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4.4.3.7. NSSA-LSAs

The LS type of an NSSA-LSA is set to the value 0x2007. NSSA-LSAs have area flooding scope. Each NSSA-LSA describes a path to a prefix external to the Autonomous System whose flooding scope is restricted to a single NSSA area.

The procedure for originating NSSA-LSAs in IPv6 is the same as the IPv4 procedure documented in [NSSA], with the following exceptions:

  • The Link State ID of an NSSA-LSA has lost all of its addressing semantics and simply serves to distinguish multiple NSSA-LSAs that are originated by the same router in the same area.

  • The prefix is described by the PrefixLength, PrefixOptions, and Address Prefix fields embedded within the LSA body. Network Mask is no longer specified.

  • The NU-bit in the PrefixOptions field should be clear.

  • Link-local addresses can never be advertised in NSSA-LSAs.

  • The forwarding address is present in the NSSA-LSA if and only if the NSSA-LSA's bit F is set.

  • The external route tag is present in the NSSA-LSA if and only if the NSSA-LSA's bit T is set.

  • The capability for an NSSA-LSA to reference another LSA has been supported through the inclusion of the Referenced LS Type field and the optional Referenced Link State ID field (the latter present if and only if the Referenced LS Type is non-zero). This capability is for future use; the Referenced LS Type should be set to 0, and received non-zero values for this field should be ignored until its use is defined.

An example of an NSSA-LSA would only differ from an AS-external-LSA in that the LS type would be 0x2007 rather than 0x4005.

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