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How can I prefer route1 but start utilizing the other routes when route1 interface utilization gets very high?
PfR.
If the traffic-share is unequal, what happens when the interface with high traffic share gets saturated? Do traffic automatically move to other routes or traffic still get sent strictly according to traffic share, causing the high share interface to drop traffic and other interfaces underutilized?
Yup.
Is this a problem better solved with BGP full table?
Nope. (Actually, although PfR can work with BGP, I once replaced full BGP tables with PfR - got better results - less load on the router.)
If BGP is not feasible, what options do I have?
PfR. Or, your own script(s), doing what PfR does for you.
PfR can probably do it but I prefer a cleaner way ;)
If you do find a cleaner way, please post it!
You only mentioned dynamic interface load utilization routing, but PfR can do more! For example, it can monitor performance to the destination, and shift traffic to obtain the best performance to the destination.
