There are two ways to achieve the configuration to successfully reach IPv6 nexthop for MP-BGP sessions. They are:
Using ipv4-mapped-ipv6 address.
Using out-bound route-maps.
The default method is ipv4-mapped-ipv6 address. However, Extreme recommends using out-bound route-maps as the preferred method for achieving this.
When both ipv4-mapped-ipv6 address and out-bound route-maps are configured, then out-bound route-maps configuration takes precedence.