分别写出1类LSA、2类LSA、3类LSA、4类LSA、5类LSA的标识

### OSPF LSA Types Identifiers Explanation In OSPF, Link State Advertisements (LSAs) are used to exchange routing information between routers within a single area or across multiple areas. Each type of LSA has specific characteristics and purposes. #### Type 1 Router LSAs Type 1 LSAs describe the router's directly connected links along with their associated metrics and states. These LSAs also include information about which interfaces belong to stub networks. This kind of LSA is flooded only within its own area[^1]. #### Type 2 Network LSAs Type 2 LSAs provide details regarding multi-access networks such as Ethernet segments where more than two OSPF routers connect. Specifically generated by Designated Routers (DRs), these LSAs list all routers attached to that network segment but do not propagate beyond the local area boundary. #### Type 3 Summary LSAs Generated by Area Border Routers (ABRs), Type 3 LSAs summarize routes learned from one area into another without revealing internal topological structure outside an originating region. They contain summarized IP address prefixes rather than detailed link-state data, thus reducing overhead when communicating inter-area route summaries. #### Type 4 ASBR-Summary LSAs Similar to Type 3 LSAs, however specifically targeting Autonomous System Boundary Routers (ASBR). An ABR will generate this LSA pointing towards an ASBR located at different non-backbone areas providing external reachability through it while hiding specifics inside those regions. #### Type 5 External LSAs These LSAs advertise destinations outside the OSPF domain introduced via redistribution commands executed on ASBR devices. Unlike other types mentioned earlier, they carry full next-hop addresses necessary for forwarding packets destined externally ensuring proper path selection even though exact interior connectivity remains abstracted away from remote parts of the autonomous system. ```python lsa_types = { "Type 1": "Router LSAs", "Type 2": "Network LSAs", "Type 3": "Summary LSAs", "Type 4": "ASBR-Summary LSAs", "Type 5": "External LSAs" } print(lsa_types) ```