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Autonomous System Number (ASN)

Last updated: April 24, 2020

What Does Autonomous System Number (ASN) Mean?

An autonomous system number (ASN) is something that businesses or other parties have to get from internet domain registrars, in order to set up internal network systems that interface with other networks over the Internet.

This procedure creates efficiencies in handling all of the different IP addresses that go into the global Internet.

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Techopedia Explains Autonomous System Number (ASN)

Here's how this typically works — a business sets up a phone or data and voice network with various workstations or individual nodes. Maybe each of these is for an individual person in an office where many people work together.

The company wants to enable this pool of internal nodes to contact the outside world through the same gateway to the global Internet. So the company would get all of the resources together, wire the systems together, and give each workstation an internet protocol or IP address.

Then it would get the autonomous system number from the proper authority and use that to establish a single gateway point.

Specifically, the nodes inside of an autonomous system communicate with each other through an Internal Gateway Protocol (IGP) and then send signals to and from the external internet through a Border Gateway Protocol (BGP).

As a type of "path vector protocol," BGP makes routing decisions with considerations of network admin rule sets and other guidance.

In order to get the autonomous system number, the company or other party has to petition the Internet Assigned Numbers Authority or IANA through one of five global Regional Internet Registries or RIRs. Regional offices are set up for Africa, America, Asia, Latin America and the Caribbean, and Europe.

Basically, the autonomous system allows voice over IP systems to benefit from the same kinds of functionality that you had with PBX systems in the days of the telephone landline prior to the emergence of voice over internet.

As phone systems evolved, businesses started wanting to route all calls through a single network point, so models emerged where each individual telephone line would be tied to a “trunking” setup that parceled out calls according to their intended destination.

Then, too, the autonomous system can provide for various end nodes to send and receive data through the internet. The point is that the party that's getting the autonomous system number is benefiting from having a bunch of different end user nodes or lines connected to one central gateway to the internet, or as we used to call it, the “information superhighway”.

The ASN is one way that regulators handle the vast amount of data communications happening over the internet through the enormous number of nodes consisting of machines and devices with IP addresses.

Provisions like autonomous systems are even more important now, as internet-connected devices and IP addresses proliferate. In order to handle the numbers, the IANA and associated groups have moved from a system called IPv4 to a new system called IPv6, where additional numerical capacity can help to manage growth in demand.

However, the transition from IPv4 to IPv6 is not yet complete, and it remains to be seen how well the current system will do in handling new demand over time.

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