CCNP Practice Question: The default OSPF hello interval on an Ethernet…

Answer analysis

Option-by-option breakdown

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

• ✓

  10 seconds

  Why this is correct

  On Ethernet (broadcast) and point-to-point links, OSPF's default hello interval is 10 seconds, as defined in RFC 2328. This 10-second hello is also paired with a default dead interval of 40 seconds (four times the hello), allowing a neighbor to be declared down after missed hellos. This setting balances fast neighbor detection with acceptable control-plane overhead on high-bandwidth LAN segments.

• ✗

  30 seconds

  Why it's wrong here

  30 seconds is the default OSPF hello interval for non-broadcast multi-access (NBMA) networks, such as Frame Relay or ATM, where neighbors may be reachable only via manual configuration and lower-speed links. However, the question asks about an enterprise network design on Ethernet, which is a broadcast network type, so 30 seconds is incorrect for that context. NBMA's longer hello interval reduces overhead on slow WAN links, but it also slows down failure detection compared to broadcast.

• ✗

  5 seconds

  Why it's wrong here

  A 5-second hello interval is not a default for any OSPF network type. While you can manually configure OSPF timers to 5 seconds (or even lower) to achieve faster convergence, this is not a standard default and would generate twice the hello traffic of the 10-second default on broadcast networks. If used, the dead interval would typically be 20 seconds (4 * 5), making OSPF less tolerant of transient packet loss. Since the question asks for the default, 5 seconds is wrong.

• ✗

  20 seconds

  Why it's wrong here

  20 seconds is not a default OSPF hello interval for any standard network type. It is not specified in RFC 2328 or the OSPFv2 standard for broadcast, point-to-point, NBMA, or point-to-multipoint links. If a network engineer sees a 20-second hello, it must have been manually configured, perhaps to deliberately slow hello traffic, but it does not align with OSPF's default behavior. Thus, this value is incorrect for a default enterprise Ethernet design.