Version 32.3 adds the ability to transport IPv6 payloads in IPv4 GRE tunnel, allowing the GRE tunnel to be configured with multiple IPv6 addresses. ECMP is also supported for IPv6 destinations reachable via GRE tunnel. IPv6 forwarding can be enabled on the GRE tunnel that has an existing IPv6 address configured, but only one ECMP Nexthop is installed in the hardware.
All platforms.
configure tunnel tunnel_name ipv6 tcp adjust-mss [off | on tcp_mss_value]