The internet is tens of thousands of independent networks, yet any of them can reach any other. That works because networks connect in three ways: they buy transit, they peer at internet exchange points, or they sit at the top as Tier 1 networks that need no transit at all. This guide explains each one and how to tell who is who.
The three ways networks connect
Every autonomous system needs a path to every other one. A network can pay a transit provider to carry its traffic everywhere, peer with other networks to exchange traffic directly, or do enough peering that it never needs to pay anyone, which is what defines a Tier 1. Most networks mix the first two; only a handful achieve the third. Each network here is identified by its ASN.
What is a Tier 1 network?
A Tier 1 network is a network that can reach every other network on the internet purely through settlement-free peering, without buying transit from anyone. They form the backbone that everyone else ultimately connects to. There is no official list, but the operators generally recognized as Tier 1 include a stable set of global backbones.
- Lumen (formerly Level 3 / CenturyLink)
- Arelion (formerly Telia Carrier)
- NTT (AS2914)
- GTT
- Cogent
- Zayo
- Tata Communications
- Telecom Italia Sparkle
When an IP's ASN belongs to one of these, you are usually looking at backbone infrastructure rather than an end-user network.
What is a transit provider?
A transit provider sells access to the rest of the internet. You pay them, usually by bandwidth, and they carry your traffic to every destination they can reach, including networks you have no relationship with. Transit is how smaller networks reach everywhere without negotiating thousands of individual peering agreements. A Tier 1 is, by definition, a transit provider that buys transit from no one.
In an AS path, a transit relationship shows up as a large carrier's ASN sitting between you and a destination. The more transit a network buys, the longer and more carrier-heavy its paths tend to look.
What is an internet exchange point (IXP)?
An internet exchange point (IXP) is a shared physical location where many networks connect to a common switching fabric and peer with each other. Instead of running a separate cable to each peer, a network plugs into the exchange once and can reach everyone else present. IXPs make peering cheap and keep local traffic local. The largest include DE-CIX (Frankfurt), AMS-IX (Amsterdam), LINX (London), and Equinix IX.
IXPs are why traffic between two networks in the same city usually stays in that city instead of detouring through another country. They are the efficient middle ground between buying transit and building private links to every peer.
Peering vs transit vs IXP: which applies when
The three fit together simply. Transit is paid, reaches everywhere, and is what you buy when you cannot peer. Peering is usually free and reaches only the peer's own routes, which you arrange either privately or across an IXP. An IXP is not a third pricing model; it is the place where public peering happens. A typical network buys some transit for full reachability and peers at one or more IXPs to cut cost and latency on the traffic it can exchange directly.
For the money-and-mechanics side of peering, see BGP peering; for how these relationships appear in live routing data, a BGP looking glass shows the AS paths directly.
Why this shows up in your ASN data
An ASN's place in this hierarchy tells you what kind of traffic to expect from it. A Tier 1 or transit ASN is infrastructure; a hosting ASN is where servers and bots live; a consumer-ISP ASN is where real users are. Abstract's IP Intelligence API returns the ASN, the operator's name, and its type for any IP, so you can tell a data-center connection from a residential one and score requests accordingly. To check a single address, use the free ASN Lookup tool.
Frequently Asked Questions
What is a Tier 1 network?
A Tier 1 network is a backbone that reaches the entire internet through settlement-free peering alone, without paying any transit provider. Examples include Lumen, Arelion, NTT, GTT, and Cogent.
How many Tier 1 networks are there?
There is no official registry, but roughly a dozen global backbones are generally recognized as Tier 1. The list is stable because becoming one requires enough peering to need no transit anywhere.
What is an internet exchange point?
An internet exchange point (IXP) is a shared fabric where many networks interconnect and peer through a single connection. Major IXPs include DE-CIX, AMS-IX, LINX, and Equinix IX.
What is the difference between transit and peering?
Transit is a paid service that carries your traffic to the whole internet. Peering is a usually-free exchange of only the two networks' own routes. Networks buy transit for full reach and peer to save cost and latency.
Is an IXP the same as a transit provider?
No. A transit provider sells reachability to the entire internet. An IXP is a neutral meeting point where networks peer with each other directly; it does not sell transit itself.
Get your free
IP Geolocation
key now
See why the best developers build on Abstract
get started for free
