How to convert mac address to ip mac#
Building the TableĮach host on a LAN builds a table of MAC addresses on its network and maps those addresses to Layer 3 (in this case, IP) addresses. How that table gets built and is maintained is important in understanding the dynamic and active role that IP plays in a network. This correlation is maintained in a table by each network-attached host.
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Given this role, it becomes clear that ARP must track the correlation between MAC addresses and IP addresses for all devices that lie within the same LAN broadcast domain. RFC 826 positioned ARP as an IP-to-Ethernet mechanism, but it was subsequently extended to all the IEEE's 802 LANs, as well as to FDDI. Thus, it is distinctly a native component of IP. In fact, ARP was originally stipulated in November 1982 in RFC 826. If that IP address appears in the ARP cache, ARP grabs the corresponding MAC address, and that gets used as the destination address in the Ethernet frame.ĭue to its function as an intermediary between a LAN and the IP suite of protocols, you might be hard-pressed to figure out whether ARP is a LAN protocol or one of the IP protocols. It then looks in its cache to see if it already knows that IP address. So, the step that was missing from the previous example is that ARP "reads" each packet's destination IP address. Its function is quite simple: It tracks the correlation between physical MAC addresses and IP addresses for every device attached to the same LAN. That's because it operates invisibly, without requiring initiative, input, or intervention from individual users. Address Resolution ProtocolĪRP is one of those network protocols you use every day without realizing it. This is where ARP comes into the picture. Thus, it is necessary to translate IP addresses into MAC addresses for the layered communications session shown in Figure 10-12 to work. Each has its own addressing system, and those systems are incompatible. Ethernet and IP are dissimilar protocols. This might seem logical enough, but a step is missing. Upon reaching its intended destination, the Ethernet frame is stripped off, thereby revealing the IP packet that was embedded in its data field. But this interoperability takes the form of Ethernet encapsulating IP packets within Ethernet frames for transport through the LAN. This well-defined separation of functions enables interoperability of IP and Ethernet. IP and other routed protocols operate at Layer 3. The concept embodied in the reference model is what has enabled open communications and cross-vendor interoperability of networking products.Įthernet and other LAN protocols operate at Layers 1 and 2 of this model. You have probably heard all about the OSI Reference Model and its seven layers. The reason has everything to do with the concept of logically separated functions. In reality, Ethernet (as is every other LAN protocol) is not IP-based. Although Networked Devices Are Uniquely Identified Via an IP Address, a Physical Address Is Required for Successful CommunicationsĮach endpoint has a unique IP address assigned to it, so this shouldn't be a problem. The other is a server that, at least in theory, is the intended destination of most communications sessions on this LAN.įigure 10-12. Two of these devices are hosts that, ostensibly, originate the majority of communications sessions. Figure 10-12 shows a few devices connected via an Ethernet. Let's assume, for the sake of example, that our local mechanism is an Ethernet network. Networked devices really communicate locally using local mechanisms. Previous chapters of this book have conveniently overlooked that point in order to focus on IP addresses and their function in a network.
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In the world of Ethernet and other networks standardized via the IEEE's 802 family of network protocols, physical addresses are known as MAC addresses.
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Physical addresses, although they are typically globally unique, are valid only for communications within a single Layer 2 domain. Network devices really communicate via physical addresses. The second of our two original translation requirements was translating IP addresses into MAC addresses.