Forwarded to my team. Nicely put.

-----Original Message-----
From: MICE Discuss [mailto:[log in to unmask]] On Behalf Of David Farmer
Sent: Tuesday, September 20, 2011 10:18 PM
To: [log in to unmask]
Subject: Re: [MICE-DISCUSS] Remote MICE members?

On 9/20/11 19:54 CDT, Jay Hanke wrote:

> Frankly, I'm surprised at the outpouring of love for spanning-tree on
> the list. I've on more than one occasion selected a vendor with a ring
> or a virtual chassis technology to avoid spanning-tree in the core. I
> was also thrilled at the prospect of something like TRILL.
>
> Can someone take it on to make a design recommendation?

Let me be clear, I don't love spanning-tree at all. But turning off spanning-tree and praying you never have a loop is worse than spanning-tree. My personal design preference is to design your network with a loop free topology at layer2. Then it is possible to run without spanning-tree. Any redundancy is provided using LAGs, GMPLS or MPLS transport technologies, not loops in the bridge topology.

However, you still run spanning-tree to catch mistakes, they will happen and spanning tree will keep them from melting the network. When the network is built and is functioning as designed, spanning-tree has nothing to converge, the network has a loop free topology. In this design, spanning-tree is only there to ensure the network is actually built and actually functioning as designed.

When you are driving your car, if you see head lights coming at you on the wrong side of the road, most people slow down and get ready to take the ditch. Rather than take a head on into the other guy, or into the ditch, at full speed. In this design, spanning-tree is looking for head light on the wrong side of the road, rather than assuming it will never happen, which is what you are doing if you just turn spanning-tree off.

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David Farmer Email:[log in to unmask]
Networking & Telecommunication Services
Office of Information Technology
University of Minnesota
2218 University Ave SE Phone: 612-626-0815
Minneapolis, MN 55414-3029 Cell: 612-812-9952
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