# Q3B · OSPF

Subject: Computer Networks

Exam: TEE

Reader: https://deep-learning-study-room.vercel.app/cn/#tee/mocks/tee-mock-c/q3b

Canonical: https://deep-learning-study-room.vercel.app/read/cn/tee/mocks/tee-mock-c--q3b/

TEE · 100 attempted marks · solutions for every choice · current syllabus 702AI0C023

### TEE practice mock · Q3B. Explain the different types of OSPF packets used for communication between routers. [5 mock marks]

#### Answer

Swipe across the diagram to read its labels ↔

![OSPFv2: five distinct packet types](https://deep-learning-study-room.vercel.app/cn/fig/ospf-packets.6093f0d178.svg)

Diagram: OSPFv2: five distinct packet types. Labels: OSPFv2: five distinct packet types | OSPFv2: five distinct packet types | 1. Hello | Discover and maintain neighbour relationships. | 2. Database Description | Summarize link-state database contents. | 3. Link State Request | Ask for particular missing or newer LSAs. | 4. Link State Update | Carry one or more LSAs. | 5. Link State Acknowledgment | Acknowledge receipt of LSAs.

Five OSPFv2 packet types.

| Packet type | What it does | Simple example |
| --- | --- | --- |
| Hello | Discover/maintain neighbours and exchange relationship parameters | Are we still neighbours? |
| Database Description (DD/DBD) | Summarize link-state database contents during synchronization | Here are the LSA headers I have |
| Link State Request (LSR) | Ask for specific missing/newer link-state information | Please send this LSA |
| Link State Update (LSU) | Carry one or more LSAs | Here is the requested or newly flooded link-state information |
| Link State Acknowledgment (LSAck) | Acknowledge receipt of LSAs | I received these LSAs |

Database Description packets carry summaries; Link State Update packets carry LSAs themselves. Do not confuse an LSA type with an OSPF packet type.

#### Practical example

After seeing a missing LSA in a database summary, a router sends an LSR, receives an LSU containing it and sends an LSAck.