Route Aggregation

Route aggregation is used to combine a set of more specific routes into a single more general route.

This reduces the number of routes advertised by a given protocol.

Example:

• A router has many stub interface routes subnetted from a Class C network.

• A router runs RIPv2 on another interface.

• In this case, these interface routes can be combined into a single aggregate route (for example, the Class C network).

  This single aggregate route can be redistributed into RIPv2, instead of the large list of individual routes.

Important - Be careful when aggregating if there are gaps in the route that is aggregated.

The interface that originates the aggregate routes does not use them to forward packets. Only the router that receives the routes uses them.

A router that receives a packet that does not match one of the component routes, should respond with an ICMP "Network Unreachable" message.

This prevents packets for unknown component routes from following a default route into another network.

In this situation, they might be continually forwarded back to the border router until their TTL expires.

To create an aggregate route, first specify the network address and subnet mask, followed by the set of contributing routes.

Define the contributing routes by specifying a source, such as a routing protocol or a static route, followed by a route filter, which is either a prefix or the keyword "all IPv4 routes".

An aggregate route can have many contributing routes. However, at least one of the routes must be already present to generate the aggregate.

Important - In a cluster, you must configure the routing settings separately on each Quantum Spark Cluster Member.