Definition - What does Supernet mean?

A supernet is created by combining several Internet Protocol (IP) networks or subnets into one network with a single classless interdomain routing (CIDR) prefix. The new combined network has the same routing prefix as the collection of the prefixes of the subnets. The procedure used to create a supernet is commonly called supernetting, route aggregation or route summarization. Supernetting enables organizations to modify their network size and minimize the extensive requirement of network routing devices by combining several independent routes. It also helps to conserve address space and helps the router to effectively store routing information and minimize processing overheads while matching the routes. Supernetting supports the CIDR address coding scheme, allowing routing table entries to be reduced.

Techopedia explains Supernet

Supernetting simplifies network routing decisions and saves storage space on route tables. While supernetting, data bits are borrowed from the network ID and allocated to the host ID. A larger and more complicated network can block other routers from making topological changes, so a supernet improves convergence speed and enables a better and more stable environment. Supernetting requires the use of routing protocols that help to support CIDR. The other protocols - Interior Gateway Routing Protocol, Exterior Gateway Protocol and Routing Information Protocol Version 1 - do not support the transmission of subnet mask information.

Network identifiers used in the supernet can have any length. This permits the organizations to customize network size based on their requirements. For instance, two blocks of class C can be supernetted for a total of approximately 500 addresses. The route aggregation feature of supernetting can be used to group routing information for multiple networks or hosts into one “summarized” route.

The supernet concept includes some drawbacks, the most notable of which is the complexity of CIDR compared to a classful addressing system and the need for new routing protocols that support the CIDR. The ability to customize the network identifier length also makes it harder for the system administrators to differentiate between a host identifier and a network identifier. In order to solve this issue, a new form of IP address writing called slash, or CIDR, notation was developed.

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