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LSA TYPES

In OSPF, different types of routers create various types of LSAs (Link-State Advertisements) depending on their roles in the network. Here’s a breakdown of the routers and the LSAs they generate:

 

1. All Routers (including internal routers):

   - Type 1: Router LSA 

     - Every router in an OSPF area generates a Type 1 LSA, which describes its own interfaces and links within the same area.

 

2. Designated Router (DR):

   - Type 2: Network LSA 

     - The DR on multi-access networks (like Ethernet) generates this LSA to describe all the routers attached to the shared network.

 

3. Area Border Router (ABR):

   - Type 3: Summary LSA 

     - ABRs generate Type 3 LSAs to advertise networks from one OSPF area to another (inter-area communication).

   - Type 4: ASBR Summary LSA 

     - ABRs also generate Type 4 LSAs to describe the path to an Autonomous System Boundary Router (ASBR) in another area.

 

4. Autonomous System Boundary Router (ASBR):

   - Type 5: External LSA 

     - ASBRs generate Type 5 LSAs to advertise routes from outside the OSPF domain (external routes like BGP or static routes) into the OSPF network.

 

5. Routers in a Not-So-Stubby Area (NSSA):

   - Type 7: NSSA External LSA 

     - An ASBR within an NSSA generates Type 7 LSAs, which are similar to Type 5 but used only in NSSAs to import external routes.

 

 Summary of Routers and LSAs:

- Internal routers: Type 1 LSA (Router LSA)

- Designated Routers (DRs): Type 2 LSA (Network LSA)

- Area Border Routers (ABRs): Type 3 (Summary LSA) and Type 4 (ASBR Summary LSA)

- Autonomous System Boundary Routers (ASBRs): Type 5 (External LSA)

- ASBR in NSSA: Type 7 (NSSA External LSA)

In OSPF, different types of routers generate specific types of LSAs (Link-State Advertisements). Here’s a quick breakdown:

  1. All OSPF Routers:

    • Every OSPF router generates Type 1 LSAs (Router LSAs), which describe the router's interfaces and links within an area.

  2. Designated Routers (DR):

    • A Designated Router (DR) on a broadcast network (like Ethernet) generates Type 2 LSAs (Network LSAs). These LSAs describe the routers connected to the shared network segment (e.g., a LAN).

  3. Area Border Routers (ABR):

    • ABRs connect different OSPF areas and generate Type 3 LSAs (Summary LSAs), which advertise networks between areas.
    • ABRs can also generate Type 4 LSAs (Summary ASBR LSAs), which advertise the presence of an ASBR (Autonomous System Boundary Router) in another area.

  4. Autonomous System Boundary Routers (ASBR):

    • ASBRs connect OSPF to external networks (such as BGP or RIP) and generate Type 5 LSAs (AS External LSAs). These LSAs advertise routes external to the OSPF domain.

In summary:

  • All OSPF routers generate Type 1 LSAs.
  • Designated Routers (DRs) generate Type 2 LSAs.
  • ABRs generate Type 3 and 4 LSAs.
  • ASBRs generate Type 5 LSAs.

 

 

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