1. CISCO NETWORKING ACADEMY Chabot College ELEC 99.08 Subnet Review

2. CISCO NETWORKING ACADEMY Address Classes Class A (0 - 127) Class B (128-191) Class C (192-223) NetworkHost Network Host Network Host 1st octet2nd octet3rd octet4th octet

3. CISCO NETWORKING ACADEMY IP Address Composition IP address may have an additional field, the subnet field, that is used to identify smaller networks within a larger network. NETWORK NUMBER SUBNET NUMBER HOST NUMBER

4. CISCO NETWORKING ACADEMY The Subnet Mask 11001111000101010011011000001000 20721548 Address Mask Network Host 11111111 00000000 255 0 Mask has: 1s in the network/subnet portion 0s in the host portion

5. CISCO NETWORKING ACADEMY The Default Subnet Masks Class A or /8 Class B or /16 Class C or /24 255000 00 0 If any additional bits in the subnet mask are set to “1,” then subnets have been created.

6. CISCO NETWORKING ACADEMY Octet - binary/decimal equivalents (memorize) Bit

7. CISCO NETWORKING ACADEMY Class C : 1-bit Mask (/25) 11001111000101010011011000001000 20721548 Address Mask Network Host 11111111 10000000 255 128 Masks can be written different ways. When the phrase “1-bit” mask is used, that means 1 more bit than the default. This example can also be called a 25-bit mask, or /25.

8. CISCO NETWORKING ACADEMY All Zeros / All Ones The address of the subnet itself (the wire) has a host portion that is all zeros. The broadcast address for the subnet has a host portion that is all ones. 000000000 = 128 = 255 = 01111111127 = 10000000 11111111 Subnet #0Subnet #1 DecimalBinary Subnet addr. Broadcast addr. Subnet addr. Broadcast addr.

9. CISCO NETWORKING ACADEMY Class C : 1-bit Mask (/25) 11001111000101010011011000000000 20721540 Address Mask Network Host 11111111 10000000 255 128 Because this is a class C, all nodes on this network will share the first three octets. Those numbers are not an issue.

10. CISCO NETWORKING ACADEMY Last Octet 1-bit Mask (/25) 00000000 0 Address Mask Host 10000000 128 How many subnets can we have with 1 bit? 2 1 = 2 different possibilities 1 bit

11. CISCO NETWORKING ACADEMY Last Octet 1-bit Mask (/25) 000000000 = 128 = 255 = How many hosts can be on each subnet? 01111111127 = 10000000 11111111 Subnet #0Subnet #1 DecimalBinary 2 7 = 128 different possibilities MINUS TWO. 7 bits

12. CISCO NETWORKING ACADEMY Test Question Type 1 IP Address 169.199.69.137 Subnet Mask 255.255.255.192 How many subnets are created by this mask? How many hosts can be on each subnet? Steps: Identify address class & network bits Count subnet bits; express as power of 2 (-2) Count host bits; express as power of 2 (-2)

13. CISCO NETWORKING ACADEMY Step 1: Identify Class & Network Bits 16919969137 Address Mask Network SubnetHost 255 192 11111111 11000000 10101001110001110100010110001001 CLASS B - ignore network octets 16 bits

14. CISCO NETWORKING ACADEMY Step 2: Count Subnet Bits 16919969137 Address Mask Network SubnetHost 255 192 11111111 11000000 10101001110001110100010110001001 10 bits 2 10 = 1,024 possible subnets MINUS TWO

15. CISCO NETWORKING ACADEMY Step 3: Count Host Bits 16919969137 Address Mask Network SubnetHost 255 192 11111111 11000000 10101001110001110100010110001001 6 bits 2 6 = 64 possible hosts / subnet MINUS TWO.

16. CISCO NETWORKING ACADEMY Test Question Type 2 Long Method IP Address 169.199.69.137 Subnet Mask 255.255.255.192 What is this host’s subnetwork number? What is the broadcast address for the subnet that contains this host? Method: Count host bits; determine how many host addresses/subnet List the host ranges in each subnet (Multiples of 2 N ) Find the subnet containing the target address The first address will have all 0s in the host portion The last address will have all 1s in the host portion

17. CISCO NETWORKING ACADEMY Step 1: Count Host Bits 16919969137 Address Mask Network Host 255 192 11111111 11000000 10101001110001110100010110001001 6 bits 2 6 = 64 host address / subnet Increment host ranges by 64.

18. CISCO NETWORKING ACADEMY Remaning Steps: List host ranges in each subnet Find subnet containing target address First address is subnet, last is broadcast Subnet address is: 169.199.69.128 Subnet broadcast address is: 169.199.69.191

19. CISCO NETWORKING ACADEMY IP Address 169.199.69.137 Subnet Mask 255.255.255.192 What is this host’s subnetwork number? Steps: 1. Convert address & mask to binary 2. Replace host portion of address with all 0s 3. Convert each octet back to dotted decimal Tip: Ignore any octets with a mask that is all 1s Test Question Type 2 Quick Method

20. CISCO NETWORKING ACADEMY Tip: Ignore octets masked with all 1s: 16919969137 Address Mask 255 192 11111111 11000000 The values of these octets are the same for the subnet network & broadcast address.

