To start with, this is a very good question, which touches upon the basic network foundations. By the way, this is how your workstation gets the MAC address of your default gateway that must exist in your same subnet. Now for communication to another IP within your subnet, direct MAC communication is needed, but to get that MAC addr requires the ARP protocol that uses a broadcast in the subnet to find it. To attempt a simple illustration, consider the L2/元 headers as a packet moves from the source IP (sIP) to a destination IP (dIP) and the source and destination MACs are rewritten along the way - fs=first-source and ld=last-destination, and r1-r3 are routers: fsMAC-r1MAC / sIP-dIPĪny L2 switches involved will not modify the MAC addresses. That first router will rewrite the source MAC to itself and the destination MAC to the next router hop, and so on, until the packet arrives at the last router that is directly connected to the destination subnet. There's no knowledge of the final destination MAC from your perspective. The Ethernet header contains your source MAC and the destination MAC of your default gateway. The IP header of a packet leaving your workstation destined to an IP in a different subnet will maintain the source IP and destination IP, forgetting about NAT for the moment. When you understand that IP-to-IP communication is really just a series of MAC-to-MAC communication taking place at each router hop, then you'll see why both are necessary. despite being the vast majority (I think :-P ), some other protocols are still in use and they rely on the MAC address.all devices are built to take care of the MAC address, in that low-level requirement, and would need to be changed.Why not simply eliminate the MAC and instead use just TCP/IP ? But the network devices need to know to which network card that message is going, so they, somehow, translate the TCP/IP address with to the MAC address. So, if a TCP/IP address needs to communicate with another, is just uses the TCP/IP address. are part of the engineering group, and those of 10.1.x.x. For example, IPX/SPX would address each computer using the MAC address and some more information.īut the TCP/IP protocol was designed a little bit different: they decided that having an virtual address, made of 4 bytes (0.0.0.0 to 255.255.255.255) was enough, and was even easier to manage: it doesn't matter if your network cards all have a similar MAC address or not we'll group our computer so that all TCP/IP address that began with 10.0.x.x. Each protocol would specify things as they thought were ok. There wasn't a unique specification on how computers would talk to each other: many protocols appeared: TCP/IP, IPX/SPX, and so on. (ok, identify each network card, but back that time, you could think of one MAC address for each computer). This ID is called MAC address, is should uniquely identify each computer. So, instead of giving each computer a name, we gave them an ID. TO do that, they need to know who was talking and who was being talked to. Without going into OSI model, TCP layer, etc.:īack in time, networks were created: some computers would communicate with each other to share something.
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