troubleshooting Question

subnet mask puzzle

Avatar of ken021600
ken021600Flag for Australia asked on
Windows 2000
5 Comments1 Solution488 ViewsLast Modified:
Hi,
considering the following scenario:
"You are the administrator of your company's network, which uses TCP/IP as its only protocol. The network uses the private address space of 172.16.0.0/16.
Your company projects rapid growth during the next three years. To reduce the risk of network saturation, you decide to subnet the network. You will eventually need to accommodate a maximum of 17 subnets. Each subnet will include a maximum of 1,200 hosts. Which subnet mask should you configure to meet both your current needs and your projected needs?"
A. 255.255.224.0
B. 255.255.240.0
C. 255.255.248.0
D. 255.255.254.0
E. 255.255.255.0

my questions are:
1) doesn't "172.16.0.0/16" mean IP address of 172.16.0.0 with a subnet mask of 255.255.0.0? why do we have to configure another subnet mask?
2) 17 subnets with each subnet including 1200 hosts will be 20400 hosts. so 2^15 is 32768 which is larger than 20400. so i thought i should leave 15 bits for these hosts and therefore 17 bits is left(32-15=17). so in binary, that would be 11111111.11111111.10000000.0000000 which in decimal would be 255.255.128.0. unfortunately my answer was wrong. Could anyone show me how to do the calculation correctly?

Thanks a lot in advance,

KEN
ASKER CERTIFIED SOLUTION
jhance

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