There are five types of OSPF areas: Backbone area (area 0), Standard area, Stub area, Totally stubby area, and No so stubby area (NSSA). Let's introduce one by one.
1.Backbone Area
Backbone area also called the backbone area, is actually area 0. According to the OSPF design principle, area 0 plays the role of the central node in the OSPF network. The link information of other areas is transmitted through area 0. This also means that all other areas must be connected to area 0. This area supports 1, 2, 3, 4, and 5 LSAs.
2.Standard Area
Standard area also called the standard area, means that in this area, OSPF packets can be normally transmitted. This area supports 1, 2, 3, 4, and 5 LSAs.
3.Stub Area
Stub area, also called stub area, the so-called stub area, means that the area does not accept any external routes of non-OSPF network, if it wants to reach those external routes, only Need to send it through the default route. This area supports 1, 2, and 3 LSAs.
4.Totally stubby Area
Totally stubby area, also called completely stub area, it means that the area does not accept external routes and does not accept the link information of other areas outside of their own area. If it wants to reach the target network outside the area, it will send out the message through the default route just like the stub area. It should be noted here that since the default route is sent using Type 3 LSAs, the completely stub area does not allow ordinary Type 3 LSA packets, but it supports this type of LSA with default routes. This area supports Type 1, Type 2 LSAs, and Type 3 LSAs with default routes.
5.No so stubby area
No so stubby area, is usually referred to as the NSSA, this NSSA is actually derived from the stub area, it means that in the case of a stub area, it also has to send external routes to other areas ability. This area supports 1, 2, 3, and 7 LSAs. Note here that there is another mode in the Totally stubby area zone, which is the NSSA of the completely stub area mode. In fact, this mode allows the introduction of external routes in a completely stub area environment. This area mode supports Class 1, Type 2 LSAs, and Class 3 LSAs with default routes.
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