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Comprehensive Guide to ASNs: Everything You Need to Know about Obtaining and Understanding an Autonomous System Number

In this in-depth guide, we will explore the concept of Autonomous System Numbers (ASNs), covering their definition, purposes, and the process of obtaining them. Our aim is to equip you with a comprehensive understanding of ASNs, empowering you to make well-informed choices for your networking requirements.

An Autonomous System Number (ASN) serves as a unique identifier for an Autonomous System (AS) on the Internet, which is a collection of IP addresses and their associated routes controlled by a single organization, such as an Internet Service Provider (ISP) or a large enterprise.

ASNs are essential for the proper functioning of the Border Gateway Protocol (BGP), which facilitates the routing of traffic between different ASes on the Internet. By utilizing ASNs, BGP can efficiently direct data packets to their intended destinations, resulting in a more stable and reliable Internet experience.

The role of ASN

There are two types of ASNs: public and private.

Public ASNs are globally unique and are assigned by authorities like IANA or RIRs. They are used for external BGP connections between ASes on the public Internet.

Private ASNs, on the other hand, are used within organizations for internal purposes and are not globally unique.

Do You Need an ASN?

Determining if your organization needs an ASN depends on your networking requirements. ISPs, multi-homed networks, and large enterprises with complex network topologies typically require ASNs to manage BGP connections and routing policies. For organizations with a single connection to an ISP and straightforward routing needs, obtaining an ASN may not be necessary.

How to Obtain an ASN

If you determine that your organization requires an ASN, follow these steps to obtain one:

  1. Identify your Regional Internet Registry (RIR): Determine the RIR responsible for managing IP addresses and ASNs in your region. The five RIRs are:
    • ARIN (North America)
    • RIPE NCC (Europe, Middle East, and Central Asia)
    • APNIC (Asia Pacific)
    • LACNIC (Latin America and the Caribbean)
    • AFRINIC (Africa)
  2. Register an account with your Regional Internet Registry (RIR) by signing up on their website. This account will be used to initiate the ASN application process.
  3. Complete the ASN application form, providing comprehensive information about your organization and its networking needs. It is crucial to have a clear and justified reason for requesting an ASN, as RIRs assess applications based on demonstrated necessity.
  4. Pay the required application fee, which is usually a one-time charge for obtaining the ASN, and be aware that there might also be an annual maintenance fee. The specific fees can vary depending on the RIR.
  5. Await the approval process. The RIR will review your application and may request additional details or clarifications if needed. Once your application is approved, you will be assigned a unique and dedicated ASN for your organization’s use.

Managing Your ASN

Once you have obtained an ASN, follow these guidelines to manage it effectively:

  1. Configure BGP on your network routers to enable communication with your Internet Service Provider (ISP) or other Autonomous Systems (ASes). Establish BGP sessions with them using your unique ASN.
  2. Implement routing policies that govern how traffic is routed between your AS and other ASes on the Internet. Consider factors like traffic engineering, load balancing, and redundancy to optimize your network’s performance.
  3. Regularly monitor your BGP sessions to ensure their stability and proper functioning. Be prepared to address any potential issues that may arise promptly.
  4. Keep your account information with your Regional Internet Registry (RIR) up to date. It is essential for maintaining your ASN registration and receiving important communications.
  5. Stay informed about BGP and ASN-related topics by actively participating in relevant mailing lists and forums within your RIR community. This will help you stay up-to-date with industry developments and best practices.

ASN Best Practices

To enhance the security and efficiency of your network’s routing, consider implementing the following measures:

ASN and BGP Routing Overview

Consider the following diagram to visualize the role of ASNs in the BGP routing process:

In this illustration, we have four Autonomous Systems: AS 100, AS 200, AS 300, and AS 400, each identified by their respective ASNs. AS 100 has established BGP peering sessions with AS 200 and AS 400, while AS 200 and AS 300 have their own BGP peering sessions. The diagram showcases how ASNs facilitate the exchange of routing information and the proper routing of traffic between these Autonomous Systems.

By comprehending the significance of ASNs and adhering to the best practices mentioned in this guide, your organization can effectively manage its ASN and contribute to a stable and secure global routing infrastructure. Whether you are an ISP, operate a multi-homed network, or manage a large enterprise, acquiring and effectively handling an ASN is vital for ensuring the seamless operation of your network and delivering a dependable Internet experience for your users.

