93
•
The port cannot detect the change.
To forcibly transit the port to operate in the original mode, you can perform an mCheck operation.
For example, Device A, Device B, and Device C are connected in sequence. Device A runs STP,
Device B does not run any spanning tree protocol, and Device C runs RSTP, PVST, or MSTP. In this
case, when Device C receives an STP BPDU transparently transmitted by Device B, the receiving
port transits to the STP mode. If you configure Device B to run RSTP, PVST, or MSTP with Device C,
you must perform mCheck operations on the ports interconnecting Device B and Device C.
Configuration restrictions and guidelines
When you configure mCheck, follow these restrictions and guidelines: The mCheck operation takes
effect on devices operating in MSTP, PVST, or RSTP mode.
Configuration procedure
Performing mCheck globally
Step Command
1.
Enter system view.
system-view
2.
Perform mCheck.
stp global mcheck
Performing mCheck in interface view
Step Command
1.
Enter system view.
system-view
2.
Enter Layer 2 Ethernet or aggregate interface
view.
interface interface-type interface-number
3.
Perform mCheck.
stp mcheck
Configuring Digest Snooping
CAUTION:
Use caution with global Digest Snooping in the following situations:
•
When you modify the VLAN-to-instance mappings.
•
When you restore the default MST region configuration.
If the local device has different VLAN-to-instance mappings than its neighboring devices, loops or
traffic interruption will occurs.
As defined in IEEE 802.1s, connected devices are in the same region only when they have the same
MST region-related configurations, including:
•
Region name.
•
Revision level.
•
VLAN-to-instance mappings.
A spanning tree device identifies devices in the same MST region by determining the configuration
ID in BPDU packets. The configuration ID includes the region name, revision level, and configuration
