56Configured multicast group policy fails to take effectSymptomAlthough a multicast group policy has been configured to allow hosts to join specific multicast groups, thehosts can still receive multicast data addressed to other multicast groups.Analysis• The ACL rule is incorrectly configured.• The multicast group policy is not correctly applied.• The function of dropping unknown multicast data is not enabled, so unknown multicast data isflooded.Solution1. Use the display acl command to check the configured ACL rule. Make sure that the ACL ruleconforms to the multicast group policy to be implemented.2. Use the display this command in IGMP-snooping view or in the corresponding interface view toverify that the correct multicast group policy has been applied. If not, use the group-policy origmp-snooping group-policy command to apply the correct multicast group policy.3. Use the display current-configuration command to verify that the function of dropping unknownmulticast data is enabled. If not, use the igmp-snooping drop-unknown command to enable thefunction of dropping unknown multicast data.AppendixProcessing of multicast protocol messagesWith Layer 3 multicast routing enabled, an IGMP snooping–enabled switch processes multicast protocolmessages differently under different conditions, as follows:1. If only IGMP is enabled on the switch, or if both IGMP and PIM are enabled on the switch, theswitch does the following:{ Maintains dynamic member ports or dynamic router ports according to IGMP packets{ Maintains dynamic router ports according to PIM hello packets2. If only PIM is enabled on the switch, the following occur:{ The switch broadcasts IGMP messages as unknown messages in the VLAN.{ After receiving a PIM hello message, the switch maintains the corresponding dynamic routerport.3. If IGMP is disabled on the switch, one of the following occurs:{ If PIM is disabled, the switch deletes all its dynamic member ports and dynamic router ports.
