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Right, im going over subnets again after doing them last year, i thought i had remembered it until the Cisco testerererer cd hit me with this: (I have put this ...
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  1. #1
    Just Joined!
    Join Date
    Jan 2005
    Posts
    68

    Subnetting help


    Right, im going over subnets again after doing them last year, i thought i had remembered it until the Cisco testerererer cd hit me with this: (I have put this in code tags as it allows spacing)

    Code:
            Given the IP address 172.156.100.100 & a subnet mask of 255.255.255.224 what is the broadcast address:
    
            A:172.156.100.127
    
            B: 172.156.100.255
    
            C: 172.156.32
    
            D: 172.156.100.128
     
    So I have done my working like this:
    
    IP = 172.156.100.100 /27
    
    .                            | N | N | N | S |  H  |
    Broadcast:                               011 11111    = 172.156.100.127
    
    But the correct answer is D: 172.156.100.128??
    
    I have tried to work through the example given again using ANDing:
    
    Subnet mask = 225.225.225.224
    IP                 = 172.156.100.100
    
    Only showing 'The intresting Octet':
    
    Subent =    224   =   11100000
    IP     =    100   =   01100100
                           ------------
    Network address =     01100000 = 96
    
    Therefore;
    
    Broadcast       =     01111111 = 127
    Could the Cisco CD have a little error, or a i doing this the wrong way?

    I have worked through another example from the same CD:

    What is the broadcast for IP subnet 192.168.100.32, given a mask of 255.255.255.244.

    So, 192.168.100.32 /27

    Code:
            | S  |    H    |
    224      111  00000
             001  00000    - Network
             001  11111    - Broadcast = 192.168.100.63
    Which, according to the CD is correct. Is the CD wrong? This is confusing me a lil.

    Thanks much

  2. #2
    Just Joined!
    Join Date
    Sep 2005
    Posts
    44
    May be you are right.There will be some mistake in cisco cd.

    Put your IP address and Subnet Mask.The result will be the same.

    http://www.subnetonline.com/subcalc/subnet8.html

  3. #3
    Linux Newbie
    Join Date
    Mar 2005
    Location
    Romania
    Posts
    186
    Yes, the CD is wrong. The broadcast address for 172.156.100.100/27 is 172.156.100.127... 172.156.100.128 is the network address for the following subnet.
    You can only be young once. But you can always be immature.

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