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Oct 07, 2019 Mac mini introduced in mid 2010 or later iMac introduced in late 2009 or later Mac Pro introduced in mid 2010 or later. To find your Mac model, memory, storage space, and macOS version, choose About This Mac from the Apple menu. If your Mac isn't compatible with macOS High Sierra, the installer will let you know. Oct 07, 2019 Mac mini introduced in mid 2010 or later iMac introduced in late 2009 or later Mac Pro introduced in mid 2010 or later. To find your Mac model, memory, storage space, and macOS version, choose About This Mac from the Apple menu. If your Mac isn't compatible with macOS High Sierra, the installer will let you know.
Each network-compatible device has at least one unique hardware ID – the media access control address (in short: MAC address). What this is all about and how you can find or rewrite the MAC address is explained below.
What is a MAC address?
Each device that is integrated into a computer network requires a network adaptor. This adapter receives a worldwide unique identification number from the manufacturer: the MAC address. This enables devices like desktop computers, tablets, or mobile phones to be identified in the network and addressed as required. If a device has several network adapters (for example, for several LAN connections or different communication standards like Ethernet, WiFi, FDDI, Bluetooth, or Token Ring), a different address is available for each standard.
The MAC address (short for media access control address) is the worldwide unique hardware address of a single network adapter. The physical address is used to identify a device in computer networks.
Since MAC addresses are assigned directly by the hardware manufacturer, they are also referred to as hardware addresses. With Microsoft Windows, the MAC address is referred to as the physical address. Apple uses the terms Ethernet ID, Airport ID, or WiFi address, depending on the communication standard. The term device address, on the other hand, is fuzzy, since a device can have several network adapters and therefore different MAC addresses.
The MAC address in practice
Conflicting MAC addresses are a basic requirement for error-free network communication.
Data transmission in computer networks is a complex communication process in which different requirements including reliability, security, and efficiency must be met. This can be illustrated using the OSI models (abbreviation for open systems interconnection) – a reference model developed by the ISO (International Organization for Standardization) that maps network communication to 7 layers. During data transmission, each layer of the OSI model is run through on both the sender and receiver sides.
MAC addresses are used on the backup layer (layer 2) of the OSI model – actually, the media access controlsublayer introduced by the Institute of Electrical and Electronics Engineers (IEEE).
In the extension of the OSI model designed by the IEEE, the backup layer (layer 2) is divided into the sublayers media access control (2a) and logical link control (2b).
The backup layer is located between the bit transfer layer (layer 1) and the switching layer (layer 3). While the bit transmission layer provides protocols and tools responsible for maintaining the physical connection, protocols on the backup layer control how different systems share the available transmission medium. Secure system connections are abstracted from the physical connection. The actual transmission of data packets takes place at the switching level via IP.
For example, if you want to send an IP packet over Ethernet, your computer transmits a data frame that is addressed to the target computer’s MAC address on the backup layer, according to the OSI model.
If the target computer is not in the local network, a router is addressed and instructed to forward it to the internet. Routers integrated into a social network also have a unique MAC address.
An Ethernet data frame contains information that is read out at different levels of the OSI model.
Data frames in IPv4 networks contain the following components:
A target computer that receives a data frame first reads it on the backup layer and compares the target address of the frame with its own MAC address. If the addresses match, the target computer starts interpreting the frame at the next higher level.
Network devices that are only used to forward data packets (repeaters) or manage parts of the network (bridges and switches) usually do not actively participate in network communication and so do not require their own MAC addresses.
To link the address assignment on the backup layer with the address assignment on the switching layer, the address resolution protocol (ARP) is used in IPv4 networks. Each computer in the local network maintains an ARP table whereby IP addresses are assigned to MAC addresses.
ARP is vulnerable to an attack pattern called ARP spoofing. The danger of ARP spoofing and the countermeasures you can take are discussed in the article above.
The new internet protocol standard IPv6 uses the neighbor discovery protocol (NDP).
MAC address syntax
MAC addresses in LAN or WLAN networks consist of 6 bytes (48 bits) and are written in hexadecimal notation. The use of separators such as hyphens or colons between two bytes increases readability.
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The following example shows the MAC address of a desktop computer in binary and hexadecimal format:
In our example, we use canonical representation of the bit sequence. This corresponds to the order in which MAC addresses are transmitted in Ethernet. Other communication standards like Token Ring provide for bit-reversed transmission, starting with the most significant bit.
The bit sequence of each MAC address is divided into 4 areas, each of which encodes different information.
