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rfc:rfc7286

Internet Engineering Task Force (IETF) S. Kiesel Request for Comments: 7286 University of Stuttgart Category: Standards Track M. Stiemerling ISSN: 2070-1721 NEC Europe Ltd.

                                                             N. Schwan
                                                    Thales Deutschland
                                                             M. Scharf
                                              Alcatel-Lucent Bell Labs
                                                               H. Song
                                                                Huawei
                                                         November 2014
   Application-Layer Traffic Optimization (ALTO) Server Discovery

Abstract

 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.
 This document specifies a procedure for resource-consumer-initiated
 ALTO server discovery, which can be used if the ALTO client is
 embedded in the resource consumer.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7286.

Kiesel, et al. Standards Track [Page 1] RFC 7286 ALTO Server Discovery November 2014

Copyright Notice

 Copyright (c) 2014 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   1.1.  Terminology and Requirements Language . . . . . . . . . .   3
 2.  ALTO Server Discovery Procedure Overview  . . . . . . . . . .   3
 3.  ALTO Server Discovery Procedure Specification . . . . . . . .   4
   3.1.  Step 1: Retrieving the Domain Name  . . . . . . . . . . .   5
     3.1.1.  Step 1, Option 1: Local Configuration . . . . . . . .   5
     3.1.2.  Step 1, Option 2: DHCP  . . . . . . . . . . . . . . .   5
   3.2.  Step 2: U-NAPTR Resolution  . . . . . . . . . . . . . . .   6
 4.  Deployment Considerations . . . . . . . . . . . . . . . . . .   7
   4.1.  Issues with Home Gateways . . . . . . . . . . . . . . . .   7
   4.2.  Issues with Multihoming, Mobility, and Changing IP
         Addresses . . . . . . . . . . . . . . . . . . . . . . . .   7
 5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
 6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   6.1.  Integrity of the ALTO Server's URI  . . . . . . . . . . .   9
   6.2.  Availability of the ALTO Server Discovery Procedure . . .  11
   6.3.  Confidentiality of the ALTO Server's URI  . . . . . . . .  11
   6.4.  Privacy for ALTO Clients  . . . . . . . . . . . . . . . .  12
 7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
   7.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
   7.2.  Informative References  . . . . . . . . . . . . . . . . .  13
 Acknowledgments   . . . . . . . . . . . . . . . . . . . . . . . .  14
 Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  14
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

Kiesel, et al. Standards Track [Page 2] RFC 7286 ALTO Server Discovery November 2014

1. Introduction

 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 [RFC5693].  ALTO is realized by a client-server protocol;
 see requirement AR-1 in [RFC6708].  Before an ALTO client can ask for
 guidance it needs to discover one or more ALTO servers that can
 provide guidance to this specific client.
 This document specifies a procedure for resource-consumer-initiated
 ALTO server discovery, which can be used if the ALTO client is
 embedded in the resource consumer.  In other words, this document
 meets requirement AR-32 in [RFC6708] while AR-33 is out of scope.  A
 different approach, which tries to meet requirement AR-33, i.e.,
 third-party ALTO server discovery, is addressed in [3PDISC].
 A more detailed discussion of various options on where to place the
 functional entities comprising the overall ALTO architecture can be
 found in [ALTO-DEPLOY].
 The ALTO protocol specification [RFC7285] is based on HTTP and
 expects the discovery procedure to yield the HTTP(S) URI of an ALTO
 server's Information Resource Directory (IRD).  Therefore, this
 procedure is based on a combination of the Dynamic Host Configuration
 Protocol (DHCP) or local configuration and URI-enabled Naming
 Authority Pointer (U-NAPTR) resource records in the Domain Name
 System (DNS), in order to deliver such URIs.

1.1. Terminology and Requirements Language

 This document makes use of the ALTO terminology defined in [RFC5693].
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [RFC2119].

2. ALTO Server Discovery Procedure Overview

 The ALTO protocol specification [RFC7285] expects that the ALTO
 discovery procedure yields the HTTP(S) URI [RFC7230] of the ALTO
 server's Information Resource Directory (IRD), which gives further
 information about the capabilities and services provided by that ALTO
 server.
 On hosts with more than one interface or address family (IPv4/v6),
 the ALTO server discovery procedure has to be run for every interface
 and address family.  For more details see Section 4.2.

