code: func GetInterfaceID(o dhcp6.Options) (InterfaceID, error) {
  	v, err := o.GetOne(dhcp6.OptionInterfaceID)
  	if err != nil {
  		return nil, err
  	}
  
  	var i InterfaceID
  	err = i.UnmarshalBinary(v)
  	return i, err
  }
docs: // GetInterfaceID returns the Interface-Id Option value, described in RFC 3315,
  // Section 22.18.
  //
  // The InterfaceID structure returned contains any raw class data present in
  // the option.