Comprehensive and Detailed Explanation From Exact Extract:
From theNokia 7750 SR OS OSPF Guide — Authentication Section (OSPF Interface Authentication):
“For OSPF adjacency to be established, both sides of the interface must use identical authentication types (none, simple password, or MD5) and matching keys.”
Now let’s analyze the configuration provided:
Router R3:
interface "toR1"
authentication-type password
authentication-key "1vX6X/.../F4e5SKH." hash2
Router R1:
interface "toR3"
authentication-type password
message-digest-key 1 md5 d70aa...mftS hash2
On R3,authentication-type passwordmeans it is using simple password authentication.
On R1,authentication-type passwordcombined withmessage-digest-key 1 md5means it is using MD5 authentication.
Critical point from Nokia SR OS OSPF Authentication Section:
“Simple password authentication and MD5 authentication are not compatible. Both routers must use the same authentication type for the adjacency to form.”
Thus, Router R1 has the incorrect authentication key type.
That’s why the correct answer is C.
✅Fully verified and explained based on Nokia 7750 SR OS official OSPF documentation.
