Common LSA types of OSPF

Common LSA types of OSPF are as follows:

Type 1 LSA: router LSA. Generated by each router, describes the router's link status and cost, and advertised within the area to which it belongs.
Type 2 LSA: network LSA. Describes the link status of all routers on the local network segment. Network-LSAs are generated by a designated router (DR) and advertised within the area to which the DR belongs.
Type 3 LSA: summary LSA. Generated by ABR, describes all routes in the area, and advertised to other relevant areas.
Type 4 LSA: ASBR-summary LSA. An ASBR-summary-LSA describes routes to the ASBR in an area. The routes are advertised to all areas except the area to which the ASBR belongs.
Type 5 LSA: AS-external-LSA. Describes AS external routes, which are advertised to all areas except stub areas and NSSAs. AS-external-LSAs are generated by an ASBR.
Type 7 LSA: NSSA AS-external-LSA. Describes AS external routes. NSSA-LSAs are generated by an ASBR and advertised only within NSSAs.

The original OSPF packet coding is not Type Length Value (TLV)-based. For the extension of OSPF functions, only the LSA types of OSPF can be extended.
Type 6 LSAs are Group-Membership-LSAs used to identify multicast group membership in the Multicast Open Shortest Path First (MOSPF) protocol. Type 6 LSAs are not supported on the firewall.
Type 8 LSAs are External-Attributes-LSAs used to redistribute Border Gateway Protocol (BGP) routes into OSPF and reserve the BGP autonomous system (AS) path information. Type 8 LSAs are not supported on the firewall.

RFC 2370 defines an important LSA type, namely, Opaque LSA, which allows for TLV-like structures. OSPF applications, such as OSPF traffic engineering, are based on the Opaque LSA extension abilities:
Type 9 LSAs are Opaque LSAs that are advertised within the local link only;
Type 10 LSAs are Opaque LSAs that are advertised within the local area only;
Type 11 LSAs, similar to Type 5 LSAs, are Opaque LSAs that are advertised within the local AS.

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