Autonomous System Number (ASN) and BGP: A Hosting Buyer's Guide
What is an autonomous system number (ASN) and what does it do?
An autonomous system number (ASN) is a unique number that identifies an autonomous system: a group of IP networks run under one clearly defined routing policy. Networks use it with BGP to tell each other which IP blocks they can reach and by which path.
RFC 1930 describes an autonomous system as a connected group of one or more IP prefixes run by one or more network operators, with a single and clearly defined routing policy. Also, ARIN uses the same definition in its own guide. So an ASN is not a company name or a brand. In other words, it is the routing identity of a network.
We wrote this guide for site owners, e-commerce managers and developers who read "we have our own AS" on a hosting page and wonder what it means. However, we are a digital marketing and web team, not a hosting company. That is why we base every explanation on standards and official documents, and why we do not praise or criticize any specific provider.
What do ASNs look like and which number ranges exist?
An autonomous system number is an integer, usually written with the prefix "AS". At first, the original design used 16 bits. RFC 6793 extended the number space to four octets (32 bits), so today you see both short and long numbers on the internet.
However, not every number is public. RFC 6996 reserves two private-use ranges: 64512 to 65534 for 16-bit numbers and 4200000000 to 4294967294 for 32-bit numbers. Also, these numbers are not globally unique. An organization can use them inside its own network, but they must be removed from the AS path before a route reaches the global internet.
In addition, a separate block exists for documentation. That is why our examples use numbers such as AS64496 and never the number of a real company.
- Public numbers: Globally unique, assigned through the regional internet registries.
- Private numbers: The RFC 6996 ranges, meaningful only inside one organization.
- Documentation numbers: Reserved for examples and teaching, they do not point to a real network.
What is BGP and what does it do for a network?
BGP, the Border Gateway Protocol, is the routing protocol that carries reachability information between autonomous systems. Specifically, RFC 4271 defines BGP-4 as an inter-autonomous-system routing protocol. Each network announces the IP blocks it holds to its neighbors and evaluates the announcements it receives.
BGP announcements carry an AS path, a list of the autonomous systems the route has crossed. In practice, a router uses this list to pick a suitable path and to detect loops. If it sees its own number in the path, it rejects the announcement.
Here is an important distinction. That said, BGP does not automatically find the fastest path. Instead, operator policies, commercial agreements and costs shape the choice. So a short path does not always mean low latency.
Operators also use filters to limit who may announce which block. A faulty filter, for example, can let a wrong announcement spread. We come back to this below.
Where do AS and BGP appear when a visitor reaches your website?
When a visitor types your domain name, DNS answers first and returns an IP address. Then the packets travel from the visitor's internet provider across several networks to your hosting network. Each of those networks is an AS, and each one forwards traffic according to the routes it learned through BGP.
So the availability of your site depends on more than a running server. It also depends on how the server's network connects to the internet. For example, if the hosting network uses a single upstream provider, a failure at that provider can cut off access to your network too.
- The visitor enters the domain name and DNS returns an IP address.
- Next, the visitor's provider looks up which AS owns that IP in its BGP table.
- Then the packets cross a chain of networks chosen by routing policy and land in the hosting network.
- The hosting network delivers the packets to your server, and the reply returns by the same logic.
Also, if you want to check the DNS side, our DNS lookup tool shows your records quickly. Next, to see whether your setup supports IPv6, use the IPv6 test.
Who needs their own autonomous system number, and who does not?
First, organizations that want an ASN request it from a regional internet registry (RIR). ARIN describes an autonomous system number as a resource that network operators need to manage internal routing and to exchange routing information with internet providers. Requirements and fees differ between registries, so read the current terms on the registry's own site.
In addition, RFC 1930 sets a clear test. You need an ASN when your routing policy differs from that of your neighbors, or when you connect to more than one service provider. The document also stresses that this is almost the only case in which an operator should create its own AS. As a result, a small network with a single provider usually does not need one.
In practice, the owner of a corporate site, a blog or an online store does not need an ASN. For example, with shared hosting, a cloud server or a VPS, the provider manages the network side and you simply use an IP address.
So "I do not have an AS number" is not a gap. It is the normal situation for most projects. Moreover, knowing this helps you read marketing claims correctly.
What are the advantages of a hosting company with its own AS?
