CCNA IP Routing Practice Question

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 OSPF hello timers do not match.

  Why this is correct

  OSPF requires neighboring routers to agree on hello and dead intervals to form and maintain adjacency. If hello timers do not match, the router will not accept the neighbor's Hello packets within the dead interval, causing the Dead Timer to expire and preventing adjacency. This specific mismatch is a classic cause when two routers are in the same area and subnet but cannot see each other as OSPF neighbors.

• ✗

  The routers need matching hostnames.

  Why it's wrong here

  OSPF router identification does not depend on hostnames; instead, it uses the Router ID, which is derived from the highest configured loopback IPv4 address or the highest IPv4 address on a physical interface. Hostnames are merely labels for configuration convenience and are not exchanged in OSPF Hello packets. Matching hostnames is never a condition for OSPF adjacency formation.

  When this WOULD be correct

  In a different scenario where the question asks about OSPF configuration issues related to hostname resolution, a candidate might be asked why two routers with mismatched hostnames cannot communicate properly. In that case, if hostname resolution is a factor, this option could be correct.

• ✗

  The subnet must be changed to /24 before OSPF can work.

  Why it's wrong here

  OSPF is classless and supports variable-length subnet masks (VLSM), so it can operate on any prefix length, including /24, /30, or /16, depending on the design. Changing the subnet to /24 would not resolve a hello timer mismatch, because the real cause is at Layer 3 OSPF parameters, not the subnet mask. In fact, altering the subnet mask could break IP addressing if the current subnet is deliberately sized.

  When this WOULD be correct

  In a different scenario where the question states that two routers are on different subnets, and OSPF is configured, a candidate might choose this option if they believe that changing the subnet to /24 would allow the routers to communicate and form an adjacency.

• ✗

  The routers must both use static routes first.

  Why it's wrong here

  OSPF is a dynamic routing protocol that builds its routing table using link-state advertisements and the SPF algorithm; static routes are not required for it to establish neighbor adjacencies. The two routers can form an OSPF adjacency without any static route configuration, and static routes would only be relevant to forwarding traffic, not to protocol operation. Therefore, this option incorrectly introduces a prerequisite that does not exist for OSPF.

  When this WOULD be correct

  In a different scenario, if a question states that two routers are configured to use OSPF but are unable to establish an adjacency due to missing static routes that are required for initial connectivity, then this option would be correct.

Option-by-option analysis

Why each answer is right or wrong

Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.

Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”