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

Guide to TCP/IP, Third Edition

Chapter 2: IP Addressing and Related Topics

IP Addressing and Related Topics 2

Objectives

• Understand IP addressing, anatomy and structures, and addresses from a computer’s point of view

• Recognize and describe the various IP address classes from A to E, and explain how they’re 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


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


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 (continued)

• 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


Anatomy of an IP Address

• IP 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


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


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


More About 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


More About 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


More About 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


More About 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


Network, Broadcast, Multicast, and 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


Broadcast Packet Structures

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


Multicast Packet and Address Structures

• 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


The 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


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


Converting Decimal to Binary

• Converting decimal number 125 to binary125 divided by 2 equals 62, remainder 1

62 divided by 2 equals 31, remainder 0







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 =

1*27+1*26+0*25+1*24+1*23+0*22+1*21+1*20 = 128+64+0+16+8+0+2+1 = 219


High-Order Bit Patterns

Binary Decimal

10000000 128

11000000 192

11100000 224

11110000 240

11111000 248

11111100 252

11111110 254

11111111 255


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


IP Networks, Subnets, And 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 MaskClass A n h.h.h 255.0.0.0Class B n.n h.h 255.255.0.0Class C n.n.n h 255.255.255.0


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


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


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 portion’s 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


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


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


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


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


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


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


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


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


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


Summary

• 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


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


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

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

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