IEEE also publishes a list of already existing OUIs. The registration is made by IEEE and costs around 1000$ - 3000$. You also have the option to register a MAC prefix (with b1=0) for your own purposes. Generating only one MAC prefix allows us to generate enough addresses for the biggest assignable private network.Ĭool thing, and we know that if we want to use it locally we only have to set the second bit in the first byte of this mac address to 1.

There are three private IPv4 address ranges specified in RFC1918:

You may think now “Hey that’s exactly the size of the biggest usable local network”. Using only the last 3 bytes we can generate up to 16^6 or 2^24 addresses which is exactly the size of a “/8 sized network. We assume that these 3 bytes are fixed for now. Some mathĪs we now know that the first 3 bytes are reserved, let’s call them the MAC prefix here. The b1 bit states if a MAC address is globally unique (0) or locally administered (1). The b0 bit states if this MAC address is a unicast (0) or a multicast (1) address. Important here are the first two bits of the first byte. If you divide these 6 octets by two, the first 3 are the so-called Organizationally Unique Identifiers (OUI), and the last 3 refer to a manufacturer-specific number. The basicsĪ MAC address or Media Access Control address is a unique hardware identifier address, often referenced as physical or hardware address.Ī classic (IPv4 referring) MAC address has 48 bits or 6 bytes, and is expressed in hexadecimal digits separated by colons between each of the 6 octets. ( The chance of a conflict is around 1/(2^48) x (count of MAC addresses in your environment) by assuming you just pick a MAC address at random.)īut anyway, sometimes you want to do things right, and understand how MAC addresses are generated in general, and how to create local MAC addresses.

You could probably just copy and paste an existing MAC address that is not used in your environment, because statistically spoken there is very low chance of generating conflicts here. Sometimes you may need a random MAC address for a purpose such as overwriting the existing one or in virtualization scenarios. In this post I will cover the topic of MAC address generation and dive into the IEEE 802 standard.

Mac addresses list