Data packets travel from router on layers 3 and 4. As this happens their headers change. Explain why this is the case with reference to ip and mac adresses.
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The process of packet transmission involves multiple layers of the networking protocol stack, including layer 3 (network layer) and layer 4 (transport layer). At each layer, the packet headers are modified for various purposes, such as adding necessary information for routing and addressing.
When data packets travel from a router on layers 3 and 4, their headers change due to differences in addressing between the network layer (layer 3) and the data link layer (layer 2), where MAC addresses come into play.
1. IP Addresses (Layer 3):
At layer 3, IP addresses are used to identify source and destination devices within a network. These addresses are unique and assigned to each device connected to the network. IP addresses consist of network and host portions, allowing routers to determine the network path and deliver the packets to the correct destination network.
Whenever a packet passes through a router, the router examines the IP packet header and makes decisions on forwarding based on routing table information. The router updates the packet's source and destination IP addresses to reflect the next hop towards the final destination. This modification ensures that the packet reaches the appropriate network segment.
2. MAC Addresses (Layer 2):
On the other hand, MAC addresses are used at layer 2 to uniquely identify devices within a local network. MAC addresses are physical addresses burned into a network interface card (NIC) and are used for communication within a local area network (LAN).
When a packet leaves a router to traverse a different network, the router encapsulates the IP packet into a new data link layer frame, such as Ethernet frames. Ethernet frames require source and destination MAC addresses for communication at the local network level. Therefore, the MAC addresses in the data link layer header must be modified at each hop, ensuring that the packet reaches the correct device within the local network.
In summary, the change in headers at layers 3 and 4 is necessary for routing and addressing purposes. The router modifies the IP addresses at layer 3 to ensure correct routing across different networks, while the MAC addresses at layer 2 are modified to facilitate communication within the local network.