About replacing inter-area-prefix-LSAs and type-7-external-LSA default routes with an AS-external-LSA default route

By default, a routing switch operating as an ABR for a stub area or NSSA injects non-default, inter-area routes (inter-area-prefix-LSAs) into the stub areas and NSSAs. For NSSAs, the routing switch also injects a type-7-LSA default external route. You can further reduce LSA traffic into these areas by using no-summary. This command option configures the routing switch to:

  • Replace injection of inter-area-prefix-LSAs into a stub area or NSSA with an inter-area-prefix-LSA default summary route (::/0).

  • Replace injection of all external routes into an NSSA with an inter-area-prefix-LSA default route.

You can enable this behavior when you first configure the stub area or NSSA, or at a later time.

The no-summary command does not affect intra-area advertisements, meaning the switch still accepts summary LSAs from OSPFv3 neighbors within its area and floods them to other neighbors. The switch can form adjacencies with other routers regardless of whether summarization is enabled or disabled for areas on each switch.

When you use no-summary, the change takes effect immediately. If you apply the option to a previously configured area, the switch flushes all of the summary LSAs it has generated (as an ABR) from the area.

NOTE:

This feature applies only when the routing-switch is configured as an ABR for a stub area or NSSA. To completely prevent summary LSAs from injection into the area, use no-summary to disable the summary LSAs on each OSPFv3 router that is an ABR for the area.

To implement the above operation for a stub area or NSSA, enter a command such as the following:

Switch(ospf3)# area 40 stub metric-cost 3 no-summary