Инструкции По Установке для 3com S7906E

 

1-6 

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A (totally) stub area cannot have an ASBR because AS external routes cannot be distributed into 

the stub area. 

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Virtual links cannot transit (totally) stub areas. 

Similar to a stub area, an NSSA area imports no AS external LSA (Type-5 LSA) but can import Type-7 

LSAs that are generated by the ASBR and distributed throughout the NSSA area. When traveling to the 

NSSA ABR, Type-7 LSAs are translated into Type-5 LSAs by the ABR for advertisement to other areas. 

In the following figure, the OSPF AS contains three areas: Area 1, Area 2 and Area 0. The other two 

ASs employ the RIP protocol. Area 1 is an NSSA area, and the ASBR in it translates RIP routes into 

Type-7 LSAs and advertises them throughout Area 1. When these LSAs travel to the NSSA ABR, the 

ABR translates Type-7 LSAs to Type-5 LSAs for advertisement to Area 0 and Area 2. 

On the left of the figure, RIP routes are translated into Type-5 LSAs by the ASBR of Area 2 and 

distributed into the OSPF AS. However, Area 1 is an NSSA area, so these Type-5 LSAs cannot travel to 

Area 1. 

Like stub areas, virtual links cannot transit NSSA areas. 

Figure 1-4 NSSA area 

 

 

Figure 1-5 Comparison between the areas 

 

 

 shows the comparison of the areas: 

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In a totally stub area, the ABR can distribute a Type 3 default route, while it does not distribute 

external routes and inter-area routes.