3Com CoreBuilder 3500, Руководство по внедрению

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OSPF Routing Policies 403
OSPF Routing
Policies
Routing policies are rules that define criteria to control the flow of routes
to and from the routing table. Your system supports two types of OSPF
routing policies:
import policies that dictate which routes are added to
the routing table and
export
polices that dictate which routes are
advertised to other routers. You can use routing policies to:
■
Increase security
— For security reasons, you may not want the
router to advertise certain routes. For example, Organization A may
have defined one of its ASBRs with a direct connection to
Organization B that they use for direct communication. For security or
performance reasons, A may not want to give other groups access to
that connection. To prevent this direct connection from being known
to other organizations, A can define an export policy that prohibits its
ASBR from advertising the direct connection that it uses to
communicate with B.
■
Conserve routing table space — The selective nature of routing
policies can minimize routing table sizes and increase network stability.
For example, you may want to limit the number of hosts and
gateways from which routing information is accepted, in which case
you can define an import policy to selectively rule out, or reject,
unnecessary routing table entries.
■
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.
■
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.