Subnetting Subnetting l l l Binary to Decimal

Subnetting

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

Binary to Decimal Conversion

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

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 0 192 = 128 + 64 + 0 + 0 + 0

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 0 0 240 = 128 + 64 + 32 + 16 + 0 + 0

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

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 1 129 = 128 + 0 + 0 + 0 + 1

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 1 129 = 128 + 64 + 32 +16 + 8 + 4 + 2 + 1

IP Address l l l 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 10010100 8 00001000 20 00010100 10 00001010

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

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

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

Subnet Masks l Tells the device which bits are host address and network address. Class Subnet Mask Binary A 255. 0. 0. 0 1111. 00000000 B 255. 0. 0 11111111. 0000 C 255. 0 11111111. 0000

Subnetting l 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.

Subnetting Class Subnet Mask Binary A 255. 0. 0. 0 1111. 00000000 B 255. 0. 0 11111111. 0000 C 255. 0 11111111. 0000

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

Class C Subnet Example – Assigned 200. 10. 20. 0

1. ) Determine # of subnets

2. ) Determine # of bits you can borrow 200 1100 1000 148 1001 0100 10 0000 1010 8 0000 1000 20 0001 0100 0 hhhh 0 hhhh 11 0000 1011 0 hhhh 0 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.

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

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

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

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

7. ) Determine Range of IP Addresses in each subnet l We’ve determined that there are 32 hosts per subnet. 200. 10. 20. 0 200. 10. 20.

7. ) Determine Range of IP Addresses in each subnet l We’ve determined that there are 32 hosts per subnet. 200. 10. 20. 0 200. 10. 20. 32 200. 10. 20. 64 200. 10. 20. 96 200. 10. 20. 31 200. 10. 20. 63 200. 10. 20. 95 200. 10. 20. 127 200. 10. 20. 128 200. 10. 20. 160 200. 10. 20. 159 200. 10. 20. 191 200. 10. 20. 192 200. 10. 224 200. 10. 223 200. 10. 255

Useable IP addresses l l l We discard the 1 st and last subnet Discard the 1 st and last IP address in each subnet. Our 1 st useable IP address in the first useable subnet that can be assigned to a node on our network would be: – 200. 10. 20. 33