The Policy Analysis of Internet Routing (PAIR) project is a Merit Network initiative dedicated to developing tools that Internet service providers (ISPs), network operators, and end users can use to troubleshoot Internet routing and policy problems. Merit is a Michigan-based company that was among the organizations responsible for developing and managing NSFnet, the successor to ARPANET and precursor of the modern Internet. The company announced the PAIR initiative in 1997 as a collaborative effort of two of their Internet Engineering workgroups, the Routing Arbiter Database and Route Server Next Generation (RSng) projects.
The PAIR project was developed to help organizations in a network that do peering (agree to forward each other's packets along through the network) rather than interconnecting with a backbone network such as Sprint's) with RSng route servers to track internal routing processes within the route server system. PAIR tools help peers discover information such as what routes they are exporting to another or why another peer is not seeing their routes. Users can compare policies being configured on the Internet with the policies prescribed by the Internet Routing Registry (IRR), which will help diagnose routing problems and enhance overall routing accuracy.
PAIR categorizes route states as belonging to one of three color categories: a green route is registered with the IRR, complies with policy, and is being proxied by the route servers; a red route is registered with the IRR, is configured to be proxied by the route servers, but is not currently announced in a configuration view; and a grey route is one that has been received by a route server, but is not configured to be proxied in any configuration view. The number of defined route states and corresponding colors may be expanded in the future to distinguish states in greater specificity.
The PAIR tools include: the route server configuration viewer (RSCV), which shows a matrix of the routes distributed by the route servers; the route server peering statistics summary, which summarizes the level of participation of peers at each exchange point; the PAIR language, which establishes the framework for designating route color; and the PAIR route color table, which is a truth table that shows how routes are colored. PAIR tools are most useful for ISPs that peer with RSng route servers, but can also be used by other ISPs to discover peers' routing information being exchanged through the route servers.