Implementing Import Policies - 3Com corebuilder 3500 Implementation Manual

Implementing Import
Policies
You can set up an IP RIP or OSPF import or export policy to accept or
advertise the default route, as long as the default route exists in the
routing table. When you define a policy, you are always prompted for
the route subnet mask after the route address, even though you
specify the wildcard route address of 0.0.0.0.
Specify a route subnet mask as follows:
If you want the wildcard subnet mask for all routes, enter 0.0.0.0
for the subnet mask. This is the default subnet mask.
If you want the default route (not all routes), enter
255.255.255.255.
For more information about IP routing policies, see Chapter 11.
Import policies control which non-self-originated (external routes
being RIP) are accepted and stored in the routing table.
Non-self-originated means that the router itself did not originate the
route; it learned it by means of an external link state advertisement. You
can also adjust the cost of each route that is accepted into the routing
table. Using RIP, you can define which external routes (RIP) a router
advertises. They are self-originated but must be external to OSPF.
Because all routers within the same OSPF area must maintain similar
databases, all routers must receive all link state advertisements that are
sent over the network, and store those advertisements in their link state
databases. By defining an import policy, however, you can control what
routes from a router's external link state database are migrated to its
routing table.
When you define an import policy, you specify a set of criteria. When a
the router receives an external link state advertisement, it consults its
routing policies to determine if the route specified in that advertisement
matches any of the defined policies criteria, and, if so, applies to the
route the actions that are defined by the policy.
OSPF Routing Policies 405