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

The information below is for an old version of the document
Document Type Expired Internet-Draft (individual)
Last updated 2015-01-05 (latest revision 2014-07-04)
Replaced by RFC 8686, RFC 8686
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This Internet-Draft is no longer active.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. In some deployment scenarios, in particular if the information about the network topology is partitioned and distributed over several ALTO servers, an ALTO client may need to discover an ALTO server outside of its own network domain, in order to get appropriate guidance. This document details applicable scenarios, itemizes requirements, and analyzes existing solution approaches for such ALTO cross-domain server discovery. However, the specification of a procedure is beyond the scope of this document. Note, that in earlier versions of this document, ALTO cross-domain server discovery was referred to as "third-party discovery", but it has been renamed to avoid naming ambiguities.


Sebastian Kiesel (
Martin Stiemerling (

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