[olug] Subnet mask

[Daniel Linder]

> I am having a brain freeze and I cannot for the life of me figure this
> out.  I have been given a range of numbers to use at my job and I cannot
> figure out the subnet mask...Help!
> The numbers are 205.202.101.64-205.202.101.93.  Class C address from
> authority.  I know that by thinking about it, it is divided into 4
> subnets, right? (30 numbers into 128 is 4 times+).  ugh.  My head hurts
> today...

Here is a handy perl code snippet to help in times like these...
(Might need to run "perl -MCPAN -e 'install Net::CIDR'" to install the
Net::CIDR module.)

--- Begin perl code ---
#!/usr/bin/perl
use Net::CIDR;
use Net::CIDR ':all';


@list2=();
$x=64;
while ($x <= 93) {
        $line = "205.202.101.".$x;
        push(@list2,$line);
        $x++;
}

printf ("These addresses:\n");
foreach (@list2) {
        @cidr_list=Net::CIDR::cidradd($_, @cidr_list);
        printf ("$_, ");
}
printf ("\n\nSummarize to the following:\n");

foreach (@cidr_list) {
                printf ("-->$_\n");
}
--- End perl code ---

This program roduces this output:
--- Begin output ---
These addresses:
205.202.101.64, 205.202.101.65, 205.202.101.66, 205.202.101.67,
205.202.101.68, 205.202.101.69, 205.202.101.70, 205.202.101.71,
205.202.101.72, 205.202.101.73, 205.202.101.74, 205.202.101.75,
205.202.101.76, 205.202.101.77, 205.202.101.78, 205.202.101.79,
205.202.101.80, 205.202.101.81, 205.202.101.82, 205.202.101.83,
205.202.101.84, 205.202.101.85, 205.202.101.86, 205.202.101.87,
205.202.101.88, 205.202.101.89, 205.202.101.90, 205.202.101.91,
205.202.101.92, 205.202.101.93,

Summarize to the following:
-->205.202.101.64/28
-->205.202.101.80/29
-->205.202.101.88/30
-->205.202.101.92/31
--- End output ---

So, these are the four subnet ranges that cover the .64 through .93
inclusively.

Dan