[No hats on, for this and the previous reply to Changming Liu]
The document assumes that it is always desirable to do load-sharing with the equivalent routers. I don't agree with this assumption.
If the router's capacity is sufficient so that it can forward all the traffic sent by its nodes, there is actually very little need for load sharing. On the contrary -- sharing load between routers produces difficult-to-debug scenarios when some destinations (which are distributed to some routers) fail in mysterious ways while others work just fine.
I have a different set of experience where customers provision two or more parallel router+firewalls and wish to divide the traffic between them. The specifically do not want the other routers to be unused. They have installed multiple routers so if one fails they want the others (using VRRP) to take over for the failure. They have found that unless all of the routers are used for live traffic that there is too high a probability that the other routers won't function correctly.
Due to that, I, as an operator, would not wish to enable load-sharing on hosts except when I specifically require that kind of functionality.
I believe that the "Default Router Preferences and More-Specific Routes" mechanisms provides the means to give the default routers different preferences. This will have the effect of keeping the load sharing from coming into play because the routers won't be seen as equivalent. This will give you the control I think you are asking for with out having some mechanism to change the default behavior in the hosts.
So, I'd propose that this document does not describe that the hosts MUST share the load, but rather describes how the hosts MUST behave if they wish to share the load -- and if turned on by default, require that there MUST be a way to toggle load balancing off. A difficult issue to settle might be whether to recommend (and if so, how strongly) to enable load-sharing by default.
I disagree about what should be the default. I think the default should be MUST, as I think it is useful in the general case. As pointed out above the "Default Router Preferences and More-Specific Routes" mechanisms provides a simple mechanisms to cause the hosts to not see the routers as equivalent if one so desires.
Regards, Bob
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