Strange fork-trlated problem

[tarkhil at over.ru]

Hello!

This problem has been persisted on two different MBs (diffrent CPUs,
different memory), half dozen of different NICs, 4.7-RELEASE and
4.8-RELEASE.

Common router/NAT (ipnat, kld loaded) behaves very strangely after about
10-20 minutes of work. New processes doesn't create anymore, process trying
to fork looks in top having -20 PRI and "temp" STATE. I was unable to find
out what that state means. New TCP connections from internal networks fails
to create as well. Top also shows absurdly high Interrupt CPU state (from 5
to even 50 sometimes!). 

I will try to work without ipnat. But surely it doesn't suppose to "work"
that way.

It should not be hardware-related, save possibly hard disk (the only common
thing).

Computer pings from outside well. 

Help please.

Alex.