3Com Switch 7750 SeriesCommand Reference Guide – MSTP Chapter 1 MSTP Configuration Commands1-12[3Com] stp bridge-diameter 51.1.12 stp config-digest-snoopingSyntaxstp config-digest-snoopingundo stp config-digest-snoopingViewSystem viewParameterNoneDescriptionUse the stp config-digest-snooping command to enable the digest snooping feature.Use the undo stp config-digest-snooping command to disable the digest snoopingfeature.The digest snooping feature is disabled by default.According to IEEE 802.1s, two connected switches can interwork with each otherthrough MSTIs in an MST region only when the two switches have the same MSTregion-related configuration. With MSTP employed, interconnected switches determinewhether or not they are in the same MST region by checking the configuration IDs ofthe BPDUs between them. (A configuration ID contains information such as region IDand configuration digest.)As some partners' switches adopt proprietary spanning tree protocols, they cannotinterwork with other switches in an MST region even if they are configured with thesame MST region-related settings as other switches in the MST region.This kind of problems can be overcome by implementing the digest snooping feature. Ifa switch port is connected to a partner's switch that has the same MST region-relatedsettings but adopts a proprietary spanning tree protocol, you can enable digestsnooping on the port. Then the switch regards the peer switch connected to the port asin the same region and records the configuration digests carried in the BPDUs receivedfrom the switch, which will be put in the BPDUs to be send to the peer switch.. In thisway, the switch can interwork with the partners' switches in an MST region.
