OSPF neighbor establishment failure troubleshooting

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display ospf peer cannot view the neighbor, common problem troubleshooting.

The failure of OSPF neighbor establishment is usually related to the configuration.

1. Is the interface starting OSPF? 

2. Is the interface configured as a silent port? 

3. Hello packets are denied in the ACL.

 4. The IP address masks are inconsistent in the broadcast network. 

Example:

RTA：

#

interface GigabitEthernet0/0

ip address 1.1.1.1 255.255.255.252

#

ospf 1

 area 0.0.0.0

  network 1.1.1.0 0.0.0.3

#

RTB：

#

ospf 1

 area 0.0.0.0

  network 1.1.1.0 0.0.0.3

#

interface GigabitEthernet0/0

ip address 1.1.1.2 255.255.255.0

#

No neighbor relationship on either end, error type is Netmask mismatch.

[RTB]dis ospf statistics error

         OSPF Process 1 with Router ID 1.1.1.2

                 OSPF Packet Error Statistics

 0         : Router ID confusion         0         : Bad packet

 0         : Bad version                 0         : Bad checksum

 0         : Bad area ID                 0         : Drop on unnumbered link

 0         : Bad virtual link            0         : Bad authentication type

 0         : Bad authentication key      0         : Packet too small

 0         : Neighbor state low          0         : Transmit error

 0         : Interface down              0         : Unknown neighbor

 24        : HELLO: Netmask mismatch     0         : HELLO: Hello-time mismatch

 0         : HELLO: Dead-time mismatch   0         : HELLO: Ebit option mismatch

……

5. Are the timer settings at both ends of OSPF matching? 

 OSPF Hello packets carry hello and dead time, and if they do not match, neighbors cannot be established.

[RTA]dis ospf statistics error

         OSPF Process 1 with Router ID 1.1.1.1

                 OSPF Packet Error Statistics

 0         : Router ID confusion         0         : Bad packet

 0         : Bad version                 0         : Bad checksum

 0         : Bad area ID                 0         : Drop on unnumbered link

 0         : Bad virtual link            0         : Bad authentication type

 0         : Bad authentication key      0         : Packet too small

 0         : Neighbor state low          0         : Transmit error

 1         : Interface down              0         : Unknown neighbor

 0         : HELLO: Netmask mismatch     8         : HELLO: Hello-time mismatch

 ……

6. OSPF verification configuration matching

Verify if one end has enabled area validation or interface validation, please ensure that the configurations on both ends match and the keys are correct.

7. OSPF area configuration matching

Inconsistent area type or area number will not form a neighbor relationship.

Inconsistent area type: If you want to configure an area as a special area, then all routers in that area must be configured with special area properties, otherwise the neighbor relationship cannot be established normally.

Note: The special bits in the Hello message determine, for example, whether the E bit determines whether external routes can be introduced.

8. Whether OSPF neighbors are established using the sub address

Limitation: Neighbors can only be established using the primary address. If only the sub address network segment is announced, neighbors cannot be established.

9. Whether NBMA and P2MP unicast networks specify neighbors

(1) When the OSPF network type is NBMA, the neighbor's IP address must be manually specified, otherwise the port cannot send Hello messages and form a neighbor relationship.

(2) After configuring the interface type as P2MP unicast, OSPF protocol sends unicast messages on that interface. Since neighboring routers cannot be dynamically discovered through broadcast Hello messages, the IP address of the neighboring interface must be manually specified.

10. Inconsistent network types on both ends

In the case of 4 different OSPF network types, if one end is an NBMA network and the other end is a non-NBMA network, neighbors may not be able to form.

11. Service provider transmission link prohibits multicast messages

First, verify that unicast direct connection is working, whether the transmission enters the wrong VLAN tag; check if the interface multicast count is increasing, and use debug, flow statistics, or mirroring to see if Hello messages are being sent. If it is confirmed that this is the case, temporarily resolve it by changing to an NBMA network or P2MP unicast form.

12. Neighbor Router ID conflictIn the case of a direct connection network, when both routers do not have neighbors, the error message indicates a Router ID conflict.

<RTA>DIS OSPF statistics error

         OSPF Process 1 with Router ID 19.1.1.1

                 OSPF Packet Error Statistics

 7         : Router ID confusion         0         : Bad packet

 0         : Bad version                 0         : Bad checksum

 0         : Bad area ID                 0         : Drop on unnumbered link

……