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Path Determination 191
Path Determination
Path determination requires the use of dynamic routing, which involves the exchange of
information between routers.
Dynamic routing protocols were created to overcome the shortcomings of static routing.
Choosing the right routing protocol depends on the customer's business and technical
requirements.
Routing protocols determine the best path to a destination network by exchanging routing
metrics. When there are several ways to get to the same destination, the router uses metrics
to calculate the best path. Figure 6-7 illustrates how path determination can be determined
by metric.
Figure 6-7
Path Determination
Load-Balancing Modes for IP
In addition to running routing protocols to develop a routing topology, a major function of a
router is to switch packets from incoming interfaces to outgoing interfaces. Switching involves
receiving a packet, determining how to forward the packet based on the routing topology and
policy requirements, and switching the packet to the right outgoing interface.
Cisco supports several switching methods, offering varying speeds and behaviors. For the most
part, the fastest switching method available should be selected for an interface type and
protocol. Using a speedy switching mode is especially important on backbone and core
enterprise routers. Fast switching is usually, but not always, the default setting. Check the
version of IOS software to be sure.
NOTE
Check Cisco's documentation for more information about the methods supported for various
router platforms, protocols, and interfaces. Documentation for Cisco products is available
online at http://www.cisco.com/univercd/home/home.htm.
A T1 to
reach
you
IGRP
2 hops
to reach
you
RIP
A low-cost
route to
reach you
OSPF
87200333.book Page 191 Wednesday, August 22, 2001 2:37 PM