What Is Peering and How Do Networks Decide Where to Peer?
Peering is a settlement-free interconnection between two autonomous systems (ASes) in which each network exchanges traffic destined for the other's customers at no charge. It is the alternative to buying transit, and it makes sense when two networks exchange meaningful amounts of traffic and both expect to benefit. Deciding where to peer usually comes down to three things: which Internet Exchange (IX) or private interconnect puts you closest to the networks you actually want to reach, what port speeds and resilience that location offers, and whether the participant mix there justifies the cost of a presence.
Peering vs. transit vs. paid peering
These three arrangements are often confused, but they differ in who pays and what is exchanged.
| Arrangement | Payment | What you get |
|---|---|---|
| Transit | You pay an upstream provider | Full global reach via that provider's routes |
| Settlement-free peering | No payment either way | Reach to the other network's customers and downstreams |
| Paid peering | You pay the other network | Same as peering, but with a commercial fee attached |
Transit is the default: it guarantees reachability to the whole Internet through a single provider. Peering does not replace transit — it reduces how much traffic you need to send through it. Paid peering sits in between and is typically used when one side would not otherwise agree to settlement-free interconnection.
Why networks peer
The main motivations are practical rather than ideological:
- Lower latency. Traffic takes a more direct path instead of routing through a transit provider's backbone.
- Reduced transit costs. Traffic that moves over peering links no longer consumes paid transit capacity, which can delay or avoid capacity upgrades.
- More direct paths. Fewer intermediate networks means fewer points where performance can degrade.
- Greater control over routing. You decide which prefixes you announce and accept, and how traffic is balanced across links.
For content networks, peering puts caches and origin servers closer to end users. For access networks, it reduces the cost of delivering traffic their subscribers request. Both sides benefit when the traffic is roughly balanced.
What you need before you can peer
Peering is not a product you switch on; it requires infrastructure and configuration on both sides.
- An ASN and public address space. You need an autonomous system number and provider-independent (PI) address space, or address space you are authorized to announce.
- A presence at the interconnection point. This means a colocation rack, a cross-connect, or a port on the IX fabric. Without physical presence, there is no link.
- A choice of public or private peering. Public peering uses the shared IX switching fabric, where one port can reach many networks. Private peering is a dedicated link between two networks, typically for high-volume or latency-sensitive traffic.
- BGP configuration. You configure BGP sessions, announce your prefixes, and apply import and export policies. The expected result is that both sides see each other's routes and traffic begins to flow.
A useful rule of thumb: start with public peering at an IX to reach many networks over one port, then add private interconnects for your largest traffic partners.
Peering at an IX vs. private interconnects
The two options trade reach against control.
| Dimension | Public peering at an IX | Private interconnect |
|---|---|---|
| Reach | Many networks over one port | One network per link |
| Cost model | Port and cross-connect costs shared across many peers | Dedicated capacity per partner |
| Scalability | Add peers by configuration, not new links | Each new partner needs new capacity |
| Control | Shared fabric, policies per session | Full control over the link |
| Best for | Broad, diverse peering | High-volume or latency-critical pairs |
Most networks use both: public peering for breadth, private links for the handful of partners that carry the most traffic.
How to choose an Internet Exchange
Once you know you want to peer, the IX decision is about proximity and ecosystem.
- Location. Choose an IX near your users or your major traffic partners to keep latency low. DE-CIX, for example, operates neutral Internet Exchanges across Europe, the Middle East, Africa, Asia, and the Americas, so geography is a primary filter.
- Participant mix. An IX is only as useful as the networks present on it. Check whether the content providers, access networks, and regional ISPs you want to reach are already there.
- Port speeds. Confirm the IX offers the port sizes you need now and can scale to later.
- Resilience. Look at redundancy within the fabric and whether you can connect from more than one location or provider.
- Neutrality. A neutral IX does not compete with its participants, which matters for fair and predictable interconnection terms.
DE-CIX describes its interconnection services as premium and operates multiple neutral exchanges, which fits the pattern of an IX chosen for ecosystem breadth rather than a single route.
Common pitfalls
- Traffic ratios. Some networks expect roughly balanced traffic before agreeing to settlement-free peering. Very asymmetric flows can make peering harder to justify to the other side.
- Route filtering. Without proper prefix and AS-path filters, you risk route leaks or hijacks. Filtering is a prerequisite, not an optional hardening step.
- Single points of failure. One peering link or one IX is not resilient. Redundant links across locations or providers protect against outages.
- Assuming peering replaces transit. Peering covers the networks you interconnect with; transit still covers the rest of the Internet.
If you are evaluating whether to peer at all, start by measuring where your traffic goes and which networks it crosses. If a large share of your traffic terminates in networks you could reach directly, peering at an IX near those networks is usually the next step.