A traceroute across a long provider path ends with rows of asterisks and never reaches the destination, although the host is reachable by other means. You establish that the target is roughly 36 hops away. Which option makes traceroute probe far enough?

LPIC-1 Exam 102-500, objective 109. Networking fundamentals medium

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The options

Correct traceroute -m 45 target.example.com

Correct. -m sets the maximum TTL, that is the highest hop number probed. The default is 30, so any destination further away appears as unreachable until the limit is raised.

Not correct traceroute -q 45 target.example.com

Wrong. -q sets the number of probe packets sent per hop, three by default. Sending 45 probes per hop makes the trace far slower without extending its reach.

Not correct traceroute -w 45 target.example.com

Wrong. -w is the time in seconds to wait for a response to a probe. It helps on very slow paths but does not change how many hops are traversed.

Not correct traceroute -f 45 target.example.com

Wrong. -f sets the first TTL used, so the trace would start at hop 45 and skip everything before it. With a default maximum of 30 this yields no output at all.

Why

traceroute works by sending probes with increasing TTL values and reading the ICMP time-exceeded messages returned by each router. The TTL walk runs from the value given by -f (default 1) to the value given by -m (default 30), so a destination beyond 30 hops needs -m raised. Trailing asterisks alone do not prove the hop limit is the cause: routers that decline to send ICMP time-exceeded messages produce the same symptom.

Where this comes from

Cited: manual page traceroute(8)

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Practise LPIC-1 Exam 102-500

A traceroute across a long provider path ends with rows of asterisks and never reaches the destination, although the host is reachable by other means. You establish that the target is roughly 36 hops away. Which option makes traceroute probe far enough?

The options

Why

Where this comes from

Practise this

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