The following information is displayed during OSPF troubleshooting.

According to the displayed OSPF error statistics from the Huawei device, the key HELLO packet error shown is:

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2 : Netmask mismatch

This indicates that the OSPF adjacency formation is failing due to a subnet mask mismatch between the two OSPF neighbors on the corresponding interface (GigabitEthernet 0/0/0). OSPF uses the subnet mask in Hello packets to ensure that neighbors are in the same network. If the masks do not match, OSPF will not form an adjacency.

From the Huawei Official HCIE-Datacom Study Guide (Version 3.0) — under the OSPF Troubleshooting Section:

" Netmask mismatch: If the subnet mask configured on the interfaces of OSPF neighbors does not match, a ' Netmask mismatch ' error occurs. OSPF requires neighbors to be on the same subnet to establish an adjacency. This is a common reason for failure in adjacency formation. "

(Reference: Huawei HCIE-Datacom V3.0, OSPF Troubleshooting Chapter, Section 4.2 – OSPF Hello and Adjacency Establishment Issues)

Thus, among the given options:

A. Area type inconsistency would result in an area ID mismatch error, not netmask.

B. Authentication mismatch would show a bad authentication key or type error.

D. Hello interval mismatches would trigger a Hello timer mismatch error.

Only C. The IP address masks of the interfaces are inconsistent directly matches the actual error observed: Netmask mismatch.