University of Stuttgart University of Stuttgart NEC Europe Ltd. The goal of Application-Layer Traffic Optimization (ALTO) is to provide guidance to applications that have to select one or several hosts from a set of candidates capable of providing a desired resource. ALTO is realized by a client-server protocol. Before an ALTO client can ask for guidance it needs to discover one or more ALTO servers that can provide suitable guidance. This document specifies a procedure for third-party ALTO server discovery, which can be used if the ALTO client is not co-located with the actual resource consumer, but instead embedded in a third party such as a peer-to-peer tracker. Technically, the algorithm specified in this document takes one IP address and a U-NAPTR Service Parameter (i.e., "ALTO:http" or "ALTO:https") as parameters. It performs several DNS lookups (for U-NAPTR and SOA resource records) and returns one or more URI(s) of information resources related to that IP address.