Important Considerations - 3Com corebuilder 3500 Implementation Manual

404 C 14: O
HAPTER PEN
Important
Considerations
S P F (OSPF)
HORTEST ATH IRST
Consider the following guidelines when you work with OSPF routing
policies:
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:
Directly connected non-OSPF interfaces — Physical interfaces
on the router itself that are not running OSPF and that are directly
connected to the network.
RIP routes — Routes to destinations outside the autonomous
system learned via the Routing Information Protocol (RIP) and
imported by autonomous system boundary routers.
Static routes — IP routes statically defined by the user.
You cannot apply export policies against directly connected OSPF
interfaces, because all routers in the area must maintain identical link
state databases.
With the ability to wildcard policy parameters (such as 0.0.0.0 to
indicate all routers or all routes), occasions may arise when several
policies match a route. In such cases, routers use the following
procedure to determine which policy to apply to the route:
If multiple policies apply to the route, the router uses the policy
that has the highest administrative weight.
If multiple matches still exist, the router uses the policy that
matches the specified source (excluding wildcards).
If multiple matches still exist, the router compares route address
bits and uses the policy that best matches the route address
(excluding wildcards).
If multiple matches still exist, the router uses the policy that
matches the origin protocol.
If multiple matches still exist, then the router uses the policy that
has the lowest index number.