Resets an attribute of an instance to its default value. To reset the kernel or ramdisk, the instance must be in a stopped state. To reset the SourceDestCheck, the instance can be either running or stopped.

The SourceDestCheck attribute controls whether source/destination checking is enabled. The default value is true, which means checking is enabled. This value must be false for a NAT instance to perform NAT. For more information, see NAT Instances in the Amazon Virtual Private Cloud User Guide.

http://docs.aws.amazon.com/AWSEC2/latest/APIReference/ApiReference-query-ResetInstanceAttribute.html