ASN Lookup - Check AS WHOIS (2024)

Before proceeding further, one must understand the concept of Autonomous System (AS)?

In short, AS, the Autonomous System is a connected group of one or more IP networks under the control of network operator(s) with a common and clearly defined external routing policy.

In other words, it is a network or the collection of the networks, managed or supervised by a single entity or organization.

Autonomous system number is the globally unique identifier that identifies and allows its autonomous system to exchange routing information with other independent systems.

For multiple autonomous systems to interact, each needs to have a unique identifier. Therefore, when an AS wants to exchange routing information with other AS on the public internet, it should register ASN.

Note: Different autonomous systems use an External routing policy to exchange the routing information between them.

Globally, the Internet Assigned Numbers Authority (IANA) is responsible for communicating information like IP addressing, DNS Root, and other internet protocol resources, including ASNs.

IANA assigns ASNs to regional internet registries (RIRs), which manage internet number resources in a particular region of the world.

There are currently five regional internet registries (RIRs) working in a particular region of the world.

• African Network Information Center (AFRINIC).
• American Registry for Internet Numbers (ARIN).
• Asia-Pacific Network Information Centre (APNIC).
• Latin American and Caribbean Network Information Centre (LACNIC).
• Réseaux IP Européens Network Coordination Centre (RIPE NCC).

These RIRs operate under the umbrella of the Number Resource Organization (NRO). The primary purpose of NRO is to provide an open, stable, and secure internet by coordinating RIR activities and projects.

There are two types of Autonomous System Number (ASN).

• Public Autonomous System Number (ASN)
• Private Autonomous System Number (ASN)

Public Autonomous System Number (ASN) is required only for the autonomous system that wants to exchange information over the internet. It is needed on the public internet when one AS intends to exchange the routing information with another.

Private Autonomous System Number (ASN) is required only for the autonomous system that wants to communicate solely with a single provider via Border Gateway Protocol (BGP). Because the routing policy between the autonomous system and the provider is not visible on the internet, it can use a private autonomous system number.

RFC6996: For private use, IANA has reserved

• A contiguous block 64512 – 65534 (1023 ASNs) from the 16-bit ASNs registry.
• An adjacent block 4200000000 – 4294967294 (94,967,295 ASNs) from the 32-bit ASNs registry.

Before obtaining an autonomous system, one must check whether its eligible for a public AS number.

An organization can obtain a public AS number if

• The organization is currently multihomed.
• Or it needs to interconnect with another AS.

On fulfilling one of the conditions mentioned above, you can submit an ASN request to one of the regional internet registries (RIRs). After the approval, you must sign a Registration Services Agreement and pay a container fee for your ASN.

There are four types of autonomous systems that require ANS.

• Multihomed: An AS that connects to more than one or multiple autonomous systems.
• Stub: An AS that connects to only one other autonomous system.
• Transit: An AS that provides connections through itself. For example, network A can connect directly to network C by crossing over network B.
• Internet exchange point: A physical infrastructure that ISPs or content delivery networks (CDNs) use to exchange internet traffic between their networks.

Until 2007, all autonomous system numbers were 16 bits or 2 bytes, which resulted in 65,536 possible ASNs for allocation. But just like the IPv4 range, that amount of ASNs was always destined to run out.

Therefore, they created new 4-byte (32-bit) ASNs to solve that issue, which resulted in 4,294,967,296 possible ASNs to distribute.

With the switch to new 4-byte (32-bit) ASNs, people were much concerned that number representation would become too complicated. IANA created two alternative ways for number representation to mitigate those concerns.

• Asplain is the standard method to display the number, which is a simple decimal representation.
• The asdot+ method breaks down the number into 16-bit values of low and high-order and separates them by a dot.
• The asdot method is a mixture of asplain and asdot+. Any number in the 2-byte range is displayed in asplain format. Any number that is outside of that range is displayed in asdot+ format.

ASN stands for autonomous system number is a collection of IP routing prefixes. It is generally the same for all IPs of any organization, network operator, or domain with the same external routing policy.

It is beneficial to recognize network traffic and set up policy-based routing. Specific ASN can be identified, allowed, or denied access to any network with policy-based routing.

To perform ASN WHOIS Lookup, follow these steps.

• Open the ASN WHOIS Lookup Tool.
• Enter the AS Number, or to get the AS Number of the IP. Perform the IP Lookup to get the AS Number of the given IP.
• After entering the AS Number, click on the "Find" button.
• The tool will perform the ASN lookup and display the results.