Appendix C IPv6
PMG5317-T20A User’s Guide
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• 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 GPON Device maintains and updates its IPv6 caches constantly using the information from
response messages. In IPv6, the GPON Device 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 GPON Device also sends out a neighbor solicitation message. When
the GPON Device receives a neighbor advertisement in response, it stores the neighbor’s link-layer
address in the neighbor cache. When the GPON Device 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 GPON Device creates an entry in the default
router list cache if the router can be used as a default router.
When the GPON Device 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 GPON Device 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 GPON Device determines the next-hop from the default router list or routing
table. Once the next hop IP address is known, the GPON Device looks into the neighbor cache to
get the link-layer address and sends the packet when the neighbor is reachable. If the GPON Device
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
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