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This is a question from a homework assignment that I’m confused on. I’m stuck but I think the answer is “manufacturing” (192.168.1.64).

You are the network administrator for an industrial machinery manufacturer in Florida. The company manufacturing facility has four buildings—administration, manufacturing, development, and dispatch.

Each building is assigned a separate network address from the private Class C address of 192.168.1.0, by virtue of the fact that a subnet mask of 255.255.255.224 is being used. The “administration” building is assigned the subnet ID 192.168.1.32, “manufacturing” is assigned 192.168.1.64, “development” is assigned 192.168.1.128, and “dispatch” is assigned 192.168.1.192.

A user calls to report a problem accessing one of the company’s four FTP servers. You ask the user for their IP. They report it as 192.168.1.77. What department is the system that the user is using in?

Giacomo1968
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Omar Miguel Sanane
  • 29

2 Answers2

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If you mask the address with the subnet mask you get the subnet:

192.168.1.77    = 11000000.10101000.00000001.01001101
255.255.255.224 = 11111111.11111111.11111111.11100000
                  ===================================
Subnet          = 11000000.10101000.00000001.01000000

Convert it back to decimal, and you have your subnet which you can relate to the department.

Ron Maupin
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FWIW, I have been doing this work for years and subnet mask math still confuses me. So no worries. But you can solve this by some simple deductive reasoning from clearly/rationally looking at the following basics given in the question:

  • “administration” is assigned 192.168.1.32.
  • “manufacturing” is assigned 192.168.1.64.
  • “development” is assigned 192.168.1.128.
  • “dispatch” is assigned 192.168.1.192.

Without knowing any subnet mask math, just seeing 192.168.1.32 and 192.168.1.64 shows each network has 32 addresses available in some way. Then knowing that it then wouldn’t be too hard to deduce the following ranges assuming each range has 31 addresses (32 minus 1 for the router/switch address itself) including a broadcast address:

  • “administration” (192.168.1.32) goes from 192.168.1.33 to 192.168.1.63.
  • “manufacturing” (192.168.1.64) goes from 192.168.1.65 to 192.168.1.95.
  • “development” (192.168.1.128) goes from 192.168.1.129 to 192.168.1.159.
  • “dispatch” (192.168.1.192) goes from 192.168.1.193 to 192.168.1.223.

Note that since all of the subnets indicate a beginning (aka: router/switch) address plus that 31 address range, 192.168.1.77 therefore fits neatly into the “manufacturing” as you correctly assume.

The “trick” part of this question is the fact that the 192.168.1.96 and 192.168.1.160 subnets are missing. So it seems a bit off if you are unsure how network ranges work. But honestly a setup like this would easily equate to a real world scenario where subnets would not be allocated unless a need arose.

Giacomo1968
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