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Class B Subnetting
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1/19
This material was developed with funding from the
National Science Foundation under Grant # DUE 1601612
A default Class B subnet mask uses the first two octets to identify the network portion of a Class B IP address and the last two octets are the host portion of the address.
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Default Subnet Mask
Range of Class “B” Network Addresses 129.x.x.x to 191.x.x.x
Network Increment
First four subnets
150.50.0.0 to 150.50.0.63
150.50.0.64 to 150.50.0.127
150.50.1.128 to 150.50.1.191
150.50.1.192 to 150.50.1.255
……………………………...
………………………………
Last four subnets
150.50.254.0 to 150.50.254.63
150.50.254.64 to 150.50.254.127
150.50.255.128 to 150.50.255.191
150.50.255.192 to 150.50.255.255
Mask
255.255.224.0
Multiplier = 32
Network Increment
First four subnets
150.50.0.0 to 150.50.0.31
150.50.0.32 to 150.50.0.63
150.50.0.64 to 150.50.0.95
150.50.0.96 to 150.50.0.127
……………………………...
………………………………
Last four subnets
150.50.255.128 to 150.50.255.159
150.50.255.160 to 150.50.255.191
150.50.255.192 to 150.50.255.223
150.50.255.224 to 150.50.255.255
Mask
255.255.240.0
Multiplier = 16
Network Increment
150.50.0.0 to 150.50.31.255
150.50.32.0 to 150.50.63.255
150.50.64.0 to 150.50.95.255
150.50.96.0 to 150.50.127.255
150.50.128.0 to 150.50.159.255
150.50.160.0 to 150.50.191.255
150.50.192.0 to 150.50.223.255
150.50.224.0 to 150.50.255.255
Network Increment
150.50.0.0 to 150.50.15.255
150.50.16.0 to 150.50.31.255
150.50.32.0 to 150.50.47.255
150.50.48.0 to 150.50.63.255
150.50.64.0 to 150.50.79.255
150.50.80.0 to 150.50.95.255
150.50.96.0 to 150.50.111.255
150.50.112.0 to 150.50.127.255
150.50.128.0 to 150.50.143.255
150.50.144.0 to 150.50.159.255
150.50.160.0 to 150.50.175.255
150.50.176.0 to 150.50.191.255
150.50.192.0 to 150.50.207.255
150.50.208.0 to 150.50.223.255
150.50.224.0 to 150.50.239.255
150.50.240.0 to 150.50.255.255
Original Network Address
150.50.0.0
Mask
255.255.255.224
Multiplier = 32
Subnets = 2,048
Mask
255.255.255.240
Multiplier = 16
Subnets = 4,096
Network Increment
First four subnets
150.50.0.0 to 150.50.0.15
150.50.0.16 to 150.50.0.31
150.50.0.32 to 150.50.0.47
150.50.0.48 to 150.50.0.63
……………………………...
………………………………
Last four subnets
150.50.255.192 to 150.50.255.207
150.50.255.208 to 150.50.255.223
150.50.255.224 to 150.50.255.239
150.50.255.240 to 150.50.255.255
Mask
255.255.248.0
Multiplier = 8
Network Increment
First four subnets
150.50.0.0 to 150.50.0.7
150.50.0.8 to 150.50.0.15
150.50.0.16 to 150.50.1.23
150.50.0.24 to 150.50.1.31
……………………………...
………………………………
Last four subnets
150.50.255.224 to 150.50.255.231
150.50.255.232 to 150.50.255.239
150.50.255.240 to 150.50.255.247
150.50.255.248 to 150.50.255.255
Network Increment
First four subnets
150.50.0.0 to 150.50.7.255
150.50.8.0 to 150.50.15.255
150.50.16.0 to 150.50.23.255
150.50.24.0 to 150.50.31.255
……………………………...
