Subnet Speed Practice #2: Answers

certskills
By certskills May 31, 2011 12:47

This post makes no sense without reading this post first. The earlier post lists 5 subnetting problems, and tells you to time yourself. The answers are below the fold in this post. Don’t look til you try it for yourself! Post questions if you have them.

Problem Network Bits Subnet Bits Host Bits # Hosts
10.1.1.1/23 8 15 9 510
172.16.203.203/25 16 9 7 126
192.168.1.161/29 24 5 3 6
10.1.99.101/26 8 18 6 62
172.16.77.177/27 16 11 5 30
  Subnet ID 1st Addr. last Addr. B’cast
1 10.1.0.0 10.1.0.1 10.1.1.254 10.1.1.255
2 172.16.203.128 172.16.203.129 172.16.203.254 172.16.203.255
3 192.168.1.160 192.168.1.161 192.168.1.166 192.168.1.167
4 10.1.99.64 10.1.99.65 10.1.99.126 10.1.99.127
5 172.16.77.160 172.16.77.161 172.16.77.190 172.16.77.191
Subnetting Speed Practice 2
Serial Link Interview Question
certskills
By certskills May 31, 2011 12:47
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12 Comments

  1. Karma March 16, 18:02

    Is 2min per question too slow?

    Reply to this comment
  2. JAMES December 21, 11:58

    Took me 12 min – 30 sec; practice makes perfect!
    Will keep at it!

    Reply to this comment
    • CCENTSkills January 18, 10:28

      James – that is the right attitude!
      Helps to do a little every day! Do it!

      Have fun, hope you’re sticking with it!
      Wendell

      Reply to this comment
  3. Bryant January 22, 20:36

    It took me 8 mins. I am going to keep practicing

    Reply to this comment
  4. parvesh June 21, 20:33

    192.168.1.161/29
    is broadcast address right
    isn’t it should be 192.168.1.163

    Reply to this comment
    • Chris June 26, 07:58

      Hello Parvesh

      /29 – 255.255.255.248
      256 – 248 = 8
      192.168.1.160 – Network address
      192.168.1.161 – 1st host
      192.168.1.166 – last host
      192.168.1.167 – Broadcast

      Reply to this comment
  5. Jorge November 4, 17:42

    Huff, took me 14:18:81

    Reply to this comment
  6. Albert November 17, 07:47

    I think the answer for the first address for sub 10.1.0.0/23 is wrong. It must be 10.1.1.0 but you put 10.1.0.1

    Are you agree with me?

    Reply to this comment
    • Wendell Odom November 17, 19:51

      Hi Albert,
      Thanks for the post! I disagree, but that’s what these exercises are great for – give it a try, struggle a bit, and learn.
      Thinking it decimal, whatever the subnet ID is, add 1 to the 4th octet to get the numerically lowest address.
      Conceptually, I think you’re thinking about the /23 mask as creating 1 host bit in the 3rd octet, but ignoring the 8 host bits in the 4th octet.
      The usable addresses in the subnet are 10.1.0.1, 10.1.0.2, .3, .4, etc to 10.1.0.255, then 10.1.1.0, 10.1.1.1, 10.1.1.2, .3, etc to 10.1.1.254 (last usable), the 10.1.1.255 as the subnet broadcast address.

      Hope this helps.
      Wendell

      Reply to this comment
  7. Albert November 19, 14:56

    Dear Wendell,

    I just noticed my logic was totally upside down, so yes your explanation helps.

    Now it’s burned in my memory : ” Add 1 to the 4th octet whatever there is before to get the first address”.

    Thank you for help.

    Reply to this comment
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