What are MA-L, MA-M and MA-S?

MA-L, MA-M and MA-S are the three sizes of address block the IEEE Registration Authority assigns. An MA-L block contains 16,777,216 EUI-48 addresses (2^24), an MA-M block contains 1,048,576 (2^20) and an MA-S block contains 4,096 (2^12). An organization buys the smallest block that covers its needs, and the size it bought decides how many hexadecimal digits a lookup must read before it can name the registrant.

How large is each block?

• MA-L — MAC Address Block Large, 2^24 addresses. It includes the 24-bit OUI and covers the first three octets of an address. This is what an OUI assignment was before 1 January 2014, and MA-L is the current name for it.
• MA-M — MAC Address Block Medium, 2^20 addresses. It is identified by a longer base than an OUI, so the registrant is only visible once more than the first three octets are read.
• MA-S — MAC Address Block Small, 2^12 addresses. It assigns a 36-bit OUI-36 (nine hexadecimal digits) and does not include a 24-bit OUI of its own — the first 24 bits of an MA-S block belong to an OUI held by the IEEE Registration Authority.

Each block also provides EUI-64 identifiers: 2^40 from an MA-L, 2^36 from an MA-M and 2^28 from an MA-S. Those are used by other protocols rather than by Ethernet or Wi-Fi addressing.

Why the block size changes a lookup

A lookup has to test prefixes of 24, 28 and 36 bits, and stop at the longest one that matches. These three records come from the live lookup:

• MA-L. EC:0D:51 → Apple, Inc., 16,777,216 addresses.
• MA-M. 38:B1:4E:6 → Universal Robots A/S, 1,048,576 addresses. 38:B1:4E on its own resolves to the IEEE Registration Authority.
• MA-S. 70:B3:D5:00:1 → SOREDI touch systems GmbH, 4,096 addresses. 70:B3:D5 on its own is an IEEE Registration Authority block.

The pattern is the same in the MA-M and MA-S cases: the shorter prefix belongs to the registry that carved the smaller block out, and only the full prefix names the organization using it. A tool that checks three octets and stops will report the wrong organization for those addresses — see how a lookup works.

What about CID and IAB?

Two further IEEE identifiers appear in MAC data and are not MAC address blocks:

• IAB (Individual Address Block) is retired. It was replaced by MA-S on 1 January 2014, and holders of an existing IAB may keep using it until it is exhausted. An IAB provided exactly 4,096 EUI-48 identifiers and no EUI-64 identifiers. 00:50:C2:00:1 is an IAB record: the lookup returns JMBS Developpements with the type IAB.
• CID (Company ID) is a 24-bit identifier the IEEE assigns for applications where unique MAC addresses are not required. The IEEE states that a CID cannot be used to generate universally unique MAC addresses: identifiers built from a CID have the local bit set, so they are local addresses that a network administrator is responsible for keeping unique within their own span of use. A CID has no block size to state.

Who assigns these blocks?

The IEEE Registration Authority, which publishes the registry of assignments. MACLookup matches addresses against that data and reports the assignment type with every result, as the API documentation describes.