According to here:
...the round trip time (RTT) for your packet to reach that point and return to your computer.
And in the example, it shows:
The RTT for hop 5 is smaller than hop 4.
RTT_4 = t1 + t2 + t5
RTT_5 = t1 + t2 + t3 + t6
How could RTT_5 < RTT_4? Or is it because it's possible that t3 + t6 < t5?
ADD 1 - 10:49 AM 3/21/2022
(Thanks to Ron Mauphin's answer.)
I think my previous illustration of how traceroute works is wrong. It should be like this:
RTT (Round Trip Time) = t1 + t2 + t3
TTL = number of hops
The lines are dashed because they are not necessarily direct traffic. There can be routers in the middle. Traceroute only cares about the source and destination of each line.
Traceroute is a smart tool that leverages the TTL and ICMP timeout error message sent by a router when a packet's TTL reaches 0. The effective result is to roughly obtain the path through which a source reaches the destination and the RTT to each of the nodes in the middle. It is rough because there's no guarantee that the nodes show by the traceroute is really/strictly one after another. It is possible that each probe packet sent by the traceroute goes through a completely different path which doesn't include all the previous middle nodes probed before.
Strictly speaking, traceroute essentially probes with a increasing distance (the TTL, i.e. max allowed hop number). It sends out 3 packets but even these 3 packets cannot be guaranteed to follow the same path. It doesn't at all measure the latency. It merely says 2 things:
- With how much TTL where can be reached for this time.
- And if a certain destination can be reached within the specified max TTL/hops.
But still, it is useful.
A related thread: Explanation of traceroute