A summary route, also known as route aggregation or superroute, is a technique used in network routing to reduce the number of routes that a router needs to handle and advertise to other routers.

This technique groups multiple networks or subnets into a single advertisement route, simplifying the routing table and improving the efficiency of the routing system.

Operation of the Summary Route

The summary route takes several individual routes that have a common part in their address and represents them as a single entry in the routing table using a less specific netmask.

For example, if a router has routes to 192.168.1.0/24 and 192.168.2.0/24, it could summarize them and advertise a single route to 192.168.0.0/22, which spans both subnets plus two other possible subnets within the same range.

Advantages of the Summary Route

1. Routing Table Simplification: Reduces the size of routing tables, which can improve router performance and decrease the amount of memory required to store these routes.
2. Reduction of Used Bandwidth: By advertising fewer routes, less bandwidth is used for routing protocols that share information between routers.
3. Minimizing the Propagation of Network Fluctuations: Summary routes can help stabilize networks by preventing minor changes in specific subnetworks from propagating across the entire network.
4. Improved Scalability: Facilitates network scalability by allowing the routing system to handle expansions without requiring significant changes to the global routing configuration.

Considerations

• Loss of Routing Detail: When summarizing, detail about individual routes is lost, which can be a problem in certain configurations where detailed traffic control is necessary.
• Choice of Suboptimal Routes: In some cases, summarization can lead to traffic following suboptimal routes, as routing is done toward the general summary address without possibly considering more specific and direct routes available.

Summary routing is especially useful in large networks where the number of routes can be very large and in situations where maintaining a large number of individual routes would be impractical or consume too many system resources.