When working with IP networks, ISPs are often the culprits for buy blocks of static IPs for use within a company’s network. The ISP takes care of subdividing its network (a WAN) of IPs and provides you only your share to use within your section of its network (LAN).

But what happens when your network grows? Or, maybe as a security precaution, VLANs are introduced, and there is no one to perform the calculations for you? With your trusty iPhone and Subnet Calculator Pro from the App Store, you’ll be subnetting in no time.

SEE: iOS 9: The smart person’s guide

How to use Subnet Calculator Pro

After launching the app, you’re greeted to the first of four sections: CIDR or Classless Inter-Domain Routing. This section is straightforward even for users that have never subnetted a network.

Start by entering an IP address located in the first subnet of your range (Figure A).

Figure A

As noted in Figure A, the slider will modify the subnet mask, which will in turn adjust the number of subnets available in the range and the hosts that each subnet will allow — either making them greater or smaller as a result (Figure B and Figure C).

Figure B

Figure C

The second section offers support for Classful networking based on one of the three A, B, or C-classes of networks and includes a wealth of information regarding the specifics of each network, including the broadcast address, beginning to ending ranges, and wildcard masks (Figure D, Figure E, and Figure F).

Figure D

Figure E

Figure F

Section three is titled Supernet. A supernetwork is formed when at least two subnets are combined using a shared CIDR prefix (Figure G).

While less common except amongst network engineers, it is a nice feature, and you never know when you might need it.

Figure G

The bottom line

Two of the greatest features of Subnet Calculator Pro are: it’s local (which means it doesn’t have to go online to retrieve results), and it’s tiny — the app is roughly 400KB, making it downloadable on even the most storage-strapped iPhone.

The app is stark and minimal, lacking the visual flair usually associated with Apple products. The inclusion of IPv6 is only available as an in-app purchase.

Subnet Calculator Pro is a remarkably easy to use free app that yields spot-on results.

What do you think of Subnet Calculator Pro?

Are you a network administrator that has used this app? If so, tell us your thoughts or provide your subnetting app recommendations in the comments.