How Mld Snooping Operates - HP 1910 User Manual

Timer
Dynamic member port
aging timer
NOTE:
In MLD snooping, only dynamic ports age out. Static ports never age out.

How MLD snooping operates

In this section, the ports involved are dynamic ports.
An MLD snooping–enabled switch performs different actions when it receives different MLD messages.
When receiving a general query
The MLD querier periodically sends MLD general queries to all hosts and routers (FF02::1) on the local
subnet to check whether any active IPv6 multicast group members exist on the subnet.
After receiving an MLD general query, the switch forwards it through all ports in the VLAN (except the
port that received the query). The switch performs the following judgment:
If the port that received the query is a dynamic router port in the router port list of the switch, the
•
switch restarts the aging timer for the port.
If the port that received the query is not in the router port list of the switch, the switch adds it into the
•
router port list as a dynamic router port and starts an aging timer for the port.
When receiving a membership report
A host sends an MLD membership report to the MLD querier in the following circumstances:
After receiving an MLD query, an IPv6 multicast group member host responds with an MLD report.
•
• When the host wants to join an IPv6 multicast group, it sends an MLD report to the querier to
announce its interest in the multicast information addressed to that group.
After receiving an MLD report, the switch forwards it through all the router ports in the VLAN, resolves the
address of the reported IPv6 multicast group. The switch also performs the following judgment:
• If no forwarding entry matches the IPv6 group address, the switch creates a forwarding entry for the
group, adds the port that received the MLD report as a dynamic member port to the forwarding
entry, and starts an aging timer for that port.
If a forwarding entry matches the IPv6 group address, but the port that received the MLD report 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 that port.
If a forwarding entry matches the IPv6 group address and the port that received the MLD report is
•
in the forwarding entry for the group, the switch resets an aging timer for that port.
A switch does not forward an MLD report through a non-router port. The reason is that if the switch
forwards a report through a member port, all the attached hosts that monitor the reported IPv6 multicast
group address, according to the MLD report suppression mechanism, suppress their own reports after
Description
When a port dynamically
joins an IPv6 multicast
group, the switch sets an
aging timer for the port.
When the timer expires,
the dynamic member port
ages out.
244
Message before expiry
MLD membership report
Action after expiry
The switch removes this
port from the MLD
snooping forwarding
table.