Network Classes

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This material was developed with funding from the National Science Foundation under Grant # DUE 1601612

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Route of the first three-network transmissions in 1977

https://www.sri.com/sites/default/timeline/timeline.php?timeline=business-entertainment#!&innovation=internetworking

Understanding Network Classes When working with IP networks, technicians must understand subnetting and network classes. When IP networks were created, those involved decided on an address range of 32 binary digits or bits. Using a 32-bit address limited the number of addresses to 4 billion addresses (the highest address is 4,294,967,295). Binary 32 bits = 1111 1111 1111 1111 1111 1111 1111 1111 Decimal = 4,294,967,295 In 1960 this seemed to be enough addresses. No one could have imagined the Internet and the hundreds of millions of smart devices today, each requiring an IP address to communicate on the Internet.

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Click each class for more information.

IP Network Classes With an IPv4 address, there are five classes of available IP ranges: A, B, C, D and E. Only Classes A, B, and C are commonly used for network devices. Each class allows for a range of valid IP addresses. The IP address space was divided as follows: Class A was used for big organizations and provided up to 16,777,214 hosts on a network Class B was used for mid-size organizations and provided up to 65,534 hosts Class C was used for small networks with up to 254 hosts Class D was reserved for multicasting Class E was reserved for research and future development

Class C

= 16,777,214 (224 – 2) Hosts

= 65,534 (216 – 2) Hosts

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Class B

= 254 (28 – 2) Hosts

Class A

reserved for research and future development

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Class D

Class E

reserved for multicasting

Class D and E IP Networks Class D networks are used for multicasting. Multicasting sends information to a predefined group of users or devices or casts to multiple devices simultaneously. Don’t confuse this with broadcasting. Broadcasting sends a message to ALL devices on the network. Class E IP networks are reserved for research and future testing and control of the worldwide Internet.

HOST ID

MULTICAST ADDRESS

NET ID

IP Address Space Allocation Remember that all IP addresses are 32 bits long. Every eight bits make up an octet. All IP addresses have two parts:The network or subnetwork portion – identifies the local network.The host address portion – identifies a local device on the local network.An IPv4 address is typically expressed in dotted-decimal notation, with each octet represented by a number from 1-255 separated by a dot. An example IPv4 address would look like this: 10.30. 230.243 or 170.125.23.9 or 192.168.10.10

RESERVED

Class A uses one octet for the network portion of the address and provides 128 networks. Each of the 128 networks can handle over 16 million (16,777,216) addresses per network because there are three octets (24 bits) available for the host ID.

Octet 3

Octet 4

Class B uses two octets for the network portion of the address and provides over 16 thousand (16,384) networks and over 65 thousand (65,536) addresses per network.

Class C uses three octets for the network portion of the address and provides over 2 million (2,097,152) networks but only 256 addresses per network (1 octet).

Octet 1

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Octet 2

Click each format for more information.

Binary

IP Address Formats IP addresses can be expressed in different formats; these are the two most common ways to express IP addresses.

Decimal Dot Notation

10.12.0.9 152.100.54.234 195.120.234.9  (4 sets of numbers from 0-255) separated by a dot.

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11000001 01101100 01111110 00001010 (32bits)

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loopback a reserved IP address, 127.0.0.1, that is assigned to the local host to test the communication on a local network card

Close 

Class A Network Addresses The first octet of a class A network will range from 1to 126. Remember address 127 is used for loopback. The default subnet mask for Class A networks is 255.0.0.0 or /8. The 32-bit IP address is divided as follows:The network address is the first 8 bits. The maximum value is 27 which equals 128. The left-most bit of the octet is always “0” (the high-order bit), and 127.0.0.0 – 127.255.255.255 are reserved for loopback and diagnostic functions. Therefore, the maximum number of networks is 126.The host address is the last 24 bits. The highest address is 224 which is equal to 16,777,216. Since you cannot use the 0 or 255 value as the host address, this leaves 16,777,214 possible hosts per network.Examples of Class A IP addresses:29.209.20.5 (subnet mask = 255.0.0.0)10.0.0.10 (subnet mask = 255.0.0.0)

default subnet mask a 32-bit number used to differentiate the network portion of the IP address from the host portion of the IP address

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Class B Network Addresses The first octet of a Class B network will range from 128 to 191. The default subnet mask for Class B networks is 255.255.0.0 or /16. The 32-bit IP address is divided as follows:The network address is the first 16 bits. The maximum number of networks is 16,384 (214) because the two left-most bits of the first octet are always “10” (the high-order bits).The host address is the last 16 bits. The highest address is 216 which is equal to 65,536. Since you cannot use the 0 or 255 value as the host address, this leaves 65,534 possible hosts per network.Examples of Class B IP addresses: 178.46.57.230 (subnet mask = 255.255.0.0)189.90.1.10 (subnet mask = 255.255.0.0)

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Class C Network Addresses The first octet of a Class C network will range from 192 to 223 and the default subnet mask is 255.255.255.0 or /24. The 32-bit IP address is divided as follows:The network address is the first 24 bits. Since the three left-most bits are always “110” (the high-order bits), this leaves 2,097,152 possible networks (221)The host address is the last 8 bits. The highest address is 28 which is equal to 256. Since you cannot use the 0 or 255 value as the host address, this leaves 254 possible hosts per network.Examples of Class C IP addresses:198.46.157.230 (subnet mask = 255.255.255.0)200.225.1.10 (subnet mask = 255.255.255.0)

CLASS C NETWORK ID

CLASS B HOST ID

Identifying Network and Host ID Click on each class to see the network and host ID portion of an IP address. Notice that there are only few Class A networks (Network ID), but many Host ID’s, whereas a Class C has a lot more networks and fewer hosts.

CLASS D NETWORK ID

CLASS A HOST ID

CLASS C HOST ID

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CLASS A NETWORK ID

CLASS B NETWORK ID

CLASS E NETWORK ID

129.0.x.x to 191.255.x.x with a default mask of 255.255.0.0

192.0.0.x to 223.255.255.x with a default mask of 255.255.255.0

IP Address Ranges

1.x.x.x to 126.x.x.x with a default mask of 255.0.0.0

Click on each network class above to view its host range and default subnet mask.

224.0.0.x to 239.255.255.x with a default mask of 255.255.255.0

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Blockchain Basics

Drag and drop each 32-bit IP address to the correct network class.

90.90.80.90

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150.128.123.78

122.100.90.10

209.101.128.90

Great Job!

11111111.00000000.00000000.00000000

255.255.0.0

255.0.0.0

Drag and drop each 32-bit subnet mask to the correct network class.

255.255.255.0

11111111.11111111.00000000.00000000

11111111.11111111.11111111.00000000

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Element with Audio HTML

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Decimal Value

No. of High-Order Bits

1 - 126

192 - 223

128 - 191

First Octet Rule The class of an IP address can be determined by looking at the first octet of the address. The left-most bits in the first octet are the high-order bits. IP addressing was classful—you recognized which class the address belonged to by looking at the most significant bits. These bits were fixed—0 for A, 10 for B, and 110 for C. That means that for class A, you could only change 7 bits, for B you could change 14 bits, and for C you could change 21 bits.

0

Address Class

110

Binary Value

10

1

First Octet

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