IPv6 address configuration and verification | static and dynamic | slaac | dhcpv6 | ccna 200-301

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There are two ways to assign / configure the IPV6 address on the router interfaces.
1.Static Unicast Address Configuration
2.Dynamic Unicast Address Configuration
Static Unicast Address Configuration
Cisco routers give us two options for static configuration of IPv6 addresses.
In one case, you configure the full 128-bit address,
while in the other, you configure a 64-bit prefix and let the router derive the second half of the address (the interface ID).
Configuring the Full 128-Bit Address
To statically configure the full 128-bit unicast address—either global unicast or unique local—the router needs an
ipv6 address address/prefix-length interface subcommand on each interface.
let’s take a basic example. The figure shows the global uni-cast IPv6 address manually configured under intetrface fa0/0 with /64 prefix length.
interface Fa 0/0
ipv6 address 2001:DB8:1111:1::1/64
!
The second option to configure static address is by Generating a Unique Interface ID Using Modified EUI-64
This second method uses rules called modified EUI-64 (extended unique identifier). people refer to modified EUI-64 as just EUI-64
The configuration that uses EUI-64 includes a keyword to tell the router to use EUI-64 rules, along with the 64-bit pre- fix.
Configuring a router interface to use the EUI-64 format uses the ipv6 address address/ prefix-length eui-64 interface subcommand.
The eui-64 keyword tells the router to find the interface MAC address and do the EUI-64 conversion math to find the interface ID
For interface GigabitEthernet0/0 we have configured this prefix along with the eui code.

ipv6 address 2001:DB8:1111:1::/64 eui-64
The mac address for this interface is 0013.1234.ABCD

To generate the unique interface ID EUI-64 rules are as follows

1.Split the 6-byte (12-hex-digit) MAC address in two halves (6 hex digits each).
i.e the mac address of gi0/0 0013.1234.ABCD

2.Insert FFFE in between the two, making the interface ID now have a total of 16 hex digits (64 bits).

3.Invert the seventh bit of the interface ID.

The final step requires that you convert the first byte (first two hex digits) from hex to binary, invert the seventh of the 8 bits, and convert the bits back to hex.
Inverting a bit means that if the bit is a 0, make it a 1; if it is a 1, make it a 0.

After that you can have this IPv6 address

Dynamic Unicast Address Configuration

Cisco routers support two ways for the router interface to dynamically learn an IPv6 address to use:

Stateful DHCP
Stateless Address Autoconfiguration (SLAAC)
Stateful Address Assignment

Similar to IPv4, IPv6 can use DHCP to state-fully assign IP addresses to any clients.
Cisco IOS routers can be configured to be Stateful DHCP servers.
Stateful DHCP means that the DHCP server is responsible for assigning the IP address to the client.
The DHCP server keeps a record of all clients and the IPv6 address assigned to them
The server can also offer other  network parameters such as DNS servers, a domain name, or any other option that a DHCP server provides..
The command used to get the IP from dhcp is

interface FastEthernet0/0
ipv6 address dhcp

Stateless Address Assignment

This is a unique feature only to IPv6 also known as Stateless Auto-configuration [SLAAC]
It is a method in which the device can obtain an IPv6 global unicast address without the services of DHCPv6 server.
Stateless address configuration means that the client picks their own address based on the prefix being advertised on their connected interface.
All Cisco devices have the ability to participate in Stateless Auto-configuration (SLAAC).
By default, SLAAC does not provide anything to the client outside of an IPv6 address and a default gateway.
Moreover, it is important to note that SLAAC most commonly uses eui-64 format for address assignment.
This means that IPv6 addresses will be built from a combination of the Layer 3 subnet prefix and the MAC address of the client.
The requirement for SLAAC is that the LAN segment must use a /64 mask.

The command to configure SLAAC is
ipv6 address autoconfig

Both methods stateful and stateless use the familiar ipv6 address command.
Of course, neither option configures the actual IPv6 address; instead, the commands configure a keyword that tells the router which method to use to learn its IPv6 address.

IPv6 routing
There is important but often overlooked step when configuring IPv6 on Cisco routers: IPv6 routing needs to be enabled.
On Cisco routers, IPv4 routing is enabled by default, but IPv6 routing is not enabled by default.
The solution takes only a single command—ipv6 unicast-routing—which enables IPv6 routing on the router.

A router must enable IPv6 globally (ipv6 unicast-routing) and enable IPv6 on the interface (ipv6 address) before the router will attempt to route IPv6 packets in and out an interface .