How to Configure Basic IPv6 on Cisco Routers

To configure basic IPv6 on a Cisco router, enable 'ipv6 unicast-routing' globally, enter interface configuration mode, and use 'ipv6 address [address/prefix]' to assign a Global Unicast Address.

Enabling IPv6 and Assigning a GUA

First, always ensure IPv6 routing is enabled globally. Next, assign a Global Unicast Address (GUA) to an interface.

``` Router(config)# ipv6 unicast-routing Router(config)# interface GigabitEthernet0/0 Router(config-if)# ipv6 address 2001:db8:acad:1::1/64 Router(config-if)# no shutdown ``` Once a GUA is configured, the router automatically generates a Link-Local Address (LLA) for the interface.

Manually Configuring a Link-Local Address

While routers auto-generate LLAs (often using EUI-64), these auto-generated addresses are long and hard to remember. It is a best practice to manually configure predictable LLAs, especially for default gateway redundancy.

``` Router(config-if)# ipv6 address fe80::1 link-local ``` The `link-local` keyword tells the router this is not a standard routable address. A router can have the same LLA (like `fe80::1`) on multiple interfaces, as they are only locally significant.

Using EUI-64 for Global Addresses

Instead of typing out the full host portion of an IPv6 address, you can tell the router to use EUI-64 to complete the address based on the interface's MAC address.

``` Router(config-if)# ipv6 address 2001:db8:acad:2::/64 eui-64 ``` The router will take the `/64` prefix provided and append the dynamically generated 64-bit Interface ID.

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