ISP Peering & Settlement-Free Peering
ISP peering is the business relationship ISPs engage in to reciprocally provide access to each others' customers using their networks. A key characteristic of an ISP peering relationship is that it is settlement-free peering. However, the costs are not zero, because there are costs associated with private co-location, the power to the routers and switches, cross-connects that are consumed to implement the peering connectivity.
In the peering case, two ISPs only exchange the routes of their downstream customers and neither can see the other's upstream routes over the peering connection. If an ISP peers with another ISP, the two agree to exchange traffic only between their endpoints and the endpoints in their customers' networks. This is in contrast to IP transit, where the Transit Provider, as part of its transit service provides routes to the rest of the Internet, including those of their downstream partners, other ISP peers, and upstream partners.
There are many localized Internet peering ecosystems around the world, each with its own set of ISPs collectively providing Internet access within their Internet Region. The global Internet peering ecosystem is a loosely coupled set of these Internet Regions each with its peering ecosystem.
ISP Peering Benefits
Network operators may be motivated to peer for a variety of reasons, both business and technical. The motivations for peering networks can include:
- Network reachability — Any network is not particularly useful if no one connects to it or those who connect to it cannot reach each other.
- Increased redundancy — ISPs strive for as redundant and as resilient a network connectivity map (called a "topology") as economically possible. Increasing the number of interconnection points between networks results in a more resilient and reliable network infrastructure for both parties, allowing them to offering more reliable Internet access and transit services.
- Increased routing control — The ability of an ISP to influence Internet path selection can lead to lower latency, decreased packet loss and increased quality of experience for users. Each new peering connection increases the network operator's control over the traffic routed between the peers, given that their traffic no longer has to traverse intermediary networks.
- Reduced latency — Traffic that flows directly between peers has lower latency than traffic that first traverses an intermediary network such as a transit provider's network before being handed off. User' quality of experience generally improves with decreased latency, especially for applications that communicate time—sensitive data, such as interactive voice or video.
- Reduced congestion — Congestion along Internet paths between the source and destination point through intermediate networks can degrade the quality of experience for network users. Direct interconnections between the networks allow for both networks to ensure sufficient bandwidth is available between network users for consistent performance.
- Improved traffic management and predictability of traffic — When networks interconnect, they have direct control in managing the flow of traffic between them. Because of this, both networks may reduce the need to maintain spare capacity on their transit and other connections to the Internet, as the traffic that is directly peered is now less likely to appear on other routes.
- Reduced costs — ISP Peering can reduce the costs of routing traffic between individual networks. For example, if an ISP exchanges a significant amount of customer traffic with another ISP, rather than sending that traffic up through its transit provider and into the other network through their transit connection, the two networks could peer at a shared facility, and each eliminates the transit cost for that traffic exchange.
ISP Peering Technical Requirements
To participate in a peering relationship on the Internet with any party some basic technical requirements need to be fulfilled. A network looking to peer must have:
- A public Autonomous System (AS) number assigned by a Regional Internet Registry (RIR). Without this, the network does not have a unique "identity" on the Internet for the purposes of routing traffic.
- At least one block of public IP addresses (independent of any upstream provider) assigned by an RIR. These addresses are what the network "announces" or "advertises" to interconnects with other networks.
- A network edge router capable of running the BGP protocol, and the technical capability to configure and manage BGP interconnections.
These basic requirements to peer may also apply to a network purchasing transit service, for example from multiple ISPs, where advanced network configuration is often used by enterprises for redundancy, performance and traffic management purposes.
ThousandEyes Network Intelligence technology addresses many of the challenges associated with IP peering connectivity. To assure optimal network performance, ISPs need detailed and accurate network path visibility, along with routing monitoring data. For more information on how ThousandEyes can help ISPs achieve network monitoring objectives visit the ThousandEyes ISP monitoring solution page.
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