What Is an ASN and Why Does It Matter for IP Addresses and Internet Routing?

At the core of web communication lies IPv4 addresses, the unique identifiers that ensure data finds its way to the correct destination. However, as we dive deeper into internet routing, we encounter a less discussed yet equally critical component: Autonomous System Numbers (ASNs). This blog post aims to explain ASNs, explore their relationship with IPv4 addresses, and talk about their significance for businesses navigating the IPv4 marketplace.

What Exactly Is an IP Address?

IP addresses are the cornerstone of internet connectivity, assigned to every device connected to the network.  NAT (Network Address Translation) can be used to map multiple private addresses inside a local network to a public IP address, thereby conserving those public addresses, but that is for another post. IP Addresses come in two versions: IPv4, which is a 32-bit address space, and IPv6, which expands the address space to 128 bits. There are 4.3 billion unique IPv4 addresses and 340 undecillion IPv6 addresses. A billion is 1 followed by 9 zeroes; an undecillion is 1 followed by 36 zeroes.

Why Are We Still Talking About IPv4 If IPv6 Exists?

The shift towards IPv6 is largely due to IPv4 address exhaustion, though IPv4 is still preferred by many individuals and businesses.

What’s an ASN and How Does It Work?

An Autonomous System (AS) is a collection of IPv4 networks managed by one or more network operators that follow a unified routing policy. An AS is like the post office.  When someone mails you a letter, it goes from their post office, perhaps through other post offices, until it gets to your post office, who then delivers the letter to you. Data packets navigate the internet by hopping from AS to AS until they get to the correct AS for the destination IP address; routers within that AS send the data packet to the IP address.

Each AS is assigned an official number, called an ASN. ASNs are unique 2 byte (16 bit) numbers between 1 and 65534 or 4 byte (32 bit) numbers 131072 or greater. There are approximately 100,000 ASNs in use, and that number continues to grow.

Regional Internet Registries (RIRs) are responsible for assigning ASNs, which can be public for routing on the global internet or private for internal use.

How Do ASNs and IP Addresses Work Together Online?

ASNs and IP addresses collaborate to direct traffic across the internet. Border Gateway Protocol (BGP), the protocol governing internet routing, relies on ASNs to make informed routing decisions. This partnership ensures that data packets travel efficiently through the complex network of autonomous systems.

How Can You Get Your Own ASN?

You can obtain an ASN from an RIR or from the transfer market.  The ASN will have to be registered with an RIR, and you will have to demonstrate the need for an autonomous system and outlining a clear routing policy. This process underscores the significance of ASNs in managing and enforcing routing policies across the internet.

Why Should Businesses Care About ASNs?

ASNs play a pivotal role in the architecture of the internet, working alongside IPv4 addresses to ensure coherent and efficient routing. For businesses involved in the buying or selling of IPv4 addresses, understanding ASNs can aid in optimizing network management.

Using an ASN allows you to be multi-homed, broadcasting your own IPv4 ranges over different internet connections for fail-over or load balancing.  Also, you can more easily turn your routes on and off without having to open a ticket with your ISP and waiting for them to respond. Some network operators place a premium on low number ASNs and are willing to pay for them, or perhaps have some older equipment that works only with 2-byte ASNs, though that is rare these days.  If you have a 4 digit ASN you no longer need and are patient, it is possible to sell them for USD $15,000 and up. A 3 digit ASN could possibly sell for over USD $50,000.  There are inter-regional transfer policies for ASNs between ARIN, RIPE and APNIC.  IPTrading did complete the first inter-regional ASN transfer back in 2018 between a RIPE seller and an APNIC buyer.

As we navigate the complexities of the digital realm, understanding these foundational elements becomes crucial for sustaining connectivity and fostering growth.

As the digital landscape continues to evolve, delving into the intricacies of internet routing and IP management is not just about staying connected; it’s about unlocking new opportunities in the ever-expanding digital frontier.