Kiesel, et al. Standards Track [Page 3] RFC 7286 ALTO Server Discovery November 2014

 The ALTO server discovery procedure is performed in two steps:
 1.  One DNS domain name is retrieved for each combination of
     interface and address family, either by local configuration
     (e.g., manual input into a menu or configuration file) or by
     means of DHCP.
 2.  These DNS domain names are used for U-NAPTR lookups yielding one
     or more URIs.  Further DNS lookups may be necessary to determine
     the ALTO server's IP address(es).
 The primary means for retrieving the DNS domain name is DHCP.
 However, there may be situations where DHCP is not available or does
 not return a suitable value.  Furthermore, there might be situations
 in which the user wishes to override the value that could be
 retrieved from DHCP.  In these situations, local configuration may be
 used.  Consequently, the algorithm first checks for a locally
 configured override, before it tries to retrieve a value from DHCP.
 Typically, but not necessarily, the DNS domain name is the domain
 name in which the client is located, i.e., a PTR lookup on the
 client's IP address (according to [RFC1035], Section 3.5 for IPv4 or
 [RFC3596], Section 2.5 for IPv6) would yield a similar name.
 However, due to the widespread use of Network Address Translation
 (NAT), trying to determine the DNS domain name through a PTR lookup
 on an interface's IP address is not recommended for resource consumer
 initiated ALTO server discovery (see also [RFC3424]).

3. ALTO Server Discovery Procedure Specification

 As already outlined in Section 2, the ALTO server discovery procedure
 is performed for every address family on every interface the
 application considers for communicating with resource providers.
 First, the algorithm checks for a locally configured domain name, as
 specified in Section 3.1.1.  If no such name was configured, it tries
 to retrieve one from DHCP, as specified in Section 3.1.2.  If still
 no domain name could be found, the procedure has failed and
 terminates with an appropriate error code.
 If one or more domain names were found, they will be used as U-NAPTR/
 DDDS (URI-Enabled NAPTR/Dynamic Delegation Discovery Service)
 [RFC4848] application-unique strings for a DNS lookup, as specified
 in Section 3.2.

Kiesel, et al. Standards Track [Page 4] RFC 7286 ALTO Server Discovery November 2014

3.1. Step 1: Retrieving the Domain Name

3.1.1. Step 1, Option 1: Local Configuration

 The preferred way to acquire a domain name related to an interface's
 point of network attachment is the use of DHCP (see Section 3.1.2).
 However, in some network deployment scenarios, there is no DHCP
 server available.  Furthermore, a user may want to use an ALTO
 service instance provided by an entity that is not the operator of
 the underlying IP network.  Therefore, we allow the user to specify a
 DNS domain name, for example, in a configuration file option.  An
 example domain name is:
    my-alternative-alto-provider.example.org
 Implementations MAY give the user the opportunity (e.g., by means of
 configuration file options or menu items) to specify an individual
 domain name for every address family on every interface.
 Implementations SHOULD allow the user to specify a default name that
 is used if no more specific name has been configured.

3.1.2. Step 1, Option 2: DHCP

 Network operators may provide the domain name to be used for service
 discovery within an access network using DHCP.
 RFC 5986 [RFC5986] defines DHCP IPv4 and IPv6 access network domain
 name options to identify a domain name that is suitable for service
 discovery within the access network.  RFC 2132 [RFC2132] defines the
 DHCP IPv4 domain name option.  While this option is less suitable, it
 still may be useful if the RFC 5986 option is not available.
 For IPv6, the ALTO server discovery procedure MUST try to retrieve
 DHCP option 57 (OPTION_V6_ACCESS_DOMAIN).  If no such option can be
 retrieved the procedure fails for this interface.  For IPv4, the ALTO
 server discovery procedure MUST try to retrieve DHCP option 213
 (OPTION_V4_ACCESS_DOMAIN).  If no such option can be retrieved, the
 procedure SHOULD try to retrieve option 15 (Domain Name).  If neither
 option can be retrieved, the procedure fails for this interface.  If
 a result can be retrieved, it will be used as an input for the next
 step (U-NAPTR resolution).  One example result could be:
    example.net

Kiesel, et al. Standards Track [Page 5] RFC 7286 ALTO Server Discovery November 2014

