Default Class Network Subnet Mask

Default Class Network/Host Bits

Subnet Mask
•Class A = 255.0.0.0
•Class B = 255.255.0.0
•Class C = 255.255.255.0

Class A

Network	Host	Host	Host
8 bits	8 bits	8 bits	8 bits

Class A default Subnet Mask = 255.0.0.0

Class B

Network	Network	Host	Host
8 bits	8 bits	8 bits	8 bits

Class B default Subnet Mask = 255.255.0.0

Class C

Network	Network	Network	Host
8 bits	8 bits	8 bits	8 bits

Class C default Subnet Mask = 255.255.255.0
Class D: Multicast
Class E: Research

Class A

Class A		Network	Host
Octet		1	2	3	4
		255(1 Byte)	255(1 Byte)	255(1 Byte)	255(1 Byte)
	8 Bits		24 Bits
	32 Bits

Class B

Class B	Network		Host
Octet	1	2	3		4
	255(1 Byte)	255(1 Byte)	255(1 Byte)		255(1 Byte)
	16 Bits			16 Bits
	32 Bits

Class C

Class C	Network			Host
Octet	1	2	3	4
	255(1 Byte)	255(1 Byte)	255(1 Byte)	255(1 Byte)
	24 Bits			8 Bits
	32 Bits

Octet = Always eight bits.

Class A

Class Bit 0	Network Bits 7-Bit	Host Bits 24-Bit	Range of IP addresses
	0NNNNNNN			1.0.0.0 -> 126.255.255.255(1-126)
	00000000 = 0 to 01111111 = 127

Class B

Class Bit 10	Network Bits 14-Bit	Host Bits 16-Bit	Range of IP addresses
	10NNNNNN		128.0.0.0 -> 191.255.255.255(128-191)
	10000000 =128 = 0 to 101111111 = 191

Class C

Class Bit 110	Network Bits 21-Bit	Host Bits 8-Bit	Range of IP addresses
	110NNNNN		192.0.0.0 -> 223.255.255.255(192-223)
	11000000 =192 = 0 to 110111111 = 223

"N" represents the network portion of the address

Following figure describes the above things:

Class Bit 1110	Multicast Address	224 to 239
Class Bit 1111	Reserved for future use	240 to 255

Class A

Class B

Class C

Decimal to Binary Conversion

Decimal	Binary	Total Bits
0	00000000	0
128	10000000	1
192	11000000	2
224	11100000	3
240	11110000	4
248	11111000	5
252	11111100	6
254	11111110	7
255	11111111	8

Memorize

Subnet mask	First Subnet	Valid Subnets
256-192	64	0, 64, 128, 192
256-224	32	0, 32, 64, 96, 128,160,192, 224
256-240	16	0, 16, 32, 48,…, 224,240
256-248	8	0, 8, 16, 24,…,240, 248
256-252	4	0, 4, 8, 12,…,248, 252