# Magic HAT Subnetting ,

Member Posts: 29 ■□□□□□□□□□
Hey guys i plan on taking the CCENT 100-105 very soon, and i understand that time is the essence for subnetting. Im pretty that I've gotten the concepts of subnetting down, and finding out what given ip address / mask belongs to which subnet using the Magic Hat,
256 - Mask = Value method. However, i am having trouble with speed, especially the bigger ip address that fall into a specific subnet like 172.16.166.1/21. Then just increment in the Interesting Octet (3rd)+8without going over the 166.My problem is doing the addition over and over which can take up a lot of time. 8+8+8+8+8+8+8+8+8+8+8+8+8+8+8+8+8+8+8= 160. Is their a special formula that i can use without just doing addition over and over and over ? To find my Subnet ID for a specific address ?

V
128 192 224 240 248 252 254 255
128 64 32 16 8 4 2 1

8............

• Member Posts: 29 ■□□□□□□□□□
also i messed up the Chart down there from the post 128 192 224 240 248 252 254 255 lol, i know how it suppose to look i just didn't get the alignment right with the page xD
• Member Posts: 29 ■□□□□□□□□□
Hey guys i plan on taking the CCENT 100-105 very soon, and i understand that time is the essence for subnetting. Im pretty that I've gotten the concepts of subnetting down, and finding out what given ip address / mask belongs to which subnet using the Magic Hat,
256 - Mask = Value method. However, i am having trouble with speed, especially the bigger ip address that fall into a specific subnet like 172.16.166.1/21. Then just increment in the Interesting Octet (3rd)+8without going over the 166.My problem is doing the addition over and over which can take up a lot of time. 8+8+8+8+8+8+8+8+8+8+8+8+8+8+8+8+8+8+8= 160. Is their a special formula that i can use without just doing addition over and over and over ? To find my Subnet ID for a specific address ?

V
128 192 224 240 248 252 254 255
128 64 32 16 8 4 2 1

8............

• Member Posts: 903 ■■■■□□□□□□
there are a couple of ways.

1) divide 166 by 8 that equals 20.something. drop the something, take 8x20 = 160

2) look at the lines of your data and do comparisons

128 192 224 240 248 252 254 255
128 64 32 16 8 4 2 1

second line, what are multiples of 8. 128 64 32 16 8
what is less than 166? biggest number is 128
128 is 8 x 16 so you have already did lots of additions.

what is 128 + 64. from the first line that is 192. that is > 166 so it isn't going to work
what is 128 + 32. that is 160. 166 - 160 is less than 8 So that is your answer. And, it only took one addition.
• Member Posts: 29 ■□□□□□□□□□
clarson wrote: »
there are a couple of ways.

1) divide 166 by 8 that equals 20.something. drop the something, take 8x20 = 160

2) look at the lines of your data and do comparisons

128 192 224 240 248 252 254 255
128 64 32 16 8 4 2 1

second line, what are multiples of 8. 128 64 32 16 8
what is less than 166? biggest number is 128
128 is 8 x 16 so you have already did lots of additions.

what is 128 + 64. from the first line that is 192. that is > 166 so it isn't going to work
what is 128 + 32. that is 160. 166 - 160 is less than 8 So that is your answer. And, it only took one addition.

wow ok i didn't know i could do it with division either Thankyou SO MUCh!, you will be rewarded in the afterlife