Hard crash on 6.x -- reproducible, multiple people affected

[Peter Thoenen]

Hallo everybody.  Will prob end up PR'ing this but want to post to the
list first and get some feelers.  At first I thought it was just me but
as the port maintainer for tor-devel I have had a couple other folk
email me with the exact same problem (believing tor to be the cause). 
Its not.

Problem: When tor (running in server mode), i2p, or freenet is ran (all
high bandwidth, high number of concurrent tcp / udp / ip connections,
maybe 2000+ sim connects @ a constant 4 mb) between the 2 and 4 hour
mark a system running FBSD 6 will hard crash and power off.  This is
reproducible (though not on demand, just on arbitrary time between 2
and 4 hours).

Troubleshooting so far: 

- It is NOT an issue on 5.x.  It is an issue on both 6.0 and 6.1BETA4. 


- It is not easy to reproduce.  I assume a couple hundred people use
these ports and I have only had a dozen or so report this problem to
me.  All of the people suffering from this though CAN reproduce this
crash on demand.  I have to assume though the other 99% of users though
do not see this error for unknown reasons.

- It is not a port issue (as tor/i2p/freenet all can cause it).  It is
not a java issue (was another early worry of mine but tor is written in
C). 

- The hard crash does NOT generate a dump or panic for anybody I have
spoken with.  /var/crash comes up empty every time.

- It is not platform or hardware specific (this was my initial guess). 
I have seen this on both the amd64 and i386 archs.  I have also seen it
on various motherboards and nic's (bge, nv, em).  To reiterate, running
5.x on identical hardware does not cause this crash.

- It is not a tunable or sysctrl issue as far as I can tell.  Spent the
last month tuning and watching my system limits and all appears to be
good.

- My gut feeling is this has something to do with the new network stack
introduced in 6.0.

- When not running one of the aforementioned ports, system does not
crash.  I have a three week uptime currently on one of my testbeds
experiencing this problem.  If I start tor / i2p / or freenet I will
crash within hours.

Help would be appreciated in resolving this or troubleshooting further.
 I am at a loss here and me (along with a couple other folk that have
emailed me) have some nice expensive paperweights now as they crash on
use.  If you are developer and want to look into this, I can provide
all the info you need, just let me know exactly what it is.

Thanks,

-Peter