Which OSPF Packet Is It? — TechKnowSurge

About this interactive

The OSPF header's type field says which packet follows: 1. **Hello**: network mask, hello and dead intervals, priority, the DR and BDR, and the router IDs of the neighbors the sender sees. Builds neighborships and keeps them alive. 2. **Database description (DBD)**: interface MTU, options, flags, a sequence number and the headers of the LSAs the sender holds. 3. **Link-state request (LSR)**: asks for full LSAs, named by type, link-state ID and advertising router. 4. **Link-state update (LSU)**: the number of LSAs, then the complete LSAs. Also sent when the topology changes. 5. **Link-state acknowledgment (LSAck)**: the headers of the LSAs received.

What you'll learn

Identify the five OSPF packet types (hello, database description, link-state request, link-state update and link-state acknowledgment) by their type number, contents and job
Describe how they work together when a router joins: hellos form the neighborship, then a database description, a request, an update and an acknowledgment

Aligned to

Cisco CCNA

3.4 Configure and verify single area OSPFv2

Key terms

OSPF Hello Packet: A message sent by an OSPF-enabled interface to discover and maintain adjacencies with neighboring OSPF routers.
Link State Advertisement: A packet generated by OSPF routers that describes the local router's links and their states, flooded throughout the OSPF area to build each router's link-state database. Different LSA types carry different information such as router links, network links, summary routes, and external routes.
Hello Interval: The configurable timer that defines how frequently an OSPF router sends hello packets out of an interface to maintain neighbor adjacencies.
Dead Interval: The configurable timer that defines how long an OSPF router waits without receiving a hello packet before declaring a neighbor down; defaults to four times the hello interval.
Router ID: A 32-bit value formatted like an IP address that uniquely identifies an OSPF router and is used as a tiebreaker in DR/BDR elections when interface priorities are equal.

Topics

Ospf Ospf Packets Hello Link State Update Lsa Interactive Categorize

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