OSPF Neighbor States

8 OSPF neighbor states:

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

• DOWN
  •  via 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