MAC Addresses Explained

officialcertbroCisco CCNA

What is a MAC Address? MAC stands for Media Access Control. It’s a unique identifier that is assigned to a network interface card, aka NIC.

This is what a MAC address looks like.

The first thing to note is that unlike IP addresses, which and can be changed, MAC addresses are unique, and cannot. Think of them like they’re set in stone. Burnt into NIC by the manufacture.

The address is 48 bits long, or 6 bytes.

The address has 2 sections. The first 24 bits (3 bytes) is called the organizationally unique identifier or OUI. It identifies the vendor. The last 24 bits (3 bytes) is a unique value assigned by the vendor.

Types of MAC Address

There are three types of MAC address.

Unicast – A particular, unique address, that identifies a single network interface card. The above example is a unicast address.
Multicast – A MAC address for an application or protocol. This will be sent to all device but only those with that application or protocol will listen.
Broadcast – A MAC address that is sent to all devices within a network. A broadcast address looks like this FF-FF-FF-FF-FF-FF.

Vendor Formats

It’s important to note, that there is more than one way to show a MAC address and it changes from vendor to vendor. Here are three ways to display the same address.

The top one is 6 groups of 2 digits separated by colons. This is typically how Linux and Apple will display their MAC addresses.

The middle one is again 6 groups of 2 digits but this time separated by dashes. This is how Microsoft display their MAC addresses

Lastly, the bottom displays the address as 3 groups of 4 digits. This is how Cisco display their MAC addresses.

Although you likely see the bottom Cisco format when going through the CCNA exam, you’ll need to be able to look at all three of these and think “That is a MAC address!”.

Why do we need MAC Addresses?

OK, so I know what you’re probably thinking. We already have IP addresses so why do we need MAC addresses?

Let’s look at an example. We have 4 computers and a switch.

Switches are commonly layer 2 devices. When our computers are talking in the local area network (LAN) this is layer 2 communication. Layer 2 communication uses MAC addresses.

When we leave our network, this is when the IP addresses are used. Routers are layer 3 devices and they mainly focus on IP addresses to get the data to the destination.

Find Your Own MAC Address

Let me show you how to check your MAC address at home.

On windows, you simply open a command prompt or PowerShell and type ipconfig /all to see you interface settings.

Find your interface, you might have more than one if you have a wireless interface, and look for the physical address.

ipconfig /all

For Linux or Apple devices, open a terminal and type ifconfig
and look for the ether address.

ifconfig

You should now know what a MAC address is, the format, what it’s used for and how to find your own.

I hope this was useful and thank you for reading.

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