A core router receives an IPv4 packet destined for a remote network host. The router's routing table contains multiple paths learned via different dynamic routing protocols, static routes, and directly connected subnets. Place the decision-making steps in the exact sequential order that the router's control plane uses to evaluate the candidate paths and forward the packet to the next hop.
- 1Filter candidate routing table entries by applying the Longest Prefix Match (LPM) rule against the packet destination IP address.
- 2Compare Administrative Distance (AD) values among the remaining candidate routes that share the longest prefix mask length.
- 3Evaluate metric values (such as cost or hop count) among candidate routes with identical prefix length and Administrative Distance.
- 4Determine the next-hop gateway address and resolve its Layer 2 MAC address for frame encapsulation and transmission on the egress interface.
Answer
The correct sequence for packet forwarding decision logic is: 1) Apply Longest Prefix Match to filter candidates by subnet specificity, 2) Compare Administrative Distance to select the most reliable route source among matching prefix lengths, 3) Compare metric values among routes from the same routing source to identify the lowest-cost path, and 4) Resolve the next-hop Layer 2 destination address for frame encapsulation on the egress interface.
Route lookup logic follows a strict hierarchy. First, Longest Prefix Match (LPM) determines subnet specificity. Second, among candidate routes with equal prefix length, Administrative Distance (AD) selects the most reliable protocol source. Third, for ties within the same protocol source, metric values isolate the optimal cost path. Finally, Layer 2 ARP resolution encapsulates the packet onto the egress link.
Step-by-Step Solution
Key Concept
Route Selection Precedence (Longest Prefix Match -> Administrative Distance -> Metric -> Egress Encapsulation)