BLE Random Address Type Bits

BLE random device addresses use the two most significant bits of the random address to indicate the address type.

One easy way to remember it is to look at the top two bits of the most significant byte.

• Address type bits
• Byte order note
• Quick check

Address type bits

Byte order note

The table is about the most significant byte of the 48-bit random address.

This matters because Bluetooth addresses are often printed in human-readable order, for example:

C2:34:56:78:9A:BC

In that representation, C2 is the most significant byte, so the top bits are 11 and the address is a static random address.

In code, however, addresses are often stored little-endian in a six-byte array. In that case the byte that contains these type bits may be the last byte of the array, not the first one printed.

Quick check

If the most significant byte is:

• 0x23, top bits are 00, so it is a non-resolvable private address
• 0x5A, top bits are 01, so it is a resolvable private address
• 0x91, top bits are 10, so it is reserved
• 0xD4, top bits are 11, so it is a static random address

So the compact rule is:

00 = non-resolvable private
01 = resolvable private
10 = reserved
11 = static random