BGP (Border Gateway Protocol) is a protocol used for exchanging routing information between different networks in the Internet. BGP Autonomous System (AS) numbers are used to identify unique networks on the Internet. These AS numbers are assigned by the Internet Assigned Numbers Authority (IANA) to Internet Service Providers (ISPs) and other organizations that run networks.
There are two types of AS numbers: public and private.
Public AS numbers are globally unique and are used for routing traffic on the Internet. Public AS numbers are assigned by IANA to organizations that provide Internet connectivity to customers. Public AS numbers range from 1 to 65,535.
Private AS numbers are used within private networks and are not globally unique. Private AS numbers are used by organizations that do not provide Internet connectivity, but still need to run BGP within their private network. Private AS numbers range from 65,536 to 65,635, and from 420,000,0000 to 4294967294.
The main difference between public and private AS numbers is that public AS numbers are globally unique and are used for routing traffic on the Internet, while private AS numbers are used within private networks and are not globally unique. Private AS numbers are often used by organizations that need to run BGP within their private network, but do not want to use public AS numbers.
It's important to note that using private AS numbers within a private network does not impact the routing of traffic on the public Internet. When traffic leaves a private network and enters the public Internet, it is still routed based on the public AS numbers used by the ISPs and other organizations that provide Internet connectivity.