CLI Reference Guide-R04

Chapter 31 | IP Interface Commands
IPv6 Interface
– 911 –
ipv6-prefix - The IPv6 network portion of the address assigned to the
interface.
prefix-length - A decimal value indicating how many contiguous bits (from
the left) of the address comprise the prefix (i.e., the network portion of the
address).
Default Setting
No IPv6 addresses are defined
Command Mode
Interface Configuration (VLAN)
Command Usage
◆ The prefix must be formatted according to RFC 2373 “IPv6 Addressing
Architecture,” using 8 colon-separated 16-bit hexadecimal values. One double
colon may be used in the address to indicate the appropriate number of zeros
required to fill the undefined fields.
◆ If a link local address has not yet been assigned to this interface, this command
will dynamically generate a global unicast address and a link-local address for
this interface. (The link-local address is made with an address prefix of FE80 and
a host portion based the switch’s MAC address in modified EUI-64 format.)
◆ Note that the value specified in the ipv6-prefix may include some of the high-
order host bits if the specified prefix length is less than 64 bits. If the specified
prefix length exceeds 64 bits, then the network portion of the address will take
precedence over the interface identifier.
◆ If a duplicate address is detected, a warning message is sent to the console.
◆ IPv6 addresses are 16 bytes long, of which the bottom 8 bytes typically form a
unique host identifier based on the device’s MAC address. The EUI-64
specification is designed for devices that use an extended 8-byte MAC address.
For devices that still use a 6-byte MAC address (also known as EUI-48 format), it
must be converted into EUI-64 format by inverting the universal/local bit in the
address and inserting the hexadecimal number FFFE between the upper and
lower three bytes of the MAC address.
◆ For example, if a device had an EUI-48 address of 28-9F-18-1C-82-35, the
global/local bit must first be inverted to meet EUI-64 requirements (i.e., 1 for
globally defined addresses and 0 for locally defined addresses), changing 28 to
2A. Then the two bytes FFFE are inserted between the OUI (i.e., company id)
and the rest of the address, resulting in a modified EUI-64 interface identifier of
2A-9F-18-FF-FE-1C-82-35.
◆ This host addressing method allows the same interface identifier to be used on
multiple IP interfaces of a single device, as long as those interfaces are attached
to different subnets.