Table: Subareas of an MAC address R for mac os x faq (see help) section 9.
Finding out your MAC address: a how-to guide
MAC addresses can be queried through the terminal in all modern operating systems with little effort – both on the local system and remotely in the network. The following table shows the corresponding command line commands for the most common operating systems.
Table: MAC address read out
On mobile devices, you can display the MAC address in the settings.
Table: Get MAC addresses on mobile devices
Read MAC address locally
If you want to read out the MAC addresses of the LAN and WiFi adapters on your Windows computer, proceed as follows if using Windows 10.
Step 1: Open the terminal of your operating system. For example, use the keyboard shortcuts [Windows button]+[R]. Then enter “cmd” in the window “Run” and confirm with “OK.”
Step 2: From Windows 2000 onwards you can use the command line utility ipconfig with the “/all” option to get the MAC address of all network adapters on your Windows computer.
Alternatively get the MAC address with the command “getmac /v”
Step 3: With Windows, the MAC address is displayed under “physical address.”
Accessing your MAC address remotely
Thanks to ARP, in IPv4 networks it is possible to determine other devices’ MAC addresses in the same local network. With Windows and most unixoid operating systems, use the command line “arp” with the option to display you system’s ARP table in the terminal.
You will receive a terminal output according to the following scheme:
If you just want to read the MAC address of a specific network adapter remotely, use the command “arp –a” in a combination with the target adapter’s local IPv4 address.
Assigning the MAC address using software
MAC addresses are invariably assigned by device manufacturers and are “burned” into the network adapter chip on the hardware side. However, numerous operating systems offer the option to overwrite hardware addresses on the software side. This is referred to as spoofing. In this case, a system does not send the addressed adapter’s real network hardware address in network communication, but instead a user-defined MAC address.
Assigning an MAC address in Windows
With Windows, you can overwrite the MAC address through the device manager if the network adapter’s device driver supports this function.
Step 1: Open the network adapter settings. To do this, follow the click path: Start à Settings à Network and Internet à Ethernet à Change Adapter Options
Step 2: Right-click on the desired network adapter and select “Disable” in the context menu.
Step 3: Right-click on the desired network adapter and select “Properties” from the context menu. A pop-up window opens called “Network adapter properties.”
Step 4: Click on the “Configure” button in the pop-up window and select the “Locally Administered Address” property under “Advanced.” Enter your chosen software MAC address under “Value.”
Assign MAC address in unixoid operating systems
Unix derivatives such as Linux, macOS, Solaris, and the BSD operating systems support the assignment of MAC addresses through the terminal on the software side.
Table: Overwriting a MAC address
We illustrate the procedure using the most commonly used Unix derivative: Linux. If you want to change your network adapter’s MAC address, proceed as follows.
Step 1: Open the operating system terminal – for example, with the key combination [CTRL]+[ALT]+[T].
Step 2: Determine the name and current MAC address of the desired network adapter. To do this, enter the following command in the command line:
Note the hardware address assigned by the manufacturer in case you want to undo the change.
Step 3: Turn off the network adapter by entering the following command in the command line:
Enter the name of the network adapter determined through “ip link” for <Interface>.
Step 4: Overwrite the network address assigned by the manufacturer with one of the options specified in the table.
Enter the chosen MAC address instead of XX:XX:XX:XX:XX:XX
Step 5: Restart the network adapter. Use the following command line command:
To ensure that the selected network adapter is accessible at the MAC address you selected, re-read the network information with “ip link” (see step 1).
Source: iMore
It is that time again. Time to decide whether to keep or replace your Mac laptop or desktop computer. If you are reading this article, chances are you've already come to the decision to replace your Mac with the newes model (or maybe you just got a new Mac as a present!), and you're thinking about selling your old one.
The first thing you should do before hitting the streets to sell your old Mac is clear it of any and all personal data. You don't want to accidentally sell your computer to a stranger when you are still logged into iCloud.
The next step is to reinstall the Mac's operating system so that the new owner can get started without having to figure out how to start up in recovering mode. Believe me, that can be a pain.
If you're going through the process of erasing your old Mac and reinstalling the operating system, we've got some common troubleshooting tips to help you out. Don't forget to follow the additional steps if you're selling a MacBook with Touch ID.
Clean the Mac of your personal data before erasing it
If you're about to sell your old Mac, the one thing you don't want to do is to give away the data you've been storing on it all these years. It's a security and privacy thing for you, but it's also important for the buyer. If you leave behind anything that needs to be logged into with a password, that buyer is going to have to track you down and get your password in order to change ownership. A completely fresh-from-scratch Mac is the best way to do this.
