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DES-7200 Configuration Guide Chapter 2 IPv6 Configuration
2-11
2.1.4 IPv6 Path MTU
Discovery
As with the path MTU discovery of the IPv4, the path MTU discovery of the IPv6 allows
one host to discover and adjust the size of the MTU in the data transmission path.
Furthermore, when the data packet to be sent is larger than the MTU of the data
transmission path, the host will fragment the packets by itself. This behavior makes it
not necessary for the router to process the fragment, and thus save resources and
improve the efficiency of the IPv6 network.
Caution
The minimum link MTU is 68 bytes in the IPv4, indicating that the links
along the path over which the packets are transmitted should support
at least the link MTU of 68 bytes. The minimum link MTU is 1280 bytes
in the IPv6. It is strongly recommended to use the link MTU of 1500
bytes for the link in the IPv6.
2.1.5 IPv6 Neighbor
Discovery
The main functions of the IPv6 Neighbor discovery protocol include Router Discovery,
Prefix Discovery, Parameter Discovery, Address Auto-configuration, Address
Resolution(ARP), Next-hop Confirmation, Neighbor Unreachability Check, Address
Conflict Check and Redirection. Neighbor discovery defines 5 types of ICMP message,
which are Router Solicitation(ICMP type133), Router Advertisement(ICMP type134),
Neighbor Solicitation or ARP request (ICMP type135), Neighbor Advertisement or APR
response(ICMP type136) and ICMP redirection message(ICMP type137).
The following describes the neighbor discovery function in detail:
2.1.5.1 Address Resolution
A node must get the link layer address of another node before communicating with it.
At this time, it should send the neighbor solicitation (NS) message to the solicitated
multicast address of the IPv6 address of the destination node. The NS message also
contains the link layer address of itself. After receiving this NS message, the
destination node responds with a message, referred to as neighbor advertisement
(NA), with its link layer address. After receiving the response message, the source
node can communicate with the destination node.
The following is the neighbor solicitation procedure: