The value of vRtrInetExtTunnelDestPfxLen indicates the mask length for vRtrInetExtTunnelDestAddr. For those systems that do not support arbitrary subnet masks, an agent constructs the value of the vRtrInetExtTunnelDestPfxLen by reference to the IP Address Class. Any assignment (implicit or otherwise) of an instance of this object to a value x must be rejected if the bitwise logical-AND of the mask representing x with the value of the corresponding instance of vRtrInetExtTunnelDestAddr is not equal to vRtrInetExtTunnelDestAddr.