RSTP- non-edge port changing to edge

[chris_gla]

I'm testing RSTP to find root cause of an inter-operation issue with another vendors switches- 802.1w-2004 compliant.

Other vendor doesn't support setting uplinks to be non-edge, only auto or various flavours of edge with bpduguard/ filter type features- so all uplinks are set to auto.

I noticed behaviour that I hadn't thought of before as I've always manually disabled portfast/edge on uplinks.

The other switches correctly transition from edge to non-edge when a bpdu is received, but when another route subsequently becomes available/ preferred on a downstream switch the then backup ports on the upstream switch transition back to edge ports after one hello timer cycle (2 seconds), this is.because bpdu's are no longer received from the downstream switch over the backup link

Is this normal that under 802.1w  a port will revert to edge after being non-edge if it becomes a backup route facing a downstream switch? I'd expected that once a port received bpdu's and became non-edge it would stay in that state until a physical up/down change.

Thanks!

[Dennis Mink]

Chis

Cisco explaination of 802.1w , as per 

http://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/24062-146.html

An edge port that receives a BPDU immediately loses edge port status and becomes a normal spanning tree port. At this point, there is a user-configured value and an operational value for the edge port state. The Cisco implementation maintains that the PortFast keyword be used for edge port configuration. This makes the transition to RSTP simpler.

it does not mention transtitioning back once the operational status has changed to edge.

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