21. CISCO NETWORKING ACADEMY Step 1: Convert to binary 16919969137 Address Mask 255 192 11111111 11000000 10001001 Convert the remaining octet(s).

22. CISCO NETWORKING ACADEMY Step 2: Set host portion of address to all 0s 16919969 Address Mask Host 255 192 11111111 11000000 10101001110001110100010110000000 (Value of this octet will change)

23. CISCO NETWORKING ACADEMY Step 3: Convert octet back to dotted decimal 16919969128 Address Mask Host 255 192 11111111 11000000 10101001110001110100010110000000 Subnet address is: 169.199.69.128

24. CISCO NETWORKING ACADEMY Quick Method - Broadcast addr. IP Address 169.199.69.137 Subnet Mask 255.255.255.192 What is the broadcast address for the subnet that contains this host? Same method, but use all 1s in step 2: 1. Convert address & mask to binary 2. Set host portion of address to all 1s 3. Convert each octet back to dotted decimal

25. CISCO NETWORKING ACADEMY Tip: Ignore octets masked with all 1s: 16919969137 Address Mask 255 192 11111111 11000000

26. CISCO NETWORKING ACADEMY Step 1: Convert to binary 16919969137 Address Mask 255 192 11111111 11000000 10001001

27. CISCO NETWORKING ACADEMY Step 2: Set host portion of address to all 1s 16919969 Address Mask Host 255 192 11111111 11000000 10101001110001110100010110111111 (Value of this octet will change)

28. CISCO NETWORKING ACADEMY Step 3: Convert each octet back to dotted decimal 16919969191 Address Mask Host 255 192 11111111 11000000 10101001110001110100010110111111 Subnet broadcast address is: 169.199.69.191

29. CISCO NETWORKING ACADEMY Second Example, Quick Method IP Address 169.199.69.137 Subnet Mask 255.255.248.0 What is this host’s subnet number? What is the broadcast address for that subnet? Steps: Convert address & mask to binary Replace host portion of address with all 0s for subnet Replace host portion of address with all 1s for broadcast Convert each octet back to dotted decimal

30. CISCO NETWORKING ACADEMY Ignore octets masked with all 1s: 16919969137 Address Mask 255 2480 11111111 1111100000000000

31. CISCO NETWORKING ACADEMY Step 1: Convert to binary 16919969137 Address Mask 255 2480 11111111 1111100000000000 0100010110001001

32. CISCO NETWORKING ACADEMY Subnet Address Step 2: Set host portion of address to all 0s 169199 Address Mask Host 255 2480 11111111 1111100000000000 0100000000000000 (Value of these octets will change) Subnet

33. CISCO NETWORKING ACADEMY 169199 Address Mask Host 255 2480 11111111 1111100000000000 0100000000000000 Step 3: Convert each octet back to dotted decimal 640 Subnet address is: 169.199.64.0 Subnet

34. CISCO NETWORKING ACADEMY Broadcast Address Step 2: Set host portion of address to all 1s 169199 Address Mask Host 255 2480 11111111 1111100000000000 0100011111111111 (Value of these octets will change) Subnet

35. CISCO NETWORKING ACADEMY 169199 Address Mask Host 255 2480 11111111 1111100000000000 0100011111111111 Step 3: Convert each octet back to dotted decimal 71255 Subnet broadcast address is: 169.199.71.255 Subnet

36. CISCO NETWORKING ACADEMY Network 200.199.69.0 Subnet Mask 255.255.255.192 What is the fourth usable host address on the second usable subnet? Steps: 1. Ignore octets masked with all ones. 2. Replace host portion of address with binary four 3. Replace subnet portion with binary two 3. Convert each octet back to dotted decimal Test Question Type 3 Quick Method

37. CISCO NETWORKING ACADEMY Step 1: Ignore octets masked with all 1s: 20019969137 Address Mask 255 192 11111111 11000000 These octets won’t change.

38. CISCO NETWORKING ACADEMY Step 2: Set host portion to binary four 20019969 Address Mask Host 255 192 11111111 11000000 101010011100011101000101 000100 000000 000001 000010 000011 000100 Reserved Fourth usable host First usable host

39. CISCO NETWORKING ACADEMY Step 3: Set subnet portion to binary two 20019969 Address Mask Host 255 192 11111111 11000000 10101001110001110100010110000100 00 01 10 11 Reserved Second usable subnet First usable subnet

40. CISCO NETWORKING ACADEMY Step 3: Convert octet back to dotted decimal 20019969132 Address Mask Host 255 192 11111111 11000000 10101001110001110100010110000100 Fourth usable address in second usable subnet is: 169.199.69.132

41. CISCO NETWORKING ACADEMY 1. Ignore octets masked 255. 2. Convert remaining octets to binary. 2. Segment binary address into portions: network | subnet | host 4. Use your understanding of binary addressing to answer the problem. 5. Convert each octet back to dotted decimal. Quick Method - General Strategy