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4.4.3.4. Inter-Area-Prefix-LSAs

The LS type of an inter-area-prefix-LSA is set to the value 0x2003. Inter-area-prefix-LSAs have area flooding scope. In IPv4, inter-area-prefix-LSAs were called type 3 summary-LSAs. Each inter-area-prefix-LSA describes a prefix external to the area, yet internal to the Autonomous System.

The procedure for originating inter-area-prefix-LSAs in IPv6 is the same as the IPv4 procedure documented in Sections 12.4.3 and 12.4.3.1 of [OSPFV2], with the following exceptions:

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

  • 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 MUST never be advertised in inter-area-prefix-LSAs.

As an example, the following shows the inter-area-prefix-LSA that Router RT4 originates into the OSPF backbone area, condensing all of Area 1's prefixes into the single prefix 2001:0db8:c001::/48. The cost is set to 4, which is the maximum cost of all of the individual component prefixes. The prefix is padded out to an even number of 32-bit words, so that it consumes 64 bits of space instead of 48 bits.

; Inter-area-prefix-LSA for Area 1 addresses
; originated by Router RT4 into the backbone

LS age = 0                  ; newly (re)originated
LS type = 0x2003            ; inter-area-prefix-LSA
Advertising Router = 192.0.2.4       ; RT4's ID
Metric = 4                  ; maximum to components
PrefixLength = 48
PrefixOptions = 0
Address Prefix = 2001:0db8:c001 ; padded to 64-bits
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