What is supernet?
Networks or subnets combined into single nework with common CIDR mask is called supernets or supernetworks. The common routing prefix of supernet is aggregated from the prefixes of given networks or subnets and it must be smaller or the same as smallest component network prefix. This concept of creating a supernet is called supernetting or routing aggregation. Route aggregation reduces the number of advertised routes on huge networks by summarizing routes.
Supernetting was introduced to solve the problem with rapidly growing routing tables and because of IP version 4 address pool exhaustion. The main benefits of route aggregation (supernetting) are less memory and CPU power requirments for storing and processing routes. More information about supernets can be found in RFC 1338 - Supernetting: an address assignment and aggregation strategy.
Consider the following networks:
192.168.1.0/24 192.168.2.0/24 192.168.3.0/24 192.168.4.0/24To determine the supernet of the component networks do the following:
Convert all IP address of the networks and align them in a list:
11000000101010000000000100000000 11000000101010000000001000000000 11000000101010000000001100000000 11000000101010000000010000000000Note: For IP conversions from dotted-decimal to binary you can use IP conversion tool.
Find the common bit pattern starting from left that is common for all IP binary IP addresses. In this case it is
- Count how many bits does the common pattern have - it will be used as network prefix.
- End the same bit string with zeroes, so that there are 32 bits. Convert result back to dotted-decimal format and add routing prefix. The result supernet of these networks is 192.168.0.0/21
How to use supernet calculator
- Input one or multiple network IDs each in separate line in CIDR notation format, for example, 10.5.200.0/16. Networks without routing prefix specified will be treated as "/32" hosts.
- Press aggregate to summarize the supernet of the input networks.
- Invalid networks will be excluded from the calculation and there will "*" append to it.