Is this a typo

[TechInfo0999]

Hello all,

I am reading Todd's book CCNA Study Guide 6th edition for exam 640-802
I got confused because on page 97, in the section titled
"Class A Valid Host IDs" it says the following :

" Notice that 0s and 255s can be valid host IDs"
but then it continues to say
" .... the host IDs can't all be turned off or all be on at the same time"


I am really confused ...

Thanks

[lammle]

Ah..the typical problem, and one that make subnetting so confusing.

Host bits can use more then one octet. For example, a 172.16.0.0/16 means you have 16 host bits.

If you have 172.16.255.1/128, that is a valid host, but there is a still a 255 in the ip address.

You can have a 0 and a 255 in the IP address, as long as all host bits are not all off: 172.16.0.0 and all on 172.16.255.255, in this example.

cheers!
Todd

[TechInfo0999]

Hi Todd,

Figured it out .... thanks for the clarification though

Cheers