Subnetting Question

dfjama

I need some clarification regarding the 2 questions which I found on Lammle's book.

1-You have network with the subnet of 172.16.17.0/22. which is the valid host address?
The Answer is book is 172.16.18.255.

2-Your router has the following IP on Ethernet0: 172.16.2.1/23. Which of the following addresses can be valid host IDs on the LAN interface attached to the router?
The Answer: 172.16.2.255 & 172.16.3.0


My question is how come .0 & .255 became a valid host IDs, please explain.

Thanks

rob_crossley

dfjama wrote: »

I need some clarification regarding the 2 questions which I found on Lammle's book.

1-You have network with the subnet of 172.16.17.0/22. which is the valid host address?
The Answer is book is 172.16.18.255.

2-Your router has the following IP on Ethernet0: 172.16.2.1/23. Which of the following addresses can be valid host IDs on the LAN interface attached to the router?
The Answer: 172.16.2.255 & 172.16.3.0


My question is how come .0 & .255 became a valid host IDs, please explain.

Thanks

1. Because the valid Host range is 172.16.16.1 - 172.16.19.254 the .255 is the broadcast address. You can use .255 provided it's not the last address in the subnet.

So you can use 172.16.16.255 172.16.17.255 and even 172.16.18.255 but you cannot use 172.16.19.255 as that's the last address in the subnet.

2. Again with this 1 the valid host range is 172.16.2.1 - 172.16.3.254 you cannot use the beginning number of the Entire range 172.16.2.0 as this is the subnet ID and you cannot use the last number 172.16.3.255 as this is the broadcast range but any numbers in between these numbers are fine for usable host addresses.

Correct me if im wrong fellow posters.