3Com CoreBuilder 3500, Руководство по внедрению, Страница: 303 / 592

Routing Policies 303
Important
Considerations
Even though Routing Policies are not true routing protocols and are
considered optional, they can increase network efficiency.
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You can increase speed and security simply by limiting the number of
devices from which the router receives data.
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You can establish a neighbor list of devices, which is a list of trusted
systems whose addresses you have confidence in.
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You can associate the list of devices with a specific traffic direction,
either incoming or outgoing. As a result, you can assign very precise
routes of traffic, thereby keeping tight control over them.
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By adjusting the relative importance of certain policies over others,
you can exercise great control over the type and amount of traffic to
and from your system.
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If an incoming RIP route has a metric set to 16, which indicates that
the route is invalid, an existing IP RIP Import Accept Policy does not
change the metric.
This ensures that an IP RIP Import Accept Policy does not overwrite RIP
poison reverse triggered updates, which could cause incorrect route
information to be placed into the routing tables.
Implementing RIP
Routing Policies
RIP routing policies determine which RIP routes can be accepted into the
routing table, and which RIP and OSPF routes can be advertised.
RIP Metric Adjustments
Use the arithmetic operators in Table 41 to adjust the RIP metrics.
CAUTION: Use caution if you use arithmetic operators to adjust the
relative value of the number of hops that you allow a route to have; you
can inadvertently make a route unreachable.
Table 41 RIP Metric Adjustments
Metric Description
+nn Increase metric by nn
-nn Decrease metric by nn
*nn Multiple metric by nn
/nn Divide metric by nn
%nn Modulus — returns the remainder of the metric