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# subnetting Class A

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

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.
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

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

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.
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.