Subnetting of IP Address

Network Number for Each Network

164.124.1.2

164.124.100.3

164.124.180.5

164.124.0.1

130.1.50.0

130.1.100.10 203.252.3.1

203.252.3.2 203.252.3.3

203.252.2.1

203.252.2.2

netA

netB

netC netD

A

B

• Unique Network Number for each Network

• Different host addresses in same Network

• 4 Network Numbers for 8 systems

s0e0 e1

Routing Table of Router B

IP Routing TableDestination Network Number Interface

130.1.0.0 e0164.124.0.0 s0203.252.2.0 s0203.252.3.0 e1

Sub-Network Number for Each Network

• Only 1 Class B Network Number for 4 networks– more effective

• We should apply subnetmask in these cases

164.124.1.2

164.124.1.3

164.124.1.4

164.124.1.1

164.124.3.2

164.124.3.1 164.124.4.1

164.124.4.2 164.124.4.3

164.124.2.1

164.124.2.2

netA

netB

netC netD

A

B

Routing Table of Router B

IP Routing TableDestination Network Number Interface

164.124.1.0 s0164.124.2.0 s0164.124.3.0 e0164.124.4.0 e1

Benefit of Subnetting• Address utilization if more Efficient

• Minimized the side effect of Broadcast message– broadcating storm exhausts the bandwithd of net

work– minimize broadcasting storm

....

....

....

....

Subnet MaskIPNetworkAddress

DefaultSubnetMask

8-bitSubnetMask

164 124 0 0

255 255 0 0

255 255 255 0

• Use host bits, starting at the high order bit position

• 1bit for network number, 0 bit for host address

Subnet Mask Bits

128 64 32 16 8 4 2 1

1 0 0 0 0 0 0 0

1 1 0 0 0 0 0 0

1 1 1 0 0 0 0 0

1 1 1 1 0 0 0 0

1 1 1 1 1 0 0 0

1 1 1 1 1 1 0 0

1 1 1 1 1 1 1 0

1 1 1 1 1 1 1 1

=

=

=

=

=

=

=

=

128

192

224

240

248

252

254

255

Subnet Mask without Subnets

• The router performs a logical AND operation to obtain the destination network number

• Subnets not in use -- the default

10000011 01101100 00000010 00000011

11111111 11111111 00000000 00000000

10000011 01101100 00000000 00000000

131 108 0 0

131.108.2.3

255.255.0.0

Network Hostsubnet

Subnet Mask with Subnets

• Network Number extended by 8 bits

10000011 01101100 00000010 00000011

11111111 11111111 11111111 00000000

10000011 01101100 00000010 00000000

131 108 2 0

131.108.2.3

255.255.255.0

Network Host

Class B Subnettingno. bits subnet mask no. subnets no. hosts

1 255.255.128.0 2 (0) 32762 2 255.255.192.0 4 (2) 16382

3 255.255.224.0 8 (6) 8190 4 255.255.240.0 16 (14) 4094

5 255.255.248.0 32 (30) 2046 6 255.255.252.0 64 (62) 1022 7 255.255.254.0 128 (126) 510 8 255.255.255.0 256 (254) 254 9 255.255.255.128 512 (510) 126 10 255.255.255.192 1024 (1022) 62

11 255.255.255.224 2048 (2046) 3012 255.255.255.240 4096 (4094) 14 13 255.255.255.248 8192 (8190) 614 255.255.255.252 16384(16382) 2

Class C Subnetting

no. bits subnet mask no. subnets no. hosts 1 255.255.255.128 2 (0) 126 2 255.255.255.192 4 (2) 62

3 255.255.255.224 8 (6) 30 4 255.255.255.240 16(14) 14 5 255.255.255.248 32(30) 6 6 255.255.255.252 64(62) 2

Subnet & Host range

• 203.252.14.0/2711001011.11111100.00001110.0000000011111111.11111111.11111111.11100000 203 . 252 . 14 .00000000 (0) 203 . 252 . 14 .00100000 (32) 203 . 252 . 14 .01000000 (64) 203 . 252 . 14 .01100000 (96) 203 . 252 . 14 .10000000 (128) 203 . 252 . 14 .10100000 (160) 203 . 252 . 14 .11000000 (192) 203 . 252 . 14 .11100000 (224)

Subnet & Host range (cont.)

• 203.252.14.32/27 203 . 252 . 14 .00100000 (32) 203 . 252 . 14 .00100001 (33) 203 . 252 . 14 .00100010 (34) 203 . 252 . 14 .00100011 (35) 203 . 252 . 14 .00100100 (36) 203 . 252 . 14 .00100101 (37) . . . . . . . . . . . . . . . . . . . . . . . . . . 203 . 252 . 14 .00111100 (60) 203 . 252 . 14 .00111101 (61) 203 . 252 . 14 .00111110 (62) 203 . 252 . 14 .00111111 (63)

Subnetting Tip0 0

128 128

64192

0

128

64192

32

96160

224

0

128

64192

32

96160

224 16

48

80

112144

176

208

240

1 Bit : 2 subnetsrange1: 0~127range2: 128 ~ 255

2 Bits: 4 subnets

3 Bits: 8 subnets

4 Bits: 16 subnets

Exercise

address subnet mask class subnet broadcast

201.222.10.60 255.255.255.248

15.16.193.6 255.255.248.0

128.16.32.13 255.255.255.252

153.50.6.27 255.255.255.128

Subnet Case 1

• 20 subnets

• 5 hosts per subnet

• class C address : 201.222.5.0

Subnet Case 1 (cont.)

• IP Host Address: 201.222.5.121

• Subnet Mask: 255.255.255.248

11001001 11011110 00000101 0111111111111 11111111 11111111 11111

201.222.5.121255.255.255.248

001000

01111 000201 222 5 120

11001001 11011110 00000101

• subnet addres: 201.222.5.120• host address: 201.222.5.121 ~ 201.222.5.126• broadcast address: 210.222.5.127

Network subnet host