What you are looking for are common bits on the network side of the addresses. To do this, you need to look at the routes in binary to see if there are any specific bit patterns that you can use to your advantage. You want to use route summarization to reduce the burden on this upstream router. Without route summarization, Vancouver would have to advertise 16 networks to Seattle. Therefore, a second reason for route summarization is that you want to minimize the amount of time and router CPU cycles that are used to route traffic.įIGURE 4-1 Four-City Network Without Route SummarizationĪs you can see from Figure 4-1, Winnipeg, Calgary, and Edmonton each have to advertise internal networks to the main router located in Vancouver. The larger the routing tables, the longer this takes, leading to more used router CPU cycles to perform the lookup. This reduces the size of the update, allowing you more bandwidth for data transfer.Īlso, when a new data flow enters a router, the router must do a lookup in its routing table to determine which interface the traffic must be sent out. But with route summarization, you can advertise many routes with only one line in an update packet. The bigger the packet, the more bandwidth the update takes, reducing the bandwidth available to transfer data. The more routes you have to advertise, the bigger the packet. In simple terms, a router that needs to advertise ten routes needs ten specific lines in its update packet. Routing updates, whether done with a distance-vector protocol or a link-state protocol, grow with the number of routes you need to advertise. It has been said that if there were no route summarization, the Internet backbone would have collapsed from the sheer size of its own routing tables back in 1997! Remember that for every route you advertise, the size of your update grows. Route summarization, or supernetting, is needed to reduce the number of routes that a router advertises to its neighbor. This chapter provides information concerning the following topics:Įxample for understanding route summarization
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