A Cisco router receives an Ethernet frame containing an IPv4 packet destined for a remote host. Place the router's forwarding decision steps in the exact chronological order in which they are evaluated from initial packet reception to egress frame transmission.
- 1Extract the destination IPv4 address from the incoming packet header.
- 2Filter the routing table to find candidate routes and select the route(s) with the longest prefix mask match.
- 3Compare Administrative Distance (AD) among remaining identical longest-prefix matches to choose the most believable route source.
- 4Compare the route metric among candidate routes from the same protocol that share identical prefix length and AD.
- 5Determine the next-hop address and exit interface, encapsulate the packet with new Layer 2 headers, and transmit the frame.
Answer
The correct sequence starts with extracting the destination IPv4 address, performing the Longest Prefix Match search, resolving ties using Administrative Distance, comparing metrics for remaining identical protocol routes, and finally rewriting Layer 2 headers to forward out the exit interface.
The router processes forwarding logic sequentially: destination IP extraction happens first, followed by selecting candidate routes based strictly on Longest Prefix Match (LPM). If multiple routes share the identical prefix length, Administrative Distance (AD) determines the trusted protocol source. If AD is also equal, metric cost breaks the tie. Once the best path is chosen, Layer 2 header rewriting and egress transmission occur as the final step.
Step-by-Step Solution
Key Concept
Router Forwarding Decision Logic Priority (LPM -> AD -> Metric -> L2 Encapsulation)