An office has 8 floors with approximately 30-40 users per floor. One subnet must be used. Which command must be configured on the router Switched Virtual Interface to use address space efficiently?
8 floors and 40 user per floor means 320 users (approx.). How many bits do you need to have 320 IP addresses?
8 bits = (2^8 – 2) =254 IP addresses, and it’s not enough.
9 bits = (2^9 – 2) = 510 IP addresses, and this is enough.
You have a class C subnet (192.168.0.0). This means a subnet mask like this:
255.255.255.0
But you need 9 bits for the hosts, so you’ve got left with a subnet mask like this:
255.255.1111111x.xxxxxxxx =255.255.254.0
This means you will use VLSM subnetting.
Answer B is correct.
The answer is B since 8x40=320
For supporting 320, you'd need to use the remaining host bits formula, 2^9 - 2 = 510
this will give you enough hosts, any less than that is not enough. then you will skip the 4th octet since you borrowed 9 host bits and not any less than 8.. that means you'd go for the 3rd octet, only 1 answer has changes made to 3rd octet, so B is your answer.
sorry, option A has changes made to 3rd octet too but it goes 0 and only B goes for 254 which is exactly leaving the last bit off for the 3rd octet and that would be borrowing 9 bits :D
The correct answer is:
C. ip address 192.168.0.0 255.255.255.128
With a subnet mask of 255.255.255.128 (or /25), we have 128 addresses per subnet, of which 126 can be assigned to devices.
This mask is enough to accommodate between 30 and 40 users on each of the 8 floors, totaling up to 320 users, and also saves address space.
40 cannot fit in 32 so it must fit in the 64, therefor you know that you need (64 addresses) * 8 (floors) = 512 addresses.
You know that /23 contains 512 addresses and the subnet mask is 255.255.254.0.
Thank you, and sorry for my english.
Calculating Total Users:
Minimum number of users: 8 floors * 30 users = 240 users
Maximum number of users: 8 floors * 40 users = 320 users
To ensure there is enough space for growth and network devices (such as printers, IP phones, and other equipment), it is best to choose a subnet that can accommodate more than the maximum number of users.
Choosing the Subnet Mask:
A /23 subnet provides 512 IP addresses (510 usable).
This will accommodate up to 510 devices, which is sufficient for the current and future needs of the office.
Convert IP address and subnet mask to binary:
IP address: 10.10.225.48 becomes 00001010.00001010.11111111.00110000
Subnet mask: 255.255.255.224 becomes 11111111.11111111.11111111.11100000
Compare the first 27 bits:
Align the two binary strings and check if the first 27 bits (from left to right) are identical:
00001010.00001010.11111111.00110000 (IP address)
11111111.11111111.11111111.11100000 (Subnet mask)
The first 27 bits (highlighted) match perfectly.
I would reread your book, mate. This is the weirdest gibberish I have ever read. You need 8 floors times 40 people that is 320 in total and the question is to use one subnet for the whole building so 320 hosts are needed in the subnet. /23 is 510 hosts /24 is 254 hosts so answer is /23 or B.
The option is B. ip address 192.168.0.0 255.255.254.0. Explanation: An office has 8 floors with approximately 30 to 40 users per floor. They make a total of 320 users, a mask of 255.55.255.0 only fits 254 users, which is not enough, so the next largest mask would be: 255.255.254.0.
To get a subnet to support 40 users we need at least 6 bits. 32-6 = /26
but we want to be able to get 8 different subnets so we need 3 more bits.
/26-3 = /23 .
We just need to find the subnet mask of /23
B is correct because i quote "One subnet must be used" one subnet is needed for all 8 floors and only A and B provide this with B uses must less address space
They most likely meant one subnet per floor, not just one big subnet for the whole office. It's a judgement call. They didn't say "per floor," but they often word things poorly, and that is probably what they meant. If the whole office is one subnet, then it's a flat network and no subnetting is needed at all, and the mask doesn't matter.
But subnetting is still needed if they want only one subnet, because with their allocated Class C address that we can see in the answer choices, they do not have enough space for that many hosts on a single subnet.
I managed to solve it by I didn't like the way I did it.
8 x 40 = 320 hosts
I manually tried to find which subnet can support this many hosts.
512, 254, 128, 64, 32, 16,8 , 4, 2, 1
If a /24 can support 254 - 2 hosts then
/23 can support 512 - 2 hosts so its must be a /23 network.
I just counted the subnet my memorizing the numbers
128, 192, 224,240,248, 252,254, 255
/17, /18, /19, /20, /21, /22, /23, /24
So the subnet mask for /23 is 255.255.254.0
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