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End-to-End Multi-Hop Packet Forwarding Engine

Multi-hop network packet journey simulator tracing Host A -> Switch 1 -> Router 1 -> Router 2 -> Switch 2 -> Host B. Inspects ARP address resolution, CAM MAC learning, Router Longest Prefix Match (LPM), and bitfield header rewriting.

NETWORKS • LABEnd-to-End Multi-Hop Packet Forwarding Engine
NETWORKING GOLDEN MILESTONE • UNIT 4Multi-Hop Packet Journey Simulator

End-to-End Multi-Hop Packet Forwarding Engine

Trace a packet across Host A → Switch 1 → Router 1 → Router 2 → Switch 2 → Host B. Inspect dynamic ARP resolution, transparent MAC learning, routing table Longest Prefix Match (LPM), hop-by-hop L2 re-encapsulation, and TTL decrement.

Router Hops
2 Hops
Current TTL
64
Stage: 1 / 10 (Payload Creation & Route Check)
Speed:
PHYSICAL TOPOLOGY: Subnet 192.168.1.0/24 ↔ WAN 10.0.0.0/30 ↔ Subnet 192.168.2.0/24
Active Node: HOST_A
LAN 1 (192.168.1.0/24)WAN Transit (10.0.0.0/30)LAN 2 (192.168.2.0/24)Host A192.168.1.1000:AA:11:22Switch 1L2 CAM TableVLAN 1Router 1E0: 192.168.1.1E1: 10.0.0.1Router 2E1: 10.0.0.2E0: 192.168.2.1Switch 2L2 CAM TableVLAN 1Host B192.168.2.2000:BB:55:66

Layer 2: Ethernet II Frame

Hop-by-Hop L2
Destination MAC:UNRESOLVED
Source MAC:00:AA:11:22:33:44
EtherType:0x0800 (IPv4)

Note: Layer 2 MAC addresses change whenever the packet crosses a router boundary.

Layer 3: IPv4 Datagram

End-to-End L3
Ver:4
TTL:64
Source IP:192.168.1.10
Dest IP:192.168.2.20
Protocol:ICMP Echo Req
Interactive Protocol Checkpoint

If the packet starts at Host A with initial TTL = 64 and traverses 2 intermediate routers before arriving at Host B, what will the final received TTL value be?

Current Router Action:
Must forward to Default Gateway: 192.168.1.1

Stage Explanation: Payload Creation & Route Check

Host A checks local subnet (192.168.1.0/24). Destination 192.168.2.20 is remote!

Host A performs bitwise AND: (192.168.2.20 & 255.255.255.0) != (192.168.1.10 & 255.255.255.0). Destination is on an outside subnet, so Host A targets its Default Gateway (Router 1 Eth0).

Networking Invariant: Host Forwarding Rule: Remote destinations are never addressed directly at Layer 2; the Layer 2 Destination MAC must be the first-hop Default Gateway.
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