MST topology change when instance updated - new region not electing new root bridge

[Ivan Mamka]

Hello,

I have 4 GNS3 lab switches. Connection look like this (Po as for portchannel):

SW1 <---Po1---> SW2                 SW4 <---Po2--->SW2

SW1 <---Po3---> SW4                 SW4 <---Po1--->SW5

SW1 <---Po2---> SW5              

When updating an instance 2 on root switch SW5, MST places that switch into different region (as I understand, nothing changes on root switch, other switches do recalculation). There are three total instances on all switches 0, 1 & 2.

Problem I see is that, when new region being created between SW1,SW2 & SW4, all switches' MST0 instances still showing as root switch SW5, and for instances 1 & 2 --> SW4 is elected as root.

Also on new MST region of three switches, two switches which connect to SW5 have port status as:

SW1: Role "Mstr"  Sts "BLK"       <-- what does it mean?

SW4: Role "Altn"  Sts  "BLK"       <-- both ports blocked?

attaching "show spanning-tree mst" results

Thanks!

[pieterh]

When updating an instance 2 on root switch SW5, MST places that switch into different region 

-> that is correct; you need to manually reconfigure all MST instances to the same MST config to form a single region again

SW1: Role "Mstr"  Sts "BLK"       <-- what does it mean?

SW4: Role "Altn"  Sts  "BLK"       <-- both ports blocked?

-> Yes multiple ports are blocked

in multiple screenshots you can observe there is an inconsistency mixing PVST and RSTP
try correcting this first to all using MST, AND same MST config