The customer could not configure IPv6 authentication in a network where there is already a VRRP running for IPv4.
The customer typed the command below followed by question mark and noticed there are no paramenters for authentication of VRRP6.
[CE12800]vrrp6 vrid 2 ?
admin Specify the administrator VRRP6
join Join to load-balance VRRP
load-balance Specify load balance mode
preempt Specify preempt mode
priority Specify priority
timer Specify timer
track Specify track configuration
virtual-ip Specify a virtual IP address
After searching the documentation and thinking that IPv6 already have the Authentication Header included in the IP packet, so it's more secure than IPv4, checked the IANA webside for RFC5798. There I found that actually the VRRP has removed any type of authentication for both IPv4 and IPv6 later versions. Only IPv4 early versions still support it.
VRRP for IPvX does not currently include any type of authentication.
Earlier versions of the VRRP (for IPv4) specification included
several types of authentication ranging from none to strong.
Operational experience and further analysis determined that these did
not provide sufficient security to overcome the vulnerability of
misconfigured secrets, causing multiple Masters to be elected. Due
to the nature of the VRRP protocol, even if VRRP messages are
cryptographically protected, it does not prevent hostile nodes from
behaving as if they are a VRRP Master, creating multiple Masters.
Authentication of VRRP messages could have prevented a hostile node
from causing all properly functioning routers from going into Backup
state. However, having multiple Masters can cause as much disruption
as no routers, which authentication cannot prevent. Also, even if a
hostile node could not disrupt VRRP, it can disrupt ARP and create
the same effect as having all routers go into Backup.