A Cisco router receives an IPv4 unicast packet on an ingress interface and prepares to forward it toward its final destination. Place the sequential steps of the router's packet forwarding decision process in the correct chronological order from first to last.
- 1Decapsulate the incoming Layer 2 frame and extract the destination IPv4 address from the IP header.
- 2Search the routing table for all matching route entries corresponding to the destination IPv4 address.
- 3Select the single best route entry based on the Longest Prefix Match (most specific subnet mask length).
- 4Determine the egress interface and next-hop IPv4 address associated with the chosen route entry.
- 5Resolve the Layer 2 hardware address of the next-hop device using ARP or cached neighbor information.
- 6Decrement the IPv4 Time-to-Live (TTL) field by 1, recompute the checksum, encapsulate the packet into a new Layer 2 frame, and transmit it out the egress interface.
Cevap
The correct sequence starts with decapsulating the incoming Layer 2 frame, searching the routing table for candidate prefix matches, selecting the best match using Longest Prefix Match (LPM), determining the egress interface and next-hop IP, resolving the Layer 2 address of the next-hop device via ARP, and finally decrementing the TTL and encapsulating the packet into a new frame for transmission.
The router processes ingress packets sequentially: it first strips the Layer 2 frame to read the destination IP, searches the routing table, applies the Longest Prefix Match rule to pick the most specific network prefix, determines the next-hop IP and egress interface, resolves the next-hop Layer 2 MAC address, and finishes by decrementing TTL, updating the checksum, encapsulating the packet, and transmitting the frame.
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Anahtar Kavram
Router IPv4 Forwarding Decision Pipeline