Chapter 30
| IP Interface Commands
IPv6 Interface
– 927 –
colon may be used in the address to indicate the appropriate number of zeros
required to fill the undefined fields.
â—† 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.)
â—† 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.
â—† If a duplicate address is detected, a warning message is sent to the console.
â—† 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.
â—† 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.
â—† 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.
Example
This example uses the network prefix of 2001:0DB8:0:1::/64, and specifies that the
EUI-64 interface identifier be used in the lower 64 bits of the address.
Console(config)#interface vlan 1
Console(config-if)#ipv6 address 2001:0DB8:0:1::/64 eui-64
Console(config-if)#end
Console#show ipv6 interface
VLAN 1 is up
IPv6 is enabled
Link-local address:
fe80::7272:cfff:fe83:3466%1/64
Global unicast address(es):
2001:db8:0:1:7272:cfff:fe83:3466/64, subnet is 2001:db8:0:1::/64[EUI]
2001:db8:2222:7272::72/96, subnet is 2001:db8:2222:7272::/96
Joined group address(es):
ff02::1:ff00:72
ff02::1:ff83:3466
ff02::1
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