Configuring Nssa Parameters Of Ospf - 3Com 3C13636 Configuration Manual

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3Com Router 3000 Ethernet Family

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4.2.23 Configuring NSSA Parameters of OSPF

RFC1587 (OSPF NSSA Option) defines the Not-So-Stubby-Area (NSSA), which keeps

the strong points of Stub area while providing flexible networking. This area can

redistribute AS external routes in a limited way.

NSSA is, in fact, the expansion of the Stub area, so it resembles the Stub area in many

ways. These points should be cared for in configuring an NSSA:

The backbone area cannot be configured as NSSA.

NSSA cannot serve as transit area, that is, a viral link cannot be set up across an

All routers in an NSSA must be configured with the corresponding attribute.

Unlikely the Stub area, an NSSA area may contain ASBRs.

Type-7 LSAs, which are similar to Type-5 LSAs, are used for the AS external route

information in the NSSA. For more details about these two types, see "4.1.5 LSA Types

Available in OSPF".

The advertisement of AS external route information in NSSA is illustrated in Figure 4-4

NSSA, where three areas are included in the OSPF process 100: area 0 is backbone

area; area 1 is non-backbone area; area 2 is NSSA.

External Route

Figure 4-4 NSSA

The ASBR in the area 2 redistributes AS external route information (the route

information of OSPF process 200) to generateType-7 LSAs and advertises them in the

area 2. When the Type-7 LSAs reach the NSSA ABR, they are converted into Type-5

LSAs which are advertised among the entire AS. The ASBR in the area 1 redistributes

AS external route information (the RIP route information) to generate Type-5 LSAs,

which are advertised among the OSPF AS. The RIP route information cannot arrive at

the area 2, the NSSA.

Perform the following configuration in OSPF area view.

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Chapter 4 OSPF Configuration

External Route

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