Please excuse me in advance if this is not the right forum for these kinds of questions, if it is the case I would appreciate any guidance towards a suitable platform.
I am trying to understand the effect of changing gap_limit on traceroute results. According to the documentation, gap_limit represents the number of unresponsive hops before the traceroute measurement is stopped. I interpreted that like: as soon as gap_limit consecutive unresponsive hops represented by * lines are observed, the traceroute measurement is stopped and flagged as “no reply” or something similar.
I am currently conducting measurements to test reachability towards a particular server from several probes. I noticed for a very large number of traceroutes that after about 6 consecutive unresponsive nodes the last hop is numbered 255 along with the RTT value from the target. I assumed that 6 unresponsive hops is the default although the documentation doesn’t mention it and that 255 is the new TTL value set after the gap_limit is reached although my hops limit is set to a smaller value such as 32 or 64. The hops column on the interface also shows the number of lines in the traceroute details, e.g., 16 instead of 255.
To understand more about how it works, I set gap_limit to 0, and indeed the responses come in faster and only 2 lines are showing with the second numbered 255 and with the hops column still showing 2.
My questions are:
- Is my interpretation of how gap_limit works and the 255 TTL behaviour correct?
- Should traceroutes that show results with last line being numbered 255 be interpreted as having <=255 number of hops instead of the number of lines in the traceroute as it currently shows?
Thank you very much for your help in advance!