6. Please define an explicit object(s) to express capability of an
   implementation. See the object dot1dDeviceCapabilities 
   as defined in rfc 2674.
   Section 4 of rfc 2460 provides the list
   of extension headers, it is probably that some implementations
   may not implement all features or if future extensions headers
   are added, it will be useful to identify what a given implementation
   supports. For IPv6, it might includes handling of
   various headers, flow label, traffic class, ..