Round robin packet routing

Hello all,

Again, I have another question. Ok, coming into us, we have four DSL
modems (short of running leased lines 50km or setting up a wireless
link, it's the best we've got). Our provider will be providing us a /24
subnet for our customers; for load balancing they say that with their
Cisco routers they will use a round robin method of sending out the
packets through the four modems to us. This sounds cool, and I assume
that our Linux router will simply take the packets in from the four PPP
interfacing and route them through our local network interface (provided
that it's on the subnet of the packets coming in and
/proc/sys/net/ipv4/ip_forward has been echoed "1").

But my question is, how do I set it up so that any packets going from
our customers to the internet are round robined out of the four DSL
modems. Right now we are giving our customers private IP addresses and
using the "ip route replace default equalize nexthop.." of doing things
but that round robins the routes, I believe, not the packets. Since all
the traffic has the destination flag set to whichever of the four modems
that the route is set to, this seems like the correct way to go iwht the
private addresses, but with our new system where the destination flag
will be set to a public address on our subnet, how do I make linux round
robin the packets?

Thanks in advance,
Kevin Brown