What’s the fault S5700, and all multicast traffic is being forwarded?

Issue Description

S5700-X-LI-28P using software V200R003C00SPC300.

Traffic belonging to multiple multicast source are forwarded to all host, even if the
”display igmp-snooping port-info” command didn’t show any entry.

Alarm Information

We don’t have to configure ”multicast-vlan enable” and ”multicast-vlan user-vlan <vlan-id>” to get multicast to an interface where customer-vlan and multicast-vlan is added simultaneously and I can’t see any groups beeing joined using ”display igmp-snooping port-info” (almost seems like igmp-snooping isn’t working).

Handling Process

To  discard unknown multicast packets in VLAN 10, we can configure like this.
<HUAWEI> system-view
[HUAWEI] vlan 10
[HUAWEI-vlan10] multicast drop-unknown

Root Cause

By default switch broadcast all unknown mcast packets, this could explain why you get multicast traffic but no entry under “display igmp snooping port-info”
Unknown multicast flows are multicast data flows that match no entry in the multicast forwarding table. By default, the switch broadcasts unknown multicast flows in the corresponding VLAN. we can use the multicast drop-unknowncommand to configure the switch to discard unknown multicast flows, which reduces instant bandwidth usage compared with the broadcast mode.