Technical data

114 CHAPTER 5: IP ROUTING PROTOCOL OPERATION
Setting a Shortest Path First (SPF) Calculation Interval for OSPF
Whenever the OSPF LSDB changes, the shortest path requires recalculation.
Calculating the shortest path after a change consumes enormous resources and
affects the operating efficiency of the router. Adjusting the SPF calculation interval,
however, can restrain the resource consumption caused by frequent network
changes.
Perform the following configuration in OSPF view.
By default, the interval for SPF recalculation is 5 seconds.
Configuring the OSPF STUB Area
STUB areas are special LSA areas in which the ABRs do not propagate the learned
external routes of the AS. In these areas, the routing table sizes of routers and the
routing traffic are significantly reduced.
The STUB area is an optional configuration attribute, but not every area conforms
to the configuration condition. Generally, STUB areas, located at the AS
boundaries, are those non-backbone areas with only one ABR. Even if this area has
multiple ABRs, no virtual links are established between these ABRs.
To insure that routes to the destinations outside the AS are still reachable, the ABR
in this area generates a default route (0.0.0.0) and advertises it to the non-ABR
routers in the area.
Note the following items when you configure a STUB area:
■ The backbone area cannot be configured as a STUB area, and virtual links
cannot pass through the STUB area.
■ If you want to configure an area as a STUB area, all the routers in this area
should be configured with the stub command.
■ No ASBR can exist in a STUB area and the external routes of the AS cannot be
propagated in the STUB area.
Perform the following configuration in OSPF Area view.
Tab le 35 Setting the SPF Calculation Interval
Operation Command
Set the SPF calculation interval spf-schedule-interval seconds
Restore the SPF calculation interval undo spf-schedule-interval seconds
Tab le 36 Configuring an OSPF STUB Area
Operation Command
Configure an area as the STUB area stub [no-summary]
Remove the configured STUB area undo stub
Set the cost of the default route to the STUB
area
default-cost value
Remove the cost of the default route to the
STUB area
undo default-cost