4.4.2. The Link-State Database

In IPv6, as in IPv4, individual LSAs are identified by a combination of their LS type, Link State ID, and Advertising Router fields. Given two instances of an LSA, the most recent instance is determined by examining the LSAs' LS sequence number, using LS checksum and LS age as tiebreakers (see Section 13.1 of [OSPFV2]).

In IPv6, the link-state database is split across three separate data structures. LSAs with AS flooding scope are contained within the top-level OSPF data structure (see Section 4.1) as long as either their LS type is known or their U-bit is 1 (flood even when unrecognized); this includes the AS-external-LSAs. LSAs with area flooding scope are contained within the appropriate area structure (see Section 4.1.1) as long as either their LS type is known or their U-bit is 1 (flood even when unrecognized); this includes router-LSAs, network-LSAs, inter-area-prefix-LSAs, inter-area-router-LSAs, NSSA-LSAs, and intra-area-prefix-LSAs. LSAs with an unknown LS type, the U-bit set to 0, and/or link-local flooding scope are contained within the appropriate interface structure (see Section 4.1.2); this includes link-LSAs.

To look up or install an LSA in the database, you first examine the LS type and the LSA's context (i.e., the area or link to which the LSA belongs). This information allows you to find the correct database of LSAs where you then search based on the LSA's type, Link State ID, and Advertising Router.

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