[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits] [IPR]

Versions: (draft-song-alto-server-discovery) 00 01 02 03 04 05 06 07 08 09 10

ALTO                                                           S. Kiesel
Internet-Draft                                   University of Stuttgart
Intended status: Standards Track                          M. Stiemerling
Expires: March 17, 2012                                  NEC Europe Ltd.
                                                               N. Schwan
                                                               M. Scharf
                                                Alcatel-Lucent Bell Labs
                                                                 H. Song
                                                                  Huawei
                                                      September 14, 2011


                         ALTO Server Discovery
                  draft-ietf-alto-server-discovery-02

Abstract

   The goal of Application-Layer Traffic Optimization (ALTO) is to
   provide guidance to applications, which have to select one or several
   hosts from a set of candidates that are able to provide a desired
   resource.

   Entities seeking guidance need to discover and possibly select an
   ALTO server to ask.  This is called ALTO server discovery.  This memo
   describes an ALTO server discovery mechanism based on several
   alternative mechanisms that are applicable in a diverse set of ALTO
   deployment scenarios.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 17, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the



Kiesel, et al.           Expires March 17, 2012                 [Page 1]

Internet-Draft            ALTO Server Discovery           September 2011


   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.  Discovery Scenarios  . . . . . . . . . . . . . . . . . . .  4
       1.1.1.  ALTO Server Discovery by Resource Consumers  . . . . .  5
       1.1.2.  ALTO Server Discovery by a Third Party . . . . . . . .  6
     1.2.  Pre-Conditions . . . . . . . . . . . . . . . . . . . . . .  7
   2.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . . .  8
   3.  Retrieving the URI by U-NAPTR  . . . . . . . . . . . . . . . . 10
     3.1.  Retrieving the Domain Name . . . . . . . . . . . . . . . . 10
       3.1.1.  Option 1: User input . . . . . . . . . . . . . . . . . 10
       3.1.2.  Option 2: DHCP . . . . . . . . . . . . . . . . . . . . 11
       3.1.3.  Option 3: Reverse DNS Lookup . . . . . . . . . . . . . 11
     3.2.  U-NAPTR Resolution . . . . . . . . . . . . . . . . . . . . 12
   4.  Applicability  . . . . . . . . . . . . . . . . . . . . . . . . 13
     4.1.  Applicability for Resource Consumer Server Discovery . . . 13
     4.2.  Applicability for Third Party Server Discovery . . . . . . 14
   5.  Deployment Considerations  . . . . . . . . . . . . . . . . . . 15
     5.1.  Reverse DNS Lookup . . . . . . . . . . . . . . . . . . . . 15
       5.1.1.  Private customers or very small businesses . . . . . . 15
       5.1.2.  Medium-size customer networks  . . . . . . . . . . . . 15
       5.1.3.  Large Customers  . . . . . . . . . . . . . . . . . . . 16
     5.2.  DHCP option for DNS Suffix . . . . . . . . . . . . . . . . 16
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
     7.1.  General  . . . . . . . . . . . . . . . . . . . . . . . . . 18
     7.2.  For U-NAPTR  . . . . . . . . . . . . . . . . . . . . . . . 18
   8.  Open Issues  . . . . . . . . . . . . . . . . . . . . . . . . . 20
   9.  Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 21
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 22
     10.2. Informative References . . . . . . . . . . . . . . . . . . 22
   Appendix A.  Contributors List and Acknowledgments . . . . . . . . 24
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25




Kiesel, et al.           Expires March 17, 2012                 [Page 2]

Internet-Draft            ALTO Server Discovery           September 2011


1.  Introduction

   The goal of Application-Layer Traffic Optimization (ALTO) is to
   provide guidance to applications, which have to select one or several
   hosts from a set of candidates, that are able to provide a desired
   resource [RFC5693].  The requirements for ALTO are itemized in
   [I-D.ietf-alto-reqs].

   ALTO is realized by a client-server protocol.  ALTO clients send
   queries to ALTO servers, in order to solicit guidance.  Hence, ALTO
   clients need to know the contact information of ALTO servers, which
   can provide appropriate guidance for a given resource consumer.  This
   information can be retrieved by invoking the ALTO discovery procedure
   defined in this document.

