guide to tcp/ip fourth edition chapter 2: ip addressing and related topics

Guide to TCP/IP Fourth Edition

Chapter 2: IP Addressing and Related Topics

2

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

© 2013 Course Technology/Cengage Learning. All Rights Reserved.

3

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


4

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


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

5© 2013 Course Technology/Cengage Learning. All Rights Reserved.

6

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


7

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


8

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


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


10

Broadcast Packet Structures

• IPv4 broadcast packets have two destination address fields– Data Link layer destination address field – Destination network address field


12

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


Broadcast Packet Structures (cont’d.)


15

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


16

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


17

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


18

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


19

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 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


20

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


Public Versus Private IPv4 Addresses (cont’d.)


22

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


23

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


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

interfaces24© 2013 Course Technology/Cengage Learning. All Rights Reserved.

25

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


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


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


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


29

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


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


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


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


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


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


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


Interface Identifiers (cont’d.)


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:BA98:7654:3210]:70/


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 address38© 2013 Course Technology/Cengage Learning. All Rights Reserved.

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


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


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


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)


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


45

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


46

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


guide to tcp/ip fourth edition chapter 2: ip addressing and related topics

Documents

broadcast address address

ip address classes contd

network addresses

address classes d

numeric ip addresses

ip addressing basics

patterns ip

physical network