What Is a MAC Address, and Why Is It Requested When Setting Up a Phone?
A MAC address is a permanent identifier burned into every network card, in a phone, a computer, or a printer. Unlike an IP address, which changes depending on the network, the MAC address stays with the device. In telephony it is used to identify a specific phone, keep an address for it, and configure it automatically.
What a MAC address is
MAC stands for Media Access Control. Every component that connects to a network (a network card in a computer, an IP phone, a printer, an access point) receives a unique identifier from its manufacturer, set at the factory. That is the MAC address.
The address is made of 12 hexadecimal characters (the digits 0-9 and the letters A-F), and is usually written in pairs: 80:5E:C0:4A:2B:9C. Sometimes the pairs are separated with hyphens (80-5E-C0-4A-2B-9C) or written with no separator at all (805EC04A2B9C). It is the same address in every notation.
If an IP address is the address of the house where you live right now, a MAC address is your ID number: if you move to a new apartment, the address changes, but the ID number stays.
The structure: manufacturer and serial number
The MAC address is divided into two halves. The first six characters identify the manufacturer: every network equipment maker receives its own prefix from an international body (IEEE), called an OUI. The last six characters are a serial number that the manufacturer assigns to each device.
Thanks to this, the address alone can tell you which manufacturer made the device. In a router's device list, phones from the same manufacturer will all appear with the same beginning, and it's easy to tell them apart from computers and printers. Some simple websites identify the manufacturer from the first six characters.
| Part | Example | What it tells you |
|---|---|---|
| Manufacturer prefix (OUI) | 80:5E:C0 | Who made the network card |
| Device number | 4A:2B:9C | The specific device out of everything the manufacturer produced |
MAC vs. IP: what's the difference
| MAC Address | IP Address | |
|---|---|---|
| Who sets it | The manufacturer, at the factory | The network (usually the router's DHCP) |
| Does it change? | No, it stays with the device | Yes, depending on the network it's connected to |
| Where it's relevant | Only on the local network | On the local network and on the internet |
| Example | 80:5E:C0:4A:2B:9C | 192.168.1.57 |
An important point: the MAC address doesn't leave the office. It is used for communication inside the local network, between the phone, the switch and the router. What reaches the internet and the PBX server is the IP address. So a cloud server doesn't "see" the phone's MAC address on its own, unless the phone sends it on purpose, as in automatic configuration.
In plain words: the MAC answers the question "who is the device," and the IP answers the question "where is it on the network right now." Both are needed, and each is used for something different.
Where to find the MAC address on a phone
There are several places, and at least one of them will work:
- A sticker on the back of the phone: almost every IP phone has a sticker with the model, the serial number (S/N) and the MAC address, sometimes with a barcode too. This is the most convenient place, even when the phone is off.
- On the box: the same sticker usually appears on the phone's packaging too. It's worth keeping the box, or taking a photo.
- In the phone's menu: in the "Status," "Info" or "About" menu. On some models you get there by pressing the OK button or the menu button.
- In the phone's admin interface: through a browser, at the phone's IP address, on the status screen.
- In the router's device list: next to each device you'll see its MAC address and the address it received.
On adapters (ATAs) and on the base stations of wireless phones, the sticker is usually on the bottom of the device.
Where to find it on a computer or mobile phone
On a Windows computer: in the command prompt, type ipconfig /all and look for the "Physical Address" line under the network card in use. A computer usually has several addresses, one for the cable and one for Wi-Fi, because each network card gets its own.
On mobile phones, the MAC address appears in Settings, under "About phone" or in the Wi-Fi network details. Note: modern mobile phones use a random MAC address for each Wi-Fi network by default, for privacy reasons. The address the router sees is different from the device's real address, and sometimes changes from time to time.
What this means: if you want to keep a fixed address for a particular mobile phone on the office network, you need to turn off the "random address" option on it for that network. Desk phones and adapters don't have this issue, because their address is fixed.
Why the MAC address is requested when setting up a phone
The most important use in telephony is automatic configuration (provisioning). Instead of typing the username, password and server address into each phone, you prepare a configuration file for each phone in advance and name the file after the phone's MAC address.
When the phone starts up, it contacts the configuration server and asks for "my file." The server identifies it by its MAC address and sends it exactly the settings of its extension: extension 105, with Miriam's name on the display and the secretary's speed-dial buttons. A different phone, with a different MAC, receives the settings of its own extension.
That's why, when you order pre-configured phones or add a phone to the system, we ask for the MAC address. It is what connects the physical device to the extension.
It's important to remember that automatic configuration by MAC is also a layer of order: a phone the system doesn't know, with an address not registered to any extension, won't receive settings. This way a phone that arrived from somewhere else, or a device someone plugged in without coordination, doesn't become an active extension on its own.
Other uses on the network
- Reserving an IP address: in the router's DHCP you can set a device with a certain MAC to always receive the same address.
