ZyXEL Communications SBG3500-N000 User Manual page 411

• Neighbor advertisement: A response from a node to announce its link-layer address.
• Router solicitation: A request from a host to locate a router that can act as the default router and
forward packets.
• Router advertisement: A response to a router solicitation or a periodical multicast advertisement
from a router to advertise its presence and other parameters.
IPv6 Cache
An IPv6 host is required to have a neighbor cache, destination cache, prefix list and default router
list. The SBG3500-N Series maintains and updates its IPv6 caches constantly using the information
from response messages. In IPv6, the SBG3500-N Series configures a link-local address
automatically, and then sends a neighbor solicitation message to check if the address is unique. If
there is an address to be resolved or verified, the SBG3500-N Series also sends out a neighbor
solicitation message. When the SBG3500-N Series receives a neighbor advertisement in response,
it stores the neighbor's link-layer address in the neighbor cache. When the SBG3500-N Series uses
a router solicitation message to query for a router and receives a router advertisement message, it
adds the router's information to the neighbor cache, prefix list and destination cache. The
SBG3500-N Series creates an entry in the default router list cache if the router can be used as a
default router.
When the SBG3500-N Series needs to send a packet, it first consults the destination cache to
determine the next hop. If there is no matching entry in the destination cache, the SBG3500-N
Series uses the prefix list to determine whether the destination address is on-link and can be
reached directly without passing through a router. If the address is unlink, the address is
considered as the next hop. Otherwise, the SBG3500-N Series determines the next-hop from the
default router list or routing table. Once the next hop IP address is known, the SBG3500-N Series
looks into the neighbor cache to get the link-layer address and sends the packet when the neighbor
is reachable. If the SBG3500-N Series 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
Appendix E IPv6
SBG3500-N Series User's Guide
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