Cisco Nexus 9000 Series Configuration Manual page 138

Guidelines and Limitations for Configuring MST
• The spanning-tree pseudo-information command is not available on Cisco Nexus 92160 and Cisco
Nexus 93180 switches running Release 7.0(3)I4(1), 7.0(3)I4(2), and 7.0(3)I4(3).
• You can assign a VLAN to only one MST instance at a time.
• You cannot map VLANs 3968 to 4095 to an MST instance. These VLANs are reserved for internal use
by the device.
• You can have up to 65 MST instances on one device.
• By default, all VLANs are mapped to MSTI 0 or the IST.
• You can load balance only within the MST region.
• Ensure that trunks carry all of the VLANs that are mapped to an MSTI or exclude all those VLANs that
are mapped to an MSTI.
• Always leave STP enabled.
• Do not change timers because you can adversely affect your network stability.
• Keep user traffic off the management VLAN; keep the management VLAN separate from user data.
• Choose the distribution and core layers as the location of the primary and secondary root switches.
• Port channeling—The port channel bundle is considered as a single port. The port cost is the aggregation
of all the configured port costs assigned to that channel.
• When you map a VLAN to an MSTI, the system automatically removes that VLAN from its previous
MSTI.
• You can map any number of VLANs to an MSTI.
• All MST boundary ports must be forwarding for load balancing between Rapid PVST+ and an MST
cloud or between a PVST+ and an MST cloud. The CIST regional root of the MST cloud must be the
root of the CST. If the MST cloud consists of multiple MST regions, one of the MST regions must
contain the CST root and all of the other MST regions must have a better path to the root contained
within the MST cloud than a path through the Rapid PVST+ or PVST+ cloud.
• Do not partition the network into a large number of regions. However, if this situation is unavoidable,
we recommend that you partition the switched LAN into smaller LANs interconnected by non-Layer 2
devices.
• When you are in the MST configuration submode, the following guidelines apply:
The software supports full nondisruptive upgrades for MST. See Cisco Nexus 9000 Series NX-OS High
Note
Availability and Redundancy Guide, for complete information about nondisruptive upgrades.
Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide, Release 7.x
124
◦ Each command reference line creates its pending regional configuration.
◦ The pending region configuration starts with the current region configuration.
◦ To leave the MST configuration submode without committing any changes, enter the abort
command.
◦ To leave the MST configuration submode and commit all the changes that you made before you
left the submode, enter the exit or end commands, or press Ctrl + Z.
Configuring MST Using Cisco NX-OS