MAE West

Mon Jul 14 17:40:36 UTC 1997

On Mon, Jul 14, 1997 at 10:14:16AM -0700, Stephen Stuart wrote:
> > Indeed.  More importantly, Bill, he wasn't suggesting duplicating the
> > 400Mbps aggregate, but _splitting_ it; it is, after all, _already_ 4
> > separate links.
> 
> The underlying physical media may be four separate links, but at L2
> it's a single 400Mb/s aggregate. If it were split up into, say two
> 200Mb/s aggregates:
> 
> 1) assuming that costs favored intra-building connections, one of the
> aggregates would be selected for pruning by the spanning tree
> calculation.
> 
> 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?

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.

Cheers,
-- jra
-- 
Jay R. Ashworth                                                jra at baylink.com
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