OSPF Neighbor States

8 OSPF neighbor states:

DOWN, ATTEMPT, INIT, 2WAY, ExStart, Exchange, Loading, FULL

  • DOWN
    • ┬ávia syslog message only
  • ATTEMPT
    • via sh ip ospf neighbor
    • only with staticly defined neighbors
    • May indicate layer 2 problem
  • INIT
    • Received HELLO packet from neighbor
    • compares names from other neighbors, doesn’t recognize you
  • 2WAY
    • Received HELLO packet from neighbor
    • compares names from other neighbors, does recognize you
  • (LSA’s ARE SEND FROM HERE)

WITHOUT DR

  • ExStart (without DR)
    • ExStart starts when the first database descriptor (DD) message is received (syncs databases).
    • Only sends LSA headers (only router ID).
    • Election is held for master and slave router. Master in charge of inital sequence number.
    • Router with higher RID is elected as master.
  • Exchange (without DR)
    • Send to multicast 224.0.0.5
    • Goes into Exchange after master/slave election
    • Multicast database descriptors (DD) packets untill they have the same LSID collectively for that area
  • Loading (without DR)
    • When routers have the same LSID move into loading.
    • For any missing LSA the router who is missing the LSA sends a Link State Request (LSR).
    • The router listening to LSR sends a Link State Update (LSU).
    • Router also sends ack message -> LSAck or ack by sending same LSA back.
  • FULL
    • When all LSAs have been send/received/ack move into FULL
    • Fully Adjacent
    • Database is fully populated
    • Routers run the SPF to calculate the best path

WITH DR

With DR/BDR on the segment, all other routers exchange databases with DR and BDR only.
Other router states are only in 2way state.

  • Exchange with DR
    • Routers send messages to DR/BDR on 224.0.0.6
    • BR/BDR send messages to routers on 224.0.0.5

 

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