
  the variable b, are reserved for special uses
• Network ID and Broadcast Address

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Class C Address Facts And Figures
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More About Address Classes D And E

• Class D addresses always take the following
  binary form
• 1110bbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb
• b 1 or 0
• 11100000 thru 11101111 for first octet
• Class E addresses always take the following
  binary form
• 11110bbb.bbbbbbbb.bbbbbbbb.bbbbbbbb
• b 1 or 0
• 11110000 thru 11110111 for first octet

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Network and Special IP Addresses

• Network addresses have all 0s in the host bit
  positions
• The Broadcast Address is to send messages to all
  hosts on the network
• Broadcast Packet and Frame Structures
• Network Packet Broadcast 255.255.255.255
• Data Link Frame Broadcast 0xFF-FF-FF-FF-FF-FF

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Multicast And Other Special IP Addresses

• Host uses a service that employs a multicast
  address
• Host registers itself to listen on that address
• Data Link layer destination address is based on
  the Network layer multicast address

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Broadcast Packet Example
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Multicast Packet Example
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IP to MAC Multicast Address Conversion
20
Vanishing IP Address Space

• Mid-1990s experts began to predict that the
  Internet would run out of available IP
  addresses
• Address space saving techniques
• Classless Inter-Domain Routing (CIDR)
• Trade in existing IP network addresses ()
• Private IP addresses (RFC 1918)
• Network Address Translation (NAT) maps private IP
  addresses to public IP address

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Understanding Basic Binary Arithmetic

• Binary equivalents
• 0000 (0), 0001 (1), 0010 (2), 0011 (3)
• 0100 (4), 0101 (5), 0110 (6), 0111 (7)
• 1000 (8), 1001 (9), 1010 (10), 1011 (11)
• 1100 (12), 1101 (13), 1110 (14), 1111 (15)
• Converting decimal to binary
• Division or subtraction methods
• Converting binary to decimal
• Add powers of 2 for each bit placement

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Understanding Basic Binary Arithmetic (cont.)

• High-Order bit patterns
• Left most bits of an octet
• 11000000
• Low-Order bit patterns
• Right most bits of an octet
• 00000011

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Network Masks and Subnetting

• a net mask is a special bit pattern that
  identifies the network portion of an IP address
• IP subnets and supernets
• Subnetting - stealing bits from the host
  portion to create additional sub networks
• Supernetting combines contiguous network
  addresses to provide more host addresses or to
  aggregate route table entries

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Types of Subnet Masks

• Subnet masks
• Constant-Length Subnet Mask (CLSM)
• Each subnet includes the same number of stations
• Variable-Length Subnet Mask (VLSM)
• Each subnet may not have the same number of
  stations

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Classless Inter-Domain Routing (CIDR)

• Ignores the traditional A, B, and C class
  designations for IP addresses
• Allows IP addresses from Class A, B, or C to be
  combined as a larger address space
• CIDR limitations
• Network addresses must be contiguous
• Routers in the routing domain must understand
  CIDR notation

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Public Versus Private IP Addresses

• Private IP addresses
• RFC 1918 designates specific addresses for use as
  private IP addresses
• Private IP addresses are not routed across the
  public Internet
• Public IP addresses
• Used when identifying servers or services that
  must be accessible to the Internet
• Assigned to routers, proxy servers, firewalls,
  web servers, e-mail servers, FTP servers, and
  news servers

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Private Address Ranges
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Managing Access To IP Address Information

• IP security
• Private IP addresses and NAT
• Proxy server
• Reverse proxy

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Obtaining Public IP Addresses

• Public IP addresses issued by ISPs
• ICANN manages all
• IP-related addresses
• Protocol numbers
• well-known port addresses
• assigns MAC layer addresses
• www.icann.org

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IP Addressing Schemes

• The Network space
• Number of physical locations
• Number of network devices at each location
• Amount of broadcast traffic at each location
• IP network is a broadcast domain
• Routing (instead of bridging) is done to prevent
  unnecessary broadcasts from clogging expensive
  WAN circuits 2
• Availability of IP addresses

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IP Addressing Schemes (cont.)

