What is Route Summarization:

Route Summarization:
Route summarization is used to reduce the number of routes that a router advertises to its neighbor router. Routing updates, if we have a distance vector or link-state protocol, we can grow with the number of routes we need to advertise. In simple terms, a router that needs to advertise ten or more routes needs ten specific lines in its update packet. If the more routes you have to advertise, the size of the packet must be increase bigger. The bigger the packet, then it will take more bandwidth the update, we are reducing the bandwidth available to transfer data. But with the help of route summarization, We can advertise many routes with only one line in an update packet. This will reduces the size of the update, allowing us more bandwidth for data transfer.

When a new data flow enters to the router, firstly the router must check its routing table to determine which interface traffic must be sent out. The increasing number of routes the routing tables, then takes longer time, also leading to more used router CPU cycles to perform the lookup. So, the second reason for route summarization is that we want to minimize the amount of time and router CPU cycles that are used to route traffic.

Requirements for Route Summarization:

Necessary requirements for Route Summarization:
  The Routers need to be running a classless routing protocol, as they carry subnet mask information with them in their routing updates. (For examples: RIP v2, OSPF, EIGRP, and BGP.)

  The Addresses need to be assigned in a hierarchical fashion for the summarized address to have the same high-order bits. It does not look good if Router1 has network and while resides in Router2 and is assigned in Router3. No summarization could take place from the edge routers to Router4.

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