MAC address Definition
A mac address is a 48 bit hexadecimal number. The first 24 bits are the OUI which can be used to identify the manufacturer. The last 24 bits are vendor assigned and uniquly identify the hardware both by type and by device. Google chrome free. download full version for windows 7 32bit. So you would need to get access to the IEEE database of vendors and hardware models to do this but it is possible. An Ethernet MAC address is a 48-bit binary value expressed as 12 hexadecimal digits. Both media access control and medium access control are the elaborated forms of the same term 'MAC' address. For the proper and to the point communication between a network's computers, MAC address is used to identify uniquely each network interface.
You do not need to be a computer expert to know what a MAC address is. It is a unique address for devices with network capabilities. We explain what you should know about the MAC address.
Explanation: What is a MAC address?
- 'MAC' stands for 'Media Access Control,' this address is used to identify your device.
- The MAC address assigns to your network adapter. You need this to be able to use the Internet via LAN or WLAN.
- The 12-digit code is displayed in the hexadecimal system and is unique to your device. The first six digits indicate from which manufacturer your network adapter is. The second six numbers represent the specific number for your device.
- On Windows devices, the MAC address is also displayed as a 'physical address,' on Apple devices as 'Airport ID.'
Structure of the MAC address
The structure of the 48-bit address is precisely defined. The first two bits specify the type of speech. Among other things, they determine whether it is a multicast or broadcast address or a globally unique individual address.
Subsequently, until the end of the third byte, the manufacturer identifier of the network card or hardware follows. The bit sequence is called Organizationally Unique Identifier (OUI) and is awarded by the IEEE to the various manufacturers of the appliance.
The manufacturer specified the last three bytes of address. It assigns this bit sequence only once, thus ensuring that the complete address is unique. The spelling is usually in hexadecimal form, where hyphens or colons separate the bytes.
The different forms of representation of MAC addresses
There are various forms of representation of MAC addresses. A distinction can be in between the canonical and the bit-reversed description. The most common is the authoritative description. It consists, as already described, of a sequence of two-digit hexadecimal numbers, separated by a hyphen (sometimes also by a colon).
Less common is the bit-reversed or non-canonical form.
The function of MAC addresses in the network
The essential feature of the MAC addresses is the delivery of a frame on layer 2. If the IP destination address is in the same subnet in an IP network, the delivery is made directly to the physical address of the target computer. Chrome 49 download offline. If the IP address belongs to another subnet, the layer two frames address to the MAC address of the responsible router (usually the default gateway).
The router is responsible for switching the packet to the next network node or the destination computer and also sends it on the following network section to a MAC address. At the same time, the router replaces the source MAC address of the source frame with its own.
Computers with multiple network interfaces have multiple MAC addresses. If the hardware of a network interface exchanges, its address also changes.
Unique MAC addresses and their function
In addition to the globally unique MAC addresses for the identification of network interfaces, addresses with special features exist. These are, for example, MAC multicast and MAC broadcast addresses. With the help of these addresses, Ethernet frames can be sent simultaneously to several or all stations of a broadcast domain.
The broadcast address in Ethernet consists of all ones and is FF-FF-FF-FF-FF-FF. Broadcasts can create a heavy burden on a network. A broadcast storm, triggered by parallel connections between switches, can paralyze the entire system.
48 Bit Hexadecimal Mac Address Book
Can you change your MAC address?
It is not the manufacturer's intention to change a MAC address. However, with various tools or programs, this is possible so that the MAC address can vary with specific programs. For Windowsoperating systems, for example, there is the SMAC tool with which it can change as required.
Conclusion
Basically, you can find MAC addresses in all the electronic goods. It is not necessary to find the MAC addresses, as it is know to all the networks by default.
Review What is a MAC Address? – Definition, Structure, Types and More.
MAC-address consists of 48 bits represented in hexadecimal format. Every 8 bits are separated either by a colon (:) or a hyphen (-). Let's come up with MAC-address example: 00:26:57:00:1f:02.
