Qu'est-ce qu'un ASN ?
Tout ce que vous devez savoir sur les Numéros de Système Autonome — la colonne vertébrale du routage internet et de la connectivité BGP.
What is an Autonomous System Number?
An Autonomous System Number (ASN) is a unique identifier assigned to a group of IP networks that are operated by one or more network operators under a single, clearly defined routing policy. ASNs are the fundamental building blocks of the internet's routing infrastructure, enabling networks to communicate their identity and exchange traffic efficiently.
Every network that participates in BGP (Border Gateway Protocol) routing requires an ASN. When your network peers with other networks or announces IP prefixes to the global routing table, your ASN serves as the identifier that distinguishes your network from every other network on the internet.
ASNs are assigned by the five Regional Internet Registries (RIRs): ARIN (North America), RIPE NCC (Europe, Middle East, Central Asia), APNIC (Asia-Pacific), LACNIC (Latin America and Caribbean), and AFRINIC (Africa). Each RIR has its own allocation policies and procedures, but the core requirements are consistent across all regions.
Why Do ASNs Exist?
The internet is composed of tens of thousands of independently operated networks. For traffic to flow between these networks, there must be a standardized way to identify each network and communicate routing decisions. ASNs provide this identification layer, allowing routers to build a map of the internet and determine the best path for each packet.
Without ASNs, it would be impossible to implement peering agreements, establish multi-homed connections for redundancy, or enforce independent routing policies. ASNs are what make the decentralized architecture of the internet possible — every network can make its own routing decisions while remaining globally interconnected.
Unique Identification
Each ASN uniquely identifies a network operator and their routing policy, preventing conflicts and ambiguity in the global routing table.
Routing Policy
ASNs allow network operators to define and enforce their own routing policies, controlling how traffic enters and exits their network.
Multi-homing
Organizations with multiple upstream providers need an ASN to announce their prefixes independently and maintain connectivity if one provider fails.
Peering
Internet exchange points and direct peering agreements rely on ASNs to identify participating networks and establish BGP sessions.
How to Get an ASN
To obtain an ASN, you must apply through a Regional Internet Registry (RIR) or through an LIR (Local Internet Registry) / sponsor that holds a membership with the relevant RIR. The specific process varies by region, but the fundamental requirement is demonstrating a legitimate need for a unique routing policy.
The most common requirement is that your network must be multi-homed — connected to at least two different upstream internet service providers. This ensures that you genuinely need an independent ASN rather than simply using your provider's AS. You'll also need to document your routing policy and provide technical details about your network infrastructure.
The typical timeline for ASN registration is 2–4 weeks, depending on the RIR and the completeness of your application. Costs vary by region: RIPE NCC charges through the sponsoring LIR, ARIN has a one-time registration fee plus annual maintenance, and APNIC includes ASN resources under its membership tiers. Working with an experienced broker like IPv4Center can significantly accelerate the process.
ASN and BGP Routing
ASNs and BGP are inseparable — BGP (Border Gateway Protocol) is the routing protocol that uses ASNs to exchange routing information between networks. When a network announces an IP prefix via BGP, the announcement includes the originating ASN and the complete AS-PATH, which records every ASN the route has traversed.
There are two forms of BGP: eBGP (external BGP) is used between different autonomous systems to exchange routes across network boundaries, while iBGP (internal BGP) is used within a single autonomous system to distribute external routing information to internal routers. Both are essential for large-scale network operations.
The AS-PATH attribute is one of the most important elements in BGP route selection. Routers typically prefer routes with shorter AS-PATHs, as fewer network hops generally mean lower latency and higher reliability. Network operators can also use AS-PATH filtering to accept or reject routes based on which networks they traverse.
eBGP Peering
External BGP sessions connect different autonomous systems, enabling route exchange between networks at internet exchange points or via private interconnects.
iBGP Internal
Internal BGP distributes externally learned routes within an autonomous system, ensuring all routers have consistent routing information.
AS-PATH Attribute
The AS-PATH records the sequence of ASNs a route has traversed, used for loop prevention and path selection in BGP decision-making.
Route Filtering
Network operators use ASN-based filters to control which routes are accepted or advertised, implementing their routing policy and security requirements.
