6850 setting the mtu size on ipv6 interface

[franke]

Hello,

I want to change the mtu size on the ipv6 interface
I an getting the following message

ipv6 interface v6if-v333 mtu 9216
ERROR: MTU parameter is not supported on this platform.

currently running
System:
Description: 6.3.1.871.R01 GA, December 20, 2007.,
Object ID: 1.3.6.1.4.1.6486.800.1.1.2.1.7.1.1,

is there an upgrade available with instructions to allow me to change the mtu size?

Thanks in advance