guide to tcp/ip, third edition
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Guide to TCP/IP, Third Edition. Chapter 2: IP Addressing and Related Topics. Objectives. Understand IP addressing, anatomy and structures, and addresses from a computer’s point of view - PowerPoint PPT PresentationTRANSCRIPT
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
IP Addressing and Related Topics 3
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 and Related Topics 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 and Related Topics 5
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
IP Addressing and Related Topics 6
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 Addressing and Related Topics 7
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 Addressing and Related Topics 8
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
IP Addressing and Related Topics 9
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
IP Addressing and Related Topics 10
IP Addressing and Related Topics 11
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
IP Addressing and Related Topics 12
IP Addressing and Related Topics 13
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
IP Addressing and Related Topics 14
IP Addressing and Related Topics 15
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
IP Addressing and Related Topics 16
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
IP Addressing and Related Topics 17
Broadcast Packet Structures
• IP broadcast packets have two destination address fields– Data Link layer destination address field – Destination network address field
IP Addressing and Related Topics 18
IP Addressing and Related Topics 19
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
IP Addressing and Related Topics 20
IP Addressing and Related Topics 21
IP Addressing and Related Topics 22
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
IP Addressing and Related Topics 23
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
IP Addressing and Related Topics 24
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
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
IP Addressing and Related Topics 25
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
IP Addressing and Related Topics 26
High-Order Bit Patterns
Binary Decimal
10000000 128
11000000 192
11100000 224
11110000 240
11111000 248
11111100 252
11111110 254
11111111 255
IP Addressing and Related Topics 27
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 Addressing and Related Topics 28
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 Addressing and Related Topics 29
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
IP Addressing and Related Topics 30
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
IP Addressing and Related Topics 31
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
IP Addressing and Related Topics 32
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
IP Addressing and Related Topics 33
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
IP Addressing and Related Topics 34
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
IP Addressing and Related Topics 35
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
IP Addressing and Related Topics 36
IP Addressing and Related Topics 37
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
IP Addressing and Related Topics 38
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
IP Addressing and Related Topics 39
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 and Related Topics 40
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
IP Addressing and Related Topics 41
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
IP Addressing and Related Topics 42
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
IP Addressing and Related Topics 43
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
IP Addressing and Related Topics 44
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
IP Addressing and Related Topics 45
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