Cisco Certified Network Associate (CCNA) Practice Exam

The command to configure an EIGRP router for a specific Autonomous System (AS) number is "ipv6 eigrp AS NUMBER." This command is used in router configuration mode and enables EIGRP for IPv6 routing while specifying the AS number that the router will join. The AS number is crucial for routing protocols because it allows routers to distinguish between different EIGRP domains and ensures that only routers within the same AS will exchange routing information.

Selecting the correct AS number is essential because having routers in different AS numbers will prevent them from forming neighbor relationships and exchanging routing updates. This command effectively sets up the routing protocol and prepares the router to participate in an EIGRP network for that specific autonomous system.

Other options have different purposes: displaying the current IPv6 protocols, configuring an interface to operate in passive mode, or entering interface configuration mode do not perform the function of enabling EIGRP with a specified AS number.