ZyXEL Communications NXC2500 User Manual page 445

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 NXC
determines the next-hop from the default router list or routing table. Once the next hop IP address
is known, the NXC looks into the neighbor cache to get the link-layer address and sends the packet
when the neighbor is reachable. If the NXC 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. The router or switch then
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.
Appendix E IPv6
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