As of now, the 2 bytes AS that we used to know are already depleted so that’s why IETF introduced 4 bytes (0-4294967295) AS. In the router implementation, an ASdot notation or ASplain format will be used to identify a 32-bit AS number. The ASplain format is just writing the whole 0-4294967295 numbers. The problem with this is that it is prone to typo errors. The ASdot format will use this number: <upper 16 bits>.<lower 16 bits>. The first set of 65,536 numbers will be written as 0.0 to 0.65535 and the second set from 1.0 through to 1.65535, and so on.

AS 23456 will play a major part as it is reserved as interface between 16-bit and 32-bit AS. The 32-bit AS numbers will appear as AS 23456 in the new BGP attribute AS4 Path (AS Path on 16-bit). The 32-bit AS number is backward compatible with the 16-bit so one thing that is required is making sure the router supports 32-bit AS under the BGP command process.

If you are having a problem converting the ASplain format to ASdot format, you may try this conversion tool provided by APNIC: 32-Bit Conversion Tool. This tool converts Autonomous System numbers from dot notation to decimal or from decimal to dot notation.

For example: 100500 ASplain is equivalent to 1.34964 ASdot notation.

Below is the IANA assignment for the 32-bit notation: