What Is an ASN?

What Is an ASN?

An ASN (Autonomous System Number) is a unique number assigned to an Autonomous System (AS) - a collection of IP networks and routers under single administrative control. ASNs are used in BGP (Border Gateway Protocol) routing to identify networks and enable internet routing.

ASNs enable networks to exchange routing information, advertise IP address blocks, and participate in global internet routing. ASNs are assigned by Regional Internet Registries (RIRs) like ARIN, RIPE NCC, APNIC, LACNIC, and AFRINIC.

ASNs are essential for internet routing - without ASNs, networks cannot participate in BGP routing and global internet connectivity. Learn more about ARIN and IP address management.

ASN Purpose

1. Network Identification

ASNs uniquely identify autonomous systems on the internet, enabling networks to be distinguished and identified in routing.

2. BGP Routing

ASNs are essential for BGP routing, enabling networks to exchange routing information and participate in global internet routing.

3. Route Advertisement

ASNs enable networks to advertise IP address blocks and routing policies to other networks through BGP.

4. Network Control

ASNs represent networks under single administrative control, enabling centralized routing policy and network management.

5. Internet Connectivity

ASNs enable internet connectivity by allowing networks to connect to other networks and exchange routing information.

Autonomous Systems

What Is an Autonomous System?

An Autonomous System (AS) is a collection of IP networks and routers under single administrative control, operating with consistent routing policy.

AS Characteristics

• Single administrative control
• Consistent routing policy
• Unique ASN identifier
• IP address blocks
• BGP routing capability

AS Types

Autonomous Systems can be: ISPs (Internet Service Providers), enterprises, content providers, or any organization with IP networks requiring internet connectivity.

AS Size

Autonomous Systems can range from small networks with single IP block to large ISPs managing thousands of IP blocks and routers.

AS Independence

Autonomous Systems operate independently with their own routing policies, though they must coordinate with other ASes for internet connectivity.

BGP Routing

What Is BGP?

BGP (Border Gateway Protocol) is the routing protocol used to exchange routing information between autonomous systems on the internet.

BGP and ASNs

BGP uses ASNs to identify networks, enabling routing information exchange and path selection between autonomous systems.

BGP Routing Process

BGP routing process: ASes exchange routing information using ASNs, advertise IP address blocks, select best paths based on routing policies, and maintain routing tables for internet connectivity.

AS Path

BGP AS path shows sequence of ASNs packets traverse, enabling path selection and loop prevention in routing.

BGP Importance

BGP is essential for internet routing - without BGP and ASNs, global internet connectivity would not be possible.

ASN Assignment

RIR Assignment

ASNs are assigned by Regional Internet Registries (RIRs): ARIN (North America), RIPE NCC (Europe), APNIC (Asia-Pacific), LACNIC (Latin America), AFRINIC (Africa).

ASN Types

ASNs come in two ranges: 16-bit ASNs (1-65535, legacy), and 32-bit ASNs (65536-4294967295, extended range for larger address space).

Assignment Requirements

Organizations must demonstrate need for ASN, provide technical justification, and follow RIR assignment policies.

ASN Registration

ASNs are registered in RIR databases, providing information about ASN ownership, IP address blocks, and routing policies.

ASN Lookup

ASN information can be looked up through RIR WHOIS databases, providing ASN ownership and network information.