A company with its own AS can manage its IP blocks and routing policy directly. Moreover, it can connect to several upstream providers. For instance, if one link fails, it can shift traffic to another. When built well, this is a meaningful form of flexibility for continuity.
Another advantage is IP portability. If the company announces its own block from its own AS, the IPs often stay the same even when it changes an upstream provider. In practice, this can spare customers surprises such as IP changes and DNS waiting times.
In addition, the company can react to some problems without waiting for a third party. For example, it can correct an unwanted path choice with its own policy.
- Direct control over routing policy.
- The option to connect to several upstream providers.
- Flexibility to move and manage IP blocks.
- A shorter chain of waiting during network incidents.
However, all of this is potential, not a guarantee. So the real outcome depends on how the network is built and operated.
What are the limits and common misunderstandings of owning an AS?
The most common misunderstanding is that an autonomous system number automatically brings speed and quality. In short, an ASN is only an identifier. Specifically, it does not tell you how many upstream providers the network has, how much capacity the links carry or how good the hardware is.
The second misunderstanding is that a company with an AS owns its data center. A company can rent space in someone else's facility, build its own network there and announce it under its own ASN. On the other hand, a company with its own data center can run its network under another provider's AS.
Then, the third limit is error. If the team running an AS makes a wrong announcement, the problem can hit other networks, not only its own customers. So running BGP takes experience and discipline.
Finally, the fourth limit is stale data. The country or organization in a registry does not always match the physical location. So read a lookup result as a clue, not as a verdict.
Is a hosting provider without its own AS a bad choice?
No. A hosting provider without an AS usually reaches the internet inside another network, under that network's AS. For example, shared hosting and many VPS services work this way, and for most websites it is enough.
The real question is not "do they have an AS" but "what does my service level guarantee". In practice, an uptime commitment, backups, support response times and security practices often matter more than the AS number. For those criteria, see our guide to choosing web hosting.
| Feature | Provider with its own AS | Provider without its own AS |
|---|---|---|
| Routing control | Direct, under its own policy | Depends on the upstream provider's policy |
| IP portability | Often more flexible | Depends on the provider |
| Operating load | Needs BGP and filter management | The upstream provider handles the network |
| Guarantee for you | Not a guarantee by itself | Not a flaw by itself |
The table summarizes a difference. However, it is not a quality ranking. Also, both models can be run well or badly.
What is the difference between marketing language and reality?
Hosting pages often say "our own network", "direct connectivity" or "custom routing". However, these phrases may have a technical meaning, but they rarely turn into a measurable commitment. So the useful move is to turn each claim into a question you can verify.
The table below lists common phrases and how you can read them. Also, it does not point at any company. Instead, it gives a general method.
| Phrase | What it can mean technically | How you verify it |
|---|---|---|
| We have our own AS | The company may hold an ASN and an IP block | Look up the IP and find the announcing AS |
| Multiple upstream providers | The AS learns routes from more than one neighbor | Check the neighbor list in public BGP tools |
| We run our own network | The company sets the routing policy | Look for network incident commitments in the contract |
| A faster network | Means nothing until measured | Measure latency and TTFB from your visitors' region |
Above all, the last row matters most. A speed claim is only a claim until someone measures it from the region where your visitors live.
How do you look up the autonomous system number of a hosting company?
First you find the site's IP address. Then you check which AS announces that IP. These two steps need no account and no special access. In other words, public registries and lookup tools are enough.
- Find the IP address from the domain's A and AAAA records. A DNS lookup works well here.
- Inspect the address you found with a lookup tool. Our IP lookup page is a fair starting point.
- Read the registered holder of the IP block from the WHOIS or RDAP service of the regional registry.
- See the announcing AS and its neighbors in a public BGP tool such as bgp.he.net, or in a registry tool such as RIPEstat.
If you also want to know who owns the domain name, a WHOIS lookup shows the domain registration. A domain record and an IP block record are different things, so do not confuse them.
You never need to enter personal data for these lookups. Instead, a domain name or an IP address is enough.
Which commands can you run from the command line?
If you use a terminal on your own computer, the examples below will do the job. For example, we used only documentation values: the reserved domain example.com and the reserved address 203.0.113.10. So we did not write any real company or address.
