# Supernetting ## What is Supernetting Supernetting, also called route aggregation or route summarization, is the process of combining multiple smaller networks into a single larger network for the purpose of routing. It is the opposite of subnetting. While subnetting divides a large network into smaller pieces, supernetting combines multiple smaller networks and represents them as a single route in a routing table. This reduces the number of entries in routing tables, which improves routing efficiency and speeds up packet forwarding decisions. ## Why Supernetting is Used As the internet grew, routing tables became extremely large, containing hundreds of thousands of entries. Large routing tables consume router memory and slow down the routing process. Supernetting addresses this problem by allowing multiple contiguous network addresses to be represented by a single aggregate route. Instead of a router needing to have separate routing table entries for 192.168.0.0/24, 192.168.1.0/24, 192.168.2.0/24, and 192.168.3.0/24, it can have a single entry for 192.168.0.0/22 that covers all four networks. ## How Supernetting Works To aggregate multiple networks into a supernet, the networks must be contiguous and their addresses must be a power-of-two aligned block. The supernet is represented with a shorter prefix length than the individual networks. The prefix length of the supernet is shortened until a single network address covers all the networks being aggregated. For example, to aggregate 192.168.0.0/24, 192.168.1.0/24, 192.168.2.0/24, and 192.168.3.0/24, you look at the binary representation of the third octet: 0, 1, 2, and 3 correspond to binary values 00, 01, 10, and 11. The first 22 bits are common to all four, so the supernet is 192.168.0.0/22. ## Route Summarization in Routing Protocols Routers running dynamic routing protocols can be configured to advertise summarized routes rather than individual subnet routes. This is especially useful at the boundaries between parts of a network. A router at the edge of a department's network can advertise a single summarized route covering all subnets in that department, rather than individual routes for each subnet. This keeps routing tables in the rest of the network small and simplifies network management. ## Classless Inter-Domain Routing and Supernetting The development of CIDR was closely tied to supernetting. CIDR allows routing prefixes of any length rather than being constrained to the 8, 16, or 24 bit boundaries of classful addressing. This flexibility enables both subnetting at arbitrary boundaries and supernetting of multiple classful networks. Modern internet routing is entirely based on CIDR and relies heavily on route aggregation to keep the global routing table manageable.