Classless subnetting
- 1. SubnettingRick GrazianiCabrillo CollegeNote: These example use classless addressing. Instead of a default classful mask, a network mask is given.
- 2. Rick Graziani graziani@cabrillo.edu2What is subnetting?NetworkNetworkSubnetHostNetworkNetworkHostHost1721600Subnetting is the process of borrowing bits from the HOST bits, in order to divide the larger network into small subnets.Subnetting does NOT give you more hosts, but actually costs you hosts.You lose two host IP Addresses for each subnet, and perhaps one for the subnet IP address and one for the subnet broadcast IP address.You lose the last subnet and all of it’s hosts’ IP addresses as the broadcast for that subnet is the same as the broadcast for the network.In older networks, you would have lost the first subnet, as the subnet IP address is the same as the network IP address. (This subnet can be used in most networks.)
- 3. Rick Graziani graziani@cabrillo.edu3Analogy Dividing the barrel of apples into small barrels or baskets does not give us any more apples…100 Apples
- 4. Rick Graziani graziani@cabrillo.edu4Analogy 10 barrels x 10 apples = 100 apples101010100 Apples (10 * 10)101010101010It is the same as taking a barrel of 100 apples and dividing it into 10 barrels of 10 apples each.10
- 5. Rick Graziani graziani@cabrillo.edu5Analogy 100 – 2 apples = 98 Usable ApplesBefore subnetting:In any network (or subnet) we can not use all the IP addresses for host addresses.We lose two addresses for every network or subnet.Network Address - One address is reserved to that of the network. Broadcast Address – One address is reserved to address all hosts in that network or subnet. 98 Apples (100 – 2)
- 6. Rick Graziani graziani@cabrillo.edu6 10 barrels x 8 apples = 80 apples888(less 2)(less 2)(less 2)88880 Apples 10 * (10 - 2)(less 2)(less 2)(less 2)888(less 2)(less 2)(less 2)In subnetting we will see that we continue to lose two apples per subnet, one for the address and one for the broadcast.8
- 7. Rick Graziani graziani@cabrillo.edu7 10 barrels x 8 apples = 80 applesX888---(less 2)(less 2)(less 2)88864 Apples 8 * (10 - 2)(less 2)(less 2)(less 2)888(less 2)(less 2)(less 2)We “might” also lose the last basket of apples, subnet, as it contains the broadcast address for the entire network.In older networks, we “might” also lost the first basket, subnet, as it contained the address of the entire network, but this is usually no longer the case.X8---
- 8. Rick Graziani graziani@cabrillo.edu8Subnet ExampleNetwork address 172.16.0.0 with /16 network maskNetworkNetworkHostHost1721600
- 9. Rick Graziani graziani@cabrillo.edu9NetworkNetworkSubnetHostSubnet ExampleNetwork address 172.16.0.0 with /16 network maskNetworkNetworkHostHost1721600Using Subnets: subnet mask 255.255.255.0 or /24Network Mask: 255.255.0.0 or /1611111111111111110000000000000000Subnet Mask: 255.255.255.0 or /2411111111111111111111111100000000Applying a mask which is larger than the default subnet mask, will divide your network into subnets.Subnet mask used here is 255.255.255.0 or /24
- 10. Rick Graziani graziani@cabrillo.edu10NetworkNetworkSubnetHost172160Host172161Host172162Host172163Host17216Etc.Host17216254Host17216255HostSubnet ExampleNetwork address 172.16.0.0 with /16 network maskUsing Subnets: subnet mask 255.255.255.0 or /24Subnets255 Subnets28 - 1Cannot use last subnet as it contains broadcast address
- 11. Rick Graziani graziani@cabrillo.edu11NetworkNetworkSubnetHost172160017216101721620172163017216Etc.0172162540172162550Subnet ExampleNetwork address 172.16.0.0 with /16 network maskUsing Subnets: subnet mask 255.255.255.0 or /24Subnets Addresses255 Subnets28 - 1Cannot use last subnet as it contains broadcast address
- 12. Rick Graziani graziani@cabrillo.edu12NetworkNetworkSubnetHosts172160117216111721621172163117216Etc.117216254117216255HostSubnet ExampleClass B address 172.16.0.0 with /16 network maskUsing Subnets: subnet mask 255.255.255.0 or /24Hosts Addresses254254254254254254Each subnet has 254 hosts, 28 – 2
- 13. Rick Graziani graziani@cabrillo.edu13NetworkNetworkSubnetHost17216025517216125517216225517216325517216Etc.2551721625425517216255255Subnet ExampleNetwork address 172.16.0.0 with /16 network maskUsing Subnets: subnet mask 255.255.255.0 or /24Broadcast Addresses255 Subnets28 - 1Cannot use last subnet as it contains broadcast address
- 14. Rick Graziani graziani@cabrillo.edu14Subnet ExampleNetwork address 172.16.0.0 with /16 network maskUsing Subnets: subnet mask 255.255.255.0 or /24172.16.0.0/24172.16.10.0/24172.16.25.0/24172.16.5.0/24
- 15. Rick Graziani graziani@cabrillo.edu15Important things to remember about SubnettingYou can only subnet the host portion, you do not have control of the network portion.Subnetting does not give you more hosts, it only allows you to divide your larger network into smaller networks.When subnetting, you will actually lose hosts:For each subnet you lose the address of that subnetFor each subnet you lose the broadcast address of that subnetYou “may” lose the first and lastlast subnets (coming)Analogy: Large barrel of 100 apples.Why subnet?Divide larger network into smaller network.Limit layer 2 and layer 3 broadcasts to their subnet.Better management of traffic.
