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Requirements of the Scalable Internetwork
The task of creating smoothly running, efficient LANs and internetworks is
obviously very important, but optimizing the bandwidth on a WAN can be
very difficult. The best way to reduce the bandwidth usage is to reduce the
amount of update traffic on the LAN that will be sent over your WAN. The
Cisco IOS features available to help reduce bandwidth usage are as follows:
Access lists Used to permit or deny certain types of traffic from entering
or exiting a specific router interface. They can stop basic traffic, broad-
casts, and protocol updates from saturating a particular link. TCP/IP,
IPX, and AppleTalk can all be filtered extensively.
Snapshot routing Commonly used for ISDN connections when running
distance-vector protocols, it allows routers to exchange full distance-
vector routing information at an interval defined by the administrator.
Compression over WANs The Cisco IOS supports TCP/IP header and
data compression to reduce the amount of traffic crossing a WAN link.
Link compression can be configured, which compresses header and data
information into packets. This is accomplished by the Cisco IOS prior to
sending the frame across the WAN.
DDR (Dial-on-Demand Routing) DDR allows wide area links to be
used selectively. With it, the administrator can define "interesting" traffic
on the router and initiate point-to-point WAN links based upon that traf-
fic. What denotes interesting traffic is defined by access lists, so a great
deal of flexibility is afforded to the administrator. For instance, an expen-
sive ISDN connection to the Internet could be initiated to retrieve e-mail,
but not for a WWW request. DDR is an effective tool in situations where
WAN access is charged according to a quantified time interval--it's best
to use it in situations where WAN access is infrequent.
Reduction in routing table entries By using route summarization and
incremental updates, you can reduce the number of router processing
cycles by reducing the entries in a routing table. Route summarization
occurs at major network boundaries, which summarize all the routes
advertised into one entry. Incremental updates save bandwidth by sending
only topology changes instead of the entire routing table when transmit-
ting updates.
Switched access Packet-switched networks such as X.25 and Frame
Relay provide global connectivity through a large number of service pro-
viders with established circuits to most major cities.
Copyright ©2001 SYBEX , Inc., Alameda, CA