# Find the IPv4 and IPv6 addresses of a domain
dig +short example.com A
dig +short example.com AAAA
# Read the registry record of an IP block
whois 203.0.113.10
# Read an ASN object from the RIPE database
whois -h whois.ripe.net AS64496The first two commands return DNS records. Then, the third shows which registry holds the IP block and usually who the block holder is. Finally, the fourth reads the object for the given ASN from the RIPE database.
The output format changes from registry to registry, and field names can differ. So read the output line by line and do not assume the meaning of a field you do not recognize.
Also, these commands are read-only. In other words, they change nothing on your server. Still, run them only against your own network or against public records.
What should you look at in the lookup result?
Focus on three things: the AS name and organization, the announced IP blocks and the neighbor networks. First, the name and organization show who operates the network. Second, the announced blocks show which IP ranges the company uses.
Then, the neighbor list gives a rough idea of how many directions the network connects from. However, many neighbors can be a good sign, but they do not prove quality on their own. Also, capacity and operating quality are not visible here.
Keep a few points in mind:
- The registered country does not map exactly to the physical location of a server.
- The organization name may differ from the hosting brand, and a group of companies can share one AS.
- If the site sits behind a CDN or a reverse proxy, the AS you see belongs to the front layer, not to the origin server.
- A lookup is a snapshot, and the BGP table changes all the time.
However, people often miss the third point. For example, if your site is behind a CDN, the result may show the CDN network and not the hosting company.
Do RPKI and route validation say anything about a hosting provider?
RPKI records which AS is authorized to announce an IP block. Specifically, RFC 6811 defines three states for an announcement: valid, invalid and not found. First, valid means a record matches the announcement. Second, invalid means a record covers the prefix but the announcing AS does not match it.
The RFC also states plainly that the mechanism gives limited protection. It describes the mechanism as protection against misconfiguration more than real security in the strong sense. Also, it only validates the origin of an announcement, not the full AS path.
For hosting selection, the value of this information is limited but real. For example, an RPKI record for the provider's IP blocks suggests the company cares about routing hygiene. However, a missing record does not by itself mean poor operations.
So treat RPKI as one extra signal, not as the only criterion.
In practice, a single question is enough: "Do our IP blocks have RPKI records?" A short and clear answer suggests a team that handles the topic. However, if the answer is vague, repeat the question in writing and keep the reply in your support ticket.
What do BGP mistakes and wrong announcements mean for your site?
If a network announces an IP block it does not own, by mistake or on purpose, part of the traffic can flow to the wrong place. Specifically, operators call this a route leak or a hijack. In practice, depending on how far the announcement spreads, the effect looks like your site being unreachable from some regions.
Still, such events happen on the internet from time to time. Also, we do not name any specific incident or company here. Instead, the point is how it feels. For example, your site runs fine on the server, yet some users say it will not open.
However, what you can do yourself is limited. First, confirm that the problem really comes from the network. Also test access from different regions and different networks. Then report it to your hosting provider as a network incident.
The fix belongs to the network that made the announcement and to its upstream providers. So you collect the access evidence and pass it on.
Also, prepare your backup and incident plan in advance. Our website backup strategy guide helps with that preparation.
What is MANRS and does it help when you choose hosting?
MANRS is an initiative that defines a set of actions network operators adopt for routing security. For network operators there are four core actions: filter announcements, prevent spoofed source addresses, keep up-to-date contact information and publish data so that others can validate it.
In short, these actions describe the behavior of a good neighbor on the network. For example, if a hosting company is a MANRS participant, it has at least stated publicly that it adopts these practices. However, that is not a certificate or a quality guarantee. Participation and implementation are also different things.
So note MANRS participation as a plus, but do not use it in place of the commitments in your contract. Also, a company outside the initiative can follow the same practices.
Keep one question in mind: how does the company manage routing security in concrete terms? So a clear answer is a good sign.
Do AS and BGP affect SEO and ad performance?
Indirectly yes, directly no. However, we know of no statement in Google's documentation that counts the AS number as a ranking signal. Instead, the effect comes through response time and availability. If the network path is long or unstable, time to first byte rises and the user experience suffers.
Also, we explain the effect of speed on rankings in our article on how site speed affects SEO. Then, for the core metrics, read our Core Web Vitals guide. Finally, for measurement, a Lighthouse performance test is a practical route.
