3Com Switch 4800G 24-Port - Configuring Digest Snooping

Configuring Digest Snooping 229
Configuring Digest
Snooping
As defined in IEEE 802.1s, interconnected devices are in the same region only
when the region-related configuration (domain name, revision level,
VLAN-to-instance mappings) on them is identical. An MSTP-enabled device
identifies devices in the same MST region by checking the configuration ID in
BPDU packets. The configuration ID includes the region name, revision level,
configuration digest that is in 16-byte length and is the result calculated via the
HMAC-MD5 algorithm based on VLAN-to-instance mappings.
Since MSTP implementations differ with vendors, the configuration digest
calculated using private key is different; hence different vendors’ devices in the
same MST region can not communicate with each other.
Enabling the Digest Snooping feature on the associated port can make a device
communicate with another vendor’s device in the same MST region.
Configuration
Prerequisites
Associated devices of different vendors are interconnected and run MSTP.
Configuration Procedure Follow these steps to configure Digest Snooping:
c
CAUTION:
■ You can only enable the Digest Snooping feature on the device connected to
another vendor’s device that uses a private key to calculate the configuration
digest.
■ 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.
To do… Use the command… Remarks
Enter system view system-view -
Enter Ethernet
interface or
port group
view
Enter Ethernet
interface view
interface interface-type
interface-number
Required
Use either command.
Configurations made in
Ethernet interface view will
take effect on the current
port only; configurations
made in port group view will
take effect on all ports in the
port group.
Enter port
group view
port-group { manual
port-group-name |
aggregation agg-id }
Enable digest snooping on the
interface or port group
stp config-digest-snooping Required
Not enabled by default
Return to system view quit -
Enable global digest snooping stp config-digest-snooping Required
Not enabled by default