20-39Configuring Digest SnoopingIntroductionAccording to IEEE 802.1s, two interconnected switches can communicate with each other throughMSTIs in an MST region only when the two switches have the same MST region-related configuration.Interconnected MSTP-enabled switches determine whether or not they are in the same MST region bychecking the configuration IDs of the BPDUs between them (A configuration ID contains informationsuch as region ID and configuration digest).As some other manufacturers' switches adopt proprietary spanning tree protocols, they cannotcommunicate with the other switches in an MST region even if they are configured with the same MSTregion-related settings as the other switches in the MST region.This problem can be overcome by implementing the digest snooping feature. If a port on a 3Com switch4500 is connected to another manufacturer's switch that has the same MST region-relatedconfiguration as its own but adopts a proprietary spanning tree protocol, you can enable digestsnooping on the port. Then the switch 4500 regards another manufacturer's switch as in the sameregion; it records the configuration digests carried in the BPDUs received from another manufacturer'sswitch, and put them in the BPDUs to be sent to the another manufacturer's switch. In this way, theswitch 4500 can communicate with another manufacturer’s switches in the same MST region.The digest snooping function is not applicable to edge ports.Configuring Digest SnoopingConfigure the digest snooping feature on a switch to enable it to communicate with other switchesadopting proprietary protocols to calculate configuration digests in the same MST region throughMSTIs.Configuration prerequisitesThe switch to be configured is connected to another manufacturer's switch adopting a proprietaryspanning tree protocol. MSTP and the network operate normally.Configuration procedureFollow these steps to configure digest snooping:To do... Use the command... RemarksEnter system view system-view —Enter Ethernet port view interface interface-typeinterface-number —Enable the digest snoopingfeature stp config-digest-snoopingRequiredThe digest snooping feature isdisabled on a port by default.
