[Kind of OT] Subnetting calculator for Linux (or a good one for WindowZ)

Steve Kratz stevek at derbyworks.com
Tue May 24 16:15:46 UTC 2005


The company I work for owns a block of 16 class-c addresses, which we
lease to our wireless networking customers. These customer's can buy as
many Ips as they need for their small business networks. I'll also throw
out that I'm a relative noob to subnetting. I understand the concept,
and how the logical AND operations work with the subnet/network ID, but
calculating it is above my head at the time

I'm trying to find a subnet (CIDR) calculator that works well for
splitting up subnets. One example I have is this:
Customer A needs 54 usable Ips
B needs 12
C needs 4...

These are already "live" as:

A 64.x.y.0 - .63 netmask /26
B 64.x.y.64 - .79 netmask /28
C 64.x.y.80 - .87 netmask /29

Now, the problem lies in the next customer (D) wants 90 Ips, which so
he's going to get a /25 block of 128 addresses. ALL of the calculators
I've tried end up choking on this. From my own guesswork, it should end
up with a range of .88 to .215... But, all of the calculators end up
saying that for 64.x.y.88 (network address) with a netmask of /25, ends
up starting back at .0 to .127, which is wrong (am I correct on this?)

Am I totally out of the ballpark on this, or is there some fundamental
calculation problem the calculators have?

I've tried sipcalc, gip (under Linux), Solarwinds and two others under
Windows.

Thoughts?




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