Hello R.B. Kumar,
in the IEEE 802.1Q standard the untagged native vlan is provided for compatibility with NICs that doesn't support vlan tagging.
In this way connecting a non vlan tagging capable device to a 802.1Q trunk port the device is still able to communicate over the native vlan.
802.1Q introduces a vlan tag just after the source mac address: from ethernet point of view a vlan tagged PDU is not an IPv4 packet but has a different ethertype that of 802.1Q
da|sa|802.1Q ethertype|vlanid!CoS|ip ethertype
an old device that is not able to handle the 802.1Q ethertype (0x8100) just discards tagged frames
Hope to help
Giuseppe