In MST a VLAN only spans within the MST instance within the region right? So the only way to advertise a VLAN between all regions would be to use the inter-region CIST? (is that correct?).
So basically you would only need to use the inter-region CIST if you wanted to span a VLAN (i.e. have L2 connectivity) between regions? i.e. if a host in one region needs to speak to a host in another region at layer 2, the VLAN must be configured in the inter-region CIST, there is no other option within MST?
Can someone verify what I'm saying is correct please?