[Beowulf] Cluster Diagram of 500 PC

Patrick Geoffray patrick at myri.com
Wed Jul 11 21:21:08 PDT 2007

Mark Hahn wrote:
> I don't think that's what I meant.  imagine instead that you have 48pt 
> GE switches, each of which has 4x 10G extra ports.  now, take
> 5 such switches and fully connect them (each switch has a 10G link
> to each of the other 4 switches).  I don't think 802.3ad helps here,
> since what you want is to _avoid_ a single spanning tree, which would 
> necessarily have one root.

Yes, there is still a spanning tree and it will prevent cycles by 
choosing a root for you.

There is no way to work around it at the pure Ethernet level. Sure, you 
can play with vlans, but it's more an hack than a well defined way to 
solve the problem.

In practice, you can do this type of topology by using a proprietary 
"stacking" interface if there is one available. These ports are not 
Ethernet links, they are backplane extensions, so they are not subject 
to spanning tree limitations. Of course, it's vendor specific and some 
switches don't have such stacking ports. You could also turn off the 
spanning tree, but you cannot call it Ethernet anymore. Another solution 
is to do layer-3 routing between switches, if you have such IP routing 


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