   The ALTO protocol specification [I-D.ietf-alto-protocol] is based on
   HTTP.  Therefore, it expects that the ALTO discovery procedure yields
   the HTTP(S) URI of the ALTO server's Information Resource Directory,
   which gives further information about the capabilities and services
   provided by that ALTO server.  Further (DNS) lookups may be necessary
   in order to find out the ALTO server's IP address.

   There are various architectural options where to place the ALTO
   client and the ALTO server discovery procedure:

   o  One option is that the ALTO client and the ALTO server discovery
      procedure are embedded directly in the resource consumer, i.e.,
      the application protocol entity that will eventually initiate data
      transmission to/from the selected resource provider(s).  In this
      case, the ALTO server discovery procedure might be able to
      interact with the user (i.e., prompt for a host name).
      Furthermore, it may use services such as DHCP, which are only
      available within the access network to which the resource consumer
      is connected.

   o  Another option is to integrate the ALTO client and the ALTO server
      discovery procedure into a third party such as a resource
      directory ("peer-to-peer tracker"), which issues ALTO queries on
      behalf of various resource consumers.  This third party may reside
      in a different part of the network (administrative domain) than
      the resource consumer.  It may occur that said third party whishes
      to issue ALTO queries on behalf of a resouce consumer, but all it
      knows about the resource consumer is the source IP address of
      messages originating from it (i.e., the resource consumer's IP
      address or the "public" IP address of the outermost NAT in front
      of the resource consumer).  This IP address will be the only input
      parameter to the ALTO server discovery procedure, which will have
      to find an ALTO server that can give appropriate guidance for that



Kiesel, et al.           Expires March 17, 2012                 [Page 3]

Internet-Draft            ALTO Server Discovery           September 2011


      resource consumer.

   A more detailed discussion of various options where to place the
   funcional entities comprising the overall ALTO architecture can be
   found in [I-D.ietf-alto-deployments].

   The goal of this memo is to propose a uniform mechanism for all types
   of ALTO client deployments that is implementable and deployable at a
   fast pace, i.e., without creating other deployment dependencies for
   ALTO.  We propose a schema which employs the UNAPTR mechanism
   [RFC4848] to determine the URI of the ALTO server and where mutliple
   input methods to the UNAPTR process can be used.

   Comments and discussions about this memo should be directed to the
   ALTO working group: alto@ietf.org.

1.1.  Discovery Scenarios

   Figure 1 below shows an overview on the different entities of a
   generic ALTO framework.  The ALTO Server discovery mechanism is used
   by the peer-to-peer (P2P) application in order retrieve the point of
   contact of the ALTO Service.


                                                   +------+
                                                 +-----+  |  Peers
                  +-----+      +------+    +=====|     |--+-oo
                  |     |......|      |====+   oo+--*--+     o
                  +-----+      +------+    |   o    *  ooooooo
                Source of       ALTO       |   o    *
                Topological     Service    |   o +--*--+
                information                +===o=|     | Tracker
                                               o +-----+ /Super-peer
                                ALTO Discovery o    o
                                    Service    o    o
                                   +------+    o    o
                                   |      |oooooooooo
                                   +------+

                 Legend:

                 ===   ALTO query protocol
                 ooo   ALTO service discovery protocol
                 ***   Application protocol (out of scope)
                 ...   Provisioning or initialization (out of scope)

                     Figure 1: ALTO Discovery Overview




Kiesel, et al.           Expires March 17, 2012                 [Page 4]

Internet-Draft            ALTO Server Discovery           September 2011


   Hereby the ALTO service discovery scenarios are classified into two
   types: one is the ALTO server discovery by the resource consumer, and
   the other is the ALTO server discovery by a third party, such as
   application trackers.  Before the specification of the discovery
   mechanism the following section illustrates and discusses both
   scenarios.

1.1.1.  ALTO Server Discovery by Resource Consumers

   The ALTO service discovery in some scenarios needs to be performed by
   the resource consumer itself.  In particular in P2P applications
   without a tracker like DHTs and other conventional client/server
   applications.

