STP problems with tagged traffic

[andyj-hng]

Hi guys,

I am struggling with tagging traffic when trying to use STP.

The problem currently resides on a test bench and is in the process fo being tested before it goes into production.

I have done a quick sketch of the test bench which has the issue broken down into its simplest form, attached.

As you can see I have three switches in a triangle. All with latest firmware and having only the default vlan defined but all traffic untagged.

Switch on spanning-tree and all works correclty.

However, if I then tag all traffic and force rstp then the network lights up in a broadcast frenzy.

If I tag the traffic in switch 1 then this causes the problem on its own.

Pretty sure it is something simple... but cant get my head around it...

[Richard Litchfield]

Use MSTP and make sure all the VLANs are in the same instance. Easiest to leave them in the default common instance (CST).