Question 1.
Using classful assumptions, what is the network address of 128.0.0.1?

a) 128.0
b) 128.0.0.0
c) 128
d) Illegal because the second octet is zero

Answer

Question 3.
Using classful assumptions, what will appear as the routing table entry for 192.168.0.0 with the subnet mask of 255.255.255.240?

a) This is an illegal subnet
b) 192.168.0.0
c) 192.168.0
d) 192.0.0.0

Answer

Answers

Question 1.
Using classful assumptions, what is the network address of 128.0.0.1?

a) 128.0
b) 128.0.0.0
c) 128
d) Illegal because the second octet is zero

Answer
b) 128.0.0.0

Explanation
The first octet is between 128 and 191, so it is a Class B address. The network part of a Class B address is in the first two octets (i.e., first 16 bits or a /16), but you must write out the full 32 bits of any IP address.

Zero in the second octet is perfectly legal. To understand how IP addressing really works, you need to stop thinking about octets and start thinking about bits. The network address part is the 16-bit string 1000000000000000.
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Question 3.
Using classful assumptions, what will appear as the routing table entry for 192.168.0.0 with the subnet mask of 255.255.255.240?

a) This is an illegal subnet
b) 192.168.0.0
c) 192.168.0
d) 192.0.0.0

Answer
a) This is an illegal subnet

Explanation
When you apply the mask, you will extract the first 28 bits; 24 bits of network and 4 bits of subnetting. The four subnet bits will be zero, which is invalid under classful assumptions.
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