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Additional Cisco IOS
features that can help optimize bandwidth use are as follows:
- Dial-on-demand
routing (DDR)
- Switched access
- Route
summarization
- Incremental
updates
Dial-on-demand routing (DDR)
Connections for
infrequent traffic flow can be accomplished using DDR. In DDR,
active links are created only after interesting traffic is detected
by the router. This "only as
required" service replaces dedicated circuits that are charged
for even when that link is idle.
Switched access
Switched access provides the
capability to enable a WAN link on an as-needed basis via automated
router controls. One model for a reliable backbone consists of dual,
dedicated links and one switched link for idle hot backup. Under
normal operational conditions, you can load balance over the dual
links, but the switched link is not operational until one of the
dedicated links fails.
Traditionally, WAN connections over
the Public Switched Telephone Network (PSTN) have used dedicated
lines. Packet-switched networks, such as X.25
and Frame Relay, offer the advantage of providing global
connectivity through a large number of service providers with
established circuits to most major cities. Packet-switched networks
enable nodes to share the bandwidth by sending data in packets.
You can reduce the
number of router processing cycles by reducing the overall number of
routing entries in a router's routing table. This can be done using
the following Cisco IOS features:
Route summarization
The number of entries
in a routing table can be reduced by using route aggregation or, as
it is more commonly known, route summarization. Summarization
of routes occurs at major network boundaries for most routing
protocols by simply finding the common bits or bytes of addresses
that a router advertises. Instead of advertising all the routes, the
router only advertises the common bits or bytes (or summary) of the
routes. Some IP routing protocols, such as OSPF and Enhanced IGRP,
allow manual summarization on arbitrary boundaries within the major
network. Careful planning and address allocation is required for
route summarization to be most effective.
Incremental updates
Protocols such as
Enhanced IGRP and OSPF make more efficient use of bandwidth than
distance vector protocols by sending only topology changes rather
than the entire routing table contents at fixed intervals.
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