Spanning Tree Protocol (STP)

Many of you have probably heard about the news coverage surrounding the downtime of the WordPress.com website (link). Perhaps the biggest lessons learned here is the complexity of spanning tree (STP), and perhaps more significantly, how the technology is taken for granted. The question for the week: do you know exactly how your spanning tree is operating within your organization? Which is your root bridge?

Without specifically designing your switching network intentionally, you leave things basically up to fate to decide on which switch is your root. Sometimes the worst connected or non-redundantly connected switch ends up being the root. Imagine a level 1 technician connecting in a basic managed switch in their cubicle to provide additional ports, but because the MAC address is the smallest, it becomes elected at the root. Probably not exactly what you want to have happen, but that is exactly what I’ve seen.

Here is a quick refresher:
http://www.cisco.com/univercd/cc/td/doc/product/rtrmgmt/sw_ntman/cwsimain/cwsi2/cwsiug2/vlan2/stpapp.htm

Along with a great list of common problems:
http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00800951ac.shtml

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