ARP Poisoning

[budsz]

Hallo,

I've Lan with configure XP system and FreeBSD acting as router. So I
get stranger troble is disconnecting each computer together. This
happened with random time, maybe about 15 minutes after running as
well. In /var/log/message I got movement ARP entry to other MAC ADDR
on the same IP ADDR. Everyone know what happen is? Is that ARP
Poisoning. If the answer yes, how to preventing or resoloving this
problem?

Thanks You For Advance.

-- 
budsz