OSPF Neighbor States

OSPF Neighbor States

Neighbor adjacencies will progress through several states, including:
Down – indicates that no Hellos have been heard from the neighboring
router.
Init – indicates a Hello packet has been heard from the neighbor, but twoway
communication has not yet been initialized.
2-Way – indicates that bidirectional communication has been established.
Recall that Hello packets contain a neighbor field. Thus, communication is
considered 2-Way once a router sees its own Router ID in its neighbor’s
Hello Packet. Designated and Backup Designated Routers are elected at
this stage.
ExStart – indicates that the routers are preparing to share link stat information. Master/slave relationships are formed between routers to
determine who will begin the exchange.
Exchange – indicates that the routers are exchanging Database Descriptors
(DBDs). DBDs contain a description of the router’s Topology Database. A
router will examine a neighbor’s DBD to determine if it has information to
share.
Loading – indicates the routers are finally exchanging Link State
Advertisements, containing information about all links connected to each
router. Essentially, routers are sharing their topology tables with each other.
Full – indicates that the routers are fully synchronized. The topology table of
all routers in the area should now be identical. Depending on the “role” of
the neighbor, the state may appear as:
• Full/DR – indicating that the neighbor is a Designated Router (DR)
• Full/BDR – indicating that the neighbor is a Backup Designated
Router (BDR)
• Full/DROther – indicating that the neighbor is neither the DR or
BDR
On a multi-access network, OSPF routers will only form Full adjacencies
with DRs and BDRs. Non-DRs and non-BDRs will still form adjacencies,
but will remain in a 2-Way State. This is normal OSPF behavior

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