The effect on advertising is also indirect. If a landing page is slow or goes down now and then, ad budget can be wasted. So the hosting and network decision is part of the marketing budget.
So think about hosting and infrastructure together with SEO. Our SEO consulting service reviews the technical side with you.
Which network questions should you ask when you choose hosting?
In practice, the questions you put to a provider are more useful than "do you have your own AS". So the list below gives a concrete frame for comparing answers. Also, a company that answers clearly and in writing is often more transparent.
- What is your uptime commitment and what happens when you miss it?
- How and how fast do you inform customers during network incidents?
- Is your network connected to more than one upstream provider, and how can I verify that?
- Do you offer IPv6 support?
- Do your IP blocks have RPKI records?
- How can I measure latency from the region where my visitors live?
However, none of these questions aims to rule out a company. Instead, the goal is to choose a provider that fits your workload. For example, for the IPv6 question, the IPv6 test gives you a quick answer.
Also, do not forget secure connections either. Our SSL certificate guide explains that part.
How do you measure latency and the path yourself?
First, the most honest way to judge network quality is to measure it. Then two simple commands in a terminal do the job. Specifically, one shows latency and the other shows the networks the packets cross. For example, below we use the reserved domain example.com.
# Measure latency with five packets
ping -c 5 example.com
# List the networks the packets cross
traceroute example.comFirst, ping returns average latency and packet loss. Then traceroute lists one router per step, and the reverse DNS names of those steps often hint at the network you are crossing. Some routers do not answer, so some lines can look empty. However, that alone is not a problem.
If you can, repeat the measurement from the region where your visitors live and at different times. Also, a single measurement is a snapshot. Your own home connection also affects the result, so keep conditions the same when you compare.
Finally, for a page-level result, a Lighthouse test shows the effect inside the browser. So reading network measurements and page measurements together gives a healthier picture.
What is the difference between an ASN, an IP block and a domain name?
In practice, people often mix up these three terms. First, a domain name is the readable name that DNS resolves to an IP address. Second, an IP address is the address of a device on the network. Finally, an autonomous system number is the identity that shows which network management those addresses belong to.
For example, a domain name points to one IP. Then that IP sits inside an IP block, and an AS announces the block. So the chain runs from domain to IP, from IP to block and from block to AS. Also, each link can have its own record and its own owner.
In practice, this distinction matters when you run a lookup. For example, you may own the domain name while a hosting company holds the IP block and a third organization operates the AS. So the name in a WHOIS result is not always the same.
- Domain name: A readable name, resolved with DNS.
- IP address and block: The address on the network, and the block is assigned to a provider.
- ASN: The routing identity of the network that announces the block.
When should you not do it yourself and leave it to your hosting provider?
In practice, for an ordinary website or online store, you do not need to get your own AS number or run BGP. Also, doing this without mistakes takes network knowledge, round-the-clock monitoring and relationships with upstream providers. A wrong announcement can hurt not only you but also others.
Leave the work to your hosting provider in these cases:
- Your site runs on a single server or on shared hosting.
- Your team has no network operations experience.
- You suspect a routing problem. Your part is diagnosis, while the provider makes the fix.
- You want to announce or move an IP block. Talk to the provider in writing first.
However, what you can do on your own is limited to reading and verifying: finding the IP, reading the record and measuring access from different regions. So these steps make you a more informed customer and make the talk with the provider easier.
If you are a larger organization that wants to build its own infrastructure, we recommend working with a team that specializes in network operations first.
How should you decide in the end?
In short, an autonomous system number is the identity of a network, not a quality badge. However, a company with its own AS can offer flexibility and control, but it must operate that well. Also, a company without one can still be reliable and sufficient for most sites.
So decide in three steps. First, define your need: where your visitors live and how much downtime you can accept. Then turn the provider's claims into verifiable questions and ask for written answers. Finally, run your own measurement: latency and TTFB from your visitors' region.
We did not praise or criticize any company in this guide, because the right choice depends on your workload. Also, if you want to think about infrastructure, SEO and advertising decisions together, our web design and development service can support you.
For sources, we recommend these documents: RFC 1930, RFC 4271, RFC 6996, RFC 6811, the ARIN ASN guide and the MANRS network operator actions.
