3Com 4500G Family Configuration Manual page 107

Before enabling digest snooping, ensure that associated devices of different vendors are
interconnected and run MSTP.
Configuring the Digest Snooping feature
You can enable Digest Snooping only on a device that is connected to a third-party device that uses its
private key to calculate the configuration digest.
Follow these steps to configure Digest Snooping:
To do...
Enter system view
Enter Ethernet
interface view, or
Layer 2 aggregate
Enter interface
interface view
view or port
group view
Enter port group
view
Enable digest snooping on the
interface or port group
Return to system view
Enable global digest snooping
With the Digest Snooping feature enabled, comparison of configuration digest is not needed for
in-the-same-region check, so the VLAN-to-instance mappings must be the same on associated
ports.
With global Digest Snooping enabled, modification of VLAN-to-instance mappings and removing of
the current region configuration using the undo stp region-configuration command are not
allowed. You can only modify the region name and revision level.
You need to enable this feature both globally and on associated ports to make it take effect. It is
recommended to enable the feature on all associated ports first and then globally, thus making the
configuration take effect on all configured ports and reducing impact on the network, and disable
the feature globally to disable it on all associated ports.
You are recommended not to enable Digest Snooping on MST region edge ports, thus avoiding
loops.
You are recommended to enable Digest Snooping first and then MSTP. Do not configure Digest
Snooping when the network works well, thus avoiding traffic interruption.
Use the command...
system-view
interface interface-type
interface-number
port-group manual
port-group-name
stp config-digest-snooping
quit
stp config-digest-snooping
1-31
Remarks
—
Required
Use either command.
Required
Not enabled by default
—
Required
Not enabled by default