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 (alto WG)
Authors Sebastian Kiesel  , Martin Stiemerling 
Last updated 2018-01-04 (latest revision 2017-07-03)
Replaces draft-kiesel-alto-xdom-disc
Stream IETF
Intended RFC status (None)
Expired & archived
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Additional Resources
- Mailing list discussion
Stream WG state WG Document (wg milestone: Nov 2017 - Submit alternative s... )
Document shepherd No shepherd assigned
IESG IESG state Expired
Consensus Boilerplate Unknown
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This Internet-Draft is no longer active.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, it may be needed to discover an ALTO server outside of the own network domain, in order to get appropriate guidance. This document details applicable scenarios, itemizes requirements, and specifies a procedure for ALTO cross-domain server discovery. Technically, the algorithm specified in this document takes one IP address or prefix and a U-NAPTR Service Parameter (i.e., "ALTO: http" or "ALTO:https") as parameters. It performs DNS lookups (for NAPTR resource records in the or tree) and returns one or more URI(s) of information resources related to that IP address or prefix.


Sebastian Kiesel (
Martin Stiemerling (

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