OSPF packet types


A Link State Update (LSU) packet in [OSPF](/ospf)  is one of several [types of OSPF protocol packets](/ospf-packet-types).  The LSU packet plays a crucial role in the OSPF operation by carrying [link-state advertisements (LSAs)](/ospf-lsa-types) to other routers within the same OSPF area or the entire [routing](/routing) domain, depending on the configuration and [OSPF area types](/ospf-backbone-area-0).

According to the RFC:

> Link State Update packets are [Multicast](/multicast) on those physical networks that support multicast/broadcast. In order to make the flooding procedure reliable, flooded LSAs are acknowledged in Link State Acknowledgment packets. If retransmission of certain LSAs is necessary, the retransmitted LSAs are always sent directly to the neighbor.

So LSUs are always sent as multicast, unless they are responding to a specific LSR, in which case they use [unicast](/unicast-traffic).

## Links

https://www.ietf.org/rfc/rfc2328.txt
https://networklessons.com/ospf/ospf-packets-and-neighbor-discovery

OSPF - Link State Updates (LSUs)

Network Design - Switch oversubscription ratios

Network Design - Traffic Engineering

Network Design - on-premises and off-premises

Network Design Achieving Redundancy with PE Devices

Network Design Considerations Involving PE and P Routers

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Networking - Understanding Chassis devices

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OSI Model

OSPF - A comparison with IS-IS

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OSPF - ASBR E-bit in an LSA

OSPF - Adjacencies in a Multi-Access network segment

OSPF - Adjacency Between NBMA and P2MP Non-Broadcast Networks

OSPF - Advertising point to multipoint networks

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OSPF - Database Example

OSPF - Default route advertisement next hop IP

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OSPF - Enabling authentication

OSPF - HMAC-SHA Extended Authentication

OSPF - Identifying the router type

OSPF - LSA Max Age

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OSPF - LSA checksum

OSPF - Link ID and ADV Router in the OSPF database

OSPF - Link ID in the OSPF database

OSPF - MPLS SuperBackbone

OSPF - NBMA neighbors listen on 224.0.0.5

OSPF - NSSA P-bit

OSPF - NSSA no automatic default route

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OSPF - what triggers a DR-BDR election

OSPF ABR Type 3 LSA filtering using access lists

OSPF ABR and Loop Prevention

OSPF Authentication for v2 and v3

OSPF BDR to DR Transition Time

OSPF DR BDR election and neighbor adjacencies

OSPF DR BDR election criteria

OSPF DR BDR election process

OSPF Database Exchange Process Master Slave Election

OSPF Design - When to create new instance

OSPF Determining which LSA is newer

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OSPF E1 E2 N1 N2 routes

OSPF Forwarding Address

OSPF Hello packets unicast and multicast

OSPF IP Unnumbered

OSPF IS-IS comparison

OSPF Incremental SPF and receipt of LSAs

OSPF LSA Persistence with DNA flag

OSPF LSA Recursion

OSPF LSA Sequence Numbers

OSPF LSA Types

OSPF NSSA ABR advertises default route

OSPF Neighbor Adjacency works with Network Type Mismatch

OSPF Not So Stubby Area NSSA

OSPF Packet Types and Their Transmission Methods

OSPF - Link State Updates (LSUs)

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