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://forum.networklessons.com/t/ospf-packets-and-neighbor-discovery/916/115?u=lagapidis

https://www.ietf.org/rfc/rfc2328.txt

https://networklessons.com/ospf/ospf-packets-and-neighbor-discovery

OSPF - Link State Updates (LSUs)

Network Design - Choosing a technology for multiple datacenter topology

Network Design - Load Balancing vs Load Sharing

Network Design - Spine and leaf architecture

Network Design - Switch oversubscription ratios

Network Design - Traffic Engineering

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Network Design Considerations Involving PE and P Routers

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OSPF - ASBR E-bit in an LSA

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OSPF - Database Example

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OSPF - Down (DN) Bit

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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

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OSPF - NSSA P-bit

OSPF - NSSA no automatic default route

OSPF - Neighbor states

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OSPF ABR Type 3 LSA filtering using access lists

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OSPF BDR to DR Transition Time

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OSPF Design - When to create new instance

OSPF Determining which LSA is newer

OSPF Discontiguous Area 0

OSPF Do Not Age (DNA) Flag

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 Not So Stubby Area NSSA

OSPF - Link State Updates (LSUs)

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