Additional ASN Resources

For further enriching your knowledge about ASNs, BGP, and Internet routing, we recommend exploring the following resources:

  1. RFC 4271 – Border Gateway Protocol 4 (BGP-4): This document serves as the primary specification for BGP, providing detailed information about its features and operations. You can read RFC 4271 here.
  2. RFC 6793 – Increasing the Number of ASNs: This RFC discusses the expansion of the ASN space to accommodate a larger number of ASNs, ensuring the continuous growth of the Internet. You can read RFC 6793 here.
  3. PeeringDB: PeeringDB is a comprehensive database containing information about networks, facilities, and interconnection services. It enables organizations to discover potential peering partners and exchange relevant details. Visit PeeringDB.
  4. BGP Route Monitoring Tools: Several tools are available for monitoring BGP routes, such as BGPStream and RIPEstat. These tools aid in analyzing routing information and detecting real-time anomalies.
  5. Internet Routing Registries (IRRs): IRRs are databases that store routing information, including ASNs, IP prefixes, and routing policies. Network operators use IRRs to configure and maintain routing policies. Some popular IRRs include RADb, RIPE NCC’s IRR, and ARIN’s IRR.
  6. BGP Training and Certification Programs: To enhance your understanding of BGP and ASN management, consider enrolling in training courses or certification programs offered by organizations like Cisco, Juniper Networks, and NANOG. These specialized programs can provide in-depth knowledge about BGP and Internet routing.

By exploring these resources and actively engaging with the networking community, you can establish a strong foundation in ASN management, BGP routing, and Internet infrastructure. This knowledge will not only benefit your organization but also contribute to a more stable, secure, and efficient global Internet.

ASN and Internet Routing Future Trends

As the Internet continues to evolve, the significance of ASNs and effective routing strategies will only become more crucial. Here are some future trends to keep an eye on in the realm of ASNs and Internet routing:

  1. Increased Adoption of RPKI: The focus on Internet routing security will lead to a rise in the adoption of RPKI for route origin validation. Implementing RPKI will enhance the overall security and stability of the Internet routing system.
  2. IPv6 Transition: With the depletion of IPv4 addresses, the transition to IPv6 is inevitable. This shift will impact BGP operations and routing practices, necessitating a familiarity with IPv6-specific routing concepts.
  3. Automation and Machine Learning: Advancements in automation and machine learning will enable network operators to leverage intelligent systems for ASN management and routing policy optimization. These technologies can enhance routing efficiency, anomaly detection, and issue prediction.
  4. Collaborative Security Initiatives: In the face of increasingly sophisticated cyber threats, collaborative security initiatives like MANRS will play a vital role in safeguarding the Internet routing system. Participating in such initiatives will contribute to a more secure Internet.
  5. Inter-domain Traffic Engineering: To optimize traffic flow between ASes, inter-domain traffic engineering techniques like Segment Routing and SDN will gain prominence. Implementing advanced traffic engineering strategies can offer better traffic control and network performance.

By staying informed about these future trends and embracing new technologies and practices, organizations can ensure that their ASN management and routing strategies remain effective and contribute to a stable and secure global Internet infrastructure.

In summary, ASNs play a crucial role in the functioning of the Internet’s routing infrastructure by uniquely identifying Autonomous Systems and enabling efficient traffic routing. By comprehending the significance of ASNs and adhering to effective management practices, organizations can optimize their networks and contribute to a more dependable and secure Internet.

To remain competitive in the ever-changing realm of Internet routing, organizations should continue to enhance their knowledge and expertise in ASN management, BGP routing, and related technologies. Embracing upcoming trends, adopting robust security measures, and engaging in collaborative initiatives will empower network operators to maintain effective routing strategies that adapt to the evolving demands of the global Internet.

Success in ASN management and Internet routing hinges on continuous learning, cooperation, and innovation. By dedicating resources to these aspects and maintaining a strong foundation in best practices, your organization will be well-prepared to thrive in the intricate domain of ASNs and the global Internet routing landscape.


Evgeny Sevastyanov

Client Support Teamleader

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