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I am confused that can we use the ip address with host id is zero?

Such as below subnet example:

Address: 192.168.18.23
Netmask: 255.255.248.0

Hosts/Net: 2046

HostMin: 192.168.16.1
HostMax: 192.168.23.254

As the min host id is 192.168.16.1, so it will increase to 192.168.16.255, and then the ip 192.168.17.0 <---- can we use this?

Thanks

http://jodies.de/ipcalc?host=192.168.18.23&mask1=21&mask2=

Samuel Lui
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1 Answers1

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Yes.

    (192.168) . 0001 0001 . 0000 0000 = 192.168. 17.  0
not (255.255) . 1111 1000 . 0000 0000 = 255.255.248.  0
    ---------------------------------------------------
    (000.000) . 0000 0001 . 0000 0000 =   0.  0.  1.  0

So actually, your real host-id is .1.0 = 0000 0001 0000 0000 = 256

PhilMasteG
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  • would you say more for this: your real host-id is = 256? Thank you !! – Samuel Lui Jul 15 '12 at 05:08
  • When you do a logical `(192.168.17.0) not (255.255.248.0)` you get `0.0.1.0` which is your host-id. Converting this "IP-Address" into a decimal number (convert each octet to binary, forget the dots, convert to decimal: `0.0.1.0 = 00000000 00000000 00000001 00000000 = 256`), you get host-id 256. This, you CAN use. If however you have the Subnet-Mask 255.255.255.0 and you do `(192.168.17.0) not (255.255.255.0)` you get `0.0.0.0` and your host-id is zero, which you CANNOT use. – PhilMasteG Jul 15 '12 at 05:25
  • WOW!!!!!! THANK YOU VERY MUCH!!! This is my first time to use stackflow, and I have your explanation ~ I feel confidence in here. Thanks again ! – Samuel Lui Jul 15 '12 at 06:16