Classless Subnetting Using the Worksheet

# Classless Subnetting Using the Worksheet

## Classless Subnetting Using the Worksheet

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1. Classless SubnettingUsing the Worksheet CIS 81 and CST 311 Rick Graziani Fall 2006

3. See these spreadsheets on my website Nutshell: Classless Subnetting in a Nutshell (Excel spreadsheet) Worksheet: Classless Subnetting Worksheet (Excel spreadsheet) Rick Graziani graziani@cabrillo.edu

4. Part 1: Determine Major Network Information Rick Graziani graziani@cabrillo.edu

6. Determine Network Address • Determine the Network Address by using the AND operation. • Perform a bit-wise AND operation on the IP Address and the Subnet Mask • Note: 1 AND 1 results in a 1, 0 AND anything results in a 0 • Express the result in Dotted Decimal Notation • The result is the Major Network Address of this for this host IP Address is 138.101.0.0 Rick Graziani graziani@cabrillo.edu

7. Determine Network Address A simple way of doing the AND operation: 1. In the Network mask locate where the 1’s end and the 0’s begin and draw a line. (I call this the “Major Network Divide” or “MD” on the worksheet.) 2. Now copy all of the bits above the 1 bits in the Network mask, to the Network address. 3. For the rest of the bits in the Network address (the bits below the 0’s in the Network mask) write all 0’s. MD Network Portion Host Portion Copy the bits from the Host IP Address to the Major Network Address Write all 0’s below the 0’s in the Major Network Mask Rick Graziani graziani@cabrillo.edu

9. Network: Determine First Host, Last Host, Broadcast Addresses • The network address has all 0’s in the host portion of the address • The broadcast address has all 1’s in the host portion of the address • The first host is all 0’s and a 1 in the host portion of the address. • The last host is all 1’s and a 0 in the host portion of the address. Network Portion Host Portion Rick Graziani graziani@cabrillo.edu

10. Network: Determine the number of usable hosts • By counting the number of host bits we can determine the total number of usable hosts for this network (before subnetting). Host bits:16 Total number of hosts: 216 = 65,536 65,536 – 2 =65,534 (Can’t use the all 0’s address, network address, or the all 1’s address, broadcast address.) Network Portion Host Portion = 16 bits Rick Graziani graziani@cabrillo.edu

11. Part 2: Determine Subnet Information Rick Graziani graziani@cabrillo.edu

13. Determine Subnet Address • Determine the Network Address by using the AND operation. • Perform a bit-wise AND operation on the IP Address and the Subnet Mask • Note: 1 AND 1 results in a 1, 0 AND anything results in a 0 • Express the result in Dotted Decimal Notation • The result is the Major Network Address of this for this host IP Address is 138.101.114.192 Rick Graziani graziani@cabrillo.edu

14. Determine Subnet Address A simple way of doing the AND operation: 1. In the Subnet mask locate where the 1’s end and the 0’s begin and draw a line. (I call this the “Subnet Divide” or “SD” on the worksheet.) 2. Now copy all of the bits above the 1 bits in the Subnet mask, to the Network address. 3. For the rest of the bits in the Subnet address (the bits below the 0’s in the Network mask) write all 0’s. SD Network/Subnet Portion Host Portion Copy the bits from the Host IP Address to the Major Network Address Write all 0’s below the 0’s in the Major Network Mask Rick Graziani graziani@cabrillo.edu

16. Subnet: Determine First Host, Last Host, Broadcast Addresses • The subnet address has all 0’s in the host portion of the subnet address • The broadcast address has all 1’s in the host portion of the subnet address • The first host is all 0’s and a 1 in the host portion of the subnet address. • The last host is all 1’s and a 0 in the host portion of the subnet address. Network Portion Subnet Portion Host Portion Rick Graziani graziani@cabrillo.edu

17. Subnet: Determine the number of usable hosts • By counting the number of host bits we can determine the total number of usable hosts for this subnet. Host bits:6 Total number of hosts: 26 = 64 64 – 2 =62 (Can’t use the all 0’s address, network address, or the all 1’s address, broadcast address.) SD Network Portion Subnet Portion Host Portion Rick Graziani graziani@cabrillo.edu

18. Subnet: Determine the number of usable subnets • By counting the number of subnet bits we can determine the total number of usable hosts for this subnet. Subnet bits:10 Total number of hosts: 210 = 1,024 1,024 – (0, 1, or 2) =? 1,024 – 1 = 1,023 usable subnets • The number of usable subnets depends upon whether or not we can use the first and/or last subnets. In today’s networks, both the first and last subnets are generally usable. • In this example, the network administrator has determined the last subnet is not to be used. MD SD Network Portion Subnet Portion Host Portion Rick Graziani graziani@cabrillo.edu

19. Overall Visual • The subnet address has all 0’s in the host portion of the subnet address • The broadcast address has all 1’s in the host portion of the subnet address • The first host is all 0’s and a 1 in the host portion of the subnet address. • The last host is all 1’s and a 0 in the host portion of the subnet address. Rick Graziani graziani@cabrillo.edu

20. Overall Visual The following information must be provided: • IP Address (host or network) • Major Network Mask If subnetted: • Subnet Mask • Number of usable subnets (less 0, 1, or 2) Rick Graziani graziani@cabrillo.edu

21. Notes Quick check • First host: 1 more than network/subnet address • Last host: 1 less than broadcast • Does the host IP address fall in the range of network host addresses? Of subnet host addresses? How do hosts view the network? • Hosts receive a host IP address and mask. • Hosts only see themselves as part of their subnet (or network if not subnetted). • They don’t know or care if they are in a network or subnet. • Almost all networks are a subnet of some larger network. Rick Graziani graziani@cabrillo.edu

22. See these spreadsheets on my website Nutshell: Classless Subnetting in a Nutshell (Excel spreadsheet) Worksheet: Classless Subnetting Worksheet (Excel spreadsheet) Rick Graziani graziani@cabrillo.edu

23. Tips • Use worksheets • Don’t do short-cuts unless you understand the process we just discussed and you know what you are doing. • Only use a subnet calculator to check your answers. • You must know how to subnet, then you can use the calculator. • Interviews, exams, and certification exams do not allow subnet calculators. • Practice, practice, practice! Rick Graziani graziani@cabrillo.edu

24. Classless SubnettingUsing the Worksheet CIS 81 and CST 311 Rick Graziani Fall 2006