How Mld Snooping Works - HP 1920 Gigabit Ethernet Switch Series User Manual

Timer
Dynamic member
port aging 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
Description
When a port dynamically joins
an IPv6 multicast group, the
switch starts or resets an aging
timer for the port. When the
timer expires, the dynamic
member port ages out.
Message received
before the timer
expires
MLD membership report.
268
Action after the timer
expires
The switch removes this
port from the MLD
snooping forwarding
table.