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

[Eric W. Biederman]

Greg Lindahl <lindahl at pbm.com> writes:

> 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.

For the most trivial of loops there is link aggregation.

For more interesting loops you can run many ethernet switches
as wire speed ip routers talking a routing protocol like ospf.

Eric