There currently is no such thing as a 6-byte AS number. Prior to 2007, AS numbers were 2-byte (or 16 bit) numbers ranging from 0-65535 where some of those were reserved for private use (ie, not to be used on the actual internet). Just like IP addresses however, there was a push to expand the number of AS numbers available as the usage continued to go up. So another RFC was published to push AS numbers from 16 bits to 32 bits (2-byte to 4-byte). Since around 2010, IANA has been issuing 32bit AS numbers rather than the older 16bit numbers.
Representation of these numbers look as follows:
For original 16bit AS number (like my personal one)
AS-Plain: 4432
AS-Dot: 0.4432
For newer 32bit AS numbers, you might see something like:
AS-Plain: 65560
AS-Dot: 1.24 (where you computed 1 * 65536 + 24 = 65560)
...
To use your router in "AS-Dot" notation, you need to use the command "bgp annotation dot" then you can use the dot notation in your BGP commands. Be aware that cisco uses "10.1" as an example ASN however they often miswrite what the AS-Plain version of that is (its really a bad example).
AS-Dot: 10.1 = 10 * 65536 + 1 = 655361 (which when written can be confusing if miswritten)
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quick example: if your ASN (AS-Plain) was 66123, then your AS-Dot would be (1 * 65536 + 587) or 1.587
bgp router 1.587
no synchronization
bgp router id 64.22.52.1
bgp annotation dot
bgp log-neighbor-changes
...etc...
Marcos (BGP Engineer since 1992)
