How To: Breakdown IP Address Blocks

One of the most common questions I have as a solution engineer revolves around an IP Address or Subnet. What is a /30? How many IP’s are in a /29?, What is my gateway IP? The company I work for typically assigns the 1st available IP as the gateway IP so I send out the following information to partners and customers to help simplify answers to these questions for the typical user.

IP Breakdown - Charts and Tools


CIDR Table
Quick Snap of CIDR Blocks

LAN Block example:

LAN IP Block: ( – 8 Total IP addresses

Subnet mask: /29 or

Network address (Subnet ID):   – Using first IP address – not usable by customer

Gateway address:   – many providers default to use 1st avail IP (Host) as gateway address

Customer usable IP Address Range left: –

Broadcast Address:   – last IP address in range – not usable by customer

You can also use this handy calculator: Online Subnet Calculator

Example of Online Subnet Calculator
Online Subnet Calculator

The online calculator is simple to use:

1st octet range dictates network class radial button selection

  • Insert IP address in box that matches range you selected
  • Select subnet mask
  • After selection and input of these items, the calculator produces usable ranges starting with Host Address Range (or usable IP address range):
  • – (6 IP Addresses)
  • Remember, first usable .225 is used by typical provider as gateway address.

This is a quick simplification to get anyone started to quickly breakdown a subnet to get their IP assignments. I hope this quick guide helps!

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.