Hello,
I have tried to answer your specific questions :-
-- Is it a requirement that it be switched?
-- Is using cross over cables in a meshed configuration a viable solution to interconnect in a three or more node cluster?
This is the same question stated differently. The answer is, you cannot use crossover cables for a three or more node cluster, and hence you must use one switch (or hub :) ) per private LLT link. The reason you cannot use crossover cables is because LLT must be able to broadcast its updates to every other node, on a particular private link. You can't cable up crossover links to support this.
-- If it must be switched and I use two interfaces per node, should each of the interfaces be cabled into a different switch?
To be precise, each set of NICs that form a private link network should be connected to a different switch.
-- This would seem to cause the ISL in my switches to have to carry the LLT traffic, [...]
This is not actually true. The private link networks are totally independent of each other, so if all the NICs on the first private network are connected to a single switch, there will be no interswitch traffic required (in fact two isolated switches will do the job nicely). If you are using VLANs, then the VLAN used on switch A for private network A, does not need to be defined on any of the ports on switch B (and vice versa).
Regards,
Leigh.