- Finding a device on the network: when you want to know which IP address a particular phone received, look for its MAC in the router's device list.
- Switches: the switch learns which MAC address is behind each port and sends each packet only to the right port. On a managed switch you can see this table and find out which port each phone is connected to.
- A separate network for phones: some switches identify phones by the manufacturer prefix in the MAC and automatically place them in the phone network (VLAN).
- Access restriction: some networks only allow devices known by their MAC to connect. This is a useful layer of order, but not a substitute for a strong password and security settings, because on several devices you can change the address they display.
Replacing a phone, and the extension that stays
Because in automatic configuration the extension is "tied" to the MAC address, replacing a broken phone requires an update: the new phone will arrive with a different address, and won't receive the old one's settings on its own.
In practice it's a short operation: you update the extension's MAC address to the new phone's address and connect it to the network. It downloads exactly the same settings (the same extension number, the same name, the same buttons), and the user doesn't feel that anything changed except the device.
The same goes when you move a phone between desks. If you want the extension to move together with the person, move the phone. If you want the extension to stay at the desk, leave the phone in place. Its settings go with it, not with the jack.
A real-world example: twenty identical phones
When setting up a collections office (fictitious name: "Direct Collections"), twenty phones of the same model arrived, in the same box, and they looked completely identical. The only difference between them was the MAC address on the sticker.
Before the installation, a simple table was filled in: extension number, employee name, patch panel jack number, and the phone's MAC address. Each phone got a small sticker with the extension number. Thanks to the table, when one phone was replaced half a year later, they knew right away which address to update, and there was no need to take apart any other phone.
Tips for staying organized
- Photograph the sticker of each phone before installing it.
- Keep a table: extension, name, location, jack, MAC.
- Attach a visible extension number to every phone.
- When you replace a phone, update the table the same day.
- Keep the table near the communications closet and also as a digital copy.
MAC addresses in adapters and wireless phones
An adapter for regular phones has one MAC address for the whole device, even if it has several phone jacks. Each jack is a separate extension, but all of them are configured through the same configuration file, which is identified by the adapter's address.
In a wireless phone system, the MAC address belongs to the base station, the box connected to the network by cable. The handsets themselves don't connect to the network directly, so they don't have their own MAC address. They register with the base station, and each handset gets its own extension within the base's settings.
A conference phone, and a desk phone with a computer port, also have one address per phone. The computer connected through it appears on the network with its own MAC address, that of the computer's network card.
When the address can't be read
Sometimes the sticker has worn off, or the phone arrived without a box. In that case, turn on the phone, connect it to the network, and look for it in the router's device list, by the time it connected or by the manufacturer prefix. Another option is the phone's own info menu, which shows the address even without a network connection.
When copying an address by hand, watch out for the classic confusion between the letter O and the digit 0, and between the letter B and the digit 8. A MAC address has no letter O at all, only 0 to 9 and A to F.
How it works with us at Kesher
The phones and adapters we supply (Yealink, Fanvil, Cisco, AudioCodes, Grandstream and the W79P wireless phones) arrive pre-configured. The customer doesn't need to look for MAC addresses or type in settings. You plug it into the jack and the phone works as an extension.
When we set up a communications closet, we label every point on the patch panel, so it's easy to know which phone is connected to which jack.
In the control panel, on the extensions screen, you set for each extension the ring time, the destination when there's no answer, a voicemail box and recording, and all of this stays with the extension even when you replace the device.
When a phone breaks or is replaced, a person at our company answers and helps, not an automated system or a queue for a representative.
FAQ
Where do I find the phone's MAC address?
On the sticker on the back of the phone, on the box, or in the phone's info menu (Status).
Does the MAC address change?
On a desk phone and an adapter, no, it's fixed. Mobile phones usually have a random address for each Wi-Fi network, for privacy reasons.
What is the difference between MAC and IP?
MAC is a permanent identifier of the device, set at the factory. IP is the address the device receives on the network it is connected to, and it changes depending on the network.
Why am I being asked for the MAC address?
To link the physical phone to its extension, so that it automatically receives the right settings.
Can the MAC tell me which manufacturer made the device?
Yes. The first six characters are the manufacturer prefix, and some websites use them to identify the manufacturer.
I replaced a phone, and the new one isn't getting its settings. Why?
Most likely the extension is still registered to the old phone's MAC address. You need to update it to the new address.
Does the MAC address reach the internet?
No. It's used only inside the local network. The IP address is what goes out to the internet.
Is restricting access by MAC enough for security?
It's a convenient layer of order, but not a substitute for strong passwords and proper security settings.
Does a wireless phone have a MAC address for each handset?
No. The address belongs to the base station connected to the network. The handsets register with the base, and each one gets its own extension.
Can I take a configured phone home and connect it to my home router?
Usually yes. The settings are tied to the phone's MAC address and not to the office, so it will connect as a regular extension from any network with internet, as long as the home router is set up properly.