def copy(self):
        """Returns a deep copy of the instance."""
        clone = self.__class__()
        clone.fields = self.copy_fields_dict(self.fields)
        clone.default_fields = self.copy_fields_dict(self.default_fields)
        clone.overloaded_fields = self.overloaded_fields.copy()
        clone.underlayer = self.underlayer
        clone.explicit = self.explicit
        clone.raw_packet_cache = self.raw_packet_cache
        clone.raw_packet_cache_fields = self.copy_fields_dict(
            self.raw_packet_cache_fields
        )
        clone.wirelen = self.wirelen
        clone.post_transforms = self.post_transforms[:]
        clone.payload = self.payload.copy()
        clone.payload.add_underlayer(clone)
        clone.time = self.time
        return clone