Autonomous System Number

Definition of Autonomous System Number

An Autonomous System Number (ASN) is a unique numerical identifier assigned to an Autonomous System (AS), which is a group of IP networks and routers under the control of a single organization that presents a common routing policy to the internet. ASNs facilitate the exchange of routing information between different ASes, allowing for optimal traffic routing across the internet. These numbers are managed and allocated by the Internet Assigned Numbers Authority (IANA) and are essential for efficient global routing.


The phonetics of the keyword “Autonomous System Number” would be:A – æ (as in ‘cat’)u – j (as in ‘you’)t – t (as in ‘top’)o – oʊ (as in ‘go’)n – n (as in ‘no’)o – ə (as in ‘sofa’)m – m (as in ‘man’)o – ʌ (as in ‘up’)u – ju (as in ‘cute’)s – s (as in ‘sleep’)S – ɛ (as in ‘set’)y – aɪ (as in ‘my’)s – s (as in ‘sleep’)t – t (as in ‘top’)e – ɛ (as in ‘set’)m – m (as in ‘man’)N – n (as in ‘no’)u – ʌ (as in ‘up’)m – m (as in ‘man’)b – b (as in ‘day’)e – i (as in ‘me’)r – ɚ (as in ‘her’)

Key Takeaways

  1. An Autonomous System Number (ASN) is a unique numerical identifier assigned to an autonomous system consisting of networks under a single administration.
  2. ASNs are crucial for Border Gateway Protocol (BGP) which is responsible for exchanging routing information and maintaining the overall internet connectivity between different autonomous systems.
  3. ASNs can be of two types: 2-byte ASNs (ranging from 1 to 65,535) and 4-byte ASNs (ranging from 65,536 to 4,294,967,295), catering to the increasing demand for unique identifiers as the internet continues to grow.

Importance of Autonomous System Number

The term Autonomous System Number (ASN) is important in technology because it plays a crucial role in ensuring the smooth functioning of the internet by facilitating the routing of data between different networks.

ASNs provide a unique identifier for each autonomous system—a collection of IP networks and routers under a single organization’s control—that participates in the global internet routing system.

They allow Internet Service Providers (ISPs) and other large network operators to exchange routing information through the Border Gateway Protocol (BGP), making sure that data packets can travel effectively between different networks to reach their intended destinations.

The efficient and seamless functioning of ASNs guarantees the stability and accuracy of internet routing, enabling users to communicate and exchange information effortlessly around the world.


An Autonomous System Number (ASN) serves a crucial role in internet routing and ensures the proper organization and delegation of authority in the allocation of IP addresses. To understand its purpose, it is essential to first grasp the concept of an Autonomous System (AS). An AS is a group of IP networks and routers under the control of one single organization that presents a common routing policy to the internet.

By consolidating multiple networks and their routing policies, ASNs allow for a more efficient and structured approach to managing connections and the exchange of routing information between these different networks. This is particularly important as the internet continues to grow, and effective methods for organizing IP networks become increasingly critical.

ASNs serve as unique identifiers which, in tandem with the Border Gateway Protocol (BGP), help ascertain the best available path to deliver data packets across distinct Autonomous Systems. By assigning an ASN, network operators are able to represent their network policies and topologies to other networks while avoiding overlapping use and confusion of network addresses.

These unique, assigned ASNs enable operators to manage the selection of routing paths and policies between ISPs, and allow for proper communication between various organizations. Consequently, the ASNs play a pivotal part in interdomain routing, ensuring the smooth and efficient exchange of data among a vast collection of networks spanning the entire global internet.

Examples of Autonomous System Number

Autonomous System Numbers (ASNs) are crucial for the proper functioning of the internet’s routing structure. Each Autonomous System (AS) is a collection of IP addresses, controlled by a single organization such as an ISP or a large enterprise network, that presents a common routing policy to the rest of the internet. As a helpful assistant, here are three real-world examples involving the use of ASNs:

Google’s Global Network (ASN: 15169): Google’s AS15169 is responsible for managing a massive number of IP addresses required to offer services like Gmail, YouTube, and Google Search. Google’s ASN allows them to control routing within their network and communicate with other ASNs, ensuring that internet users around the world have reliable access to Google services.

AT&T (ASN: 7018): AT&T is a major Internet Service Provider (ISP) in the United States. With an ASN of 7018, it manages a broad range of IP address spaces that serve millions of customers across the country. The ASN enables AT&T to implement routing policies and efficiently exchange traffic with other ISPs and organizations worldwide, ensuring seamless internet connectivity for its users.

CERN (ASN: 513): The European Organization for Nuclear Research (CERN) is a top-tier research institution responsible for groundbreaking discoveries in particle physics, such as the Higgs boson. Given the massive amount of data generated by experiments at CERN, their ASN (513) ensures efficient data transfer and communication within their network and with affiliated research institutions, enabling the global scientific community to access and share critical information.

Autonomous System Number FAQ

What is an Autonomous System Number (ASN)?

An Autonomous System Number (ASN) is a unique identifier assigned to an autonomous system (AS) in order to route Internet Protocol (IP) packets on a global network. An autonomous system is a collection of IP networks and routers under the control of a single organization that presents a common routing policy to the rest of the internet.

Who assigns ASNs?

ASNs are assigned by the Internet Assigned Numbers Authority (IANA) and managed by Regional Internet Registries (RIRs) such as ARIN, RIPE, APNIC, LACNIC, and AFRINIC.

Why are ASNs important?

ASNs play a crucial role in maintaining the global routing table and ensuring optimal connectivity between networks. They enable routers to exchange information about the best routes to reach specific IP addresses, facilitating efficient communication between systems across the internet.

What are the types of ASNs?

There are two types of ASNs: 2-byte and 4-byte. 2-byte ASNs have a range from 1 to 65,535, while 4-byte ASNs range from 65,536 to 4,294,967,295. 4-byte ASNs were introduced to accommodate the growing demand for additional autonomous systems on the internet.

How do I obtain an ASN for my network?

To obtain an ASN, you must contact your respective Regional Internet Registry (RIR) and submit an application. The RIR will assess your need for an ASN and provide one if it is deemed necessary for your network’s routing requirements.

Related Technology Terms

  • Border Gateway Protocol (BGP)
  • Internet Assigned Numbers Authority (IANA)
  • Regional Internet Registry (RIR)
  • Internet Service Provider (ISP)
  • Routing Policy Specification Language (RPSL)

Sources for More Information


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