Hi, I don't know if is exactily it that u is asking.
But a long time ago... when u send a ICMP package type 13 (timestamp-request) you will recive a ICMP package type 14 (timestamp-reply). But in nowdays it is blocked by default in all "modern" distribuitions. Some distro like debian, by default print in stderr the try of request. :) ps.: Exist a program that make this test, i think that it is called icmpinfo. :) Best Regards. [ ]'s
