Configuring Digest Snooping 177Configuring DigestSnoopingIntroduction According to IEEE802.1s, two interconnected switches can communicate witheach other through MSTIs in an MST region only when the two switches have thesame MST region-related configuration. Interconnected MSTP-enabled switchesdetermine whether or not they are in the same MST region by checking theconfiguration IDs of the BPDUs between them. (A configuration ID containsinformation such as region ID and configuration digest.)As some other manufacturers’ switches adopt proprietary spanning tree protocols,they cannot communicate with the other switches in an MST region even if theyare configured with the same MST region-related settings as the other switches inthe MST region.This problem can be overcome by implementing the digest snooping feature. If aport on a Switch 4210 is connected to another manufacturer’s switch that has thesame MST region-related configuration as its own but adopts a proprietaryspanning tree protocol, you can enable digest snooping on the port. Then theSwitch 4210 regards another manufacturer’s switch as in the same region; itrecords the configuration digests carried in the BPDUs received from anothermanufacturer’s switch, and put them in the BPDUs to be sent to the othermanufacturer’s switch. In this way, the Switch 4210 can communicate withanother manufacturer’s switches in the same MST region.c CAUTION: The digest snooping function is not applicable to edge ports.Configuring DigestSnoopingConfigure the digest snooping feature on a switch to enable it to communicatewith other switches adopting proprietary protocols to calculate configurationdigests in the same MST region through MSTIs.Configuration prerequisitesThe switch to be configured is connected to another manufacturer’s switchadopting a proprietary spanning tree protocol. MSTP and the network operatenormally.Configuration procedureTable 135 Configure digest snoopingOperation Command DescriptionEnter system view system-view -Enter Ethernet port view interface interface-typeinterface-number-Enable the digest snoopingfeaturestp config-digest-snooping RequiredThe digest snooping feature isdisabled on a port by default.Return to system view quit -Enable the digest snoopingfeature globallystp config-digest-snooping RequiredThe digest snooping feature isdisabled globally by default.
