IPsec's use of processors

[Riaan Kruger]

I would like to know how IPsec makes use of a multi processor machine?

I have gateway (FreeBSD 7.0) with four SAs configured. When testing
throughput through the configured SAs, I see (with systat) that only one cpu
works really hard (+-10% idle min), two others work a bit (+-70% idle min)
and the fourth CPU does pretty much nothing.

Is this normal, shouldn't at least the two cpus work hard because of the
high throughput?

I hope i am on the right list.

Riaan