How to Calculate Subnets
Subnets and Hosts Borrow 2 bits
S S H H H H H H # of subnets = 22 = 4 Subnet mask = 2 bits = 128 + 64 = 192 Range of hosts = 26 = 64 TT Range Useable Range Network ID 0 – 63 64 – 127 65 - 126 128 – 191 129 - 190 Broadcast 192 – 255 Address

Borrow 3 bits
S S S H H H H H # of subnets = 23 = 8 Subnet mask = 3 bits = 128 + 64 + 32 = 224 Range of hosts = 25 = 32 Range 0 – 31 32 – 63 64 – 95 96 – 127 128 – 159 160 – 191 192 – 223 224 – 255 Useable Range 33 - 62 65 - 94 97 -126 129 -158 161 -190 193 -222

Network ID

Broadcast Address

©1999 Dan Foss

How to Calculate Subnets
Decimal/Binary Subnet Ranges

Borrow 2 bits
S S H H H H H H # of subnets = 22 = 4 = 00000100 Subnet mask = 2 bits = 128 + 64 = 192 = 11000000 Range of hosts = 26 = 64 = 01000000 [Range ……………………………] [Useable Range …………………...] Network ID 0 – 63 00 000000 – 00 111111 64 – 127 01 000000 – 01 111111 65 - 126 01 000001 – 01 111110 128 – 191 10 000000 – 10 111111 129 – 190 10 000001 – 10 111110 Broadcast 192 – 255 11 000000 – 11 111111 Address

Borrow 3 bits
S S S H H H H H # of subnets = 23 = 8 Subnet mask = 3 bits = 128 + 64 + 32 = 224 = 11100000 Range of hosts = 25 = 32 = 00100000 [Range ……………………………] Network ID 0 – 31 000 00000 – 000 11111 32 – 63 001 00000 – 001 11111 64 – 95 010 00000 – 010 11111 96 – 127 011 00000 – 011 11111 128 – 159 100 00000 – 100 11111 160 – 191 101 00000 – 101 11111 192 – 223 110 00000 – 110 11111 Broadcast 224 – 255 111 00000 – 111 11111 Address [Useable Range …………………...] 33 – 62 65 – 94 97 – 126 129 – 158 161 – 190 193 – 222 001 00001 – 001 11110 010 00001 – 010 11110 011 00001 – 011 11110 100 00001 – 100 11110 101 00001 – 101 11110 110 00001 – 110 11110

©1999 Dan Foss

How to Calculate Subnets
Binary Subnet Ranges

Borrow 2 bits
S S H H H H H H # of subnets = 22 = 4 = 00000100 Subnet mask = 2 bits = 128 + 64 = 192 = 11000000 Range of hosts = 26 = 64 = 01000000 [Net] [ID] 0 64 128 192 [Useable] [Broadcast] [Range] 63 65 – 126 127 129 – 190 191 255 [Network] [Useable Range …….] [ID] 00 000000 01 000000 01 000001 – 01 111110 10 000000 10 000001 – 10 111110 11 000000 [Broadcast] 00 111111 01 111111 10 111111 11 111111

Borrow 3 bits
S S S H H H H H # of subnets = 23 = 8 Subnet mask = 3 bits = 128 + 64 + 32 = 224 = 11100000 Range of hosts = 25 = 32 = 00100000 [Net] [ID] 0 32 64 96 128 160 192 224 [Useable] [Broadcast] [Range] 31 33 – 62 63 65 – 94 95 97 – 126 127 129 – 158 159 161 – 190 191 193 – 222 223 255 [Network] [ID] 000 00000 001 00000 010 00000 011 00000 100 00000 101 00000 110 00000 111 00000 [Useable Range …….] [Broadcast] 000 11111 001 11111 010 11111 011 11111 100 11111 101 11111 110 11111 111 11111

001 00001 – 001 11110 010 00001 – 010 11110 011 00001 – 011 11110 100 00001 – 100 11110 101 00001 – 101 11110 110 00001 – 110 11110

©1999 Dan Foss

How to subnet in your head.
Subnet Patterns

Step One

left to right

Count

1

2

3

4

5

6
Right to left

7

8

Step two
Document Binary Place Value

2^7 2^6 2^5 2^4 2^3 2^2 2^1 2^0 128 64 32 16 8 4
"+4"

2
"+2"

1
"+1"

Step Three
ADD Equals

left to right

128

"+64" "+32" "+16" "+8"

128 192 224 240 248 252 254 255
Close your eyes and Repeat steps 1-3

Step Four
Bits Borrowed Range of Hosts Subnet Mask
Written by Daniel Foss http://ohiocatc.treca.org

1 128

2 64

3 32

4 16

5 8

6 4

7 2

8 1

128 192 224 240 248 252 254 255
Subnet Patterns Page 1

How to subnet in your head.
1 Bit Borrowed Range of Hosts Subnet Mask 2 Bits Borrowed Range of Hosts Subnet Mask 3 Bits Borrowed Range of Hosts Subnet Mask 4 Bits Borrowed Range of Hosts Subnet Mask 5 Bits Borrowed Range of Hosts Subnet Mask 6 Bits Borrowed Range of Hosts Subnet Mask 7 Bits Borrowed Range of Hosts Subnet Mask 8 Bits Borrowed Range of Hosts Subnet Mask
Written By Daniel Foss http://ohiocatc.treca.org

1 128

2 64

3 32

4 16

5 8

6 4

7 2

8 1

128 192 224 240 248 252 254 255 1 128 2 64 3 32 4 16 5 8 6 4 7 2 8 1

128 192 224 240 248 252 254 255 1 128 2 64 3 32 4 16 5 8 6 4 7 2 8 1

128 192 224 240 248 252 254 255 1 128 2 64 3 32 4 16 5 8 6 4 7 2 8 1

128 192 224 240 248 252 254 255 1 128 2 64 3 32 4 16 5 8 6 4 7 2 8 1

128 192 224 240 248 252 254 255 1 128 2 64 3 32 4 16 5 8 6 4 7 2 8 1

128 192 224 240 248 252 254 255 1 128 2 64 3 32 4 16 5 8 6 4 7 2 8 1

128 192 224 240 248 252 254 255 1 128 2 64 3 32 4 16 5 8 6 4 7 2 8 1

128 192 224 240 248 252 254 255
Subnet Masks 4/4/01