wdiff rfc7286v1.txt rfc7286.txt

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
Stuttgart, Germany
Thales Deutschland
M. Scharf
Alcatel-Lucent Bell Labs
H. Song
Huawei
June
September 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.

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 . . . . . . . . . . . . . . . . . . . . . . . . 2
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 . . . . . . . . . . . 4
3.1.1. Step 1, Option 1: Local Configuration . . . . . . . . 4
3.1.2. Step 1, Option 2: DHCP . . . . . . . . . . . . . . . 5
3.2. Step 2: U-NAPTR Resolution . . . . . . . . . . . . . . . 5
4. Deployment Considerations . . . . . . . . . . . . . . . . . . 6
4.1. Issues with Home Gateways . . . . . . . . . . . . . . . . 6
4.2. Issues with Multihoming, Mobility, and Changing IP
Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6.1. Integrity of the ALTO Server's URI . . . . . . . . . . . 9
6.2. Availability of the ALTO Server Discovery Procedure . . . 10
6.3. Confidentiality of the ALTO Server's URI . . . . . . . . 10
6.4. Privacy for ALTO Clients . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . 12
Appendix A. Contributors . . Acknowledgments . . . . . . . . . . . . . . . . . . 14
Appendix B. Acknowledgments Contributors . . . . . . . . . . . . . . . . . . . . 14

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 [DISC].

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.

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.

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

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.).

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, irrespectively 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.

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.

Related publications: This document specifies a procedure for
discovering an HTTP or HTTPS URI of an ALTO server. HTTP is
specified in [RFC2616] and
HTTPS is are specified in [RFC2818]. [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" (defining publication: [RFC2616]) and "https" (defining
publication: [RFC2818]), "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 14.1. 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).

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 14.1 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 14.2 15.2 of [RFC7285]).

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 14.5 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.

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.

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. 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997. 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. 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.
2010, <http://www.rfc-editor.org/info/rfc5986>.

[RFC7285] Alimi, R., Penno, R., and Y. Yang, Y., Kiesel, S., Previdi, S.,
Roome, W., Shalunov, S., and R. Woundy, "Application-Layer
Traffic Optimization (ALTO) Protocol", RFC 7285, June
2014. September
2014, <http://www.rfc-editor.org/info/rfc7285>.

7.2. Informative References

[ALTO-DEPLOY]
Stiemerling, M., Kiesel, S., Previdi, S., and M. Scharf,
"ALTO Deployment Considerations", Work in Progress,
February draft-
ietf-alto-deployments-10, July 2014.

[DISC] Kiesel, S., Krause, K., and M. Stiemerling, "Third-Party
ALTO Server Discovery (3pdisc)", Work in Progress, draft-
kist-alto-3pdisc-05, January 2014.

[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.

[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 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. 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. 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. 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.
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. 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.

Appendix A. 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 2012,
<http://www.rfc-editor.org/info/rfc6708>.

[RFC7230] Fielding, R. and Martin Thomson provided excellent feedback J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Message Syntax 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. Routing", RFC 7230, June
2014, <http://www.rfc-editor.org/info/rfc7230>.

Appendix B. A. 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)
<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),
<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.

Appendix B. 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.

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
Stuttgart,
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
URI: www.alcatel-lucent.com/bell-labs

Haibin Song
Huawei

EMail: melodysong@huawei.com haibin.song@huawei.com