Question

Which of the following are not valid Class A network IDs?

1) 10.0.0.0
2) 126.0.0.0
3) 172.16.0.0
4) 192.168.0.0

Answer 1

From the options provided, 172.16.0.0 and 192.168.0.0 are not valid Class A network IDs because they fall outside the Class A range and are classified as Class B and Class C private network IDs respectively.

Step-by-step explanation:

The valid Class A network IDs range from 1.0.0.0 to 126.0.0.0, where the first bit of the first octet is always 0. This means that any network ID beyond this range is not a valid Class A address. Thus:

1. 10.0.0.0 is a valid Class A network ID.
2. 126.0.0.0 is the last valid Class A network ID.
3. 172.16.0.0 is not a valid Class A network ID; it is a Class B private network ID.
4. 192.168.0.0 is not a valid Class A network ID; it is a Class C private network ID.

Therefore, the non-valid Class A network IDs from the options given are 172.16.0.0 and 192.168.0.0.