We have used the unabbreviated address format in the configuration for R1 while using the abbreviated address format on R2.//
Key Concept You must use the ipv6 unicast-routing command to enable IPv6 routing on the router.//
We used an easily forgotten command while configuring IPv6 addresses on R1 and R2 and that is ipv6 unicast-routing. We are used to configuring IPv4 addresses on routers and you don’t have to enable IPv4 processing on routers as it is enabled by default. That’s not the case with IPv6 yet and you must enable IPv6 routing using the single ipv6 unicast-routing command. If you configure IPv6 addresses on router interfaces but leave out the ipv6 unicast-routing command, the router can still be configured with interface IPv6 addresses, but it acts more like a host and cannot route IPv6 packets.
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You can use the show ipv6 interface brief or show ipv6 interface commands to verify IPv6 addresses configured on router interfaces. The router always displays IPv6 addresses in the abbreviated format even if you had configured them in the unabbreviated format. The output of show ipv6 interface brief command executed on R1 and R2 demonstrates the fact, as shown below.