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.

• ✓

  Step 1: Examine the destination IP address of the packet. Step 2: Perform a longest prefix match on the routing table. Step 3: Determine the next-hop IP address and outgoing interface. Step 4: Forward the packet to the next hop.

  Why this is correct

  This sequence correctly describes the routing table lookup process: the router first extracts the destination IP address from the incoming packet's header, then performs a longest prefix match (LPM) to identify the most specific matching route in the routing table. That matched route provides both the next-hop IP address and the outgoing interface, which the router then uses to forward the packet. Critically, this order respects the dependency chain: without the destination IP, no route lookup is possible, and without the lookup, no next-hop can be determined.

• ✗

  Step 1: Perform a longest prefix match on the routing table. Step 2: Examine the destination IP address of the packet. Step 3: Determine the next-hop IP address and outgoing interface. Step 4: Forward the packet to the next hop.

  Why it's wrong here

  This ordering is logically invalid because the router cannot perform a longest prefix match on the routing table without first knowing the destination IP address of the packet. The routing table entries are keyed by prefix, and the lookup algorithm compares the destination IP against those prefixes to find the longest match; with no destination to compare, the lookup has no basis. Placing the lookup before examining the destination IP is therefore impossible in practice—the router must always read the destination field from the packet header as the very first step.

• ✗

  Step 1: Examine the destination IP address of the packet. Step 2: Determine the next-hop IP address and outgoing interface. Step 3: Perform a longest prefix match on the routing table. Step 4: Forward the packet to the next hop.

  Why it's wrong here

  This sequence is incorrect because the next-hop IP address and outgoing interface are derived directly from the result of the longest prefix match; they cannot be determined independently before the routing table lookup. The routing table does not simply map destinations to arbitrary next-hops—it uses the longest matching prefix to select a route, and only then does that route reveal the next-hop and outgoing interface. By skipping the LPM step, this order inverts the causal relationship and would require the router to guess the next-hop without any routing information.

• ✗

  Step 1: Determine the next-hop IP address and outgoing interface. Step 2: Examine the destination IP address of the packet. Step 3: Perform a longest prefix match on the routing table. Step 4: Forward the packet to the next hop.

  Why it's wrong here

  This ordering is fundamentally backwards because the next-hop IP address and outgoing interface are outputs of the routing process, not inputs to it. A router cannot determine where to send a packet before it even knows the destination IP address, as the next-hop is entirely dependent on both the destination and the routing table's content. This sequence also skips the packet header examination at the start, making the first step impossible—there is no way to select a next-hop without first knowing the destination and performing a prefix match.

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?”

Go deeper

Related to this question