Data Link Layer

Hi, I am bit confused in Data Link Layer. When a sender machine send a data to Reciever machine then it starts from App--Pres--Sess--Transp---Network---Data??? I have understood all upper 5 layer function but in the Network layer the packet has information of Soure and Destination Address then why it needs to have MAC address. Please answer me in details. Thanks

The Network Layer header hast the Source and Destination Address (IP address) of the sender and the end receiver. The Data Link header has the Source and Destination address (MAC address) of the sender and the following device in the path to reach the sender.
The sender know where it wants to go (Destination IP address), to reach that destination it has to reach the next device in the path and for that it needs the Destination MAC address of that device... once the packet is in that second device (and it still knows where it wants to go (Destination IP address), now it has a new source MAC address and a new destination MAC address because it wants to get to the next device (may be router 2)... once it gets to router 2 (and it still knows where it wants to go) the packet (in its data link header) now has a new MAC Address in its source and destination.... finaly it gets to the last device and it knows that the Destination IP is in its LAN.
Data link header helps the frame to make it to the next device.... Network Layer header helps you to reach the final destination through all the devices.
Hope it is not so confusing.
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