2) assuming that costs favored having both aggregates in service, if utilization on the two aggregates was 50% on (call it) A and 100% on B, the 50% available on A would be wasted. Note that latency would go up, because spanning tree would have pruned some intra-building link would have been pruned in order to keep the inter-building link active.
If this is true, then the Layer 2 bandwidth aggregation design is pretty weak, no?
You're mixing apples and oranges.
For example, (and yes, I know there's a world of difference) a MLPPP link is at (effectively) layer 2 (if not 1.5), and if one side of the link drops, the other side will carry what it can.
That is what happens within an aggregate. The multi-link PPP channel corresponds to an "aggregate" in the terminology that I am using. The topic being discussed is not what happens within an aggregate, but what happens when two aggregates are using. This would be akin to having two multi-link PPP connections (each constructed out of some number of physical links). Stephen