I'm a student of electronics and get lessons in networking as well. But on one of my tests I got the question:

What subnet mask is indicated by the network address

I know the answer is but I don't understand why the answer must be and how to calculate the subnet mask? Also what does the /18 mean?


1 Answer 1


You must read a subnet mask in binary. Since your IP address ends with /18 it means the first 18 bits are high and the others are low. Getting a binary code of 11111111.11111111.11000000.0000. Put it back to decimals and you'll get

  • So in other words when I have an IP address like the subnet mask will be And will be
    – user5913
    May 30, 2014 at 22:30
  • That is correct.
    – user43384
    May 30, 2014 at 22:31
  • Ok thanks man! That cleared things up for me! Thanks for the fast reply!
    – user5913
    May 30, 2014 at 22:32

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