+ Reply to Thread
Results 1 to 3 of 3
  1. Senior Member 2URGSE's Avatar
    Join Date
    Jun 2010
    Location
    RTP, North Carolina
    Posts
    196

    Certifications
    A+, Network+, CCNA
    #1

    Default VLSM Question help

    Objective:

    Given 172.16.8.0/22, divide the network so the following are requirements are met:


    Sales Department needs 300 hosts.
    Marketing Department needs 76 hosts.
    Administration Department needs 24 hosts.
    HR Department needs 12 hosts.
    Accounting Department needs 5 hosts.


    So I start with the Sales Department.

    (2^n)-2 = 300

    When n=9, the max number of hosts is 510, so that will satisfy the 300 hosts Sales needs.

    Next I take 32-9= 23, so the mask for the Sales subnet is /23.

    Now comes the part that I get lost and need help.

    I'm trying to find the first host address and last host address.

    The first host address is 172.16.8.1, the last host address is 172.16.9.254. I get that part.

    Next is the Marketing Department. (2^n)-2 = 76, so n=7 to satisfy this requirement.

    This subnet is 172.16.10.0. Can someone please shed some light on how the got to that subnet?

    The next subnet is 172.16.10.128, how did they get there?


    * Please no binary stuff, I don't use it in my studies, and surely not on the exam.
    Reply With Quote Quote  

  2. SS -->
  3. Junior Member Registered Member
    Join Date
    Aug 2017
    Posts
    5

    Certifications
    CCNA Security & Voice, CCNP R/S
    #2
    It’s been awhile for me but without using binary, 172.16.10.0 and 172.16.10.128, are simply the next usable addresses with the range 172.16.8.0/22


    Your starting subnet is 172.16.8.0/22, which provides the range 172.16.8.1 - 172.16.11.254.


    Your calculations so far are on point, for Sales you'd use 172.16.10.0/25 which would allow hosts in the range 172.16.8.1 to 172.16.9.254.


    172.16.9.255 is the broadcast address for that range. The very next address would be 172.16.10.0


    Your next calculations:


    (2^h) - 2 = hosts
    (2^7) - 2 = 126
    h = 7
    32 - 7 = 25


    172.16.10.0/25 the usable range is 172.16.10.1 - 172.16.10.126


    172.16.10.127 would be the broadcast address, 172.16.10.128 would be the next address.


    Then, just keep going.


    172.16.10.128/27 - 30 hosts/24 needed - 172.16.10.129 - 172.16.10.158, broadcast 172.16.10.159


    172.16.10.160/28 - 14 hosts/12 needed - 172.16.10.161 - 172.16.10.174, broadcast 172.16.10.175


    172.16.10.176/29 - 6 hosts/5 needed - 172.16.10.177 - 172.16.10.182, broadcast 172.16.10.183
    Reply With Quote Quote  

  4. Senior Member Mr.Robot255's Avatar
    Join Date
    Apr 2017
    Location
    Ireland
    Posts
    111

    Certifications
    A+, MTA 98-366 ,Net+,CCent
    #3
    i'm not great at explaining stuff but i will give it a go. (and hope i'm right)


    300=/23 - /23 = 512 host
    76=/25 - /25 = 128 host
    24=/27 -/27 = 32 host
    12=/28 -/28 =16 host
    5=/29 -/29 =8 host

    and we lose the first host and last host of each of them ,1st being Network I.D and last host being Broadcast.

    so from 172.16.8.0 /22
    the first block of 300 hosts will take 512 hosts a /23 as the its the nearest match bringing it to
    172.16.8.0 - 172.16.9.255 /23
    next block will then start from 172.16.10.0

    so we then have
    172.16.10.0 - 172.16.10.127 /25 (this covers our 76 hosts to nearest match/block size)

    next will start as 172.16.10.128 - 172.16.10.159 /27

    next will start as 172.16.10.160.............................




    Something i use>
    This is the chart i use for subnetting if you look for a /27 directly below it u see it will see it is for class C -255.255.224.0 and directly under the 224 is 32 for your block size which then will directly map to 8 subnets.
    The mapping works like this using the bottom row we can say host and subnets
    255 to the 1 (255 hosts to 1 subnet)
    128 to the 2 (128 hosts to 2 subnets) etc
    64 to the 4
    32 to the 8
    16 to 16


    --------/25 ---/26 ----/27--- /28--- /29 ----/30 -----/31--- /32

    0 - ----128--- -192 -----224 ----240---- 248-----252------254 ----255
    255 - -128 -----64 -----32-------16 ------8--------4 ---------2 -------1




    The quality isn't great but this is the video that made everything make sense to me.
    https://www.youtube.com/watch?v=GSX1GlaznKM&t=41s

    and part 2
    https://www.youtube.com/watch?v=U9dVVIk8_zA&t=42s
    Last edited by Mr.Robot255; 09-10-2017 at 01:46 AM.
    Reply With Quote Quote  

+ Reply to Thread

Social Networking & Bookmarks