Identifying Valid OSPF Packet Types vs LSAs

H12-811 By islever Editorial Last updated

OSPF Principles and Configuration

Short answer

ABC HELLO, LSR, and LSU are valid OSPF packets, while LSA is data carried within an LSU.

Question

Which of the following packets are OSPF packets? (Choose all that apply.)
  1. HELLO Correct Answer
  2. LSR Correct Answer
  3. LSU Correct Answer
  4. LSA

Key Takeaways

The main trap is confusing LSA (Link State Advertisement) with an OSPF packet; LSA is the information payload, whereas LSU (Link State Update) is the packet that carries it.

Learn to distinguish OSPF packet types from their contents. The correct OSPF packets are HELLO, LSR, LSU, and DBD; LSA is not a packet but data inside an LSU.

Common mistake: Selecting D (LSA) because it sounds like a packet name. Candidates often forget that LSAs are records stored in the database and transported by LSU packets, not standalone protocol messages.

Expert Analysis

The question asks to identify OSPF packets, which are the actual Layer 3 protocol messages exchanged between routers. To answer correctly, one must distinguish between the five defined OSPF packet types and the data structures they carry.

A. HELLO: Correct. This is a fundamental OSPF packet used for neighbor discovery and maintaining adjacency relationships. It corresponds to Packet Type 1 in the OSPF header.

B. LSR (Link State Request): Correct. Routers use this packet type (Type 2) to request specific Link State Advertisements from neighbors after receiving a DBD (Database Description) packet indicating missing information.

C. LSU (Link State Update): Correct. This packet type (Type 4) carries the actual Link State Advertisement information to update the neighbor's link-state database. As noted in the comments, LSUs contain the LSA data.

D. LSA (Link State Advertisement): Incorrect. An LSA is not an OSPF packet itself; it is a unit of routing information (a structure or record) contained within an LSU packet. Confusing the container (packet) with the content (advertisement) is the primary trap here.

Therefore, only HELLO, LSR, and LSU are valid OSPF packet types.

Official Reference

https://www.rfc-editor.org/rfc/rfc2328

This link opens the official vendor documentation in a new tab.

Exam Strategy

When asked about protocol messages, strictly differentiate between the 'envelope' (the packet type like UDP port or OSPF Header Type) and the 'letter' (the data payload). Memorize the five OSPF packet types (Hello, DBD, LSR, LSU, LSAck) separately from the LSA types (Router, Network, Summary, ASBR, External). If an option describes a piece of information rather than a transmission mechanism, it is likely not a packet.

Frequently Asked Questions

What are the 5 OSPF packet types?

The five OSPF packet types are Hello, Database Description (DBD), Link State Request (LSR), Link State Update (LSU), and Link State Acknowledgment (LSAck).

Is LSA an OSPF packet?

No. LSA stands for Link State Advertisement. It is a block of routing information that is encapsulated inside an LSU (Link State Update) packet.

More H12-811 FAQ →

Community Votes

B
50%
A
38%
C
12%

50% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 8 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 8

  1. iitc_duo 👍 2
    A,B and C. LSA is not a specific packet type, which is carried via as an Information on LSU.
  2. 4c4da48 👍 1
    A. HELLO This packet is used to establish and maintain OSPF neighbor relationships by sending periodic hello messages. B. LSR (Link State Request) This packet is sent by a router to request Link State Updates (LSUs) from its neighbors. C. LSU (Link State Update) This packet contains the actual link-state information, such as LSAs (Link State Advertisements), used to update the OSPF routing tables. D. LSA (Link State Advertisement) This is not a packet type by itself but rather a type of information contained within LSUs. LSAs describe the state of the links and are the building blocks of the routing information in OSPF. Therefore, the OSPF packets from the given options are A, B, and C. The option D refers to the content of LSUs but is not a packet type on its own.
  3. Fmoura17 👍 1
    Answer: A, B, and C A. HELLO ✅ — Used to discover and maintain OSPF neighbors. B. LSR (Link State Request) ✅ — Used to request specific LSA information from a neighbor. C. LSU (Link State Update) ✅ — Used to send LSA information to neighbors. D. LSA ❌ — LSA (Link State Advertisement) is not a packet type. It is the data carried inside LSU packets.
  4. IBB90704 👍 1
    Todas las opcines son paquetes OSPF
  5. agirgis2 👍 1
    All of them Page 239
Show 3 more comments
  1. amiie00 👍 1
    A,B,C LSAck not LSA
  2. Chleong 👍 1
    ABCD All of them
  3. rolandotorres 👍 1
    All of them

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