Types of ASN
ASNs come in two sizes: 16-bit and 32-bit. The original 16-bit ASN range (0–65535) was defined in RFC 1930 and quickly became a scarce resource as the internet grew. To address this, 32-bit ASNs (RFC 6793) were introduced, expanding the total pool to over 4.2 billion unique numbers. Today, most new allocations are 32-bit ASNs, and all modern BGP implementations support them.
ASNs are also classified as public or private. Public ASNs are globally unique and used for routing on the public internet. Private ASNs (64512–65534 for 16-bit, and 4200000000–4294967294 for 32-bit) are reserved for internal use within an organization and must not appear in the global routing table. Private ASNs are commonly used in stub networks that peer with a single upstream provider using BGP.
16-bit ASN
The original format with a range of 0–65535. Most legacy networks use 16-bit ASNs. The pool is nearly exhausted, making them increasingly scarce.
32-bit ASN
Extended format with a range up to approximately 4.2 billion. All new ASN allocations are 32-bit. Represented in "asplain" notation (e.g., AS200001).
Public ASN
Globally unique ASNs assigned by RIRs for use on the public internet. Required for any network that peers with multiple providers or participates in IXPs.
Private ASN
Reserved ranges (64512–65534, 4200000000–4294967294) for internal use. Must be stripped from BGP announcements before reaching the global routing table.
ASN Registration at IPv4Center
IPv4Center provides end-to-end ASN registration services across all five Regional Internet Registries. Whether you need an ASN under RIPE NCC, ARIN, APNIC, LACNIC, or AFRINIC, our experienced team handles the entire process — from initial application and documentation to RIR coordination and final allocation.
For organizations without direct RIR membership, we offer ASN sponsorship services through our LIR accounts. This eliminates the need for your own RIR membership, significantly reducing costs and administrative overhead. Our typical turnaround time is 5–10 business days, and we provide ongoing support for RPKI setup, route object creation, and IRR database registration after your ASN is allocated.
Questions Fréquentes
Questions courantes sur les Numéros de Système Autonome et l'enregistrement d'ASN.
Vous avez besoin d'un ASN si votre réseau est connecté à plusieurs fournisseurs en amont (multi-homing), si vous prévoyez de peerer aux points d'échange internet (IXP) ou si vous devez mettre en œuvre une politique de routage indépendante. Les réseaux connectés à un seul FAI n'ont généralement pas besoin de leur propre ASN.
Les coûts d'ASN varient selon le RIR. Sous RIPE NCC, les ASN sont obtenus via un LIR sponsor avec des frais annuels allant typiquement de 50 à 500€ selon le LIR. ARIN facture des frais d'enregistrement uniques de 500$ plus des frais annuels de 100$. APNIC inclut les allocations d'ASN dans ses niveaux d'adhésion. IPv4Center propose des forfaits compétitifs d'enregistrement d'ASN auprès de tous les RIRs.
L'enregistrement standard d'un ASN prend 2 à 4 semaines par demande directe au RIR. Avec le service accéléré d'IPv4Center, la plupart des enregistrements d'ASN sont terminés en 5 à 10 jours ouvrables. Le délai dépend du RIR, de l'exhaustivité de votre documentation et de la nécessité d'une justification supplémentaire.
Un ASN privé est un numéro de la plage réservée (64512–65534 pour 16 bits, 4200000000–4294967294 pour 32 bits) destiné uniquement à un usage réseau interne. Les ASN privés sont utilisés lorsque vous avez besoin de BGP en interne mais n'avez pas besoin d'un numéro globalement unique. Ils doivent être supprimés des annonces de route avant d'atteindre l'internet public.
Oui, les ASN peuvent être transférés entre organisations, bien que le processus varie selon le RIR. RIPE NCC et ARIN prennent tous deux en charge les transferts d'ASN. Le transfert implique la mise à jour des registres d'inscription pour refléter le nouveau titulaire. IPv4Center peut faciliter les transferts d'ASN et gérer toutes les exigences administratives auprès du RIR concerné.
Vous devez vous enregistrer auprès du RIR qui couvre la région où se trouve principalement votre infrastructure réseau : ARIN pour l'Amérique du Nord, RIPE NCC pour l'Europe et le Moyen-Orient, APNIC pour l'Asie-Pacifique, LACNIC pour l'Amérique latine et AFRINIC pour l'Afrique. Si vous opérez à l'échelle mondiale, l'emplacement de votre centre de données principal détermine généralement le RIR approprié.