How does SonosNet elect its root bridge?

  • 16 May 2009
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Rather an arcane topic, but does anyone have any insight into how the SonosNet nodes elect a root bridge for their own internal Spanning Tree? By juggling ZPs and ZBs I'm trying to exert some control over which nodes generally forward to which, as in some cases it helps to strengthen signals on default paths and avoid RF interference.

Reviewing the Network Matrix - and from sniffing an ethernet port - the root is the node (a ZoneBridge in my case) with the largest MAC address. This being counter-intuitive, I dig further and find that the bridge ID for the root node is actually "8000." whereas all the rest are "9000.", so this would explain why that node is the root. But what told that node to set a bridge priority of 0x8000 (32768) and the remainder 0x9000? One could be forgiven for inferring that SonosNet elects the largest MAC as root (ignoring priority) and then post-justifies it by "fixing" the bridge priorities. 😉 Or is there some other kind of mechanism at work?

Thanks for any info.

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