Large scale NAT problems

[Andriy Korud]

Hi,
I'm tring to make NAT on FreeBSD box for 2500 clients on 35Mbit uplink.
Box is Xeon 2.8GHz, 1G RAM, 2xIntel PRO/1000 (em) adapters.
FreeBSD 4.9-STABLE, kernel is configured for single processor (HT not used),
with DEVICE_POLLING and HZ=2000, LARGE_NAT defined.
Nat was done using ipnat, no additional filtering.

The problem is that when traffic grows to 10Mbit and number of active NAT
sessions reach 70000, CPU usage exponentialy grows and system spends all CPU
time in interrupts handling. 
The system become completely unreponsible and unsable and only hard reset is the
solution.

And worse thing is that Linux on Cel/800 with SOHO cards do that NATing with 5%
CPU load without any problem :-(.

Maybe I shoud try natd? May this help?
Any suggestions?

thanks in advance,

Andriy Korud