What is a PNI?

A PNI (Private Network Interconnect) is a dedicated point-to-point peering link between two autonomous networks, set up outside the shared fabric of an internet exchange point. Instead of exchanging traffic over a shared IXP port, both sides connect through a separate physical port, usually a cross-connect within one data center, and run a BGP session over it. A PNI is still peering, meaning traffic is exchanged only between these two networks and their customers, but it travels over a private, non-shared link.

PNI versus public peering at an IXP

Public peering runs on the shared layer-2 fabric of an internet exchange, where a single port lets you exchange traffic with dozens of networks at once, often through a route server. A PNI inverts that model: one dedicated link serves exactly one partner. You give up the convenience of establishing many sessions cheaply, but you gain full, guaranteed capacity and isolation from the other fabric participants. In practice operators run both mechanisms in parallel: they move the heaviest traffic flows onto PNIs and leave the rest on public peering.

• Link: a PNI is a dedicated port or cross-connect for one partner; public peering is a shared IXP port.
• Capacity: on a PNI the whole link capacity is yours; on the IXP fabric the port is shared with traffic to many networks.
• Control: a PNI removes any dependence on fabric stability and route-server policy.
• Cost: a PNI means an extra port and cross-connect, so it pays off only at sufficiently high volume.
• Scaling: public peering adds new partners faster, while a PNI scales capacity to a single partner better.

When a PNI makes sense

A PNI makes sense once traffic between two networks becomes large and steady enough to fill a significant share of a shared IXP port or threatens to congest it. A common decision threshold is a stable few gigabits per second to one partner, though the exact line depends on the cost of ports and cross-connects in a given facility. PNIs are also sometimes mandated by the policy of large content providers, who expect a dedicated link above a certain volume, and by the need for predictable quality on traffic sensitive to packet loss.

On the other hand, for small or bursty traffic a PNI is not cost-effective. A dedicated port and cross-connect carry a fixed cost regardless of utilization, and a single link without redundancy is a point of failure. If you exchange a few hundred megabits with a partner, public peering at an IXP is almost always cheaper and simpler.

Technical aspects of a PNI

In BGP terms, a session over a PNI is no different from a session on the IXP fabric: it is still eBGP between two AS numbers. The differences sit in the physical and operational layers. A PNI usually uses a dedicated point-to-point subnet, most often a /31 for IPv4 per RFC 3021 and a /127 for IPv6 per RFC 6164. The link can be upgraded from 10GE to 100GE without affecting other participants, and it is good practice to run BFD over the session for fast failure detection. For full resilience a PNI is built as a pair of links across different facilities or devices, so that a single port failure does not break the traffic exchange.

PNI on the AS202520 SkyPass network

AS202520 SkyPass runs both public peering at Polish internet exchanges, including THINX, TPIX, WRIX and 1-IX, and private peering in the form of PNIs with key partners. We operate PoPs in Warsaw and Wrocław, where we provide cross-connects for setting up a dedicated point-to-point link. If traffic with us outgrows a comfortable share of the shared fabric, we move it onto a PNI with an eBGP session, optional BFD and redundancy across locations. For operators without their own presence in our facilities we offer remote IXP access as a cheaper starting point.