• The Network space (cont.)
• Delay caused by routing from one network to
  another
• Size of the routing tables
• Time required for the network to converge
• Route aggregation or summary addresses
• The Host space
• Assign IP addresses based function (.1-.6 network
  devices)(.9-.14 servers)

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Chapter Summary

• IP addresses provide the foundation for
  identifying individual network interfaces (and
  therefore computers or other devices as well) on
  TCP/IP networks
• Understanding address structures, restrictions,
  and behavior is essential to designing TCP/IP
  networks and appreciating how existing TCP/IP
  networks are organized
• IP addresses come in five classes named A through
  E

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Chapter Summary (cont.)

• Classes A through C use the IPv4 32-bit address
  to establish different break points between the
  network and host portions of such network
  addresses
• Class A uses a single octet for the network
  address and three octets for the host address
  Class B uses two octets each for network and host
  portions and Class C uses three octets for the
  network portion and one octet for the host
  portion

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Chapter Summary (cont.)

• Thus, only a few (124) Class A networks exist,
  but each can support more than 16,000,000 hosts
  numerous (over 16,000) Class B networks exist,
  and each can support around 65,000 hosts
  finally, approximately 2,000,000 Class C networks
  exist, each with only 254 hosts per network
• Understanding binary arithmetic is essential to
  knowing how to deal with IP addresses,
  particularly when working with subnet masks

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Chapter Summary (cont.)

• Knowing how to convert from decimal to binary,
  and vice versa, helps you understand how the
  concept of stealing bits from the host portion of
  an IP address permits a network to be subdivided
  into logical subnetworks, or subnets
• Likewise, it helps you understand how stealing
  bits from the network portion of multiple
  contiguous IP addresses increases the number of
  addressable hosts To help ease address scarcity,
  the IETF created a form of classless addressing
  called Classless Inter-Domain Routing (CIDR) that
  permits the network-host boundary to fall away
  from octet boundaries

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Chapter Summary (cont.)

• CIDR is best used to aggregate multiple Class C
  addresses to decrease the number of networks,
  while increasing the total number of addressable
  hosts
• This technique is called supernetting
• Likewise, to make best use of IP network
  addresses, a technique called subnetting permits
  additional bits to be taken from the host portion
  of a network
• Recognizing the following bit patterns (decimal
  values follow in parentheses) helps when
  calculating or examining subnet masks 11000000
  (192), 11100000 (224), 11110000 (240), 11111000
  (248), and 11111100 (252)

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Chapter Summary (cont.)

• Several techniques exist to hide internal network
  IP addresses from outside view, including address
  masquerading and address substitution
• These techniques replace the actual internal
  network address from the source field in the IP
  header with a different value that reveals
  nothing about the actual address structure of the
  originating network
• Either Network Address Translation software or a
  proxy server usually handles this kind of task
• Within the Class A, B, and C IP address ranges,
  the IETF has reserved private IP addresses or
  address ranges

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Chapter Summary (cont.)

• Any organization may use these private IP
  addresses without charge and without obtaining
  prior permission, but private IP addresses may
  not be routed across the public Internet
• Another important job for Network Address
  Translation software, in fact, is to map a range
  of private IP addresses to a single public IP
  address to permit computers that use private IP
  addresses to obtain Internet access

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Chapter Summary (cont.)

• When it comes to obtaining public IP addresses,
  the Internet Corporation for Assigned Names and
  Numbers (ICANN previously the Internet Assigned
  Numbers Authority, or IANA, handled this task) is
  the ultimate authority
• Today, unassigned public IP addresses are
  extremely scarce and therefore unlikely to be
  allocated to most ordinary organizations
• In fact, most IP address assignments come from
  ISPs that subdivide already assigned Class A, B,
  or C addresses to assign public IP addresses to
  their customers