IPv6 Addressing
Link-Local Unicast Address
Because all VLANs configured on the switch use the same MAC address, all automatically generated link-local addresses on the switch will have the same link-local address. However, since the scope of a link-local address includes only the VLAN on which it was generated, this should not be a problem.
For example, executing ipv6 address dhcp full on a VLAN for which IPv6 was not previously configured does all of the following:
■enables IPv6 on the VLAN
■causes the switch to generate a stateless link-local unicast address on the
VLAN
■configures the VLAN to send DHCPv6 requests
N o t e | Only one link-local unicast address can exist on a VLAN interface at any time. |
| Configuring a new address of this type on an interface on which IPv6 is already |
| enabled replaces the previously existing link-local address with the new one. |
| Any link-local address must include the well-known link-local prefix |
|
| fe80::/64 plus a 64-bit device identifier. |
| Any of the following commands enable IPv6 on a VLAN and automatically |
| generate a link-local address: |
| ■ | ipv6 enable (page 4-6) |
| ■ ipv6 address autoconfig (page 4-7) |
| ■ ipv6 address dhcp full [rapid-commit] (page 4-9) |
| ■ | ipv6 address < network-prefix><device-id >/< prefix-length > (page 4-13) |
Extended Unique Identifier (EUI)
When the link-local address is automatically generated, the device identifier is derived from the switch's 48- bit (hexadecimal) MAC address to create a 64 bit Extended Unique Identifier (EUI) to be appended to the fe80 link-local prefix, as follows:
■ff-fe is inserted between third and fourth bytes of MAC address
■The second low-order bit (the Universal/Local bit) in the first byte of the MAC address is complemented, which usually means the bit is originally set to 0 and is changed to 1. This indicates a globally unique IPv6 interface identifier. For example: