[CentOS] OpenVPN throughput

Hello listmates,

We are working on setting up two private networks linked by a public
network which is fast (1 Gbit/s) but potentially insecure. Since the
hosts on our two networks need to talk to each other, and do so
securely, we have decided to use OpenVPN to connect them, making one
gateway a server and the other a client. The connectivity part was
easy to establish and worked like a charm. The only problem was, and
is, performance.

We have two old PIII-class machines that are being tested for the role
of the gateways. We have put new 1 Gbit NIC's in them and they work
find for everything (data transmission, DHCP, DNS, routing) except the
VPN. When traffic goes through the VPN the OpenVPN process goes to 99%
CPU on the server, about 70% CPU on the client and the effective
transmission rate goes down to about 6 MB/s whereas in non-VPN mode it
can be as high as 50+ MB/s (the top for the 1 Gbit/s is, obviously,
125 MB/s hence with the VPN we are down to about 5% of the capacity).

While this may be usable we would like to hope we can do better. Hence
the following questions:

1) Have you used OpenVPN in a similar setup?

2) If so what sort of performance did you see?

3) What kind of equipment did you use?

Personally, I'd like to hope that if we find VPN-enabled gateways with
more processing power we'd get drastically better performance. So if
you have data to confirm or deny that please share it.

Thanks.

Boris.