   In addition also P2P application which are tracker based may embed
   the ALTO client into the resource consumer to allow peers a selection
   of peers after retrieving the peer list from the application tracker.
   Another option is that the resource consumer peer sends its ALTO
   server address information to the application tracker or any other
   third party entity, which in turn will contact the specific ALTO
   server in order to retrieve ALTO guidance on behalf of the resource
   consumer.

   The following figure illustrates this scenario, showing the
   relationship between the different entities as discussed before.

                 +---------------+
                 |  ALTO Server  |
                 +---------------+
                      ^        ^         +-----------+
                      |        |         | ALTO      |
                      |    +---+---+     | Service   |
                      |    |tracker|     | Discovery |
                      |    +-------+     +---------+-+
                      |        |           o       o
         +------------+--+     |           o       o
         |P2P Application|ooooo|oooooooooooo       o
         |   Client A    |     |                   o
         +---------------+     |                   o
                               |                   o
                            +--+-------------+     o
                            | P2P Application|oooooo
                            |   Client B     |
                            +----------------+

        Figure 2: Resource Consumer ALTO Server Discovery (Example)





Kiesel, et al.           Expires March 17, 2012                 [Page 5]

Internet-Draft            ALTO Server Discovery           September 2011


1.1.2.  ALTO Server Discovery by a Third Party

   Some P2P applications have trackers, and these applications might not
   need to have their clients looking for the ALTO server guidance.  In
   these scenarios trackers query the ALTO servers for guidance
   themselves, and then return the final ranked result to the
   application clients.  However, application clients are distributed
   among different network operators and autonomous systems.  Trackers
   thus need to find different ALTO servers for the clients located in
   different operator networks or autonomous systems.  In such scenarios
   the discovery is thus not performed by the resource consumer, but a
   third party entity on behalf of the resource consumer.

   Figure 3 shows an example for a third party ALTO server discovery.
   For Client1 (1), the tracker has not cached yet the mapping between
   Client1's network operator and its ALTO server address, so it uses
   the ALTO Discovery Service to determine the address of the ALTO
   server in that operator's domain (2).  Then the tracker interacts
   with ALTO Server1 (3)(4) on behalf of Client1 (to get the network map
   and cost map), finally, the ranked list is sent back to Client1 (5).
   For Client2, the tracker has cached the mapping between Client2's
   network operator and ALTO Server2's address, so it does not need to
   perform the discovery process (which are the labels (a),(b), (c), and
   (d)).  If the application tracker already has the network map and
   cost map from ALTO Server2, then it does not need to query the ALTO
   Server for network map and cost map frequently.

























Kiesel, et al.           Expires March 17, 2012                 [Page 6]

Internet-Draft            ALTO Server Discovery           September 2011


                       +-------------+    +-------------+
                       | ALTO Server1|    | ALTO Server2|
                       +-------------+    +-------------+
                          ^     |            ^   |
                         3|    4|           b|   |c
                          |     |            |   |
                                v /----------+-\ v
      +-----------+         //////              \\\\\
      |           |      |||                         |||
      |   ALTO    |<===>|                               |
      | Discovery |  2  |     Application Tracker       |
      |  Service  |      |||                         |||
      |           |         \\\\\\              /////
      +-----------+     ^    |    \------------/  |
                        |    |5               ^   |d
                       1|    |               a|   |
                        |    v                |   v
                      +-+---------+       +---+--------+
                      |Application|       |Application |
                      |  Client1  |       |  Client2   |
                      +-----------+       +------------+

           Figure 3: Third Party ALTO Server Discovery (Example)

1.2.  Pre-Conditions

   The whole document assumes certain pre-conditions, in particular:

   o  The ALTO server discovery procedure is executed on a per IP
      address base.  Multiple IP addresses per interface or multiple IP
      addresses assigned to different IP interfaces require to repeat
      the procedure for every IP address.  It may be fine to group IP
      addresses according their domain suffixes and to perfom the
      procedure for such a group.  However, this is out of scope of this
      document.[Editor's note: this may relate to the work of the MIF
      WG]

   o  The ALTO server discovery procedure is executed on a per IP family
      base, i.e., seperate for IPv4 and IPv6.  It is up to the ALTO
      client to decide which of the possible multiple results of
      different IP address families to use.  The choice of whether to
      use IPv4 or IPv6 is out of scope of this document.

   o  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 run the ALTO server discovery procedure for the new
      IP address without relying on earlier gained information.



