11 common reasons why OSPF neighbors cannot be established, how to diagnose and solve them!

Today, I will share the diagnosis and solution of factors affecting the establishment of OSPF neighbors.

1. Basic topology

The OSPF neighbor relationship between routers failed to be successfully established, resulting in the inability to exchange routing information normally, which in turn affects the connectivity of the network. So what are the factors that affect the establishment of OSPF neighbors?

2. Factors affecting the establishment of OSPF neighbors
1. Router-id conflict
Diagnosis:

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2. Inconsistent area ID
Diagnosis:

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3. The interface does not announce the corresponding directly connected network segment into OSPF
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4. The interface type is inconsistent
Diagnostic solution:

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5. The interface mask is inconsistent
Diagnostic solution:

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6. The interface MTU value is inconsistent
Diagnostic solution:

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7. Interface status is abnormal
Diagnostic solution:

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8. Hello Interval is inconsistent
Diagnostic solution:

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9. Router Dead Interval is inconsistent
Diagnostic solution:

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10. The authentication type is inconsistent or the authentication password is incorrect
Diagnosis:

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11. ACL filters out OSPF multicast message 224.0.0.5
Diagnosis command:

Solution:

Note: OSPF relies on multicast communication, ACL must allow 224.0.0.5/224.0.0.6