How many usable IP addresses can you get from a conventional Class C address?

admin2009-05-19  8

问题 How many usable IP addresses can you get from a conventional Class C address?

选项 A、128
B、192
C、254
D、256
E、510

答案C

解析 Explanation:
Class Caddresses range from 192.0.0.0 through 223.225.225.225 and default subnet maskof 255.255.255.0. In Class C addresses, the first 24 bits are used as for the network IDwhile only the last 8 bits is used for the host ID. Using the 2n-2 formula, we can calculate that Class C addresses can support a maximum of 254 (28-2) hosts.

Incorrect Answers:
D. Note that the question asked for the number of usable addresses, and not the total number of all addresses. We must subtract 2 for the network and broadcast addresses to calculate the number of usable addresses in any subnet.
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