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I'm asked to divide up 10.64.0.0/15 into three subnets for
|Group | Min # of Hosts|
|Group 1| 70,000 |
|Group 2| 30,000 |
|Group 3| 12,000 |
so I start by figuring out that 32-15 = 17 => 2^17 = 131072 are the total amount of addresses. Begin to split that number into powers of 2 in order to find the proper amount of addresses that can be pooled in order to get the proper network, broadcast netmask addresses.
I am then asked to to find the Network address, Broadcast Address, Netmask and total addresses.
I start by, for group 1, converting 10.64.0.0 to binary then adding 65k + 16k
(got this by branching 65 -> 2x 32 -> 1x 32 -> 2x 16k)
.
After adding them in binary I get 10.65.64.0
(not sure if that is right). Then to calculate the brodcast address i tried to |~
the network address I found previously with the netmask (15), which was wrong. I'm not sure how to find the netmask for that group as I assumed it was 15 for each group which again was wrong. And the total addresses I found above which was 65k+16k = 81,920
which again was wrong, haha.
Then from here I assumed for the next group I would just do the same adding 32k to the previous network address I found for group one and then do the same process as I did calculating group 1's data.
Any guidance on what I'm doing wrong or if there is an easier way to do this is welcome.
Is this real world? Or cert prep / test stuff? Cisco and real world do not line up 100%, likewise another vendor may have another approach. – Austin T French – 2013-05-04T16:34:08.227
First thought: Can't really work - your Bitmask leaves you with 2 x 255 x 255 possible combinations which if it has to be broken into 3 subnets means you have to move 2 bits to the network part leaving you with 127 x 255 (32385) combinations...how are you going to get a group with 70000 hosts? – M.Bennett – 2013-05-04T16:54:36.873
@M.Bennett He can't do it with 3 equal sized /16 subnets but maybe there's another way? 'cos technically 17 bits is enough. – barlop – 2013-05-05T00:51:47.270
I don't know if this is perfect for serverfault, but it might be very suited to it. And certainly more likely to get an answer there than here. And good answers. Serverfault has questions on subnetting so I think it's worth a shot there. great question though. Been a while since i played with subnetting. – barlop – 2013-05-05T00:54:58.750
@AthomSfere I think you're somewhaht mistaken here. The only aspect that subnetting questions can be not real world, is when they're classes of ip address, but even there, this question does not involve classes. this question seems to me to be suitable for real world / is real world. And cisco involves CIDR too which is very much real world. – barlop – 2013-05-05T01:06:29.137
btw this may help it's an online subnet calculator that supports CIDR http://www.subnet-calculator.com/cidr.php
– barlop – 2013-05-05T01:18:48.7331
Server Fault would close this question as a duplicate of How does IPv4 Subnetting Work?.
– Michael Hampton – 2013-05-05T01:22:12.347@MichaelHampton how do you know? do they close all subnetting questions ever since that question on how IPv4 subnetting works? – barlop – 2013-05-05T01:26:29.497
2@barlop Yes, they get closed fairly rapidly since a Q&A already exists which covers the topic in sufficient depth to answer the question. – Michael Hampton – 2013-05-05T01:29:04.197