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Guide to TCP/IP
Fourth Edition
Chapter 2:
IP Addressing and Related Topics
Objectives
• Describe IP addressing, anatomy and structures,
and addresses from a computer’s point of view
• Recognize and describe IPv4 addressing and
address classes, describe the nature of IPv4
address limitations, and define the terms subnet,
supernet, subnetting, and supernetting
• Describe how to obtain public and private Internet
addresses
• Explore IPv4 addressing schemes
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Objectives (cont'd.)
• Describe the nature of IPv4 address limitations and
why IPv6 is needed
• Discuss new and enhanced IPv6 features
• Recognize and describe IPv6 addressing schemes,
features, and capacities
• Describe the impediments involved in transitioning
from IPv4 to IPv6
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IP Addressing Basics
• Computers deal with network addresses as bit
patterns
• IP uses a three-part addressing scheme
– Symbolic
• Example “support.dell.com”
– Logical numeric
• Example 172.16.1.10
– Physical numeric
• Six-byte numeric address, burned into firmware (on a
chip) by network interface manufacturers
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IP Addressing Basics (cont'd.)
• Address Resolution Protocol (ARP)
– Permits computers to translate numeric IP
addresses to MAC layer addresses
• ReverseARP (RARP)
– Translates MAC layer addresses into numeric IP
addresses
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IPv4 Addressing
• Numeric IPv4 addresses
– Dotted decimal notation
– 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
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IPv4 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 (cont'd.)
• Address Classes D and E are for special uses
– Class D addresses
• Multicast communications
– Class E addresses
• Reserved entirely for experimental use
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Network, Broadcast, Multicast, and
Other Special IPv4 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
• IPv4 broadcast packets have two destination
address fields
– Data Link layer destination address field
– Destination network address field
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Broadcast Packet Structures (cont’d.)
• Multicast Packet and Address Structures
– Host listens on the multicast and broadcast
addresses besides its own
• IP gateway
– Router or other device that will forward traffic to the
host’s physical network
• The Internet Corporation for Assigned Names and
Numbers (ICANN)
– Allocates multicast addresses on a controlled basis
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Broadcast Packet Structures (cont’d.)
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IPv4 Networks and 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
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IPv4 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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IPv4 Subnets and Supernets (cont’d.)
• 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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IPv4 Subnets and Supernets (cont’d.)
• Bitcricket IP Calculator
– Free subnet mask calculator from WildPackets
– First to support IPv6
– Classless Inter-Domain Routing (CIDR) routes can
also be calculated
• SolarWinds IP Subnet Calculator
– Provides address details such as reverse DNS
resolution and response time
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Classless Inter-Domain Routing in
IPv4
• 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 lowerorder 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 IPv4 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 IPv4 Addresses
(cont’d.)
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Public Versus Private IPv4 Addresses
(cont'd.)
• 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 IPv4 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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IPv4 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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The End of the IPv4 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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Introducing IPv6
• IPv6
– Provides a vast abundance of IP addresses and
better management of its address space
– Eliminates the need for NAT
– Has modernized routing support and natively allows
for expansion along with the growing Internet
– Supports network security by using authentication
and encryption extension headers
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Request for Comments Pages and
Depreciation
• Request for Comments (RFC)
– Describe the methods, innovations, and standards
that are applied to every aspect of the Internet,
including IPv6
• RFC 5156
– Contains a summary of various other RFCs
regarding special usage of IPv6 addresses
• When reviewing RFCs
– Make special note of depreciated and obsolete
information and documents
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IPv6 Addressing
• IPv6 addresses
– 128 bits long
– String that uniquely identifies one single network
interface on the global Internet
– Contains a network portion and a host portion
– Network and host portion depend on who’s looking
at it and where they are located
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Address Format and Notation
• Addresses in IPv6 are also binary numbers
• Expressed using hexadecimal notation (00–FF)
• Broken up differently
– IPv6 uses groups of four 16-bit numbers called
“words,” separated by a colon character (:)
• Examples:
– 1090:0000:0000:0000:0009:0900:210D:325F or
– 1090::9:900:210D:325F
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Network and Host Address Portions
• Network prefix similar to CIDR
• Examples:
– 1090::9:900:210D:325F / 60
– 1018:FD0C:0:9:90:900:10BB:A / 24
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Scope Identifier
• 4-bit field
• Limits the valid range for a multicast address
• Defines the portion of the Internet to which the
multicast group pertains
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Interface Identifiers
• IPv6 requires that every network interface have its
own unique identifier
– Hardware vendors tend to use the modified EUI-64
format
– Software makers, including Microsoft, use the
privacy format defined in RFC 4941
• Having the right-hand portion of your IPv6 address
based on the computer’s MAC or hardware
address presents a security concern
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Interface Identifiers (cont’d.)
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Native IPv6 Addresses in URLs
• RFC 2732 (originally proposed in 1999)
– Describes a method to express IPv6 addresses in a
form compatible with HTTP URLs
– Uses square brackets ([ and ]), to enclose a literal
IPv6 address
• Example:
– http://[FEDC:BA98:7654:3210:FEDC:BA98:7654:321
0]:70/
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Address Types
• Special addresses
– Unspecified address
• All zeroes and can be represented as two colon
characters (::) in normal notation
– Loopback allows a host on a network to check the
operation of its own local TCP/IP protocol stack
• Multicast addresses
– Used to send an identical message to multiple hosts
• Anycast address
– Packets addressed to an anycast address go to the
nearest single instance of that address
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Address Types (cont’d.)
• Unicast address
– Sent to one network interface
• Aggregatable global unicast address
– Can be combined with other addresses into a single
entry in the router table
• Link-local address
– First 10 (leftmost) bits set to 1111111010
• Site-local address
– First 10 (leftmost) bits set to 1111111011
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Address Allocations
• IPv6 pre-allocates only about 15 percent of its
available addresses
• Network Service Access Point (NSAP) addressing
– Holds 1/128 of all the IPv6 address space
• Unicast and anycast allocations
• Multicast allocations
– All IPv6 addresses beginning with 0xFF
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IPv6 Addressing and Subnetting
Considerations
• In general IPv6 does not require subnetting
– Although possible
• Extent to which you can “subnet” an IPv6 address
depends on the length of the prefix
• How you apportion the host addressing depends
on the prefix length
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The IPv4 to IPv6 Transition
• Transition technologies:
– Teredo tunneling
– ISATAP or Intra-Site Automatic Tunnel Addressing
Protocol
– 6to4 tunneling
– NAT-PT (Network Address Translation-Protocol
Translation)
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Summary
• IP addresses
– Provide foundation for identifying individual network
interfaces on TCP/IP networks
• IPv4 addresses
– Come in five classes named through E
• 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
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Summary (cont'd.)
• Address masquerading and address substitution
– Techniques used to hide internal network IP
addresses from outside view
• 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
• The world has all but run out of IPv4 addresses
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Summary (cont'd.)
• IPv6 introduces a number of improvements and
updates to the IP protocol
• IPv6 supports three address types: unicast,
multicast, and anycast
• IPv6 employs two private or local-use address
schemes
• IPv6 prefix lengths define the number of bits
apportioned to the network address and to the host
address
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