35.1.7 IPv6 important reminder for use

<Structure of this section>

(1) Changing MTU length of interfaces for which IPv6 is set

The minimum-packet-length for IPv6 is defined to be 1280 bytes or more (RFC8200). Therefore, if the MTU size is less than 1280 bytes, IPv6 communication is not possible. Specify at least 1280 bytes for the MTU size for interfaces that perform IPv6 communication.

(2) Duplicate IPv6 addressing

IPv6 has DAD(Duplicate Address Detection) function defined in RFC4862. If DAD detects a duplicate IPv6 address, that address cannot be used for communication. If you execute the show ipv6 interface command or show ip-dual interface command and duplicated is indicated next to an IPv6 address in the list, that IPv6 address is already being used by another device.For each case, perform the following procedure:

If the IPv6 address assigned to the other device is incorrect

After correcting IPv6 address of another device, either remove IPv6 address of the Switch and set it again, or bring down VLAN interfaces to make it go up.
If the IPv6 address assigned to the Switch is incorrect

Delete the duplicate IPv6 address assigned to the Switch in the configuration, and assign a correct IPv6 address.
If duplicate IPv6 addresses are automatically generated

A loop occurred on a VLAN interface or a terminal is illegally using the IPv6 address of the Switch. Eliminate the problem and execute the no ipv6 enable command.Next, execute the ipv6 enable command.

(3) Notes on Static NDP

When you specify the IPv6 address that is assigned to an interface in the Switch as a static NDP entry, the operation of the Switch becomes unstable and communication might become impossible. To prevent this problem, when you configure an interface, the Switch checks whether the IPv6 address assigned to the interface is specified as a static NDP entry.However, the Switch does not check the following IPv6 addresses for duplication:

Link-local addresses (automatically and manually generated)
Global addresses that are automatically generated when interface IDs are omitted

Therefore, do not specify these IPv6 addresses assigned to interfaces as static NDP entries. If you have mistakenly specified such a static NDP entry, delete it and restart the VLAN for the applicable interface.