Step 1: Back up your Mac
If you already have your new Mac on hand, you can transfer all of your data from your old Mac or use an older Time Machine backup. If you don't have your new Mac yet, well .. then you probably shouldn't be selling your old one yet. But, if you really don't think you'll need your old computer before getting your new one, just make sure to back up your data so that nothing happens to it before you get what you need onto your new Mac.
Step 2: Sign out of everything
The software you have on your Mac is licensed to you, which means it doesn't get transferred to the new owner of your computer (except the operating system). In order to avoid complications with the new owner attempting to download and install software that is licensed by you, make sure to sign out of everything your personal information is connected to.
How to sign out of iTunes (macOS Mojave and older)
How to sign out of iMessage
How to sign out of iCloud
Step 3: Unpair your Bluetooth devices
If you're keeping your Bluetooth devices, you don't want to leave them paired to a Mac that you're getting rid of. It isn't really that important of a step, but if you sell your old Mac to, say, a roommate or someone living in the same house as you, you may experience accidentally connecting back to it.
Note: If you're unpairing a keyboard, trackpad, or mouse on a desktop Mac, be sure to have a wired one plugged in or you won't be able to type or use a curser and you'll have to repair it all again.
Step 4: Erase your hard drive
Once your data is backed up and you've signed out of everything that might connect your old Mac to your personal information, you can erase everything on it by reformatting the hard drive.
Change Mac Address Of Macbook
Repeat this process for all data disks under your startup disk. Do not use Delete Volume Group. Once you've deleted all of your data drives, you'll move on to erasing your startup disk.
Source: Christine Romero-Chan / iMore
After you erase your hard drive it will be ready for a clean installation of the operating system. You should already be in the Utilities window after erasing your Mac. If not, restart your computer and hold down Command and R at the same time until you see the Apple logo.
Make sure to reinstall macOS through Recovery Mode, holding down Command+R. You may be asked to sign in with your Apple ID.
If you get stuck during reinstallation, see our troubleshooting section for additional help.
Note: Make sure your Mac is connected to the internet in order to verify the software. You'll be asked to do so during the installation process.
If, while reinstalling macOS, you're asked to enter a password, enter the password you use to unlock your Mac, not your Apple ID.
Your Mac is now clean and ready for a new owner. They will complete the setup instructions to get started using the Mac, as well as download the latest macOS operating system that is available and supported on their Mac.
Troubleshooting erasing your hard drive or reinstalling macOS
I've gotten a lot of very specific questions about issues some readers have with erasing or reinstalling macOS (usually reinstalling). Sometimes, the easiest way to fix issues with reinstalling macOS is to start by holding Shift+Option+Command+R which will put your Mac into an alternate version of Recovery Mode that allows you to install the original macOS that came with your Mac. From here, you can either keep that operating system and let the new owner update to their preferred macOS, or go through the macOS update process.
If, during the macOS reinstallation process, the installer doesn't see your disk or says you can't install the operating system on the disk, you may need to try erasing your hard drive again. Restart your Mac and hold down Command+R to bring up Recovery mode and repeat Step 4.
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Since macOS changed to APFS, some readers have struggled with which format option to choose when erasing their disk. Here are some other possible troubleshooting issues from Apple's support document that may help you.
Change Mac Address For Apple Laptop Running Sierra CaAre you formatting the disk that came built into your Mac?
If the built-in disk came APFS-formatted, don't change it to Mac OS Extended.
Are you about to install macOS High Sierra or later on the disk?
If you need to erase your disk before installing High Sierra or later for the first time on that disk, choose Mac OS Extended (Journaled). During installation, the macOS installer decides whether to automatically convert to APFS—without erasing your files:
Are you preparing a Time Machine backup disk or bootable installer?
Choose Mac OS Extended (Journaled) for any disk that you plan to use with Time Machine or as a bootable installer.
Will you be using the disk with another Mac?
If the other Mac isn't using High Sierra or later, choose Mac OS Extended (Journaled). Earlier versions of macOS don't mount APFS-formatted volumes.
To learn which format is currently in use, use any of these methods:
Mac Address For Apple Computer
If you're still having trouble with either erasing your hard drive or reinstalling macOS, please reach out to us in the forums. We have a wonderful community of Apple users that are happy to help someone in need.
Any questions?
Is there anything about resetting your Mac to prepare it for sale that you need help with? Let me know in the comments and I'll get you squared away.
Updated May 2020: Updated for macOS Catalina.
macOS CatalinaMain
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