the last ASN of the 32-bit numbers (4,294,967,295) are reserved and should not be used by operators; AS0 is used by all five RIRs to invalidate unallocated space. ASNs 64,496 to 64,511 of the original 16-bit range and 65,536 to 65,551 of the 32-bit range are reserved for use in documentation. ASNs 64,512 to 65,534 of the original 16-bit AS range, and 4,200,000,000 to 4,294,967,294 of the 32-bit range are reserved for Private Use.

The number of unique autonomous networks in the routing system of the Internet exceeded 5,000 in 1999, 30,000