How to enable IPv6 on a Cisco Router

Now in order for you to allow (enable) a Cisco router to begin routing IPv6 packets, you'll need to perform the following two tasks.

Step1 - Enable IPv6 routing globally on the router

Step2 - enable IPv6 processing on a particular interface(s).

To begin completing task number one (enabling IPv6 routing globally on a router) you'll need to enter Global Configuration mode and type ipv6 unicast-routing on the router like you see here:

Router>enable
Router#configure terminal
Router(config)#ipv6 unicast-routing
Router(config)#exit
Router#

Notice, that I typed the word "enable" while the router was in User Exec mode (Router>) which then placed the router into Privileged Exec mode (Router#). Then once the router was in Privileged Exec mode (Router#) I typed the words "configure terminal" which then placed the router into Global Configuration mode (Router(config)#) so I could begin configuring the router to globally route IPv6 packets; and as you can see, I typed the Global Configuration command "ipv6 unicast-routing" to complete task number one.

So, to make a long story short, the command that you need to type on a Cisco router to enable it globally for IPv6 packet routing is "ipv6 unicast-routing".
Now, that I've successfully completed task number one, I typed the word "exit" to leave Global Configuration mode (Router(config)#) and re-entered into Privileged Exec mode (Router#).

Router>enable
Router#configure terminal
Router(config)#ipv6 unicast-routing
Router(config)#exit
Router#configure terminal
Router(config)#interface fastethernet 0/0
Router(config-if)#ipv6 enable
Router(config-if)#

Now, since the router is back into Privileged Exec mode (Router#), I continued on to completing task number two (enabling IPv6 processing on a particular interface(s). By re-typing the command "configure terminal" which placed the router back into Global Configuration mode (Router(config)#), so I could use the "interface" command to specify the interface type (fastethernet) and its slot and port information (0/0). Notice, that the router has entered into Interface Configuration mode (Router(config-if)#) by hitting the enter key, and once the router was in Interface Configuration mode (Router(config-if)#); I used the interface command "ipv6 enable" to enable the fastethernet 0/0 interface for IPv6 processing to complete task number 2.

Here's another way the previous commands could have been typed:

Router>enable
Router#configure terminal
Router(config)#ipv6 unicast-routing
Router(config)#interface fastethernet 0/0
Router(config-if)#ipv6 enable
Router(config-if)#exit
Router#

Notice, that it wasn't really necessary to leave Global Configuration mode (Router(config)#) to complete both tasks; I just did it, to show you each task individually.
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