MSTP instance 0 question

[dguigo]

Hello all,

If you create a new vlan on MSTP instance 0 you will impact all the other instances, is it correct ?.

If you encountered flapping on one vlan of the MSTP isntance 0 it will impact all the MSTP instances ?.

is it correct ?.

Thanks and regards,

David.

[smehrnia]

Hi David,

Thats my understanding from MST instance 0, it's the Internal Spanning Tree (IST) instance, made available on MSTP to allow it to ineract with none MSTP switches. the instance 0 is simply an RSTP instance that makes the whole MST region to appear as one virtual bridge running Common Spanning Tree, to the outter world.

with that in mind i dont think creating vlans on instance 0 affects other instances of MST, but it might affect how the outter world interacts with the virtual bridge (IST).

Be advised that MST does not send different BDPU for different instances, all are IST BPDU with an MRecord for other instances, and this might result in unexpected topology for vlans mapped in instance 0 (IST). it is not advised to map vlans to instance 0 !

Hope it Helps,

Soroush.