3.2. Step 2: U-NAPTR Resolution

 The first step of the ALTO server discovery procedure (see
 Section 3.1) retrieved one or -- in case of multiple interfaces and/
 or IPv4/v6 dual-stack operation -- several domain names, which will
 be used as U-NAPTR/DDDS (URI-Enabled NAPTR/Dynamic Delegation
 Discovery Service) [RFC4848] application unique strings.  An example
 is:
    example.net
 In the second step, the ALTO server discovery procedure uses a
 U-NAPTR [RFC4848] lookup with the "ALTO" Application Service Tag and
 either the "http" or the "https" Application Protocol Tag to obtain
 one or more URIs (indicating protocol, host, and possibly path
 elements) for the ALTO server's Information Resource Directory.  In
 this document, only the HTTP and HTTPS URI schemes are defined, as
 the ALTO protocol specification defines the access over both
 protocols, but no other [RFC7285].  Note that the result can be any
 valid HTTP(S) URI.
 The following two U-NAPTR resource records can be used for mapping
 "example.net" to the HTTPS URIs "https://alto1.example.net/ird" and
 "https://alto2.example.net/ird", with the former being preferred.
     example.net.
     IN NAPTR 100  10   "u"    "ALTO:https"
          "!.*!https://alto1.example.net/ird!"  ""
     IN NAPTR 100  20   "u"    "ALTO:https"
          "!.*!https://alto2.example.net/ird!"  ""
 If no ALTO-specific U-NAPTR records can be retrieved, the discovery
 procedure fails for this domain name (and the corresponding interface
 and IP protocol version).  If further domain names retrieved by Step
 1 are known, the discovery procedure may perform the corresponding
 U-NAPTR lookups immediately.  However, before retrying a lookup that
 has failed, a client MUST wait a time period that is appropriate for
 the encountered error (NXDOMAIN, timeout, etc.).

Kiesel, et al. Standards Track [Page 6] RFC 7286 ALTO Server Discovery November 2014

4. Deployment Considerations

4.1. Issues with Home Gateways

 Section 3.1.2 describes the usage of a DHCP option that provides a
 means for the network operator of the network in which the ALTO
 client is located to provide a DNS domain name.  However, this
 assumes that this particular DHCP option is correctly passed from the
 DHCP server to the actual host with the ALTO client, and that the
 particular host understands this DHCP option.  This memo assumes the
 client to be able to understand the proposed DHCP option; otherwise,
 there is no further use of the DHCP option, but the client has to use
 the other proposed mechanisms.
 There are well-known issues with the handling of DHCP options in home
 gateways.  One issue is that unknown DHCP options are not passed
 through some home gateways, effectively eliminating the DHCP option.
 Another well-known issue is the use of home-gateway-specific DNS
 domain names that "override" the DNS domain name provided by the
 network operator.  For instance, a host behind a home gateway may
 receive a DNS domain name ".local" instead of "example.net".  In
 general, this domain name is not usable for the server discovery
 procedure, unless a DNS server in the home gateway resolves the
 corresponding NAPTR lookup correctly, e.g., by means of a DNS split
 horizon approach.

4.2. Issues with Multihoming, Mobility, and Changing IP Addresses

 If the user decides to enter only one (default) DNS domain name in
 the local configuration facility (see Section 3.1.1), only one set of
 ALTO servers will be discovered, irrespective of multihoming and
 mobility.  Particularly in mobile scenarios, this can lead to
 undesirable results.
 The DHCP-based discovery method can discover different sets of ALTO
 servers for each interface and address family (i.e., IPv4/v6).  In
 general, if a client wishes to communicate using one of its
 interfaces and using a specific IP address family, it SHOULD query
 the ALTO server or servers that have been discovered for this
 specific interface and address family.  How to select an interface
 and IP address family as well as how to compare results returned from
 different ALTO servers are out of the scope of this document.

Kiesel, et al. Standards Track [Page 7] RFC 7286 ALTO Server Discovery November 2014

 A change of the IP address at an interface invalidates the result of
 the ALTO server discovery procedure.  For instance, if the IP address
 assigned to a mobile host changes due to host mobility, it is
 required to re-run the ALTO server discovery procedure without
 relying on earlier gained information.
 There are several challenges with DNS on hosts with multiple
 interfaces [RFC6418], which can affect the ALTO server discovery.  If
 the DNS resolution is performed on the wrong interface, it can return
 an ALTO server that could provide suboptimal or wrong guidance.
 Finding the best ALTO server for multi-interfaced hosts is outside
 the scope of this document.
 When using Virtual Private Network (VPN) connections, there is
 usually no DHCP.  The user has to enter the DNS domain name in the
 local configuration facility.  For good optimization results, a DNS
 domain name corresponding to the VPN concentrator, not corresponding
 to the user's current location, has to be entered.  Similar
 considerations apply for Mobile IP.

