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Remembering tricky Private addresses with 15, or is there a reason for 15?

Member Posts: 21 ■□□□□□□□□□
So 15 is the number i found in 3 instances that i and anyone that needs a trick to remember certain private addresses should know. Such as Class A private address is 10.0.0.1 - 10.0.0.255 , class C is 192.168.0.1 to 192.168.255.255 , yes it doesn't use the entire 192 address block but most of us know that from dealing with Lans at home we usually use 192.168. Now Class B always confused me because its take a chunk of address's 172.16.0.1 - 172.31.255.255 unlike class A and C it doesn't just use 172.16.0.1 - 172.16.255.255 so it was hard for me to remember where it started and ended but 16 + (15) = 31, 172.16.0.1 - 172.(31).255.255 . Now on to class D, E . you could start from class C which ends at 223 , So D starts with 224, add 15 you get 239 so theirs class D 224-239, class E would start at 240 add 15 = 255. or start at 255 minus 15 = 240 . so you know E is 240-255 then 239 - 15 = 224 so theirs class D. IDK if this is a number they chose to use are maybe there is something im missing.

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Member Posts: 646 ■■■■■■□□□□
As far as why they chose 172.16.0.0 to 172.31.255.255, it was just chosen at random.

To explain the rest, you need to break down the first octet into binary:

Class A must start with a 0, Class B must start with a 10, Class C 110, Class D 1110, and Class E 1111.

A = 00000000 - 01111111 = 0 - 127
B = 10000000 - 10111111 = 128 - 191
C = 11000000 - 11011111 = 192 - 223
D = 11100000 - 11101111 = 224 - 239
E = 11110000 - 11111111 = 240 - 255

The numbers that are 15 apart are just coincidence in working with the binary scale.
Master of Business Administration in Information Technology Management - Western Governors University
Master of Science in Information Security and Assurance - Western Governors University
Bachelor of Science in Network Administration - Western Governors University
Associate of Applied Science x4 - Heald College
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Member Posts: 693 ■■■■■■□□□□
Well 15 is F in hexadecimal which means it's the highest number in each digit, it's like the 9 in decimal, after F follows 10, so it makes since to me that 15 would fit a pattern in IP addressing schemes.