Troubleshooting mld snooping, Layer 2 multicast forwarding cannot work, Symptom – H3C Technologies H3C S12500 Series Switches User Manual

Page 329: Analysis, Solution

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When Host A leaves the IPv6 multicast group, it sends an MLD done message to Switch A.

Receiving the message, Switch A removes port GigabitEthernet 3/0/3 from the member port list

of the forwarding entry for the group; however, it does not remove the group or forward the done
message to Router A because Host B is still in the group. Use the display mld-snooping group

command to display information about MLD snooping groups. For example:
# Display information about MLD snooping groups on Switch A.

[SwitchA] display mld-snooping group

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

Port flags: D-Dynamic port, S-Static port, C-Copy port, P-PIM port

Subvlan flags: R-Real VLAN, C-Copy VLAN

Vlan(id):100.

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

Router port(s):total 1 port(s).

GE3/0/1 (D)

IP group(s):the following ip group(s) match to one mac group.

IP group address:FF1E::101

(::, FF1E::101):

Host port(s):total 1 port(s).

GE3/0/4 (D)

MAC group(s):

MAC group address:3333-0000-0101

Host port(s):total 1 port(s).

GE3/0/4

Troubleshooting MLD snooping

Layer 2 multicast forwarding cannot work

Symptom

Layer 2 multicast forwarding cannot work.

Analysis

MLD snooping is not enabled.

Solution

1.

Use display current-configuration command to view the running status of MLD snooping.

2.

If MLD snooping is not enabled, use the mld-snooping command to enable MLD snooping globally,
and then use the mld-snooping enable command to enable MLD snooping in VLAN view.

3.

If MLD snooping is disabled only for the corresponding VLAN, use the mld-snooping enable
command in VLAN view to enable MLD snooping in the corresponding VLAN.

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