3Com 4007, Руководство по внедрению, Страница: 491 / 684

OSPF Routing Policies 491
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Isolate suspect networks — Misconfigured hosts can sometimes
send inappropriate routing information, which can compromise
network integrity. In such a case, you can define an import policy on
an ASBR that rejects all routes from the suspect network.
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Adjust route cost — Both import and export policies let you change
the cost that is associated with routes without physically changing the
cost of an interface. For example, router A may advertise a route with
one cost, but router B may use an import policy to write the same
route to its routing table with a different, or adjusted, cost. Similarly,
router A may have a route in its routing table with one cost but
choose to advertise the route to other routers with a different cost.
Important
Considerations
Consider the following guidelines when you work with OSPF routing
policies:
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You can only apply OSPF policies against external routes. External
routes refer to routes that are advertised over the network using
external link state advertisements (LSAs). These routes include:
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Directly connected non-OSPF interfaces — Physical interfaces
on the router itself that are not running OSPF and that are directly
connected to the network.
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RIP routes — Routes to destinations outside the autonomous
system learned via the Routing Information Protocol (RIP) and
imported by autonomous system boundary routers.
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Static routes — IP routes statically defined by the user.
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You cannot apply export policies against directly connected OSPF
interfaces, because all routers in the area must maintain identical link
state databases.