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3Com Switch 7750 Series
Command Reference Guide – MSTP Chapter 1
MSTP Configuration Commands
1-12
[3Com] stp bridge-diameter 5
1.1.12 stp config-digest-snooping
Syntax
stp config-digest-snooping
undo stp config-digest-snooping
View
System view
Parameter
None
Description
Use the stp config-digest-snooping command to enable the digest snooping feature.
Use the undo stp config-digest-snooping command to disable the digest snooping
feature.
The digest snooping feature is disabled by default.
According to IEEE 802.1s, two connected switches can interwork with each other
through MSTIs in an MST region only when the two switches have the same MST
region-related configuration. With MSTP employed, interconnected switches determine
whether or not they are in the same MST region by checking the configuration IDs of
the BPDUs between them. (A configuration ID contains information such as region ID
and configuration digest.)
As some partners' switches adopt proprietary spanning tree protocols, they cannot
interwork with other switches in an MST region even if they are configured with the
same MST region-related settings as other switches in the MST region.
This kind of problems can be overcome by implementing the digest snooping feature. If
a switch port is connected to a partner's switch that has the same MST region-related
settings but adopts a proprietary spanning tree protocol, you can enable digest
snooping on the port. Then the switch regards the peer switch connected to the port as
in the same region and records the configuration digests carried in the BPDUs received
from the switch, which will be put in the BPDUs to be send to the peer switch.. In this
way, the switch can interwork with the partners' switches in an MST region.