ZyXEL Communications OLT2406, User Manual

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Chapter 25 Multicast
OLT2406 User’s Guide
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generates no additional network traffic, allowing you to significantly reduce multicast traffic passing
through your OLT.
IGMP Snooping and VLANs
The OLT can perform IGMP snooping on up to 16 VLANs. You can configure the OLT to automatically
learn multicast group membership of any VLANs. The OLT then performs IGMP snooping on the first 16
VLANs that send IGMP packets. This is referred to as auto
mode. Alternatively, you can specify the VLANs
that IGMP snooping should be performed on. This is referred to as fixed mode. In fixed mode the OLT
does not learn multicast group membership of any VLANs other than those explicitly added as an IGMP
snooping VLAN.
IGMP Proxy
IGMP proxy maintains a joined member list for each IGMP group on the OLT. This OLT automatically and
periodically sends queries to the subscriber ports to get the subscribing information and response the
upper layer router’s query for the member list. In addition, it enables the OLT not to report the leave
request sent from one subscriber to upper layer router if there are still other subscriber(s) in the same
IGMP group. It also allows the OLT not to report the join request sent from one subscriber to upper layer
router if any subscriber is still in the same IGMP group. In other words, an IGMP proxy OLT only forward the
first join request and the last leave request in an IGMP network to its upper layer router. It can reduce
multicast traffic significantly.
Note: You must set one of Gigabit Ethernet ports to “Fixed mode” before enabling IGMP
proxy.
Multicast Listener Discovery
The Multicast Listener Discovery (MLD) protocol (defined in RFC 2710) is derived from IPv4's Internet
Group Management Protocol version 2 (IGMPv2). MLD uses ICMPv6 message types, rather than IGMP
message types. MLDv1 is equivalent to IGMPv2 and MLDv2 is equivalent to IGMPv3.
MLD allows an IPv6 switch or router to discover the presence of MLD hosts who wish to receive multicast
packets and the IP addresses of multicast groups the hosts want to join on its network.
MLD snooping and MLD proxy are analogous to IGMP snooping and IGMP proxy in IPv4.
MLD filtering controls which multicast groups a port can join.
MLD Messages
A multicast router or switch periodically sends general queries to MLD hosts to update the multicast
forwarding table. When an MLD host wants to join a multicast group, it sends an MLD Report message
for that address.
An MLD Done message is equivalent to an IGMP Leave message. When an MLD host wants to leave a
multicast group, it can send a Done message to the router or switch. If the leave mode is not set to
immediate, the router or switch sends a group-specific query to the port on which the Done message is
received to determine if other devices connected to this port should remain in the group.