Route summarisation is the ability to take a number of contiguous network numbers in a routing table and advertise these contiguous routes as a single summarised route. Thus cutting down on the number of networks being advertised.
Route summarisation, is needed to reduce the number of routes that a router advertises to its neighbour. Remember that for every route you advertise, the size of your update grows. Some experts have said that if it hadn’t have been for route summarisation, the Internet backbone would have collapsed from the sheer size of its own routing tables back in 1997.
Routing updates, whether done with a distance vector or link-state protocol, grow with the number of routes you need to advertise. In simple terms, a router that needs to advertise ten routes needs ten specific lines in its update packet. The more routes you have to advertise, the bigger the packet. The bigger the packet, the more bandwidth the update takes, reducing the bandwidth available to transfer data. But with route summarisation, you can advertise many routes with only one line in an update packet. This reduces the size of the update, allowing you more bandwidth for data transfer.
Summarisation allows you to create a more efficient routing environment by providing the following advantages:
- It reduces the size of routing tables, requiring less memory and processing.
- It reduces the size of updates, requiring less bandwidth.
- It contains network problems