A. 255.255.255.254 cannot be used as a subnet mask because only one bit is left for node addresses. So the node address could only be a "0" or a "1"; a node address of "0" is a reference to the network itself, and a node address of 1 is used as the broadcast address for that network. Therefore, there would not be any valid node addresses for such a network.
Q. Which two devices are on the same network?
The subnet mask of #1 tells us the first 3 octets specify the network number, so #1 is on network 92.192.192.
The subnet mask of #2 tells us that the first octet only specifies the network number, so #2 is on network 92.
The subnet mask of #3 tells us that the first 3 octets specify the network number, so #3 is on network 92.192.193.
The subnet mask of #4 tells us that the first 3 octets specify the network number, so #4 is on network 92.192.192.
Because #1 and #4 have the same network number, they must be on the same network.
Q. What other IP addresses have the same network number as 128.253.10.10 with subnet mask 255.255.240.0?
A: The network number portion of 128.253.10.10 is the first two octets plus the first 4 bits of the third octet, as indicated by the mask: (11111111.11111111.11110000.00000000). If we look at the network number of 128.253.10.10, it is 10000000.11111101.0000. So other devices on this same subnet can be in range 128.253.0.x through 128.253.15.x, as seen from below. Note that 128.15.255 would be the broadcast address for the network.
| Network bits | Node bits | |
| mask:255.255.252.0 | 11111111.11111111.1111 | 0000.00000000 |
| 128.253.10.10 | 10000000.11111101.0000 | 1010.00001010 |
| 128.253.0.1 | 10000000.11111101.0000 | 0000.00000001 |
| 128.253.1.1 | 10000000.11111101.0000 | 0001.00000001 |
| 128.253.8.92 | 10000000.11111101.0000 | 1000.01011100 |
| 128.253.11.5 | 10000000.11111101.0000 | 1011.00000101 |
| 128.253.12.1 | 10000000.11111101.0000 | 1100.000000001 |
| 128.253.15.255 | 10000000.11111101.0000 | 1111.11111111 |