- 16. Rick Graziani graziani@cabrillo.edu16Host IP Address: 172.16.18.33Network Mask: 255.255.0.0Subnet Mask: 255.255.255.0Given the following Host IP Address, Network Mask and Subnet mask find the following information:Major Network InformationMajor Network AddressMajor Network Broadcast AddressRange of Hosts if not subnettedSubnet InformationSubnet AddressRange of Host Addresses (first host and last host)Broadcast AddressOther Subnet InformationTotal number of subnetsNumber of hosts per subnetSubnetting – Example #1 (on the board)
- 17. Rick Graziani graziani@cabrillo.edu17Host IP Address: 138.101.114.250Network Mask: 255.255.0.0Subnet Mask: 255.255.255.192Given the following Host IP Address, Network Mask and Subnet mask find the following information:Major Network InformationMajor Network AddressMajor Network Broadcast AddressRange of Hosts if not subnettedSubnet InformationSubnet AddressRange of Host Addresses (first host and last host)Broadcast AddressOther Subnet InformationTotal number of subnetsNumber of hosts per subnetSubnetting – Example #2
- 18. Rick Graziani graziani@cabrillo.edu18Major Network InformationHost IP Address: 138.101.114.250Network Mask: 255.255.0.0Subnet Mask: 255.255.255.192Major Network Address: 138.101.0.0Major Network Broadcast Address: 138.101.255.255Range of Hosts if not Subnetted: 138.101.0.1 to 138.101.255.254
- 19. Rick Graziani graziani@cabrillo.edu19128 64 32 16 8 4 2 1Step 1:Translate Host IP Address and Subnet Mask into binary notationStep 1: Convert to Binary
- 20. Rick Graziani graziani@cabrillo.edu20Step 2:Determine the Network (or Subnet) where this Host address lives:1. Draw a line under the mask2. 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 03. Express the result in Dotted Decimal Notation4. The result is the Subnet Address of this Subnet or “Wire” which is 138.101.114.192Step 2: Find the Subnet Address
- 21. Rick Graziani graziani@cabrillo.edu21Step 2:Determine the Network (or Subnet) where this Host address lives:Quick method:Find the last (right-most) 1 bit in the subnet mask.Copy all of the bits in the IP address to the Network AddressAdd 0’s for the rest of the bits in the Network AddressStep 2: Find the Subnet Address
- 22. Rick Graziani graziani@cabrillo.edu22Step 3:Determine which bits in the address contain Network (subnet) information and which contain Host information:Use the Network Mask: 255.255.0.0 and divide (Great Divide) the from the rest of the address.Use Subnet Mask: 255.255.255.192 and divide (Small Divide) the subnet from the hosts between the last “1” and the first “0” in the subnet mask.Step 3: Subnet Range / Host Range
- 23. Rick Graziani graziani@cabrillo.edu23Step 4: First Host / Last HostHost PortionSubnet Address: all 0’s First Host: all 0’s and a 1Last Host: all 1’s and a 0Broadcast: all 1’s
- 24. Rick Graziani graziani@cabrillo.edu24Total number of subnetsNumber of subnet bits 10210 = 1,0241,024 total subnetsSubtract one “if” all-zeros subnet cannot be usedSubtract one “if” all-ones subnet cannot be usedStep 5: Total Number of Subnets
- 25. Rick Graziani graziani@cabrillo.edu25Total number of hosts per subnetNumber of host bits 626 = 6464 host per subnetsSubtract one for the subnet addressSubtract one for the broadcast address62 hosts per subnetStep 6: Total Number of Hosts per Subnet
- 26. Rick Graziani graziani@cabrillo.edu26Your Turn!Problem 1Host IP Address: 10.10.10.193Network Mask: 255.255.0.0Subnet Mask: 255.255.255.0Problem 2Host IP Address: 10.10.10.193Network Mask: 255.255.255.0Subnet Mask: 255.255.255.240Problem 3Host IP Address: 10.10.10.193Network Mask: 255.255.255.0Subnet Mask: 255.255.255.252