Information Technology Reference
In-Depth Information
Summarization
Another characteristic of routing protocols is the capability to summarize routes. Protocols that
support CIDR and variable length subnet masks (VLSMs) have the capability to perform
summarization outside of IP class boundaries. By summarizing, the routing table size is
reduced and fewer routing updates appear on the network. Refer to the network in Figure 2-10.
Route Summarization
Figure 2-10
10.1.16.0/24
10.1.17.0/24
Router A
Router B
10.1.18.0/23
10.1.20.0/22
10.1.16.0/20
10.1.24.0/23
10.1.26.0/24
10.1.27.0/24
10.1.28.0/22
Router B has the following networks:
•
10.1.16.0/24
•
10.1.17.0/24
•
10.1.18.0/23
•
10.1.20.0/22
•
10.1.24.0/23
•
10.1.26.0/24
•
10.1.27.0/24
•
10.1.28.0/22
Router B generates eight route entries from these networks and forwards the routes to Router A.
Router B can summarize all these routes with a single route: 10.1.16.0/20. Protocol specifics on
how to summarize are discussed in the applicable chapters in this topic.
Default Routing
Another routing concept you must understand is the default route for the network. This route
becomes the gateway of last resort for packets with destination IP addresses that are not in the
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