The internet world is the network of the networks. Autonomous systems are the extensive networks that make up the internet.
In simple words, the autonomous system (AS) is the network or the group of networks with a SINGLE and CLEARLY DEFINED routing policy. So if the autonomous systems have to communicate with each other, they need a unique number or identifier.
Each autonomous system (AS) assigns a unique autonomous system number(ASN), a unique identifier that is globally available. It allows its AS to exchange routing information with other systems.
Consider an AS as a town's post office. The mail moves from one office to another until it reaches the proper town, and that town's post office is responsible for delivering it to the correct destination.
Similarly, the data packets move from one AS to another AS, until it reaches the proper AS, containing the destination IP address. The routers within the AS sends that packet to the destined IP address.
Every AS controls a specific set of IP addresses. Just like the town's post office, which is responsible for delivering the post to all the addresses within its territory. The range of IP addresses on which an AS has control is called IP address space. More specifically, you can also call it IP block.
When the network engineers communicate which IP addresses are controlled by which AS, they do so by talking about the IP address prefixes owned by each AS. An IP address prefix is the range of IP addresses represented in that fashion: 192.0.2.0/24.
Suppose a company, XYZ, operates AS and owns the range of IP addresses that include an IP 192.0.2.253. If the computer sends a packet to IP 192.0.2.253, it will eventually reach the AS operates by XYZ.
If that first computer also sends a packet to IP address 198.51.100.255, the packet will move to a different AS.
Note: For reaching its destined IP address (198.51.100.255), the packet may even have to pass through the AS operates by XYZ.
Each AS is assigned an official number, which is a unique identifier. It's globally available and allows its AS to exchange routing information with other systems.
The Autonomous system number (ASN) can be public or private.
The ASNs were introduced to regulate networking organizations such as Internet Service Providers (ISP), government agencies, and educational institutions.
Three types of autonomous systems need an autonomous system number (ASN).
Till 2007, all autonomous system numbers were 2 bytes (16 bit). That gave Internet Assigned Numbers Authority (IANA) 65,536 possible ASNs to distribute. The IANA has reserved 1,023 ASNs (64,512 to 65,534) for private use.
But just like IPv4, these were also destined to run out. Just like the creation of IPv6, created 4-byte (32-bit) ASNs to overcome that issue. That gave IANA 4,294,967,296 possible ASNs to distribute. The IANA has reserved 94,967,295 ASNs (4,200,000,000 to 4,294,967,294) for private use.
Obtaining an autonomous system number (AS) requires the company or other party to submit a petition to the IANA through one of five global Regional Internet Registries or RIRs. The Regional offices are established for Africa, America, Asia, Latin America, the Caribbean, and Europe.
For example, to qualify for the ASN, an organization must have either.
Follow the procedure provided by ARIN for requesting an ASN if you lie in their regional territory.
Note: There is a limited number of ASNs available. And if the governing bodies provide ASNs too freely, the supply would run out, and routing becomes more complex.
Autonomous systems connect and exchange network traffic through a process called peering. Autonomous systems peer together by connecting at physical locations called Internet Exchange Points (IXPs).
ASN Lookup is an act of querying the different RIR databases to get information about the ASN. From the ANS Lookup, you can grab the following information, such as
ASN is generally the same for all IPs of any organization, network operator, or domain with the same and clear external routing policy.
The specific ASN can be allowed or denied access to any network with policy-based routing.
To perform the ASN Lookup, perform the following steps.