Second question: At each hop, does the data link layer change the destination MAC address in the frame to the MAC address of the next hop? So, the destination MAC address is the address of your gateway if the final target is not on the same LAN. The MAC addresses are used in the layer 2 of the frame, and the layer 2 define the local network.
Layer-2 MAC addresses are removed at each layer2/3 boundary along the routes to be replaced with the MAC addresses of the new source and destination, but the layer-3 IP addresses stay the same along the path (with certain exceptions like NAT).įirst question: The destination MAC address - is this the final destination or the destination of the gateway?
The layer-3 packet will contain the layer-3 source IP address of the originator of the packet, and the layer-3 destination address of the final layer-3 destination. The new layer-2 frame will contain the source MAC address of the router's interface in the new layer-2 domain, and the destination MAC address of the next hop in the new layer-2 domain. The original layer-2 frame will contain the source MAC address of the sender, and the destination MAC address of the router's interface in that layer-2 domain. If the layer-3 packet needs to be forwarded through another layer-2 domain, a new layer-2 frame is created using MAC addresses in the new layer-2 domain to encapsulate the layer-3 packet. The layer-2 frame is stripped off at a layer-2/3 boundary (e.g. The layer-2 frame encapsulates the layer-3 IP packet. MAC addresses are layer-2 addresses in the frame header. Once the receiving gateway receives the frame/packet, how does it know
Switch to ensure it ends up at the correct device? This obviouslyĪssumes that the destination MAC address is not amended by the routersĪs the frame/packet traverses the internet - if it is amended then Receiving LAN is the destination MAC address in the frame used by a Third question: Once the frame/packet reaches the gateway of the The packet/frame is routed to the destination address (which is the gateway ) Second question: At each hop, does the data link layer change theĭestination MAC address in the frame to the MAC address of the next The packet/frame is then sent onto the internet and routed (using the IP address) to the next hop towards the final destination This is then turned into a frame which will go to the gateway for the LAN - this happens at the data link layer and the frame has a MAC sending and destination address addedįirst question: The destination MAC address - is this the finalĭestination or the destination of the gateway? So as I understand it the following happens when a device on a LAN sends a packet/frame to a device on another separate LAN via the internet.Ī packet is created at the sending end with the destination and sending IPįirst question: Is the destination IP actually the IP of the gateway for the receiving device’s LAN I have enough to get them through the syllabus, but I like to have more knowledge than the spec so that I can explain how things work in more meaningful way. I have to teach my sixth form about MAC Addresses and IP Addresses in a few weeks time and there are some areas I am unclear on which I am hoping some of you will be able to clarify for me.
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