Teaching Subnetting Sam Bowne City College San Francisco Web: samsclass.info

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

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

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

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

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

Example Lesson: Binary Lesson 3 Hexadecimal

Counting to 15 Base Base Base 16 Base Base Base 16 Two Ten (Hex) Two Ten (Hex) A A B B C C D D E E F F

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

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

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

Binary iClicker Questions

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

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

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

OLD WAY S09 OLD WAY F09 NEW WAY S10 # Students Total # 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%

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

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