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4.4.3.5. Inter-Area-Router-LSAs

The LS type of an inter-area-router-LSA is set to the value 0x2004. Inter-area-router-LSAs have area flooding scope. In IPv4, inter-area-router-LSAs were called type 4 summary-LSAs. Each inter-area-router-LSA describes a path to a destination OSPF router (i.e., an AS Boundary Router (ASBR)) that is external to the area yet internal to the Autonomous System.

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

  • The Link State ID of an inter-area-router-LSA is no longer the destination router's OSPF Router ID and now simply serves to distinguish multiple inter-area-router-LSAs that are originated by the same router. The destination router's Router ID is now found in the body of the LSA.

  • The Options field in an inter-area-router-LSA should be set equal to the Options field contained in the destination router's own router-LSA. The Options field thus describes the capabilities supported by the destination router.

As an example, consider the OSPF Autonomous System depicted in Figure 6 of [OSPFV2]. Router RT4 would originate into Area 1 the following inter-area-router-LSA for destination router RT7.

; inter-area-router-LSA for AS boundary router RT7
; originated by Router RT4 into Area 1

LS age = 0                  ; newly (re)originated
LS type = 0x2004            ; inter-area-router-LSA
Advertising Router = 192.0.2.4  ; RT4's ID
Options = (V6-bit|E-bit|R-bit)  ; RT7's capabilities
Metric = 14                     ; cost to RT7
Destination Router ID = Router RT7's ID
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