300-410 Practice Question: An engineer configures OSPFv2 on two routers with…

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  The interface MTU on one router is 1500, and on the other is 1400.

  Why this is correct

  Mismatched interface MTUs cause OSPFv2 neighbours to stall in EXSTART because the database description packets exchanged during master/slave negotiation are padded to the interface MTU; the 1400-byte side rejects the larger 1500-byte DBD packets, so the routers never progress to EXCHANGE.

• ✗

  The OSPF hello and dead intervals are mismatched.

  Why it's wrong here

  Mismatched hello or dead intervals prevent neighbours reaching 2-Way, not EXSTART; the routers would not form an adjacency at all. It is tempting because timers are a common OSPF fault, but EXSTART specifically indicates an MTU mismatch or duplicate router ID during DBD exchange.

• ✗

  One router has OSPF authentication configured, and the other does not.

  Why it's wrong here

  Authentication mismatch causes packets to be discarded, so neighbours stall at INIT or 2-Way, never reaching EXSTART. It is tempting because authentication is a frequent OSPF issue, but EXSTART requires successful hello exchange; the failure occurs later, during database description negotiation.

• ✗

  The OSPF network type is point-to-point on one router and broadcast on the other.

  Why it's wrong here

  Differing network types do not block EXSTART; both broadcast and point-to-point form adjacencies and exchange DBD packets. It is tempting because network type affects DR election, but EXSTART stalls stem from MTU mismatch or duplicate router IDs, which break DBD exchange.