1. Teaching Subnetting Sam Bowne City College San Francisco Email: sbowne@ccsf.edu Web: samsclass.info Twitter: @sambowne

2. The Old Way  Subnetting covered in one chapter  Students find it overwhelming and frustrating  We spent the rest of each class going over subnetting again and again with small groups of students  Only the best students learned it quickly  Most students struggled with it to the end

3. Why is Subnetting So Hard?  Subnetting is math  It contains six major concepts  Each concept is abstract and subtle, and takes time to learn  You cannot get to the next concept until you have grasped the previous one  The other chapters are not like this

4. The New Way  Start at the very beginning--a nybble (four bits)  Teach one very small lesson each week  Follow with lots of interactive practice using an audience response system

5. Lessons  Binary Lesson 1: Nybbles  Binary Lesson 2: Bytes  Binary Lesson 3: Hexadecimal  Binary Lesson 4: Hexadecimal Practice  Binary Lesson 5: Classful IP Addresses  Binary Lesson 6: Classful Subnetting  Worksheet: Classful Subnet Square  Worksheet: Classless Subnet Square

6. Why is Subnetting So Hard?  Subnetting is math  It contains six major concepts  Each concept is abstract and subtle, and takes time to learn  You cannot get to the next concept until you have grasped the previous one  The other chapters are not like this

7. Example Lesson: Binary Lesson 3 Hexadecimal

8. Counting to 15 Base Base Base 16 Base Base Base 16 Two Ten (Hex) Two Ten (Hex) 0 0 0 1000 8 8 0 0 0 1000 8 8 1 1 1 1001 9 9 1 1 1 1001 9 9 10 2 2 1010 10 A 10 2 2 1010 10 A 11 3 3 1011 11 B 11 3 3 1011 11 B 100 4 4 1100 12 C 100 4 4 1100 12 C 101 5 5 1101 13 D 101 5 5 1101 13 D 110 6 6 1110 14 E 110 6 6 1110 14 E 111 7 7 1111 15 F 111 7 7 1111 15 F

9. Four Bits Make a Nybble 1 0 0 1 A nybble can be represented by one hexadecimal digit Values from 0 to 15, or 0 to F 8s 4s2s1s

10. Eight Bits Make a Byte 1 0 0 1 1 0 0 1 So this number is 128 + 16 + 8 + 1 = 153 8s4s2s1s8s4s2s8s4s1s2s8s4s 16s32s 128s 64s16s32s64s16s32s One nybble: 0 through F One nybble: 0 through F

11. Two hexadecimal digits make a byte 1 0 0 1 1 0 0 1 So this number is $99 = 9*16 + 9 = 144+9 = 153 One nybble: 0 through F # of 16s One nybble: 0 through F # of 1s

12. Binary iClicker Questions

13. What is 6 in hexadecimal? A.$0A B.$06 C.$60 D.$66 E.$A6 1 of 6

14. What is $15 in decimal? A.9 B.15 C.20 D.21 E.31 2 of 6

15. What is 32 in hexadecimal? A.$32 B.$20 C.$10 D.$24 E.$30 3 of 6

16. OLD WAY S09 OLD WAY F09 NEW WAY S10 # Students Total313341 # Passed (A, B, or C)2122 % Passed67.7%71.0%53.7% Subnetting final avg. score (all students)61.3%58.7%64.2% Subnetting final avg. score (Passed)85.1%90.5%98.9%

17. Results: Subjective  Students enjoyed the binary lessons and looked forward to them  They found them easy  The best students cut class on the subnetting lesson's week because it was boring  The average students understood it easily  Very little review or struggle with it later

18. Results: Objective OLD WAY S09 OLD WAY F09 NEW WAY S10 Subnetting final avg. score (Passed)85.1%90.5%98.9% # Students Total313341 # Passed (A, B, or C)2122 % Passed67.7%71.0%53.7% Subnetting final avg. score (all students)61.3%58.7%64.2%