Link-state advertisement

Types

• Type 1 – Router LSA – the router announces its presence and lists the links to other routers or networks in the same area, together with the metrics to them. Type 1 LSAs are flooded across their own area only. The link-state ID of the type 1 LSA is the originating router ID.
• Type 2 – Network LSA – the designated router on a broadcast segment lists which routers are joined together by the segment. Type 2 LSAs are flooded across their own area only. The link-state ID of the type 2 LSA is the IP interface address of the DR.
• Type 3 – Summary LSA – an Area Border Router takes information it has learned on one of its attached areas and summarizes it before sending it out on other areas it is connected to. This summarization helps provide scalability by removing detailed topology information for other areas, because their routing information is summarized into just an address prefix and metric. The summarization process can also be configured to remove a lot of detailed address prefixes and replace them with a single summary prefix, helping scalability.
• Type 4 – ASBR-Summary LSA – this is needed because Type 5 External LSAs are flooded to all areas with the source as the Autonomous System Boundary Router's router ID, but router IDs are not advertised between areas. This is solved by an Area Border Router flooding the information of the ASBR where the type 5 originated. The link-state ID is the router ID of the described ASBR for type 4 LSAs.
• Type 5 – External LSA – these LSAs contain information imported into OSPF from other routing processes. They are flooded to all areas unchanged. For "External Metric Type 1" LSAs the metric sent is the cost from the ASBR to the External destination network and must be added to the OSPF cost to the ASBR advertising the Type 5, while for "External Type 2" LSAs routing decisions are made using the Type 1 metric cost sent as the total cost to get to the external destination including the cost to the ASBR. The link-state ID of the type 5 LSA is the external network number.
• Type 6 – Group Membership LSA – this was defined for Multicast extensions to OSPF, a multicast OSPF routing protocol which was not in general use. MOSPF has been deprecated since OSPFv3 and is not currently used. It may be reassigned in the future.
• Type 7 – Routers in a Not-so-stubby-area do not receive external LSAs from Area Border Routers, but are allowed to send external routing information for redistribution. They use type 7 LSAs to tell the ABRs about these external routes, which the Area Border Router then translates to type 5 external LSAs and floods as normal to the rest of the OSPF network.
• Type 8 – A link-local only LSA for OSPFv3. A Type 8 LSA is used to give information about link-local addresses and a list of IPv6 addresses on the link. In OSPFv2, however, the Type 8 was originally intended to be used as a so-called External-Attributes-LSA for transit autonomous systems where OSPFv2 could replace the internal Border Gateway Protocol. In these networks, the BGP destinations would be carried in LSA Type 5 while their BGP attributes would be inserted into LSA Type 8. Most OSPFv2 implementations never supported this feature, and it was never standardised for OSPFv2.
• Type 9 – a link-local "opaque" LSA in OSPFv2 and the Intra-Area-Prefix LSA in OSPFv3. It is the OSPFv3 LSA that contains prefixes for stub and transit networks in the link-state ID. It is also used for IETF NSF.
• Type 10 – an area-local "opaque" LSA as defined by RFC2370. Opaque LSAs contain information which should be flooded by other routers even if the router is not able to understand the extended information itself. Typically type 10 LSAs are used for traffic engineering extensions to OSPF for creating the Traffic Engineering Database, by flooding extra information about links beyond just their metric, such as link bandwidth and color.
• Type 11 – an AS "opaque" LSA defined by RFC 5250, which is flooded everywhere except stub areas. This is the opaque equivalent of the type 5 external LSA.

OSPF v3 LSA Packet Header Formats