# Subnetting

 Rehman . · June 9, 2015 I was doing a problem: ": An organization is granted the block 16.0.0.0/8. The administrator wants to create 500 fixed-length subnets. a.  Find the subnet mask. b.  Find the number of addresses in each subnet. c.  Find the first and last addresses in subnet 1. d.  Find the first and last addresses in subnet 500. "As by some data given, i found the subnet mask by 32-8=24 which meansa) 255.0.0.0and other thing how many bits we need to create 500 fixed-length subnets should be 2(powe)9 as its equal to 512what i could understand by searching is we have:0001000 00000000 00000000nnnnnnn sssssssss shhhhhhhthe part 's' is of 9 bit as we figured it out can be changed from 000000000 to 111111111 & part of host as well from all 0 to all 1.still what are the total number of address in each as if the 's' part is whole '1' how would we count it? because its exceeding 255? So because of it part c & d are stuck for me

## Replies

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 Pere Garau Burguera · June 10, 2015 Because you use the 7 first bits of the 2nd octave to set the subnetThe other ones are from the hostCorrect me if I got those addresses wrong Pere Garau Burguera · June 10, 2015 Adresses wouldn't be those in the 100 subnets exampleThey would beFirst one16.0.0.0 - 16.1.255.255100th one16.198.0.0 - 16.199.255.255 Rehman . · June 10, 2015 i can say if question says you have an ip address 16.0.0.0 | 8 and you have to make 100 subnets.a. Find the subnet mask. b. Find the number of addresses in each subnet. c. Find the first and last addresses in subnet 1. d. Find the first and last addresses in subnet 100a) 255.0.0.0b) 2^7 = 128 the nearest. 32-8-7 = 17 bits for the host.2^17 = 131072 address c)subnet would be11111111.11111110.00000000.00000000255.254.0.0Address would be 16.0.0.0 ---- 16.0.128.255d) 16.100.128.255 --- 16.100.255.255 Pere Garau Burguera · June 10, 2015 YeahYou are given 8 bits for the general net (The same as saying that you have to use 16 in your first octave)Then you have to add to those already assigned bits the ones to create subnets (In this case you have to add 9) Rehman . · June 10, 2015 okay okay, what i can say is when ever we are given any number (e.g. 500) to make subnets we will convert them into the power of 2 and then we will add those bits with the already given bits and proceed further ? :3 Am i right ?(General formula) Pere Garau Burguera · June 10, 2015 Sorry if I confused you with the mask at the beginning, it should be the one taking 17 bits Pere Garau Burguera · June 10, 2015 So, the subnet mask will take the first 8+9 bits = 17 bitsSo 11111111.11111111.10000000.00000000 = 255.255.128.0 Pere Garau Burguera · June 10, 2015 Look at my first answerThe bits of the 2nd octave and the first one of the 3rd octave are the ones indicating the subnet Pere Garau Burguera · June 10, 2015 If you are designing 2 subnets, the subnet would be indicated with the first bit of the second octave:First subnet00010000.0000000.00000000.00000000 - 00010000.01111111.11111111.11111111 (The last address has 1's on the host part, while the first one has 0's in it) That would be 16.0.0.0 - 16.127.255.255Second subnet00010000.10000000.00000000.00000000 - 00010000.11111111.11111111.11111111 That is 16.128.0.0 - 16.255.255.255As I said, you're only designing 2 subnets, you have to design 512 subnets (only 500 will be used)When you're granted 16.0.0.0/8 you can do whatever you want with your 2nd, 3rd, and 4th octaves Pere Garau Burguera · June 10, 2015 So you are designing 2 subnets?
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## Networking

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