Hello,
This question essentially focuses on what addresses, IP and MAC, change as an IP packet moves between end hosts through intermediary devices.
Without giving off the correct answers, here is a couple of rules:
- When an IP packet moves through a network from its sender towards its destination host, the IP source and destination addresses never change. The IP addressing remains unchanged along the entire path of the packet. This is because IP provides packet delivery between end hosts, and so their identities must not change, otherwise the packet would divert to a different end host. The only exception to this rule is the NAT (Network Address Translation), but this is out of scope of this question.
- As the packet is encapsulated into a frame, the source and destination MAC address of this frame change when the packet traverses a router. This is because the frame with the packet inside needs first to be received by the router's incoming NIC, and when the packet is routed and sent out in a new frame, it is sent from a different NIC and addressed to the next router and its own NIC. In other words, Ethernet and any other Layer2 technology provides frame delivery between neighboring hosts. The MAC addresses do not change when the frame passes through hubs, bridges, or switches.
Please feel welcome to ask further!
Best regards,
Peter
