Interoperability With Ieee 802.1D; High Availability For Mst; Virtualization Support For Mst - Cisco Nexus 7000 Series Configuration Manual

Configuring MST Using Cisco NX-OS
The system uses port priorities to break ties among ports with the same cost. A lower number indicates a
higher priority. The default port priority is 128. You can configure the priority to values between 0 and 224,
in increments of 32.

Interoperability with IEEE 802.1D

A device that runs MST supports a built-in protocol migration feature that enables it to interoperate with
802.1D STP devices. If this device receives an 802.1D configuration BPDU (a BPDU with the protocol version
set to 0), it sends only 802.1D BPDUs on that port. In addition, an MST device can detect that a port is at the
boundary of a region when it receives an 802.1D BPDU, an MST BPDU (Version 3) associated with a different
region, or an 802.1w BPDU (Version 2).
However, the device does not automatically revert to the MST mode if it no longer receives 802.1D BPDUs
because it cannot detect whether the 802.1D device has been removed from the link unless the 802.1D device
is the designated device. A device might also continue to assign a boundary role to a port when the device to
which this device is connected has joined the region.
To restart the protocol migration process (force the renegotiation with neighboring devices), enter the clear
spanning-tree detected-protocols command.
All Rapid PVST+ switches (and all 8021.D STP switches) on the link can process MST BPDUs as if they are
802.1w BPDUs. MST devices can send either Version 0 configuration and topology change notification (TCN)
BPDUs or Version 3 MST BPDUs on a boundary port. A boundary port connects to a LAN, the designated
device of which is either a single spanning tree device or a device with a different MST configuration.
MST interoperates with the Cisco prestandard MSTP whenever it receives prestandard MSTP on an MST
port; no explicit configuration is necessary. In Cisco NX-OS Release 4.0(2) and later releases, you can configure
specified interfaces to send prestandard MSTP messages all the time; it does not have to wait to receive a
prestandard MST message to begin sending prestandard MST messages.
You can also configure the interface to proactively send prestandard MSTP messages.

High Availability for MST

The software supports high availability for MST. However, the statistics and timers are not restored when
MST restarts. The timers start again and the statistics begin from 0.
The device supports full nondisruptive upgrades for MST. See the Cisco Nexus 7000 Series NX-OS High
Availability and Redundancy Guide for complete information on nondisruptive upgrades and high-availability
features.

Virtualization Support for MST

The system provides support for virtual device contexts (VDCs), and each VDC runs a separate STP.
You can run Rapid PVST+ in one VDC and run MST in another VDC as shown in this figure. Each VDC
will have its own MST. Ensure that you are in the correct VDC.
Cisco Nexus 7000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.x
Interoperability with IEEE 802.1D
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