How Mld Snooping Works - HP FlexNetwork NJ5000 User Manual

Timer
NOTE:
In MLD snooping, only dynamic ports age out.

How MLD snooping works

The ports in this section are dynamic ports.
MLD messages include general query, MLD report, and done message. An MLD snooping-enabled
switch performs differently depending on the MLD message.
General query
The MLD querier periodically sends MLD general queries to all hosts and routers on the local subnet
to check whether any active IPv6 multicast group members exist on the subnet. The destination IPv6
address of MLD general queries is FF02::1.
After receiving an MLD general query, the switch forwards the query to all ports in the VLAN except
the receiving port. The switch also performs one of the following actions:
•
If the receiving port is a dynamic router port in the router port list, the switch restarts the aging
timer for the router port.
•
If the receiving port is not in the router port list, the switch adds the port as a dynamic router port
to the router port list and starts an aging timer for the port.
MLD report
A host sends an MLD report to the MLD querier for the following purposes:
•
Responds to queries if the host is an IPv6 multicast group member.
•
Applies for an IPv6 multicast group membership.
After receiving an MLD report, the switch forwards it through all the router ports in the VLAN and
resolves the address of the reported IPv6 multicast group. The switch also performs one of the
following actions:
•
If no forwarding entry matches the IPv6 group address, the switch creates a forwarding entry for
the group, adds the receiving port as a dynamic member port to the forwarding entry, and starts
an aging timer for the port.
•
If a forwarding entry matches the IPv6 group address, but the receiving port is not in the
forwarding entry for the group, the switch adds the port as a dynamic member port to the
forwarding entry, and starts an aging timer for the port.
•
If a forwarding entry matches the IPv6 group address and the receiving port is in the forwarding
entry for the group, the switch resets an aging timer for the port.
A switch does not forward an MLD report through a non-router port. If the switch forwards a report
through a member port, the MLD report suppression mechanism causes all attached hosts that
monitor the reported IPv6 multicast group address to suppress their own reports. In this case, the
switch cannot determine whether the reported IPv6 multicast group still has active members
attached to that port.
Done message
When a host leaves an IPv6 multicast group, the host sends an MLD done message to the multicast
router. When the switch receives an MLD done message on a member port, the switch first examines
Description
member port ages out.
Message received
before the timer
expires
218
Action after the
timer expires