05-13-2012 01:35 AM - edited 03-07-2019 06:40 AM
Hi,
This is my IP address 174.121.14.165/23
/23 - 255.255.254.0
:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
Magic number is: 256-254=2
:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
Networks:
0
2
4
6
8
10
12
14
16 ...
Network address: 174.121.12.0
Broadcast address: 174.121.13.255 (12+Magic number -1 = 12+2-1 =13)
Where is mistake?
-------------------------------------------------------------------------------------------------------------------------
Please help me,
Greetings.
Solved! Go to Solution.
05-13-2012 04:53 AM
Joni,
Your math is fine, but the network address that you have on your interface (your IP) will start at 174.121.14.0 - 172.121.15.255.
HTH,
John
05-13-2012 05:38 AM
Joni,
The magic number, as you call it, is indeed 2 in the third octet of the netmask. Hence, you need to round down the third octet of the IP address to the nearest integral multiple of 2 when calculating the network address. However, in the IP address 174.121.14.165, the "14" is already an integral multiple of 2 so you do not change it. Right?
Best regards,
Peter
05-13-2012 05:57 AM
Joni,
In addition to what Peter said, the "magic number" is considered your boundary. For example, if your address the magic number is 2. Multiples of 2 would be the starting network address for the next block:
172.121.2.0
172.121.4.0
172.121.6.0
etc.
The magic number is the starting boundary for that network, and the broadcast address is -1 less than the next starting boundary:
172.121.2.0 - 172.121.3.255 (broadcast) (256 - 1)
The useable addresses are calculated like:
254 (in the second octet) (11111110)
0 = There are 8 bits left in the 4th octet = 00000000
So together it's 11111110.0000000
There are 9 0s in the host portion of your mask, so you get 512 hosts per network. Then you take 512 - 2 leaving you with 510 useable addresses (172.121.2.1 - 172.121.3.254)
HTH,
John
05-13-2012 03:31 AM
Was your ip not in x.x.14.0?
05-13-2012 04:53 AM
Joni,
Your math is fine, but the network address that you have on your interface (your IP) will start at 174.121.14.0 - 172.121.15.255.
HTH,
John
05-13-2012 05:11 AM
Thanks for the reply,
I know my IP address should be in the range 174.121.14.0 - 172.121.15.255, in my calculation
Network Address is: 174.121.12.0
Broadcast address is : 174.121.13.255, which is obviously wrong.
But I ask myself why, if I calculate correctly all.
05-13-2012 05:38 AM
Joni,
The magic number, as you call it, is indeed 2 in the third octet of the netmask. Hence, you need to round down the third octet of the IP address to the nearest integral multiple of 2 when calculating the network address. However, in the IP address 174.121.14.165, the "14" is already an integral multiple of 2 so you do not change it. Right?
Best regards,
Peter
05-13-2012 05:57 AM
Joni,
In addition to what Peter said, the "magic number" is considered your boundary. For example, if your address the magic number is 2. Multiples of 2 would be the starting network address for the next block:
172.121.2.0
172.121.4.0
172.121.6.0
etc.
The magic number is the starting boundary for that network, and the broadcast address is -1 less than the next starting boundary:
172.121.2.0 - 172.121.3.255 (broadcast) (256 - 1)
The useable addresses are calculated like:
254 (in the second octet) (11111110)
0 = There are 8 bits left in the 4th octet = 00000000
So together it's 11111110.0000000
There are 9 0s in the host portion of your mask, so you get 512 hosts per network. Then you take 512 - 2 leaving you with 510 useable addresses (172.121.2.1 - 172.121.3.254)
HTH,
John
05-13-2012 10:15 AM
Thank you all for help, now I understand
Thank you!.
greeting from Bosnia
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