BGP 4 byte ASN

The internet growth is awesome, day by day people recognizes how internet is important in their daily personal  and business life and even for their culture, so the internet has a good bit of newbie everyday which depleted some internet resources such as IPv4 address space and the BGP AS numbers (IPv4 exhaustion dilemma is more severe than the BGP ASN dilemma).

The BGP AS number space is a finite amount of address space. It is defined as a 16 bit integer and hence limited to 65535 unique AS numbers.

Not all can be used!! Out of the AS number space  there are 1023 numbers are reserved for local or private use, and 3 are reserved for special use. The remaining range which is  64510 numbers are available for publicly use on the internet, today there are 56318  AS numbers already allocated (according to http://www.potaroo.net/tools/asns ).

The 4-byte ASN

In 2007 IETF standardized the BGP support for 4-octet AS number space in RFC4893, following the IETF standards, IANA has extended the AS number field to 32 bits which increasing the pool size from 65535 to 4294967295.

(The 4-byte AS number space is just an extension so it covers the old range and provides more.)

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