Based on RFC 4271, '''Autonomous System (AS)''' is defined as a set of routers under a single technical administration, using an interior gateway protocol (IGP) and common metrics to determine how to route packets within the AS, and using an inter-AS routing protocol to determine how to route packets to other ASes.The [[NWG|Network Working Group]] explained that since the introduction of this definition, several IGP is commonly used for a single AS and several sets of metrics within an AS is sometimes used. The NWG also explained that the administration of an AS to other ASes still emerge with a single coherent interior routing plan and a consistent picture of the destinations that are reachable through it even when multiple IGPs and metrics are utilized.<ref>[http://tools.ietf.org/html/rfc4271 RFC 4271]</ref>
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Based on RFC 4271, '''Autonomous System (AS)''' is defined as a set of routers under a single technical administration, using an interior gateway protocol (IGP) and common metrics to determine how to route packets within the AS, and using an inter-AS routing protocol to determine how to route packets to other ASes.The [[NWG|Network Working Group]] explained that since the introduction of this definition, several IGP is commonly used for a single AS and several sets of metrics within an AS is sometimes used. The NWG also explained that the administration of an AS to other ASes still emerge with a single coherent interior routing plan and a consistent picture of the destinations that are reachable through it even when multiple IGPs and metrics are utilized.<ref>[http://tools.ietf.org/html/rfc4271 RFC 4271- A Border Gateway Protocol 4]</ref>