Each product, possessing communication interface, has the unique MAC-address. IEEE is the organization that provides manufacturers with source MAC-addresses range to be used in their products: for this, first three octets of a specific value are fixed for each manufacturer. These three octets are called OUI (ORGANIZATIONALLY UNIQUE IDENTIFIER). So, as you already may see, one can easily identify a device manufacturer by its MAC-address. You can do this online by yourself – check for IEEE online database (Be attentive! OUI should be entered with a hyphen!). For the MAC-address given earlier as an example one can define that it belongs to Russian relay protection manufacturer EKRA. The remaining three octets are set by the manufacturer and should never repeat each other in combination with the first three octets of the same value. Since these last three octets identify the network controller of a device, they are usually referred as NIC Specific (Network Interface Card Specific).
Typically, MAC-address of the device can be determined by looking at IED labels – often network interface panel has the label, indicating IED's MAC-address.
Let's see what values destination MAC-address can take.
48 Bit Hexadecimal Mac Addresses
When it comes to transferring data from one device to another, then destination MAC-address field has the value of the recipient – that is, the address which we have discussed above. In this case, destination MAC-address is a unicast (unicast) MAC-address. In substation environment, specifically in IEC 61850 context, destination unicast MAC-address is there in MMS packets.
But what if the same data packet needs to be transmitted to multiple network devices? For this purpose there is a destination multicast (multicast) MAC-address. These MAC-addresses are easily identifiable – least significant bit of the first octet of the destination MAC-address is set to 1, for example, 01-0C-CD-00-00-01. If such a packet is received by Ethernet switch, then the latter forwards it to all other ports – in case no recipient groups are specified at the switch. The possibility of organizing data transfer for the group of devices is one of the differences between using the destination multicast MAC-address and destination broadcast (broadcast) MAC-address. Switch to google chrome. In substation environment, specifically in IEC 61850 context, destination multicast MAC-address is there in GOOSE and Sampled Values messages. For example, one can find a GOOSE with destination MAC-address 01:0C:CD:01:01:21.
Speaking about the destination multicast MAC-addresses it is worth noting another interesting point – IEEE not only assigns MAC-addresses' bands to device manufacturers, but also to standardization bodies, to uniquely identify the traffic transmitted according to the standards. For this, again, IEEE reserves the values of first three octets. For example, for IEC TC 57 the following three octets are reserved – 01-0C-CD-xx-xx-xx. Then standardization body decides the rules of MAC-address assignment to specific protocols by itself. For GOOSE messages TC 57 WG 10 then determined the fourth octect to be equal to 01 and the range of addresses as: 01-0C-CD-01 -00-00 to 01-0C-CD-01-01-FF; for Sampled Values - the fourth octet equal to 04 and range of addresses as: 01-0C-CD-04 -00-00 to 01-0C-CD-04-01-FF. For example, for PTP and RSTP protocols traffic specific destination MAC-addresses are determined.
32 Bit Hexadecimal
Broadcast MAC-address – is always the same: ff: ff: ff: ff: ff: ff. When switch receives such a packet it forwards it to all its ports. Broadcast destination MAC-address is used only by some service protocols such as ARP (Address Resolution Protocol), which we will have a look at next time and which plays an important role in information exchange process in Layer 2 networks.
Summary
- If you are IED developer and your IED is to have communication interface, make sure IEEE reserves MAC-addresses band for your products. Company will have to pay for this.
- For protection and control system designers of the future and for the commissioning guys there may be another recommendation – never set the same destination multicast MAC-address for different GOOSE and Sampled Value messages (there are examples of the configuration software not restricting you from doing this). Otherwise, you risk to lose the capability of using multicast filtering function on switches. Keep in mind that there are many IEDs on the market which do not support this multicast filtering functionality. If you are not capable of activating this functionality on the switch then all network devices, including IEDs, will listen to all the messages, even those that they do not really need and this as we have already mentioned, places an impact on GOOSE transfer time. It will increase with the increased loa
