The simplest method is to enable stateless autoconfiguration on the interface. Enabling stateless autoconfiguration on the interface configures IPv6 addresses based on prefixes received in Router Advertisement messages. A link-local address, based on the Modified EUI-64 interface ID, is automatically generated for the interface when stateless autoconfiguration is enabled. To enable stateless autoconfiguration, enter the following command:
hostname(config-if)# ipv6 address autoconfig
That's as may, but the question states automatically I.E. upon entering the command the address is added without the need for further information to be acquired first.
EUI-64 (Extended Unique Identifier) is a method we can use to automatically configure IPv6 host addresses. An IPv6 device will use the MAC address of its interface to generate a unique 64-bit interface ID. However, a MAC address is 48 bit and the interface ID is 64 bit.
Implementing IPv6 Addressing on Routers
ipv6 address address/prefix-length: Static configuration of a specific address
ipv6 address prefix/prefix-length eui-64: Static configuration of a specific prefix and
prefix length, with the router calculating the interface ID using EUI-64 rules
ipv6 address dhcp: Dynamic learning on the address and prefix length using DHCP
ipv6 address autoconfig: Dynamic learning of the prefix and prefix length, with the router
calculating the interface ID using EUI-64 rules (SLAAC)
The EUI-64 (Extended Unique Identifier) method is used to automatically generate the interface identifier (last 64 bits of an IPv6 address) from the MAC address of the network interface. The command:
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ipv6 address 2001:DB8:5:112::/64 eui-64
Assigns an IPv6 address using the 2001:DB8:5:112::/64 prefix.
The EUI-64 process takes the MAC address (48 bits), inserts FFFE in the middle, and flips the 7th bit to form the 64-bit interface identifier.
The answer is B:
As per OCG, you can use the 2 methods to configure a stable ipv6 address using the ipv6 address command.
1. ipv6 address [full 128bit address] command statically configures your desired 128bit address.
2. ipv6 address [prefix::/64] EUI-64 command allows the engineer to configure the 64-bit ipv6 prefix for the interface and lets the router automatically generate a unique interface ID.
This 2nd command answers the question because after you provide the 64bit prefix the router automatically generates the final part of the ipv6 address using the MAC address of the interface or a MAC address that you specify.
The command "ipv6 address 2001:DB8:5:112::/64 eui-64" automatically generates an IPv6 address from a specified IPv6 prefix and MAC address of an interface using the EUI-64 method. The EUI-64 method uses the MAC address of the interface to create an interface identifier (IID) that is used to complete the IPv6 address.
Option A ("ipv6 address dhcp") configures an interface to obtain an IPv6 address through DHCPv6.
Option C ("ipv6 address autoconfig") configures an interface to automatically obtain an IPv6 address using Stateless Address Autoconfiguration (SLAAC).
Option D ("ipv6 address 2001:DB8:5:112::2/64 link-local") configures an IPv6 link-local address on the interface.
You are correct that the "ipv6 address autoconfig" command enables automatic configuration of the IPv6 address using the SLAAC mechanism, which generates an IPv6 address based on the prefix information advertised by the router. So, in a sense, this command does generate an IPv6 address automatically.
However, it is important to note that the IPv6 address generated using SLAAC is not based on the MAC address of the interface, unlike the IPv6 address generated using the "ipv6 address 2001:DB8:5:112::/64 eui-64" command.
So, to answer your question, if the requirement is to generate an IPv6 address based on the MAC address of an interface, then the correct command would be "ipv6 address 2001:DB8:5:112::/64 eui-64". On the other hand, if the requirement is to enable automatic configuration of the IPv6 address using the router-advertised prefix information, then the correct command would be "ipv6 address autoconfig".
B is correct
The command that automatically generates an IPv6 address from a specified IPv6 prefix and MAC address of an interface is the 'ipv6 address eui-64' command. This command uses the Extended Unique Identifier (EUI-64) format to convert the 48-bit MAC address to a 64-bit interface identifier, completing the full 128-bit IPv6 address. The output from 'ipv6 address eui-64' will be a unique, non-duplicable address for each interface.
For example, if your IPv6 prefix is 2001:DB8::/64 and the MAC address is 00-14-22-01-23-45, the 'ipv6 address eui-64' command would generate the IPv6 address as: 2001:DB8::214:22FF:FE01:2345.
ipv6 address eui-64
Use ipv6 address eui-64 to configure an EUI-64 IPv6 address for an interface.
Use undo ipv6 address eui-64 to remove the EUI-64 IPv6 address of the interface.
Syntax
ipv6 address { ipv6-address prefix-length | ipv6-address/prefix-length } eui-64
undo ipv6 address [ ipv6-address prefix-length | ipv6-address/prefix-length ] eui-64
Default
No EUI-64 IPv6 address is configured for an interface.
EUI-64 (Extended Unique Identifier) is a method we can use to automatically configure IPv6 host addresses. An IPv6 device will use the MAC address of its interface to generate a unique 64-bit interface ID. However, a MAC address is 48 bit and the interface ID is 64 bit.
Generated from a MAC address automatically... This does not refer to an IPv6 address provided by autoconfiguration, rather using EUI-64, so B is the answer
Having reviewed SLAAC, I see that SLAAC also generates the address based on the host's MAC address. With this question's wording, it seems that B or C could be correct.
Answer is B. The key is "specified prefix".
SLAAC aka auto config dynamically learns prefix and specified prefix is with eui 64. Such a straight forward question that people are arguing on.
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