subnetting Class A

x5150x5150 Posts: 42Member ■■□□□□□□□□
Theres a question in my Sybex cd that came with the Lammle book that doesn't make sense to me.

The question reads.

Which of the following IP's fall into the CIDR block of
110.68.4.0/18? (Choose three).

a) 110.68.8.32
b) 110.68.7.64
c) 110.67.6.255
d) 110.66.3.254
e) 110.65.5.128
f) 110.64.12.128


This is how i am trying to solve the question.
Class A address
Mask /18 255.255.192.0
So 2nd octet, we have block size of 1
third octet, size 64
Therefore my choices would only be a and b, they are the only ones even in the 110.68 subnet

But the answers are b,c,e.
The cd says...
A class A network address with a /18 is 255.255.192.0 The subnets in the third octet are 0,64,128,192. The network address in question is 110.64.0.0, with a broadcast of 110.64.127.255, since the next subnet is 110.64.128.0

Comments

  • lowfokuslowfokus Posts: 3Member ■□□□□□□□□□
    x5150 wrote:
    Theres a question in my Sybex cd that came with the Lammle book that doesn't make sense to me.

    The question reads.

    Which of the following IP's fall into the CIDR block of
    110.68.4.0/18? (Choose three).

    a) 110.68.8.32
    b) 110.68.7.64
    c) 110.67.6.255
    d) 110.66.3.254
    e) 110.65.5.128
    f) 110.64.12.128

    This is how i am trying to solve the question.
    Class A address
    Mask /18 255.255.192.0
    So 2nd octet, we have block size of 1
    third octet, size 64
    Therefore my choices would only be a and b, they are the only ones even in the 110.68 subnet

    But the answers are b,c,e.
    The cd says...
    A class A network address with a /18 is 255.255.192.0 The subnets in the third octet are 0,64,128,192. The network address in question is 110.64.0.0, with a broadcast of 110.64.127.255, since the next subnet is 110.64.128.0

    seems you are right to me. 265-192= 64.
    the ips in that /18 would go:

    110.68.0.0, 110.68.64.0, 110.68.128.0, 110.68.192.0, etc.

    so a+b fall in that subnet of 110.68.0.0/18.

    cheers.
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