Autonomous System (AS) is a collection of connected Internet Protocol (IP) routing prefixes under the control of one or more network operators that presents a common, clearly defined routing policy to the Internet. From 01/01/2007, International number registries brought to use 32 bit ASN. In AP region, since 01/01/2009, 4byte ASN was issued for all application on default basis.
In Vietnam, VNNIC required its IP members to improve network equipment OS to support ASN 4 byte since 01/01/2009. From 10/06/2009, VNNIC issued 4 byte ASN for all application on default basis. Any member applying 2 byte ASN must provide clarification and explanatory document.