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 OSPF broadcast multi-access networks such as Ethernet, the default hello interval is 10 seconds, and the associated dead interval is 40 seconds (four times the hello). This is the standard value defined in RFC 2328 for broadcast and point-to-point network types, ensuring timely neighbor discovery and liveness detection without excessive control-plane overhead. Because both routers must agree on the hello interval to form an adjacency, the Ethernet default of 10 seconds is the correct answer.

• ✗

  30 seconds

  Why it's wrong here

  30 seconds is the default hello interval for OSPF on non-broadcast multi-access (NBMA) networks such as Frame Relay and ATM, not on Ethernet. NBMA networks lack the multicast capability of broadcast links, so OSPF uses a lower hello frequency to compensate for the different failure-detection requirements and manual neighbor configuration. For a standard Ethernet segment, the expected hello is 10 seconds, so choosing 30 seconds reflects the wrong network type.

• ✗

  40 seconds

  Why it's wrong here

  40 seconds is not an OSPF hello interval at all; it is the default dead interval on broadcast networks, which is four times the 10-second hello. The dead interval is the period a router waits without receiving a hello before declaring the neighbor down. Confusing the dead timer with the hello timer is a common misstep, but for the hello interval specifically on Ethernet, the correct default remains 10 seconds.

• ✗

  5 seconds

  Why it's wrong here

  A 5-second hello interval is not the OSPF default on any standard network type; it is an optionally configured value that an administrator might set to accelerate neighbor convergence, often paired with a proportional dead interval. While fast hello timers are supported (e.g., configured in milliseconds via the 'ip ospf hello-interval' command), they are not the IEEE or RFC default. Therefore, 5 seconds is incorrect as the default for Ethernet, where OSPF defaults to 10 seconds.