Supernet

A supernetwork, or supernet, is an (IP) network that is formed, for routing purposes, from the combination of two or more networks (or subnets) into a larger network. The new routing prefix for the combined network represents the constituent networks in a single routing table entry. The process of forming a supernet is called supernetting, prefix aggregation, route aggregation, or route summarization.

Supernetting within the Internet serves as a strategy to avoid topological fragmentation of the IP address space by using a hierarchical allocation system that delegates control of segments of address space to regional network service providers. This method facilitates regional route aggregation.

The benefits of supernetting are conservation of address space and efficiencies gained in routers in terms of memory storage of route information and processing overhead when matching routes. Supernetting, however, can introduce interoperability issues and other risks.

In Internet networking terminology, a supernet is a block of contiguous subnetworks addressed as a single subnet in the larger network. Supernets always have a subnet mask that is smaller than the masks of the component networks.

The size of routing tables has been rapidly increasing during the expansion of the Internet. Supernetting is the process of aggregating routes to multiple smaller networks, thus saving storage space in the routing table and simplifying routing decisions. Routing advertisements to neighboring gateways are reduced.

Supernetting in large, complex networks can isolate topology changes from other routers. This can aid in improving the stability of the network by limiting the propagation of routing traffic after a network link fails. For example, if a router only advertises a summary route to the next router, then it does not advertise any changes to specific subnets within the summarized range. This can significantly reduce any unnecessary routing updates following a topology change. Hence, it increases the speed of convergence and allows for a more stable environment.

Supernetting requires the use of routing protocols that support Classless Inter-Domain Routing (CIDR). , and version 1 of the (RIPv1) assume classful addressing, and therefore cannot transmit the subnet mask information required for supernetting.

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