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Configured multicast group policy fails to take effect
Symptom
Although a multicast group policy has been configured to allow hosts to join specific multicast groups,
the hosts 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 is
flooded.
Solution
1. Use the display acl command to evaluate the configured ACL rule. Make sure that the ACL rule
conforms to the multicast group policy to be implemented.
2. Use the display this command in IGMP snooping view or in the corresponding interface view to
determine whether the correct multicast group policy has been applied. If not, use the group-policy
or igmp-snooping group-policy command to apply the correct multicast group policy.
3. Use the display current-configuration command to determine whether the function of dropping
unknown multicast data is enabled. If not, use the igmp-snooping drop-unknown command to
enable the function of dropping unknown multicast data.
Appendix (available only on the A5500 EI)
Processing of multicast protocol messages
With Layer 3 multicast routing enabled, an IGMP snooping–enabled switch processes multicast protocol
messages 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, the
switch does the following:
{ Maintains dynamic member ports or dynamic router ports according to IGMP packets
{ Maintains dynamic router ports according to PIM hello packets
2. 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 router
port.
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.
{ If PIM is enabled, the switch deletes only its dynamic member ports but not its dynamic router
ports.
NOTE:
On a switch with Layer-3 multicast routing enabled, use the display igmp group port-info command to
display Layer-2 port information. For more information about this command, see the
IP Multicast
Command Reference
.
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