Data Delivery from the source device to a destination device is the basic responsibility of the network layer and data link layer. Protocols at both layers contain a source and destination address, but their addresses have different purposes.
Network Layer Addresses
Network Layer addresses are responsible for delivery the IP packet from the original source device to the destination device. The destination may be on the same network or may be on the remote network. An IP addresses also know as the network layer addresses. The IP address is also known as a logical address. Any IP packet has contained two network layer addresses:-
- Source IP address– The IP address of the sending device and the original source of the packet.
- Destination IP address– The IP address of the receiving device and the final destination of the packet.
The figure below illustrates the source and destination IP address in the packet sending over the network.
Data Link Layer Addresses
The data link layer is responsible for delivering the data link frame from one network interface card (NIC) to another network interface (NIC) on the same network. The address working on data link layer is called physical address or MAC address. It has a different role than the IP address. It delivers the data link frame from one network interface card to another network interface card on the same network. Before an IP packet to sent over a wired or wireless network, it encapsulated in a data link frame and then transmitted over the physical medium.
The figure below illustrates the data link layer address or L2 address. As the IP packet travels from host to router, router to router, and finally router to host at each point along the way the IP packet is encapsulated in a new data link frame. Each data link frame has the source data link address of the NIC card sending the frame, and the destination data link address of the NIC card receiving the frame.
Layer 2, data link protocol is only used to deliver the packet from NIC-to-NIC on the same network. The router removes the Layer 2 information as it received on one NIC and adds new data link information before forwarding out the exit NIC on its way towards the final destination. The IP packet encapsulated in a data link frame that has data link information, including a:
- Source data link layer addresses – The physical address of the device’s NIC that is sending the data link frame.
- Destination data link layer addresses – The physical address of the NIC that is receiving the data link frame. This address is either the next hop router or of the final destination device.