350-401 Question #744: Real Exam Question with Answer & Explanation

Question

Which two options describe the effect of configuring an interface as passive under OSPF? (Choose two)

Options

• AAn adjacency cannot be established, and the interface is not included in the routing protocol
• BThe interface processes OSPF hello packets but does not send hello packets.
• CAn adjacency cannot be established, and the interface is included in the routing protocol update.
• DThe interface processes OSPF hello packets and also sends hello packets.
• EAn adjacency can be established, and the interface is not included in the routing protocol update.

Explanation

When an interface is configured as passive under OSPF, it stops sending OSPF hello packets, preventing the formation of adjacencies with other OSPF routers. However, the network connected to this passive interface will still be advertised by OSPF into the routing domain.

Common mistakes.

• A. While an adjacency cannot be established, the network connected to a passive interface is included in the routing protocol updates, making the second part of the statement incorrect.
• D. A passive OSPF interface explicitly does not send hello packets; this statement directly contradicts the function of a passive interface.
• E. An adjacency cannot be established on a passive OSPF interface because it does not send the necessary hello packets for neighbor discovery and adjacency formation.

Concept tested. OSPF passive interface behavior

Reference. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_ospf/configuration/xe-3s/iro-xe-3s-book/ospf-passive-int.html

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