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OSPF

OSPF Network Types and DR Election

Learn how OSPF treats broadcast and NBMA networks, how routers discover neighbors, and how the Designated Router and Backup Designated Router are selected and used.

Intermediate12 min read
OSPF lessonNetworkingPractice

UNTIMED COACHING

Practice before the pressure

Use feedback to correct the model, not merely memorize an option position.

GUIDED PRACTICE

Practice the lesson questions

Answer normal lesson questions without a timer. Every answer includes an explanation, and incorrect answers can be tried again before continuing.

CONCEPT MODELS

See the lesson as a system

Use these visual guides to connect the key ideas before answering the questions.

OSPF Shared-Network CoordinationNetwork type determines neighbor discovery and DR coordination.
OSPF Shared-Network CoordinationA shared network sends Hellos to routers, then uses DR and BDR coordination.
Shared networkBroadcast or NBMA segment
Hello packetsDiscover and maintain neighbors
DR electionSelect coordinator and backup
Designated RouterCoordinates shared-network adjacencies
DR and BDR RolesThe DR limits adjacency growth, while the BDR prepares for handoff.
DR and BDR RolesRouters connect through DR and BDR roles, with BDR ready to replace failed DR.
Segment routersForm selected adjacencies
DRCoordinates shared segment
BDRPrepared replacement router
Network LSADescribes broadcast network
Election Eligibility ChecksIdentify the network type, remove priority-zero candidates, then evaluate roles.
Election Eligibility ChecksElection reasoning filters network type and priority before comparing role eligibility.
Network typeIdentify election behavior
Router PriorityFilter priority-zero routers
Priority precedenceCompare eligible candidates
Selected roleEvaluate DR or BDR