C
HAPTER
45
| IP Interface Commands
IPv6 Interface
– 1410 –
◆ 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.
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::2E0:CFF:FE00:FD/64
Global unicast address(es):
2001:DB8::1:2E0:CFF:FE00:FD/64, subnet is 2001:DB8::1:0:0:0:0/64[EUI]
2001:DB8:2222:7272::72/96, subnet is 2001:DB8:2222:7272::/96[EUI]
Joined group address(es):
FF02::1:FF00:72
FF02::1:FF00:FD
FF02::1
IPv6 link MTU is 1500 bytes
ND DAD is enabled, number of DAD attempts: 3.
ND retransmit interval is 1000 milliseconds
ND advertised retransmit interval is 0 milliseconds
ND reachable time is 30000 milliseconds
ND advertised reachable time is 0 milliseconds
Console#
RELATED COMMANDS
ipv6 address autoconfig (1408)
show ipv6 interface (1414)
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