Hello, This is Ibrahim Ethem Coskun from University of Nevada, Reno. I'm currently working on an Internet Measurement project with Professor Mehmet Hadi Gunes. We are modifying paris-traceroute's source code and set the flow identifier of each packet (both sending and returning packets) to a constant value for every traces. So that, we want a trace to follow the same path whenever we traceroute the same target. However, I get the below warning messages from each probe : paris-traceroute -T 500 -i -l -M 5 -p icmp -r 44000 -a hopbyhop -n " + target_ip [WARN](TracertImpl.cc, 335)ICMP reserved words 0 0 0 0 0 [WARN](TracertImpl.cc, 330)Bad return flow id 0xd24e from 4.69.152.80 So, what does this warning mean, I checked the source code but couldn't find and information regarding this issue, I also email paris-traceroute team, but no responses. I googled my question and found a similar question emailed to to you ( https://www.ripe.net/ripe/mail/archives/ripe-atlas/2012-July/000534.html). I would be very pleased if you can answer my question. Thank you;