What is difference between neighbor and adjacency in OSPF?

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Sr. Network Engineer
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CCNA Routing and Switching

Diffrence between neighbour and adjaceny in OSPF : 

We will see this diffrence according to above scenario : 

OSPF Messges  : Used in Neighbourship and Adjacency 

1. Hello

2. Database Description ( DBD ).

3. Link State Request ( LSR ).

4. Link State Update ( LSU ) .

5. Link State Acknowledgment ( LSACK ).

States in OSPF through which a router goes in case of Neighbour and Adjacency :

1. Down

2. Init

3. Two-way

4. Ex-start

5.Ex-change

6.Loading

7. Full.

 

1. Neighbour : 

Down State : When interface is down or no neighbour is there .

Initialization State : Both Router's R1 and R2 will Exchange Hello message with some of configuration parameters .

Two-way : Both Routers Become Neighbour and  Active neighbour Field  contain router - id of its neighbour .

At the End of Two-way state DR/BDR election is done .

 

Hello Message Paramaters : 

1. Area number must Match.

2. Router-Id must be diffrent.

3. Timers  :  Hello and Dead  Must Match.

4. Stub Flag Must be same.

5. Ip address on both routers must be in same subnet.

6. Authentication Ip applied then it's type and parameters must be same .

R1 and R2 are now neighbour and properly exchanged configuration parameters properly.

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Adjacency Process :  Now they will exchange their routes with each other 

Ex-Start : In this state both routers will send Empty DBD's to negotiate MTU and Seq Number . A router having higher router-id it's sequence number will be used.

Ex-change  : Actual Database Description are exchange between R1 and R2.

Loading : In this state both routers will send LInk State Request ( LSR ) and it's neighbour will reply with Link State Update Message and giving back Acknowledgement .

Full : Now both routers are adjacent.

So during adjacency process both routers has exchanged their routes with each other using ospf messages

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author

Well explained Rajan. keep helping people.