[Beowulf] Spanning Tree Protocol and latency: allowing loops in switching networks for minimizing switch hops

[Greg Lindahl]

On Tue, Feb 23, 2010 at 03:15:28PM -0600, Rahul Nabar wrote:
> On Tue, Feb 23, 2010 at 3:10 PM, Greg Lindahl <lindahl at pbm.com> wrote:
> > On Tue, Feb 23, 2010 at 01:23:59PM -0600, Rahul Nabar wrote:
> >
> >> In the interest of latency minimum switch hops make sense and for that
> >> loops might sometimes provide the best solution.
> >
> > STP disables all loops. All you gain is a bit of redundancy, but the
> > price is high.
> 
> I see! That makes sense. Too bad.  I wish there was some non-STP way
> of dealing with loops then.

Managed switches often include a non-STP way of finding and
suppressing broadcast storms -- I know HP and Cisco have that.
I don't know if it's any better than STP, though.

In the InfiniBand world loops are encouraged & provide a nice
performance benefit -- the routes are worked out globally by the
Subnet Manager. Also, there is ethernet switch silicon that has an
alternate routing mechanism that's as good as IB -- but I don't
remember if it's standardized or compatible between different silicon
vendors.

-- greg