Guide to TCP/IP, Third Edition : Guide to TCP/IP, Third Edition Chapter 2:
IP Addressing and Related Topics
Objectives : 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) : 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 Basics : 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 Basics (continued) : 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
Anatomy of an IP Address : 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 Address Classes : 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 Address Classes (continued) : 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
More About Class A Addresses : 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
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More About Class B Addresses : 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
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More About Class C Addresses : 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
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More About Address Classes D and E : 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
Network, Broadcast, Multicast, and Other Special IP Addresses : 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
Broadcast Packet Structures : 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
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Multicast Packet and Address Structures : 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
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The Vanishing IP Address Space : 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
Understanding Basic Binary Arithmetic : 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
Converting Decimal to Binary : IP Addressing and Related Topics 24 Converting Decimal to Binary Converting decimal number 125 to binary
125 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
Converting Binary to Decimal : 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
High-Order Bit Patterns : 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
Low-Order Bit Patterns : 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 Networks, Subnets, And Masks : 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 Mask
Class A n h.h.h 255.0.0.0
Class B n.n h.h 255.255.0.0
Class C n.n.n h 255.255.255.0
IP Subnets and Supernets : 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
Calculating Subnet Masks : 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
Designing a Constant-Length Subnet Mask : 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
Designing a Variable-Length Subnet 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
Calculating Supernets : 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
Classless Inter-Domain Routing : 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
Public Versus Private IP Addresses : 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
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Public Versus Private IP Addresses (continued) : 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
Managing Access To IP Address Information : 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
Obtaining Public IP Addresses : 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 Schemes : 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
The Network Space : 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
The Host Space : 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
Summary : 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
Summary (continued) : 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
Summary (continued) : 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