I have a router Cisco 2610 IOS 12.3.
I have two totally separate networks connected there through two ethernet ports. I want one port (port A) to have priority in traffic, and the second one (port B) to use up to 1Mbps if the port A is not using the bandwidth. Once port A starts sending traffic port B should use only what port A leaves behind and should give up the bandwidth right away. The important thing is that either for incoming or traffic port A should have priority and by the way port A is a public subnet so the traffic can originate from outside. So even when port B is taking up bandwidth and there is a connection from outside to port A it should give up the bandwidth immediately to port A.
Port B is a NATed network that has traffic coming only from inside - nothing comes from outside (port A has servers - port B has a couple of users that connect from time to time)