It seems like my OpenBSD box generates time stamp replies by default without any issues when being
hping'ed from OS X, per
17:27:43.220109 osx.example.net > openbsd.example.net : icmp: time stamp request 17:27:43.220138 openbsd.example.net > osx.example.net: icmp: time stamp reply
However, my OS X 10.8, when being hping'ed from OpenBSD, doesn't seem to generate any replies, and, according to its own tcpdump, it doesn't look like this is related to any external firewalls, since the local tcpdump doesn't reveal any replies being generated, unless I'm misunderstading the tcpdump readings, or, more specifically, lack thereof:
20:26:47.330517 IP openbsd.example.net > osx.example.net: ICMP time stamp query id 14881 seq 0, length 20
It'd be more convenient to hping my OS X laptop from my OpenBSD server, than the other way around; how do I make OS X work here?