Kiesel, et al.           Expires March 17, 2012                 [Page 7]

Internet-Draft            ALTO Server Discovery           September 2011


2.  Protocol Overview

   We define multiple alternatives to discover the IP address of the
   ALTO server, as there are a number of ways possible how such
   information can be provided to the ALTO client.  The choice of method
   is up to the local network deployment.  For instance, there can be
   deployments where the ALTO server in charge for ALTO client is
   provisioned by the network operator and communicated to the ALTO
   client's host via a DHCP option, while in other deployments no such
   means may exist.  It should be noted that there is no silver bullet
   solution to the ALTO server discovery, as there too many deployment
   scenarios in the server discovery space.

   The following figure illustrates the different protocols that are
   used to find the URI of a suitable ALTO server.

                    Descending Order of Preference
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~>

    --------------   --------------    ---------------------
    | User Input |   | DHCP query |    | DNS PTR lookup on |
    | in res.c.  |   | by res.c.  |    | res.c's IP addr.  |
    --------------   --------------    ---------------------
                |          |            |
                 \         |           /
                  \--------+----------/
                           |
                           V
                       DNS suffix
                           |
                           V
                   ------------------
                   | U-NAPTR lookup |
                   ------------------
                           |
                           V
        ALTO Server's Information Resource Directory URI


                        Figure 4: Protocol Overview

   Figure 4 illustrates the U-NAPTR based resolution process to retrieve
   the ALTO Server URL.  As a precondition for resolution the U-NAPTR
   process needs the right domain name as input.  This domain name is
   determined by the IP address of the client and the DNS suffix of the
   access network where the client is registered in.  In order to
   retrieve the DNS suffix we specify three options, as are listed in
   descending order of preference:



Kiesel, et al.           Expires March 17, 2012                 [Page 8]

Internet-Draft            ALTO Server Discovery           September 2011


   User input:  a user may manually specify the DNS suffix on its own,
      either to access a 3rd party ALTO service provider or as it does
      know such information.  This input may also origin from a web page
      where the user downloads the configuration which is loaded as user
      input.

   DHCP:  a network provider provides the DNS suffix through a DHCP
      option.

   Reverse DNS:  the DNS system can be used to retrieve the DNS suffix
      through reverse lookup of an FQDN associated with an IP address.
      This is the last resort if all other options failed.







































Kiesel, et al.           Expires March 17, 2012                 [Page 9]

Internet-Draft            ALTO Server Discovery           September 2011


3.  Retrieving the URI by U-NAPTR

   This section specifies the U-NAPTR based resolution process.  To
   start the U-NAPTR resolution process a domain name is required as
   input.  Thus the section is devided into two parts: Section 3.2
   describes the U-NAPTR resolution process itself.  How the client
   identifies this DNS suffix of the access network where the resource
   consumer is registered in is described in Section 3.1.

3.1.  Retrieving the Domain Name

   The U-NAPTR resolution process requires a domain name as input.  The
   algorithm that is applied to determine this domain name is described
   in this section.  We specify three different options.  In option 1
   the user manually configures a specific ALTO service instance that he
   wants to use.  Option 2 defines a DHCP option to allow the network
   service provider a remote configuration of the client.  In option 3
   the client tries to get the domain name by performing a reverse DNS
   lookup on its IP address.

   The resource consumer may have private IP addresses and public IP
   addresses and depending on the deployment it might be necessary to
   determine for all IP addresses the ALTO server in charge of.  To
   determine its public IP address the resource consumer may need to use
   STUN[RFC5389] or BEP24[bep24].  For the following examples we assume
   that the IP address of the resource consumer is a.b.c.d.