………………………………
Last four subnets
150.50.224.0 to 150.50.231.255
150.50.232.0 to 150.50.239.255
150.50.240.0 to 150.50.247.255
150.50.248.0 to 150.50.255.255
Drag the slider to view the number of bits borrowed.
Mask
255.255.255.248
Multiplier = 8
Subnets = 8,192
Mask
255.255.255.252
Multiplier = 4
Subnets = 16,384
Mask
255.255.252.0
Multiplier = 4
Network Increment
First four subnets
150.50.0.0 to 150.50.3.255
150.50.4.0 to 150.50.7.255
150.50.8.0 to 150.50.11.255
150.50.12.0 to 150.50.15.255
……………………………...
………………………………
Last four subnets
150.50.240.0 to 150.50.243.255
150.50.244.0 to 150.50.247.255
150.50.248.0 to 150.50.251.255
150.50.252.0 to 150.50.255.255
Network Increment
First four subnets
150.50.0.0 to 150.50.0.3
150.50.0.4 to 150.50.0.7
150.50.0.8 to 150.50.0.11
150.50.0.12 to 150.50.0.15
……………………………...
………………………………
Last four subnets
150.50.255.240 to 150.50.255.243
150.50.255.244 to 150.50.255.247
150.50.255.248 to 150.50.255.251
150.50.255.252to 150.50.255.255
Network Increment
First four subnets
150.50.0.0 to 150.50.0.1
150.50.0.2 to 150.50.0.3
150.50.0.4 to 150.50.0.5
150.50.0.6 to 150.50.0.7
……………………………...
………………………………
Last four subnets
Not Allowed
150.50.255.248 to 150.50.255.249
150.50.255.250 to 150.50.255.251
150.50.255.252 to 150.50.255.253
150.50.255.254 to 150.50.255.255
Network Increment
First four subnets
150.50.0.0 to 150.50.31.255
150.50.2.0 to 150.50.63.255
150.50.4.0 to 150.50.95.255
150.50.6.0 to 150.50.127.255
……………………………...
………………………………
Last four subnets
150.50.248.0 to 150.50.249.255
150.50.250.0 to 150.50.251.255
150.50.252.0 to 150.50.253.255
150.50.254.0 to 150.50.255.255
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Borrowing Bits
Mask
255.255.255.0
Multiplier = 1
Mask
255.255.254.0
Multiplier = 2
Mask
255.255.255.254
Multiplier = 2
Subnets = 32,768
Mask
255.255.255.255
Multiplier = 1
No Hosts
Network Increment
First four subnets
150.50.0.0 to 150.50.0.255
150.50.1.0 to 150.50.1.255
150.50.2.0 to 150.50.2.255
150.50.3.0 to 150.50.3.255
……………………………...
………………………………
Last four subnets
150.50.252.0 to 150.50.252.255
150.50.253.0 to 150.50.253.255
150.50.254.0 to 150.50.254.255
150.50.255.0 to 150.50.255.255
Network Increment
First four subnets
150.50.0.1 to 150.50.0.1
150.50.0.2 to 150.50.0.2
150.50.0.3 to 150.50.0.3
150.50.0.4 to 150.50.0.4
……………………………...
………………………………
Last four subnets
Not Allowed
150.50.255.252 to 150.50.255.252
150.50.255.253 to 150.50.255.253
150.50.255.254 to 150.50.255.254
150.50.255.255 to 150.50.255.255
Mask
255.255.128.0
Multiplier = 128
Network Increment
150.50.0.0 to 150.50.127.255
150.50.128.0 to 150.50.255.255
Mask
255.255.255.128
Multiplier = 128
Subnets = 512
Network Increment
First four subnets
150.50.0.0 to 150.50.0.127
150.50.0.128 to 150.50.0.255
150.50.1.0 to 150.50.1.127
150.50.1.128 to 150.50.1.255
……………………………...
