Re: [OT] CIDR Mask calculation

[Jeff Vian <jvian10 charter net>]

On Thu, 2006-10-12 at 18:44 +0100, Rob Andrews wrote:
> On 12-Oct-2006 17:52.11 (BST), Dave Ihnat wrote:
>  > Anyway, the addresses you gave, converted to binary, are:
>  > 
>  >   219.128.0.0    : 11011011.10000000.00000000.00000000
>  >   219.137.255.255: 11011011.10001001.11111111.11111111
>  >                                ^
>  > The last bit that is invariant between the two is marked with the caret;
>  > converting back to a decimal dotted-quad (you can use 'dc' again--to set
>  > the input to binary, simply change the 'o' operand in the above example
>  > to an 'i', then input the binary value and print.)
>  > 
>  >   Mask
>  >   255.240.0.0    : 11111111.11110000.00000000.00000000
>  > 
>  > or, in conventional notation, 219.128.0.0/12.
> 
> That's 219.138.0.0 - 219.143.255.255 though :)
> 
Yep, as someone else already said, it cannot be done with a single
netmask.  The desired range encompasses 2 subnets. or you have overlap
with other ranges as noted above.


> -- 
> rob andrews                       :: pgp 0x01e00563 :: rob choralone org
>