Subby - Subnet Calculator | IP Calculator

Description

This subnet calculator is a handy tool for finding the number of possible subnets for any given network address block. You can use this IP calculator to choose the combination of subnets and number of hosts per subnet that suits your network and get the host address range and broadcast address for any given subnet mask. IP calculations can usually be performed mentally but it's better to have an option to double check the calculations before configuring them to your devices using this handy subnet calculator.

This online subnet calculator can be used to calculate network configurations, using an IP or network address, a netmask, a Cisco wildcard mask or CIDR notation. The IP calculator can also be used to do reverse subnetting where the number of hosts is known, but the netmask is unknown. By giving a second netmask, it's possible to design subnets and supernets.

What is CIDR?

CIDR or Classless Inter Domain Routing was developed to reduce the increasing size of routing tables of large routers, which was quite hard with classful routing. The memory usage of classful routing is enormous, which results in unreasonable expensive hardware. But also the performance was compromised, since large tables need to be looked up without a more dynamic IP interval mechanism, like CIDR imposes. Another problem with a classful setup is, that the bandwidth usage is quite high when routers exchange their routing information.

Simply spoken, CIDR using address aggregation can be used to address multiple networks with one single routing entry. Consider this example, where a router needs to distribute traffic for eight separate networks through the gateway 192.168.1.1:

Without CIDR, the routing table would become quite large, as every network needs an own entry. With CIDR, the networks can be condensed into one single rule (using 192.168.2.64/27/24 syntax for the calculator):

By using this Subby subnet calculator allows you to find available addresses, save time provisioning or reclaiming IP addresses, and increase network and application uptime.

Key Features
• IP calculator
• Netmask calculator
• CIDR calculator
• List generator for subnet addresses