Joe Shaw writes:
A Network General sniffer will do this for you, and it's a really nice
(read expensive) piece of equipment to have. They go for around $26,000
(someone correct me if I'm wrong... I've never bought one myself).
tcpdump on a cheap NetBSD/FreeBSD/BSDI box (even an old 486 will do
just fine) will easily keep up with all of your ethernet traffic, and
its free, not $26,000. Its also VERY flexible -- I've never needed
anything else. Best to do this on a box that does native BPF, though
(asn an example SunOS does not do BPF and NIT can't handle the traffic
without dropping most stuff).