………………………………
Last four subnets
150.50.224.0 to 150.50.231.255
150.50.254.128 to 150.50.254.0
150.50.255.0 to 150.50.247.127
150.50.255.128 to 150.50.255.255
Mask
255.255.192.0
Multiplier = 64
Network Increment
150.50.0.0 to 150.50.63.255
150.50.64.0 to 150.50.127.255
150.50.128.0 to 150.50.191.255
150.50.192.0 to 150.50.255.255
Mask
255.255.255.192
Multiplier = 64
Subnets = 1,024
The number of bits borrowed determines the new subnet mask. For example, borrowing 7 bits from a Class B network results in the following:
Default Class B subnet mask = 255.255.0.0
New subnet mask with
7 borrowed bits = 255.255.254.0
255.255.254 represented as a bitwise mask = /23
Note: The bitwise mask value equals the default subnet mask bits (16) plus the borrowed bits (7)
You can write 150.50.0.0
255.255.254.0 as 150.50.0.0 /23
The usable hosts per subnet equals 2n where n equals the number of zeros, minus the two unusable hosts.
Use the slider below to see the effect of borrowing bits from the subnet mask. Slide to the right to increase the number of bits borrowed, slide it to the left to decrease the bits borrowed.
Usable Hosts per Subnet
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Bits Borrowed Slider
Element
with Audio
HTML
Test Your Knowledge 1 of 6
Borrowed Bit Count =
Mask = . . .
Number of Subnets =
Usable Hosts per Subnet =
Correct!
Try Again!
6/19
Borrowed Bit Count =
Mask = . . .
Number of Subnets =
Usable Hosts per Subnet =
Test Your Knowledge 2 of 6
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Borrowed Bit Count =
Mask = . . .
Number of Subnets =
Usable Hosts per Subnet =
Test Your Knowledge 3 of 6
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Test Your Knowledge 4 of 6
Borrowed Bit Count =
Mask = . . .
Number of Subnets =
Usable Hosts per Subnet =
Borrowed Bit Count =
Mask = . . .
Number of Subnets =
Usable Hosts per Subnet =
Test Your Knowledge 5 of 6
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Test Your Knowledge 6 of 6
Borrowed Bit Count =
Mask = . . .
Number of Subnets =
Usable Hosts per Subnet =
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4th Subnet
Network:
Broadcast:
Host Addresses:
130.130.3.1 – 130.130.3.254
4th to last Subnet
Network:
130.130.252.0
Broadcast:
Host Addresses:
–
2nd to last Subnet
Network:
Broadcast: 130.130.254.255
Host Addresses:
–
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Sample Subnet Class B
Network Address: 130.130.0.0
Bits Borrowed:
Number of Subnets:
256
Usable Hosts per Subnet: 254
New Subnet Mask:
255.255.
3rd to last Subnet
Network:
130.130.253.0
Broadcast:
Host Addresses:
–
Last Subnet
Network:
Broadcast: 130.130.255.255
Host Addresses:
–
Go to http://www.t1shopper.com/tools/calculate/ip-subnet/ to create the full table.
