The document discusses subnetting networks. It explains how to convert between binary and decimal, classes of IP addresses, and subnet masks. It provides a 7 step method for subnetting a class C network: 1) determine number of subnets, 2) borrow bits from host field, 3) determine borrowed bits, 4) set high order bits, 5) create subnet mask, 6) determine IP ranges, 7) assign IP addresses within ranges. An example shows applying these steps to create 8 subnets within the 200.10.20.0/24 network.

1. Subnetting

2. Subnetting
 Binary to Decimal Conversion
 Decimal to Binary Conversion
 Classes of IP Addresses
 Subnet Masks
 7 step method to practical subnetting
– Class C
– Class B

3. Binary to Decimal Conversion

4. Binary to Decimal Conversion
 Place Card Method
128 64 32 16 8 4 2 1
27 26 25 24 23 22 21 20

5. Binary to Decimal Conversion
Place Card Method for 1100 0000
128 64 32 16 8 4 2 1
27 26 25 24 23 22 21 20
1 1 0 0 0 0 0 0
192 = 128 + 64 + 0 + 0 + 0 + 0 + 0 + 0

6. Binary to Decimal Conversion
Place Card Method for 1111 0000
128 64 32 16 8 4 2 1
27 26 25 24 23 22 21 20
1 1 1 1 0 0 0 0
240 = 128 + 64 + 32 + 16 + 0 + 0 + 0 + 0

7. Decimal to Binary Conversion
Place Card Method for 129
128 64 32 16 8 4 2 1
27 26 25 24 23 22 21 20
129 = 128 + 0 + 0 + 0 + 0 + 0 + 0 + 1

8. Decimal to Binary Conversion
Place Card Method for 129
128 64 32 16 8 4 2 1
27 26 25 24 23 22 21 20
1 0 0 0 0 0 0 1
129 = 128 + 0 + 0 + 0 + 0 + 0 + 0 + 1

9. Decimal to Binary Conversion
Place Card Method for 255
128 64 32 16 8 4 2 1
27 26 25 24 23 22 21 20
1 1 1 1 1 1 1 1
129 = 128 + 64 + 32 +16 + 8 + 4 + 2 + 1

10. IP Address
 Example of an IP address is 148.8.20.10 (4 octets)
 Each octet is an 8 bit binary number
 Therefore, an IP address is 32 bits.
148 8 20 10
10010100 00001000 00010100 00001010

11. IP Address
 Each IP address is
broken up into a
Network Address and a
Host address
148 8 20 10
10010100 00001000 00010100 00001010

12. IP Address Classes
Class Network Address Host Address
A 1st Octet Last three Octets
B 1st Two Octets Last Two Octets
C 1st Three Octets Last Octet

13. IP Address Classes
A . B . C . D
Class 1st Octet Number of
Networks
Number of
Hosts
A 1-126 126 224 =
16,777,216
B 128-191 16,384 216 = 65,536
C 192-223 2,097,152 28 = 256

14. Subnet Masks
 Tells the device which bits are host
address and network address.
Class Subnet
Mask
Binary
A 255.0.0.0 11111111.00000000.00000000.00000000
B 255.255.0.0 11111111. 11111111. 00000000.00000000
C 255.255.255.0 11111111. 11111111. 1111111.00000000

15. Subnetting
 What is subnetting
– Process of subdividing a single class of
network into multiple subnetworks.
– A subnetted network address contains
a network address, subnet address and
host address.

16. Subnetting
Class Subnet
Mask
Binary
A 255.0.0.0 11111111.00000000.00000000.00000000
B 255.255.0.0 11111111. 11111111. 00000000.00000000
C 255.255.255.0 11111111. 11111111. 1111111.00000000

17. Subnetting
 Why subnet
– Reduce Collision Domain
– Makes it easier to manage your network
(lower TCO)
– Makes you network more secure

18. Class C Subnet Example – Assigned
200.10.20.0
Router
Router Router
Tower box

19. 1.) Determine # of subnets
Router
Router Router
Tower box

20. 2.) Determine # of bits you can
borrow
200
1100 1000
10
0000 1010
20
0001 0100
0
hhhh hhhh
148
1001 0100
8
0000 1000
0
hhhh hhhh
0
hhhh hhhh
11
0000 1011
0
hhhh hhhh
0
hhhh hhhh
0
hhhh hhhh
For a class C address we have 8 host address bits to work with.
You need to borrow at least 2 bits for the subnet address and you must
leave at least 2 host bits for the host address. Therefore, we can borrow 2
to 6 bits on a class C address.

21. 3.) Determine # of bits you need to
borrow
 2^n -2 = number of
useable subnets
Borrowed Bits Useable
Subnets
Useable Host
Addresses

22. 4.) High Order Bits
 Set the high order bits (determined above)
to 1.

23. 5.) Subnet Mask
 Combine the
Default Subnet
Mask with value
determined in step
#4.

24. 6.) Determine the IP range of each
subnet.
1 1 1 0 0 0 0 0
Sub Sub Sub Host Host Host Host Host
5 host address bits or 2^5 hosts per subnet

25. 7.) Determine Range of IP Addresses
in each subnet
 We’ve determined that there are 32 hosts per
subnet.
200.10.20.0 200.10.20.
200.10.20. 200.10.20.
200.10.20. 200.10.20.
200.10.20. 200.10.20.
200.10.20. 200.10.20.
200.10.20. 200.10.20.
200.10.20. 200.10.20.
200.10.20. 200.10.20.

26. 7.) Determine Range of IP Addresses
in each subnet
 We’ve determined that there are 32 hosts per
subnet.
200.10.20.0 200.10.20.31
200.10.20.32 200.10.20.63
200.10.20.64 200.10.20.95
200.10.20.96 200.10.20.127
200.10.20.128 200.10.20.159
200.10.20.160 200.10.20.191
200.10.20.192 200.10.20.223
200.10.20.224 200.10.20.255

27. Useable IP addresses
 We discard the 1st and last subnet
 Discard the 1st and last IP address in each
subnet.
 Our 1st useable IP address in the first
useable subnet that can be assigned to a
node on our network would be:
– 200.10.20.33