How it works
Traffic crosses many networks between source and destination, and each step is a decision made with the information available at that point. A path-tracing tool reveals those steps one at a time.
Read a trace as a sequence. Where the responses stop, or where the delay jumps, usually indicates where to look next.
Common error
A delay at one intermediate step does not by itself indicate a problem there. Only a delay that persists through the remaining steps is meaningful.
Worked example
Read end-to-end behavior in an example path trace.
Evidence
Hop 1: 2 ms
Hop 2: * * *
Hop 3: 8 ms
Destination: 11 ms
Required application: worksThe silent second hop is not proof that forwarding fails there: later hops and the destination answer. Some routers filter or deprioritize diagnostic replies. Look for persistent degradation at later hops and in the required application before attributing a fault.
Exercises
4.5.1
A trace reports 90 ms at hop 3, 10 ms at hop 4, and 12 ms at the destination. Does the 90 ms response alone prove a persistent path delay?
Show solution
No. The later responses are faster, so hop 3 may simply prioritize diagnostic replies differently. Evaluate repeated end-to-end measurements and the application behavior.
4.5.2
A trace becomes slow at hop 4 and remains slow to the destination, while the application also slows. What next action is justified?
Show solution
Investigate the path around and beyond that transition using repeated tests and provider or device evidence. Treat it as a lead rather than proof of the exact failing router.