?? Subnet
Network:
130.130.129.0
Broadcast:
Host Addresses:
–
Subnet Challenge 1
1st Subnet
Network:
130.130.0.0
Broadcast:
130.130.0.255
Host Addresses:
–
3rd Subnet
Network:
Broadcast:
Host Addresses:
130.130.2.1 – 130.130.2.254
2nd Subnet
Network:
130.130.1.0
Broadcast:
130.130.1.255
Host Addresses:
–
2nd Subnet
Network:
Broadcast:
175.100.0.255
Host Addresses:
175.100.0.129 –
175.100.0.254
Last Subnet
Network:
Broadcast:
175.100.255.255
Host Addresses:
–
4th Subnet
Network:
175.100.1.128
Broadcast:
Host Addresses:
175.100.1.129 –
175.100.1.254
Sample Subnet Class B
Network Address:
175.100.0.0
Bits Borrowed: 9
Number of Subnets: 512
Usable Hosts per Subnet: 126
New Subnet Mask:
255.255.255.128
3rd to last Subnet
Network:
175.100.254.128
Broadcast:
175.100.254.255
Host Addresses:
–
13/19
?? Subnet
Network:
175.100.148.0
Broadcast:
Host Addresses:
–
Subnet Challenge 2
2nd to last Subnet
Network:
175.100.255.0
Broadcast:
Host Addresses:
–
1st Subnet
Network:
Broadcast:
175.100.0.127
Host Addresses:
175.100.0.1 –
175.100.0.126
4th to last Subnet
Network:
175.100.254.0
Broadcast:
175.100.254.127
Host Addresses:
–
3rd Subnet
Network:
175.100.1.0
Broadcast:
Host Addresses:
175.100.1.1 – 175.100.1.126
4th Subnet
Network:
Broadcast: 150.150.127.255
Host Addresses:
150.150.96.1 – 150.150.127.254
4th to last Subnet
Network:
150.150.128.0
Broadcast:
Host Addresses: 150.150.128.1 – 150.150.159.254
3rd to last Subnet
Network:
150.150.160.0
Broadcast:
Host Addresses: 150.150.160.1 – 150.150.191.254
2nd to last Subnet
Network:
150.150.192.0
Broadcast:
Host Addresses:–
Last Subnet
Network:
Broadcast: 150.150.255.255
Host Addresses:–
--- Subnet
Network: 15.0.64.0
Broadcast:
Host Addresses:
–
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Sample Subnet Class B
Network Address: 150.150.0.0
Bits Borrowed: 3
Number of Subnets:8
Usable Hosts per Subnet: 8190
New Subnet Mask:
Subnet Challenge 3
1st Subnet
Network: 150.150.0.0
Broadcast: 150.150.31.255
Host Addresses:
–
2nd Subnet
Network:
150.150.32.0
Broadcast: 150.150.63.255
Host Addresses:
–
3rd Subnet
Network:
Broadcast: 150.150.95.255
Host Addresses:
150.150.64.1 – 150.150.95.254
Last Subnet
Network:
150.25.252.0
Broadcast:
Host Addresses:
4th to last Subnet
Network:
Broadcast: 150.25.243.255
Host Addresses:
–
2nd to last Subnet
Network:
150.25.248.0
Broadcast:
Host Addresses:
4th Subnet
Network:
150.25.12.0
Broadcast:
Host Addresses:
150.25.12.1 -
150.25.15.254
?? Subnet
Network:
150.25.128.0
Broadcast:
Host Addresses:
–
15/19
3rd Subnet
Network:
150.25.8.0
Broadcast:
Host Addresses:
150.25.8.1 -
150.25.11.254
3rd to last Subnet
Network:
Broadcast: 150.25.247.255
Host Addresses:
–
Sample Subnet Class B
Network Address: 150.25.0.0
Bits Borrowed:
Number of Subnets: 64
Usable Hosts per Subnet:
New Subnet Mask:
255.255.252.0
2nd Subnet
Network:
Broadcast:
150.25.7.255
Host Addresses:
150.25.4.1 -
150.25.7.254
1st Subnet
Network:
Broadcast:
150.25.3.255
Host Addresses:
150.25.0.1 -
150.25.3.254
Subnet Challenge 4
Subnet Challenge 5
2nd Subnet
Network:
Broadcast:
150.25.0.31
Host Addresses:
150.25.0.17 -
150.25.0.30
Last Subnet
Network:
Broadcast: 150.25.255.255
Host Addresses:
?? Subnet
Network:
150.25.243.64
Broadcast:
Host Addresses:
–
4th to last Subnet
Network:
150.25.255.192
Broadcast:
Host Addresses:
–
3rd Subnet
Network:
150.25.0.32
Broadcast:
Host Addresses:
150.25.0.33 -
150.25.0.46
3rd to last Subnet
Network:
150.25.255.208
Broadcast:
Host Addresses:
–
16/19
2nd to last Subnet
Network:
Broadcast: 150.25.255.239
Host Addresses:
4th Subnet
Network:
150.25.0.48
Broadcast:
Host Addresses:
150.25.0.49 -
150.25.0.62
1st Subnet
Network:
Broadcast:
150.25.0.15
Host Addresses:
150.25.0.1 -
150.25.0.14
Sample Subnet Class B
Network Address: 150.25.0.0
Bits Borrowed: 12
Number of Subnets: 4096
Usable Hosts per Subnet:
New Subnet Mask: 255.255.