3.1.1.  Option 1: User input

   A user may want to use a third party ALTO service instance.
   Therefore we allow the user to specify a DNS suffix on its own, for
   example in a config file option.  The DNS suffix given by the user is
   combined with the IP address of the resource consumer to allow the
   third party ALTO service to direct the client to a suitable ALTO
   server based on the location of the client.  A possible DNS suffix
   entered by the user may be:

      myaltoprovider.org

   This DNS suffix is prepended with the IP address of the resource
   consumer in reverse order to compose the domain name used for the
   final U-NAPTR lookup Section 3.2.  In case there are multiple ALTO
   servers deployed, the third party ALTO service instance can direct
   the ALTO client to the ALTO server closest to the client based on the
   IP address.

   Multiple lookups with different domain names might be necessary to
   complete the U-NAPTR resolution process.  If there is no response for



Kiesel, et al.           Expires March 17, 2012                [Page 10]

Internet-Draft            ALTO Server Discovery           September 2011


   a lookup the domain name is shortened by one part for the succeeding
   lookup, until a lookup is successful, as for example

      d.c.b.a.myaltoprovider.org.

      c.b.a.myaltoprovider.org.

      b.a.myaltoprovider.org.

      a.myaltoprovider.org.

      myaltoprovider.org.

3.1.2.  Option 2: DHCP

   As a second option network operators can configure the domain name to
   be used for service discovery within an access network.  RFC
   5986[RFC5986] defines DHCP IPv4 and IPv6 access network domain name
   options that identify a domain name that is suitable for service
   discovery within the access network.  The ALTO server discovery
   procedure uses these DHCP options to retrieve the domain name as an
   input for the U-NAPTR resolution.  One example could be:

      example.com

3.1.3.  Option 3: Reverse DNS Lookup

   The last option to get the domain name is to use a DNS PTR query for
   the IP address of the resource consumer.  The local DNS server
   resolves the IP address to the FQDN that also contains the DNS suffix
   for the respective IP address.  A possible answer for a PTR lookup
   for d.c.b.a.in-addr.apra might be, for example:

      d-c-b-a.dsl.westcoast.myisp.net

   This domain name can be used for the final U-NAPTR lookup
   Section 3.2.  If there is no response to the lookup the domain name
   is shortened by one part for one succeeding lookup.  If there is
   still no response we consider the reverse lookup being failed.  The
   domain names used for the example as described above are:

      d-c-b-a.dsl.westcoast.myisp.net.

      dsl.westcoast.myisp.net.







Kiesel, et al.           Expires March 17, 2012                [Page 11]

Internet-Draft            ALTO Server Discovery           September 2011


3.2.  U-NAPTR Resolution

   The ALTO protocol specification [I-D.ietf-alto-protocol] , it expects
   that the ALTO discovery procedure yields the HTTP(S) URI of the ALTO
   server's Information Resource Directory, which gives further
   information about the capabilities and services provided by that ALTO
   server.  The first step of the ALTO server discovery procedure (see
   Section 3.1) yielded an U-NAPTR/DDDS (URI-Enabled NAPTR/Dynamic
   Delegation Discovery Service) [RFC4848] application unique strings,
   in the form of a DNS name.  An example is "example.com".

   In the second step, the ALTO Server discovery procedure needs to use
   the U-NAPTR [RFC4848] specification described below to obtain a URI
   (indicating host and protocol) for the ALTO server's Information
   Resource Directory.  In this document, only the HTTP and HTTPS URL
   schemes are defined, as the ALTO protocol specification defines the
   access over both protocols, but no other [I-D.ietf-alto-protocol].
   Note that the HTTP URL can be any valid HTTP(s) URL, including those
   containing path elements.

   The following two DNS entries show the U-NAPTR resolution for
   "example.com" to the HTTPS URL
   https://altoserver.example.com/secure/directory or the HTTP URL
   http://altoserver.example.com/directory, with the former being
   preferred.


       example.com.

       IN NAPTR 100  10   "u"    "ALTO:https"
            "!.*!https://altoserver.example.com/secure/directory!"  ""

       IN NAPTR 200  10   "u"    "ALTO:http"
            "!.*!http://altoserver.example.com/directory!"  ""

















Kiesel, et al.           Expires March 17, 2012                [Page 12]

Internet-Draft            ALTO Server Discovery           September 2011


4.  Applicability

   This section discusses the applicability of the proposed solution
   with respect to the resource consumer server discovery and the third
   party deployment scenarios.  Each section discusses the proposed
   steps that are needed to determine the ALTO Server URI.

