Application Layer Traffic Optimization (ALTO) Cross-Domain Server Discovery - Experimental Algorithm Specification

Document Type Expired Internet-Draft (individual)
Authors Sebastian Kiesel  , Kilian Krause , Martin Stiemerling 
Last updated 2015-01-05 (latest revision 2014-07-04)
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This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


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 contains a strawman proposal for an ALTO Cross-Domain Server Discovery procedure (also known as Third-Party Discovery). 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. The functionality has been validated in a lab environment. However, the feasibility and possible side-effects of Internet-wide "production use" are not yet understood. The purpose of this document is to foster further discussion within the ALTO working group. Readers of this document should exercise caution in evaluating its value for implementation and deployment.


Sebastian Kiesel (
Kilian Krause (
Martin Stiemerling (

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)