18.1.6 Handling of IPv6 Addresses Used by the Switch

(1) Address that can be set

The following IPv6 addresses can be assigned to the interfaces of the Switch:

1. Global unicast addresses

2. Link-local unicast addresses

Although the following IPv6 addresses can be assigned, they are treated as global unicast addresses:

1. Site-local unicast addresses

2. Anycast addresses

3. Unicast addresses with address format prefix unassigned

4. NSAP-compatible addresses

5. IPX-compatible addresses

(2) Addresses that cannot be set

The following IPv6 addresses cannot be assigned to the interfaces of the Switch:

1. Multicast addresses

2. The unspecified address

3. The loopback address

4. IPv4-compatible addresses

5. IPv4-mapped addresses

6. Addresses with 1111 1110 10 as upper 10 bits and all of bits 11 to 64 not set to 0s

7. Addresses with 1111 1111 10 as upper 10 bits and all later bits set to 0s

8. Addresses with prefix length other than 64 and interface ID set to all 0s

(3) Automatically generate an address when the interface ID is omitted.

In the Switch, when you assign an IPv6 address to an interface, you can specify only the format prefix and omit the interface ID. When you specify the format prefix and the prefix length is 64, the Switch automatically generates the interface ID based on the MAC address. The following figure shows how an address is automatically generated.

Figure 18-19: Example of automatic address generation

If an IPv6 address other than a link-local address is assigned to an interface and the interface does not have a link-local address, the Switch automatically generates and assigns a link-local unicast address to the interface. In addition, the Switch can automatically generate and assign only link-local unicast addresses to interfaces.

(4) Conditions that can be set with the prefix length

The Switch automatically generates interface IDs when they are not specified. Because the length of an interface ID is fixed at 64 bits, if you specify a prefix of 65 or more, the Switch does not automatically generate an interface ID. Instead, it treats the entered prefix as an address and leaves the interface ID portion as 0s. This means you cannot specify a prefix that causes all of the lower 64 bits to be set to 0. The following table describes the specifiable prefix lengths.

Table 18-3: Conditions that can be set with the prefix length

Prefix length range	Specifiable	Description
3ffe:501::/1~3ffe:501::/31	OK	If the specified prefix length is within this range, the prefix length is shorter than the allowed prefix length. Because not all of the bits in the interface ID portion are set to 0, the prefix length can be specified.
3ffe:501::/32~3ffe:501::/63	NG	If the specified prefix length is within this range, the prefix length is longer than the allowed prefix length. Because all the bits in the interface ID portion are set to 0, the prefix length cannot be specified.
3ffe:501::/64 or 3ffe:501::	OK	If the specified prefix length is 64 or no prefix length is specified and the interface ID is omitted, the interface ID is automatically generated by the Switch. Therefore, this prefix length can be specified.