5. IANA Considerations

 IANA has registered the following U-NAPTR [RFC4848] application
 service tag for ALTO:
 Application Service Tag:  ALTO
 Intended usage:  see [RFC5693]  or: "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."
 Defining Publication:  The specification contained within this
    document
 Contact information:  The authors of this document
 Author/Change controller:  The IESG
 Interoperability considerations:  No interoperability issues are
    known or expected.  This tag is to be registered specifically for
    ALTO, which is a new application without any legacy deployments.
 Security considerations:  see Section 6 of this document.

Kiesel, et al. Standards Track [Page 8] RFC 7286 ALTO Server Discovery November 2014

 Related publications:  This document specifies a procedure for
    discovering an HTTP or HTTPS URI of an ALTO server.  HTTP and
    HTTPS are specified in [RFC7230].  The HTTP(S)-based ALTO protocol
    is specified in [RFC7285].
 Application Protocol Tag:  This document specifies how to use the
    application service tag "ALTO" with the application protocol tags
    "http" and "https", which have already been registered in the
    relevant IANA registry.  Therefore, IANA is not requested by this
    document to register any new application protocol tag.

6. Security Considerations

 A high-level discussion of security issues related to ALTO is part of
 the ALTO problem statement [RFC5693].  A classification of unwanted
 information disclosure risks, as well as specific security-related
 requirements can be found in the ALTO requirements document
 [RFC6708].
 The remainder of this section focuses on security threats and
 protection mechanisms for the ALTO server discovery procedure as
 such.  Once the ALTO server's URI has been discovered and the
 communication between the ALTO client and the ALTO server starts, the
 security threats and protection mechanisms discussed in the ALTO
 protocol specification [RFC7285] apply.

6.1. Integrity of the ALTO Server's URI

 Scenario Description
    An attacker could compromise the ALTO server discovery procedure
    or infrastructure in a way that ALTO clients would discover a
    "wrong" ALTO server URI.
 Threat Discussion
    This is probably the most serious security concern related to ALTO
    server discovery.  The discovered "wrong" ALTO server might not be
    able to give guidance to a given ALTO client at all, or it might
    give suboptimal or forged information.  In the latter case, an
    attacker could try to use ALTO to affect the traffic distribution
    in the network or the performance of applications (see also
    Section 15.1. of [RFC7285]).  Furthermore, a hostile ALTO server
    could threaten user privacy (see also Section 5.2.1, case (5a) in
    [RFC6708]).
    However, it should also be noted that, if an attacker was able to
    compromise DHCP and/or DNS servers used for ALTO server discovery
    (see below), (s)he could also launch significantly more serious
    other attacks (e.g., redirecting various application protocols).

Kiesel, et al. Standards Track [Page 9] RFC 7286 ALTO Server Discovery November 2014

 Protection Strategies and Mechanisms
    The ALTO server discovery procedure consists of three building
    blocks (local configuration, DHCP, and DNS) and each of them is a
    possible attack vector.
    The problem of users possibly following "bad advice" that tricks
    them into manually configuring unsuitable ALTO servers cannot be
    solved by technical means and is out of the scope of this
    document.
    Due to the nature of the protocol, DHCP is rather prone to
    attacks.  As already mentioned, an attacker that is able to inject
    forged DHCP replies into the network may do significantly more
    harm than only configuring a wrong ALTO server.  Best current
    practices for safely operating DHCP should be followed.
    A further threat is the possible alteration of the DNS records
    used in U-NAPTR resolution.  If an attacker was able to modify or
    spoof any of the DNS records used in the DDDS resolution, this URI
    could be replaced by a forged URI.  The application of DNS
    security (DNSSEC) [RFC4033] provides a means to limit attacks that
    rely on modification of the DNS records used in U-NAPTR
    resolution.  Security considerations specific to U-NAPTR are
    described in more detail in [RFC4848].
    A related risk is the impersonation of the ALTO server (i.e.,
    attacks after the correct URI has been discovered).  This threat
    and protection strategies are discussed in Section 15.1 of
    [RFC7285].  Note that if Transport Layer Security (TLS) is used to
    protect ALTO, the server certificate will contain the host name
    (CN).  Consequently, only the host part of the HTTPS URI will be
    authenticated, i.e., the result of the ALTO server discovery
    procedure.  The U-NAPTR based mapping within the ALTO server
    discovery procedure needs to be secured as described above, e.g.,
    by using DNSSEC.
    In addition to active protection mechanisms, users and network
    operators can monitor application performance and network traffic
    patterns for poor performance or abnormalities.  If it turns out
    that relying on the guidance of a specific ALTO server does not
    result in better-than-random outcomes, the use of the ALTO server
    may be discontinued (see also Section 15.2 of [RFC7285]).

