|Subject:||rtt is not true round-trip time|
It would appear that syn pings do not return true round-trip time but merely the time between when packet sent and when ack() returns. That is, if you send off a whole load of pings then start ack'ing then the rtt includes any delay in sending other packets. I see that Ping.pm contains some syn_forking stuff, but it doesn't seem to be able to be enabled. Forking to collect the responses would certainly help provide a more accurate rtt.