
[OSPF](/ospf) uses different types of messages to allow OSPF routers to create [adjacencies](/ospf-requirements-for-forming-adjacency) to exchange [LSAs](/ospf-lsa-types) and other information.  Each type of message has specific transmission methods, using either [unicast](/unicast-traffic) or [Multicast](/multicast).  The following lists the message types and transmission methods:

1. **[Hello Packets](/ospf-hello-packets-unicast-and-multicast)**: Initially these multicast, but OSPF's RFC allows vendors flexibility in implementation.

2. **Database Description (DBD) Packets**: Transmitted via unicast. These packets provide summaries of a router's [Link-State Database (LSDB)](/ospf-database-example).

3. **Link-State Request (LSR) Packets**: Contrary to some assertions, LSR packets are unicast. They request specific information about Link-State Advertisements (LSAs).

4. **Link-State Update (LSU) Packets**: These packets are unicast in response to LSRs and multicast for flooding LSAs throughout the network. They help maintain updated LSDBs.

5. **Link-State Acknowledgment (LSAck) Packets**: Utilized as unicast for individual LSA receipt and multicast for acknowledging multiple LSAs simultaneously.

Understanding these packet types and their transmission methods is crucial for the implementation and troubleshooting of OSPF on network devices.

Links:

https://forum.networklessons.com/t/ospf-packets-and-neighbor-discovery/916/120?u=lagapidis

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

https://datatracker.ietf.org/doc/html/rfc2328

OSPF Packet Types and Their Transmission Methods

OSPF - Link State Updates (LSUs)

OSPF - MPLS SuperBackbone

OSPF - NBMA neighbors listen on 224.0.0.5

OSPF - NSSA P-bit

OSPF - NSSA no automatic default route

OSPF - Neighbor states

OSPF - Neighbor vs Adjacency

OSPF - OSPFv3 authentication

OSPF - Propagation of routes between areas

OSPF - Stub areas and allowed LSAs

OSPF - Stuck in ATTEMPT neighbor state

OSPF - Stuck in ExStart or Exchange states

OSPF - Type 5 LSA filtering on an ASBR

OSPF - Type1 LSA

OSPF - Update pacing timers

OSPF - capablity vrf-lite

OSPF - control plane vs data plane loops

OSPF - default-information originate always command

OSPF - distance command

OSPF - distribute-list filtering

OSPF - manual neighbor configuration

OSPF - network type mismatch

OSPF - non-zero Forwarding Address example

OSPF - point-to-multipoint network type

OSPF - route filtering

OSPF - route summarization

OSPF - summary-address nssa-only on an ABR

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 Design - When to create new instance

OSPF Determining which LSA is newer

OSPF Discontiguous Area 0

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 Recursion

OSPF LSA Sequence Numbers

OSPF LSA Types

OSPF NSSA ABR advertises default route

OSPF Not So Stubby Area NSSA

OSPF Path selection

OSPF Prefix Suppression Considerations

OSPF Routing Bit

OSPF SPF Scheduling and throttling timers

OSPF Summarization Restrictions Within an Area

OSPF TTL Security Check

OSPF Troubleshooting

OSPF Type 3 LSA

OSPF Type 4 LSA

OSPF Type 5 LSA

OSPF Type 7 LSA

OSPF Understanding LSA Aging and Refreshing

OSPF Why it is not suitable for use on the Internet

OSPF advertising loopback network

OSPF area inactive

OSPF area notation

OSPF area type mismatch

OSPF backbone area 0

OSPF default metric values

OSPF design - when to create a new area

OSPF does not redistribute default route

OSPF downheap LSA

OSPF duplicate router IDs

OSPF extent of reconvergence process

OSPF immediate hello packet

OSPF in a GRE multipoint environment

OSPF loop prevention

OSPF master slave election

OSPF message options field

OSPF metric sum of outgoing interface costs

OSPF modifying the router ID

OSPF network command

OSPF network types

OSPF non directly connected neighbor adjacencies

OSPF packet types

OSPF point to point network type for Ethernet

OSPF requirements for forming adjacency

OSPF router ID in an IPv6 environment

OSPF router ID

OSPF sham-link cost

OSPF sham-link

OSPF virtual link and ABRs

OSPF where do you configure a virtual link

OSPF why is a backbone area 0 necessary

OSPF within what area is an OSPF router considered to be

OSPF

OSPFv2 and OSPFv3 comparison

OSPFv3 - router ospfv3 command

OSPFv3 communication between routers and next hop addresses

OSPFv3 instance ID