Kiesel, et al. Standards Track [Page 10] RFC 7286 ALTO Server Discovery November 2014

6.2. Availability of the ALTO Server Discovery Procedure

 Scenario Description
    An attacker could compromise the ALTO server discovery procedure
    or infrastructure in a way that ALTO clients would not be able to
    discover any ALTO server.
 Threat Discussion
    If no ALTO server can be discovered (although a suitable one
    exists), applications have to make their decisions without ALTO
    guidance.  As ALTO could be temporarily unavailable for many
    reasons, applications must be prepared to do so.  However, the
    resulting application performance and traffic distribution will
    correspond to a deployment scenario without ALTO.
 Protection Strategies and Mechanisms
    Operators should follow best current practices to secure their
    DHCP, DNS, and ALTO (see Section 15.5 of [RFC7285]) servers
    against Denial-of-Service (DoS) attacks.

6.3. Confidentiality of the ALTO Server's URI

 Scenario Description
    An unauthorized party could invoke the ALTO server discovery
    procedure, or intercept discovery messages between an authorized
    ALTO client and the DHCP and DNS servers, in order to acquire
    knowledge of the ALTO server's URI.
 Threat Discussion
    In the ALTO use cases that have been described in the ALTO problem
    statement [RFC5693] and/or discussed in the ALTO working group,
    the ALTO server's URI as such has always been considered as public
    information that does not need protection of confidentiality.
 Protection Strategies and Mechanisms
    No protection mechanisms for this scenario have been provided, as
    it has not been identified as a relevant threat.  However, if a
    new use case is identified that requires this kind of protection,
    the suitability of this ALTO server discovery procedure as well as
    possible security extensions have to be re-evaluated thoroughly.

Kiesel, et al. Standards Track [Page 11] RFC 7286 ALTO Server Discovery November 2014

6.4. Privacy for ALTO Clients

 Scenario Description
    An unauthorized party could intercept discovery messages between
    an ALTO client and the DHCP and DNS servers, and thereby find out
    the fact that said ALTO client uses (or at least tries to use) the
    ALTO service.
 Threat Discussion
    In the ALTO use cases that have been described in the ALTO problem
    statement [RFC5693] and/or discussed in the ALTO working group,
    this scenario has not been identified as a relevant threat.
 Protection Strategies and Mechanisms
    No protection mechanisms for this scenario have been provided, as
    it has not been identified as a relevant threat.  However, if a
    new use case is identified that requires this kind of protection,
    the suitability of this ALTO server discovery procedure as well as
    possible security extensions have to be re-evaluated thoroughly.

7. References

7.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
            Extensions", RFC 2132, March 1997,
            <http://www.rfc-editor.org/info/rfc2132>.
 [RFC4848]  Daigle, L., "Domain-Based Application Service Location
            Using URIs and the Dynamic Delegation Discovery Service
            (DDDS)", RFC 4848, April 2007,
            <http://www.rfc-editor.org/info/rfc4848>.
 [RFC5986]  Thomson, M. and J. Winterbottom, "Discovering the Local
            Location Information Server (LIS)", RFC 5986, September
            2010, <http://www.rfc-editor.org/info/rfc5986>.
 [RFC7285]  Alimi, R., Penno, R., Yang, Y., Kiesel, S., Previdi, S.,
            Roome, W., Shalunov, S., and R. Woundy, "Application-Layer
            Traffic Optimization (ALTO) Protocol", RFC 7285, September
            2014, <http://www.rfc-editor.org/info/rfc7285>.

