Peering is a cost-efficient way for two large networks to connect and exchange traffic. Peering can shorten network paths and reduce latency.
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Peering is a connection between two networks that allows each network to send traffic to destinations within the other network, or to downstream destinations connected to that network. Peering occurs between very large networks, especially autonomous systems (ASes) — mostly Internet service providers (ISPs) or large organizations managing hundreds or thousands of IP addresses.
Peering results in more efficient routing, as networks can send traffic more directly to its destination instead of sending it through additional intermediary backbone networks. Because it is mutually beneficial, peering is free in over 99% of cases. Free peering is called "settlement-free peering" to differentiate it from the (comparatively rarer) paid arrangements. Peering agreements can be as informal as a handshake agreement, or defined by contractual terms.
Imagine two neighbors who decide to remove the fence between their houses and use each other's yards. This is somewhat like peering: they can use the other's space, even though their properties are still their own. Ideally, the result is beneficial for both neighbors.
For network operators, the alternative to peering is called transit or IP transit. This is a paid arrangement with another network that gives the paying network access to the rest of the Internet, allowing the network's traffic to pass through. Imagine if one of the neighbors from the above example moved to a house that bordered a paid arboretum or zoo; this is like the difference between peering and transit.
Peering relies on the use of the Border Gateway Protocol (BGP). This protocol allows networks to communicate with other networks, announcing which blocks of IP addresses (these blocks are called "prefixes") they control.
Peering typically takes place through physical interconnections. The two methods used are public peering at locations called Internet exchange points (IxPs), and private peering through private network interconnections.
IxPs are hosted in colocation facilities, which are data centers where multiple businesses can host networking equipment and servers. Essentially, IxPs are large local area networks (LAN) connected via Ethernet cables and switches. Within this local network, ASes connect via BGP. They announce their IP addresses to each other, along with the IP addresses that are connected downstream (for an ISP, this would be their customers). With this information communicated, the networks can exchange traffic through the cables and switches.
A private network interconnection (PNI) is a direct connection between networks. Some PNI connections are simply a large fiber optic cable that plugs into a physical port on each network. Some PNI connections are virtual, running through a third-party network. Just as in a public peering connections, the networks use BGP to announce their IP prefixes and downstream connections to each other.
Depeering is the process of ending a peering agreement. The two networks may unplug from each other altogether, or one network may simply decide to start charging the other network for transit. The latter is more likely to happen if one network is larger than the other and has an advantage in the market.
Since peering results in the most direct connection possible between networks, peering with a public cloud can vastly improve cloud performance.
Traffic to and from the cloud ordinarily goes over the public Internet, which means it may take different routes each time and can get slowed down by network congestion or outages. It may also be expensive if an organization has to send a lot of traffic to the cloud via paid IP transit. Directly peering with a public cloud provider, in contrast, allows traffic to pass immediately to destinations in the cloud, for a more reliable and faster connection.
Cloudflare has an open peering policy: in fact, there is no need to be a Cloudflare customer to peer with Cloudflare. Today Cloudflare interconnects with over 13,000 networks globally. The result is that Cloudflare is tightly connected with networks and ISPs all over the globe for extraordinarily fast traffic routing anywhere.
For customers, Cloudflare offers Cloudflare Network Interconnect, the most direct connection possible to the connectivity cloud. Connections can be physical or virtual, and can take place at any of a number of IxPs or through several partners. Cloudflare also enables customers to set up BGP peering, which can improve performance and reduce the bandwidth used via Internet transit links.
Peering or interconnecting with Cloudflare can help organizations begin to modernize their networks, optimizing for cloud usage and hybrid workforces. Learn more about getting started with network modernization.