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Sample Subnet Class B
Network Address: 190.200.0.0
Bits Borrowed:
Number of Subnets:
Usable Hosts per Subnet:
New Subnet Mask:
255.255.
Subnet Challenge 6
4th to last Subnet
Network:
Broadcast:
190.200.231.255
Host Addresses:–
3rd to last Subnet
Network:
Broadcast:
190.200.239.255
Host Addresses:–
2nd to last Subnet
Network:
190.200.240.0
Broadcast:
Host Addresses:
–
2nd Subnet
Network:
190.200.8.0
Broadcast:
190.200.15.255
Host Addresses:
–
?? Subnet
Network:
190.200.144.0
Broadcast:
Host Addresses:
–
3rd Subnet
Network:
Broadcast:
Host Addresses:
190.200.16.1 – 190.200.23.254
1st Subnet
Network: 190.200.0.0
Broadcast:
190.200.7.255
Host Addresses:
–
4th Subnet
Network:
Broadcast:
Host Addresses:
190.200.24.1 – 190.200.31.254
Last Subnet
Network:
190.200.248.0
Broadcast:
Host Addresses:
–
Sample Subnet Class B
Network Address: 175.10.0.0
Bits Borrowed:
Number of Subnets:
Usable Hosts per Subnet: 62
New Subnet Mask: 255.255.
3rd to last Subnet
Network:
175.10.255.64
Broadcast:
Host Addresses:
–
Subnet Challenge 7
3rd to last Subnet
Network:
Broadcast:
175.10.255.191
Host Addresses:
–
3rd Subnet
Network:
175.10.0.128
Broadcast:
175.10.0.191
Host Addresses:
–
Last Subnet
Network:
Broadcast:
175.10.255.255
Host Addresses:–
4th Subnet
Network:
175.10.0.192
Broadcast:
175.10.0.255
Host Addresses:
–
2nd Subnet
Network:
Broadcast:
Host Addresses: 175.10.0.65 – 175.10.0.126
4th to last Subnet
Network:
175.10.255.0
Broadcast:
Host Addresses:–
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?? Subnet
Network:
175.10.192.128
Broadcast:
Host Addresses:
–
1st Subnet
Network:
Broadcast:
Host Addresses: 175.10.0.1 – 175.10.0.62
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Sample Subnet Class B
Network Address: 140.123.0.0
Bits Borrowed:
Number of Subnets:
8192
Number of Hosts/
per Subnet: 6
New Subnet Mask:
255.255.
Subnet Challenge 8
1st Subnet
Network:
140.123.0.0
Broadcast:
140.123.0.7
Host Addresses:
–
2nd to last Subnet
Network:
Broadcast:
140.123.255.247
Host Addresses:
–
3rd to last Subnet
Network:
140.123.255.232
Broadcast:
Host Addresses:–
3rd Subnet
Network:
Broadcast:
Host Addresses:
140.123.0.17 – 140.123.0.22
?? Subnet
Network:
140.123.248.184
Broadcast:
Host Addresses:
–
Last Subnet
Network:
Broadcast:
140.123.255.255
Host Addresses: –
2nd Subnet
Network:
140.123.0.8
Broadcast:
140.123.0.15
Host Addresses:
–
4th to last Subnet
Network:
140.123.255.224
Broadcast:
Host Addresses:–
4th Subnet
Network:
Broadcast:
Host Addresses:
140.123.0.25 – 140.123.0.30