Explain how Traceroute builds a list of the routers on the path from the host through the network to the destination.
Try an answer before revealing the guidance below.
Key Concepts
- TTL
- ICMP Time Exceeded
- Hop
- Increasing TTL
Answer Approach
- Send a probe with TTL 1, then TTL 2, and so on.
- Use each expiry response to identify a hop.
- Stop when the destination responds.
Full Answer
Answer status: Verified against study notes. Revision notes, not an official marking scheme.
Traceroute sends probes with successively larger TTL (or IPv6 Hop Limit) values. Each router decrements the value; when it reaches zero, that router discards the probe and normally returns an ICMP Time Exceeded message. The message identifies that hop. Repeating with larger values reveals later routers until a probe reaches the destination, which responds in a way that ends the trace.
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