Enables MSTP and VLAN configuration on network-to-network interface (NNI) ports. The default is disabled.
Note
Spanning Tree is disabled on all NNIs.
You cannot add an SPBM NNI port or MLT port to any non SPBM B-VLAN. You cannot add additional C-VLANs to a brouter port.
enable
configure terminal
boot config flags nni-mstp