Kiesel, et al. Standards Track [Page 12] RFC 7286 ALTO Server Discovery November 2014

7.2. Informative References

 [3PDISC]   Kiesel, S., Krause, K., and M. Stiemerling, "Third-Party
            ALTO Server Discovery (3pdisc)", Work in Progress,
            draft-kist-alto-3pdisc-05, January 2014.
 [ALTO-DEPLOY]
            Stiemerling, M., Kiesel, S., Previdi, S., and M. Scharf,
            "ALTO Deployment Considerations", Work in Progress,
            draft-ietf-alto-deployments-10, July 2014.
 [RFC1035]  Mockapetris, P., "Domain names - implementation and
            specification", STD 13, RFC 1035, November 1987,
            <http://www.rfc-editor.org/info/rfc1035>.
 [RFC3424]  Daigle, L. and IAB, "IAB Considerations for UNilateral
            Self-Address Fixing (UNSAF) Across Network Address
            Translation", RFC 3424, November 2002,
            <http://www.rfc-editor.org/info/rfc3424>.
 [RFC3596]  Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
            "DNS Extensions to Support IP Version 6", RFC 3596,
            October 2003, <http://www.rfc-editor.org/info/rfc3596>.
 [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
            Rose, "DNS Security Introduction and Requirements", RFC
            4033, March 2005,
            <http://www.rfc-editor.org/info/rfc4033>.
 [RFC5693]  Seedorf, J. and E. Burger, "Application-Layer Traffic
            Optimization (ALTO) Problem Statement", RFC 5693, October
            2009, <http://www.rfc-editor.org/info/rfc5693>.
 [RFC6418]  Blanchet, M. and P. Seite, "Multiple Interfaces and
            Provisioning Domains Problem Statement", RFC 6418,
            November 2011, <http://www.rfc-editor.org/info/rfc6418>.
 [RFC6708]  Kiesel, S., Previdi, S., Stiemerling, M., Woundy, R., and
            Y. Yang, "Application-Layer Traffic Optimization (ALTO)
            Requirements", RFC 6708, September 2012,
            <http://www.rfc-editor.org/info/rfc6708>.
 [RFC7230]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
            (HTTP/1.1): Message Syntax and Routing", RFC 7230, June
            2014, <http://www.rfc-editor.org/info/rfc7230>.

Kiesel, et al. Standards Track [Page 13] RFC 7286 ALTO Server Discovery November 2014

Acknowledgments

 Olafur Gudmundsson provided an excellent DNS expert review on an
 earlier version of this document.  Thanks to Tina Tsou for an
 accurate security review.
 Michael Scharf is supported by the German-Lab project
 <http://www.german-lab.de> funded by the German Federal Ministry of
 Education and Research (BMBF).
 Martin Stiemerling is partially supported by the CHANGE project
 <http://www.change-project.eu>, a research project supported by the
 European Commission under its 7th Framework Program (contract no.
 257422).  The views and conclusions contained herein are those of the
 authors and should not be interpreted as necessarily representing the
 official policies or endorsements, either expressed or implied, of
 the CHANGE project or the European Commission.

Contributors

 The initial version of this document was coauthored by Marco Tomsu.
 Hannes Tschofenig provided the initial input to the U-NAPTR solution
 part.  Hannes and Martin Thomson provided excellent feedback and
 input to the server discovery.
 The authors would also like to thank the following persons for their
 contribution to this document or its predecessors: Richard Alimi,
 David Bryan, Roni Even, Gustavo Garcia, Jay Gu, Xingfeng Jiang,
 Enrico Marocco, Victor Pascual, Y. Richard Yang, Yu-Shun Wang, Yunfei
 Zhang, Ning Zong.

Kiesel, et al. Standards Track [Page 14] RFC 7286 ALTO Server Discovery November 2014

Authors' Addresses

 Sebastian Kiesel
 University of Stuttgart Information Center
 Networks and Communication Systems Department
 Allmandring 30
 Stuttgart  70550
 Germany
 EMail: ietf-alto@skiesel.de
 URI:   http://www.rus.uni-stuttgart.de/nks/
 Martin Stiemerling
 NEC Laboratories Europe
 Kurfuerstenanlage 36
 Heidelberg  69115
 Germany
 Phone: +49 6221 4342 113
 EMail: mls.ietf@gmail.com
 URI:   http://ietf.stiemerling.org
 Nico Schwan
 Thales Deutschland
 Thalesplatz 1
 Ditzingen  71254
 Germany
 EMail: ietf@nico-schwan.de
 Michael Scharf
 Alcatel-Lucent Bell Labs
 Lorenzstrasse 10
 Stuttgart  70435
 Germany
 EMail: michael.scharf@alcatel-lucent.com
 Haibin Song
 Huawei
 EMail: haibin.song@huawei.com

Kiesel, et al. Standards Track [Page 15]

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