How Mld Snooping Works - HP MSR2003 Configuration Manual

NOTE:
In MLD snooping, only dynamic ports age out. Static ports never age out.

How MLD snooping works

The ports in this section are dynamic ports. For information about how to configure and remove static
ports, see "Configuring static
MLD messages include general query, MLD report, and done message. An MLD snooping-enabled
switch performs differently depending on the MLD message types.
General query
To check for the existence of IPv6 multicast group members, the MLD querier periodically sends MLD
general queries to all hosts and routers on the local subnet. All these hosts and routers are identified by
the address FF02::1.
After receiving an MLD general query, the Layer 2 device forwards the query to all ports in the VLAN
except the port that received the query. The Layer 2 device also performs one of the following actions:
If the receiving port is a dynamic router port in the router port list, the Layer 2 device restarts the
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aging timer for the router port.
If the receiving port does not exist in the router port list, the Layer 2 device adds the port to the router
•
port list. It also 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.
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Applies for an IPv6 multicast group membership.
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After receiving an MLD report, the Layer 2 device forwards it through all the router ports in the VLAN,
resolves the IPv6 address of the reported IPv6 multicast group, and looks up the forwarding table for a
matching entry as follows:
If no match is found, the Layer 2 device creates a forwarding entry for the group with the receiving
•
port an outgoing interface. It also marks the receiving port as a dynamic member port and starts an
aging timer for the port.
If a match is found but the matching forwarding entry does not contain the receiving port, the Layer
•
2 device adds the receiving port to the outgoing interface list. It also marks the port as a dynamic
member port to the forwarding entry and starts an aging timer for the port.
If a match is found and the matching forwarding entry contains the receiving port, the Layer 2
•
device restarts the aging timer for the port.
In an application with an IPv6 multicast group filter configured on an MLD snooping-enabled Layer 2
device, when a user requests a multicast program, the user's host initiates an MLD report. After receiving
this report message, the Layer 2 device resolves the IPv6 multicast group address in the report and l
performs ACL filtering on the report. If the report passes ACL filtering, the Layer 2 device creates an MLD
snooping forwarding entry for the group with the receiving port as an outgoing interface. Otherwise, the
Layer 2 device drops this report message, in which case, the IPv6 multicast data for the IPv6 multicast
group is not sent to this port, and the user cannot retrieve the program.
ports."
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