ZyXEL Communications XS3800-28 Cli Reference Manual page 155

Chapter 42 IPv6 Commands
whether the destination address is on-link and can be reached directly without passing through a router.
If the address is onlink, the address is considered as the next hop. Otherwise, the Switch determines the
next-hop from the default router list or routing table. Once the next hop IP address is known, the Switch
looks into the neighbor cache to get the link-layer address and sends the packet when the neighbor is
reachable. If the Switch cannot find an entry in the neighbor cache or the state for the neighbor is not
reachable, it starts the address resolution process. This helps reduce the number of IPv6 solicitation and
advertisement messages.
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 listeners 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.
MLD Port Role
A port on the Switch can be either a downstream port or upstream port in MLD. A downstream port (DSP
in the figure) connects to MLD hosts and acts as a multicast router to send MLD queries and listen to the
MLD host's Report and Done messages. An upstream port (USP in the figure) connects to a multicast
router and works as a host to send Report or Done messages when receiving queries from a multicast
router.
Proxy
Snooping
USP
DSP
Ethernet Switch CLI Reference Guide
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