A Cisco router receives an IPv4 unicast packet and must select the best path from its routing table to forward the traffic. Arrange the steps in the correct sequential order that the router follows to evaluate candidate routes and make a forwarding decision.
- 1Identify candidate routes in the routing table that encompass the destination IPv4 address.
- 2Select the route(s) with the longest prefix match (most specific subnet mask).
- 3Compare Administrative Distance (AD) if multiple candidate routes have identical longest prefix lengths from different routing sources.
- 4Compare route metrics if multiple candidate routes have identical longest prefix lengths from the same routing protocol.
Answer
The correct order of steps in router forwarding decision logic is: 1) Identify candidate routes that match the destination IP, 2) Select the route with the longest prefix match, 3) Compare Administrative Distance if equal-length prefix ties exist between different routing sources, and 4) Compare route metrics if equal-length prefix ties exist within the same routing protocol.
The forwarding engine follows a strict evaluation hierarchy: first, matching candidate routes are identified; second, Longest Prefix Match (LPM) filters for the most specific subnet mask; third, Administrative Distance breaks ties between routes of equal prefix length from different protocols; fourth, metric breaks ties between routes of equal prefix length from the same protocol.
Step-by-Step Solution
Key Concept
Router Forwarding Decision Hierarchy (LPM > AD > Metric)
Estimated Time:1m 30s