The Cisco IOS also supports the
following bandwidth optimization features:
- Dial-on-demand routing (DDR)
- Switched access
- Route summarization
- Incremental updates
Dial-on-Demand Routing
An organization cannot always afford dedicated WAN circuits, or even
Frame Relay, for every remote site. At sites that require only
occasional WAN connectivity, dial-on-demand routing (DDR) offers an
efficient, economical alternative. As shown in the figure, a router
configured for DDR will listen for interesting traffic and wait to
build the WAN link. When the router receives interesting traffic (as
defined by the administrator), it places a call to activate the
link, which is commonly ISDN.
Route Summarization
The number of entries in a routing table can be reduced if the
router uses one network address and mask to represent multiple
networks or subnetworks. This technique is called route aggregation,
or route summarization. Some routing protocols automatically
summarize subnet routes based on the major network number. Other routing
protocols, such as OSPF and EIGRP, allow manual summarization. You
will learn more about route summarization in the next chapter.
Incremental Updates
Some routing protocols, such as OSPF and EIGRP, send routing updates
that contain information only about routes that have changed. These
incremental routing updates use the bandwidth more efficiently than
simple distance-vector protocols, which transmit their complete
routing table at fixed intervals, regardless of whether a change has
occurred.
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