IPv6 Abode Autoconfiguration
One of the goals of IPv6 is to accomplish activity easier for arrangement administrators, abnormally in dealing
with the about unimaginably all-inclusive abode amplitude that IPv6 provides compared to IPv4. Automatic
address configuration, or artlessly autoconfiguration, was created to accommodated that need.
An IPv6 host can automatically configure its complete address, or aloof the interface ID allocation of
its address, depending on which of the several methods for autoconfiguration it uses. Those
methods include
■ Stateful autoconfiguration
■ Stateless autoconfiguration
■ EUI-64
One method, stateful autoconfiguration, assigns a host or router its absolute 128-bit IPv6 address
using DHCP. Addition method, stateless autoconfiguration, dynamically assigns the host or router
interface a 64-bit prefix, and again the host or router derives the aftermost 64 $.25 of its abode application the
EUI-64 action declared in this section.
Because the EUI-64 architecture is apparent so frequently, it is important to awning those capacity now.
However, decidedly for those who accept not abstruse abundant about IPv6 afore account this chapter,
it is bigger to adjourn the blow of the capacity about autoconfiguration until the area blue-blooded “IPv6
Address Autoconfiguration” afterwards in this chapter.
EUI-64 Abode Format
One key aspect of IPv6 acclamation is automated configuration, but how does an IPv6 host ensure
that autoconfigured addresses are globally unique?
The acknowledgment to this catechism comes in two parts. The aboriginal allotment is to set abreast a ambit and structure
for aggregatable all-around addresses, as declared earlier. Once a arrangement ambassador has set the
prefix for a accustomed network, the additional allotment takes over. That additional footfall is abode autoconfiguration,
but what architecture should a host use for these addresses to ensure that they are globally
unique? That architecture is EUI-64
IPv6 Acclamation and Abode Types 755
With EUI-64, the interface ID is configured locally by the host to be globally unique. To do that,
the host needs a globally different allotment of advice that it already knows. That allotment of
information cannot be added than 64 $.25 long, because EUI-64 by analogue requires a 64-bit
prefix and a 64-bit interface ID. But it needs to be both continued abundant and from a antecedent that is
known to be globally unique.
To accommodated this need, Ethernet hosts and Cisco routers with Ethernet interfaces use their 48-bit MAC
addresses as a berry for EUI-64 addressing. But because the MAC abode is 48 $.25 continued and the
EUI-64 action makes up the aftermost 64 $.25 of an IPv6 address, the host needs to acquire the other
16 $.25 from addition source. The IEEE EUI-64 accepted places the hex amount FFFE into the center
of the MAC abode for this purpose. Finally, EUI-64 sets the universal/local bit, which is the 7th
bit in the Interface ID acreage of the address, to announce all-around scope.
Here is an example. Accustomed the IPv6 prefix 2001:128:1F:633 and a MAC abode of
00:07:85:80:71:B8, the consistent EUI-64 abode is
2001:128:1F:633:207:85FF:FE80:71B8/64
The adventurous allotment of the abode is the complete interface ID. Note how the accent characters
indicate the ambience of the U/L bit and the admittance of FFFE afterwards the OUI in the MAC address.
Configure this abode on a router’s Fast Ethernet interface, as apparent in Archetype 20-1.
To appearance the result, use the accordant appearance commands. Archetype 20-2 shows a sample of the show
ipv6 interface abrupt command. This shows both the all-around unicast addresses and link-local
address assigned to this interface. The archetype shows interface Fa0/0 with the aggregatable global
unicast abode configured in Archetype 20-1, and the link-local unicast abode automatically
created by the router.
The black area of the unicast abode in Archetype 20-2 shows the EUI-64-derived allocation of
the address. To see the abounding output, omit the abrupt keyword and specify the interface, as apparent in
Example 20-1 Configuring an EUI-64 IPv6 Address
Matsui(config)# int fa0/0
Matsui(config-if)# ipv6 abode 2001:128:1f:633::/64 eui-64
Example 20-2 Checking an IPv6 Interface’s Configured Addresses
Matsui# appearance ipv6 interface brief
FastEthernet0/0 [up/up]
FE80::207:85FF:FE80:71B8
2001:128:1F:633:207:85FF:FE80:71B8
Example 20-3. In this example, the router absolutely informs you that the abode was acquired by
EUI-64 by the “[EUI]” at the end of the all-around unicast address.
Detailed Interface Agreement Output
Matsui# appearance ipv6 interface fa0/0
FastEthernet0/0 is up, band agreement is up
IPv6 is enabled, link-local abode is FE80::207:85FF:FE80:71B8
No Virtual link-local address(es):
Global unicast address(es):
2001:128:1F:633:207:85FF:FE80:71B8, subnet is 2001:128:1F:633::/64 [EUI]
Joined accumulation address(es):
FF02::1
FF02::2
FF02::A
FF02::1:FF80:71B8
MTU is 1500 bytes
ICMP absurdity letters bound to one every 100 milliseconds
ICMP redirects are enabled
ICMP unreachables are sent
ND DAD is enabled, cardinal of DAD attempts: 1
ND attainable time is 30000 milliseconds
ND advertised attainable time is 0 milliseconds
ND advertised retransmit breach is 0 milliseconds
ND router advertisements are beatific every 200 seconds
ND router advertisements alive for 1800 seconds
ND advertised absence router alternative is Medium
Hosts use stateless autoconfig for addresses. IPv6 addressing:EUI-64;EUI-64 address