An autonomous system (AS) is a network with its own routing policies and an assigned Autonomous System Number (ASN). The Internet Protocol (IP) is the protocol used for communication between computer systems and is responsible for moving packets of information. To become a public autonomous system, the AS must have a clear internal routing plan, be able to indicate which networks are reachable, and be connected to more than one other AS. There are three categories of autonomous systems: multihomed, autonomous transit, and stub. ASNs are assigned by regional Internet registries.
An autonomous system (AS) is essentially a network that has different policies than the networks or service providers to which it is connected. The network consists of a group of connected Internet Protocol routing prefixes controlled by a network operator. To be accepted as an autonomous system, the network must demonstrate that it has a clearly defined routing policy. The AS is then assigned an Autonomous System Number (ASN) to identify it.
The format and rules for exchanging messages between computer systems is called a protocol. A protocol describes the syntax and vocabulary to be used in communication, as well as how communications will be synchronized. It can also establish rules for signal authentication and error detection. The Internet Protocol (IP) is the protocol that makes up most of the Internet.
IP is responsible for moving packets of information between computer networks. An IP routing prefix or IP address is used to send these packets from a source network to a destination network in the same way that a mail address ensures that a letter reaches the correct recipient.
Like a postal service, a group of IPs can have rules about how information must be packaged, sorted, and routed in order to be sent. If the rules meet certain criteria, the group of IPs can be assigned an autonomous system number and become a public autonomous system. First, the AS must have an internal routing plan that is clear to other autonomous systems. Second, other autonomous systems should be able to clearly indicate which networks are reachable via the AS in question. Finally, the AS should be connected to more than one other AS.
There are three different categories of autonomous systems. The multihomed AS maintains connections to multiple service providers. This allows the user to have a different policy than the service providers. Autonomous transit systems provide connections to other networks. Internet service providers are an example of this type of system.
The latter type of system is not a true autonomous system. It is connected to only one other AS and should technically fall under the service provider’s AS. A stub can only become its own autonomous system if its policies are sufficiently different from those of the service provider.
ASNs are assigned by regional Internet registries. These registries obtain sets of numbers from the Internet Assigned Numbers Authority (IANA). They then assign numbers to local groups from these sets. Current assignments are listed on the IANA website.
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