Topic starter
In OSPF (Open Shortest Path First), Link State Advertisements (LSAs) are used to distribute routing information within an OSPF routing domain. OSPF routers exchange LSAs to build and maintain a topology database, which is then used to calculate the shortest path tree and determine the best routes to reach destinations.
There are several types of LSAs in OSPF, each serving a specific purpose. Here are the main types of LSAs:
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Type 1: Router LSA (LSA Type 1):
- Generated by every OSPF router.
- Describes the state and cost of each router's links to its directly connected networks.
- Flooded within the area.
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Type 2: Network LSA (LSA Type 2):
- Generated by the Designated Router (DR) on multi-access networks (like Ethernet).
- Describes the state of the DR's links and the routers attached to the network.
- Flooded within the area.
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Type 3: Summary LSA (LSA Type 3):
- Generated by Area Border Routers (ABRs).
- Summarizes routes from one area and advertises them into another area.
- Contains information about routes to networks outside the local area.
- Flooded throughout the entire Autonomous System (AS), but not beyond.
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Type 4: ASBR Summary LSA (LSA Type 4):
- Generated by the ABR.
- Advertises the existence of an Autonomous System Boundary Router (ASBR) within the area.
- Provides a route to reach the ASBR.
- Flooded within the area.
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Type 5: Autonomous System External LSA (LSA Type 5):
- Generated by ASBRs.
- Advertises external routes (routes learned from outside the OSPF domain) into the OSPF domain.
- Flooded throughout the AS.
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Type 6: Multicast OSPF LSA (LSA Type 6):
- Used by multicast OSPF implementations.
- Allows OSPF routers to share multicast group membership information.
- Not widely implemented or used.
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Type 7: NSSA External LSA (LSA Type 7):
- Similar to Type 5 LSA but used in Not-So-Stubby-Areas (NSSAs).
- Translated into Type 5 LSAs by the NSSA Area Border Router (ABR) when leaving the NSSA.
- Flooded within the NSSA area.
Posted : 30/04/2024 1:43 pm
