Configure OSPF special areas on S series switches

1. Configure a stub area.
A stub area is a special area where ABRs do not flood received AS external routes, significantly reducing the routing table size and transmitted routing information of routers. A border area on an OSPF network is often configured as a stub area. For example, configure Area1 as a stub area.
[SwitchA] ospf 1
[SwitchA-ospf-1] area 1
[SwitchA-ospf-1-area-0.0.0.1] stub
[SwitchA-ospf-1-area-0.0.0.1] quit
[SwitchA-ospf-1] quit
Precautions:
1. To configure an area as a stub area, you must run the stub command on all the devices in this area.
2. To configure an area as a totally stub area, run the stub no-summary command on the ABR in this area and run the stub command on other devices in this area. This prevents the ABR from transmitting Type 3 LSAs to the stub area, making the area a totally stub area.

2. Configure an NSSA area.
In an NSSA, an ABR does not flood AS external routes received from other areas, similar to the situation in a stub area. The difference is that an ABR can import and flood AS external routes to the entire OSPF domain. A border area connected to another AS on an OSPF network is often configured as an NSSA. For example, configure Area2 as an NSSA.
[SwitchB] ospf 1
[SwitchB-ospf-1] area 2
[SwitchB-ospf-1-area-0.0.0.2] nssa
[SwitchB-ospf-1-area-0.0.0.2] quit
[SwitchB-ospf-1] quit
Precautions:
1. To configure an area as an NSSA, you must run the nssa command on all the devices in this area.
2. To configure an area as a totally NSSA, run the nssa no-summary command on the ABR in this area and run the nssa command on other devices in this area. This prevents the ABR from transmitting Type 3 LSAs to the NSSA, making the area a totally NSSA.

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