4.1.  Applicability for Resource Consumer Server Discovery

   In this scenario the ALTO server discovery procedure is performed by
   the resource consumer, for example a peer in a P2P system.  After the
   discovery the peer does the ALTO query on its own, or it might share
   the ALTO server contact information with a third party, for example a
   tracker, which then executes the ALTO query on behalf of the peer.

   To complete the ALTO server discovery process the resource consumer
   first SHOULD check whether the user has provider the domain name
   through manual configuration.  If this is not the case the next step
   SHOULD be to check for the access network domain name DHCP option
   (Section 3.1.2).  Finally the client SHOULD try to retrieve the
   domain name by the last option, the DNS reverse lookup on its IP
   address as described in Section 3.1.3.

   A client can have several candidate IP addresses that it may use for
   the discovery process.  For example if it is located behind a NAT, a
   private and a public IP address may be used for the discovery
   process.  It depends on the deployment scenario which of the IP
   addresses is the correct one.  Thus it is out-of-scope of this
   document to specify how exactly the client finds the right IP
   address.  However in the following we list methods that may be used
   in order to determine these candidate IP addresses.  Generally in P2P
   environments peers already have implemented mechanisms for NAT-
   traversal.  This includes proprietary solutions to determine a peer's
   public IP address, for example by asking a neighbour peer about its
   record of the own IP address.  Non-proprietary solutions that are
   favorable include the Session Traversal Utilities for NAT (STUN)
   [RFC5986] protocol to determine the public address.  If the client is
   behind a residential gateway another option may be to use Universal
   Plug and Play (UPnP) [UPnP-IGD-WANIPConnection1] or the NAT Port
   Mapping Protocol (NAT-PMP) [I-D.cheshire-nat-pmp].

   In case the ALTO discovery client has determined the domain name
   through one of the described options it proceedes with the U-NAPTR
   lookup as described in Section 3.2.







Kiesel, et al.           Expires March 17, 2012                [Page 13]

Internet-Draft            ALTO Server Discovery           September 2011


4.2.  Applicability for Third Party Server Discovery

   In case of the third party server discovery deployment scenario the
   entity performing the ALTO server discovery process is different from
   the resource consumer.  Typically the resource consumer is a peer
   whereas the ALTO client is a resource directory which seeks for ALTO
   guidance on behalf of the peer.  Another use case for the third party
   discovery is an application that looks for ALTO guidance
   transparently for the resource consumer, for example a CDN.

   Here the ALTO server discovery process can also retrieve guidance
   through the DHCP option or manual user configuration, but only if the
   provided discovery information is forwarded by the resource consumer
   to the third party entity.  In this case, additional mechanisms for
   the forwarding of this discovery information need to be specified.
   However these mechanisms are out of scope of this doument.

   If the third party entity cannot obtain this discovery information,
   the ALTO server discovery process relies on retrieving the domain
   name used as input to the U-NAPTR lookup through reverse DNS lookup
   of the IP address of the resource consumer as described in
   Section 3.1.3.  Usually the third party entity already knows the IP
   address of the resource consumer which was used to establish the
   initial connection.  In general this IP address is a public address,
   either of the resource consumer or of the last NAT on the path to the
   ALTO client.  This makes the IP address a good candidate for the DNS
   PTR query.  Thus, we expect that the DNS query will be successfully
   resolved to the FQDN of the domain where the resource consumer is
   registered in.

   In case the resource consumer needs guidance for a different IP
   address, for example one from a private network, we recommend that
   the resource consumer discovers the server itself and forwards the
   ALTO server contact information directly to the third party entity,
   which in turn can then do the third party ALTO query.  Again,
   forwarding the contact information from the resource consumer to the
   third party entity is out of scope of this document.














Kiesel, et al.           Expires March 17, 2012                [Page 14]

Internet-Draft            ALTO Server Discovery           September 2011


5.  Deployment Considerations

   The mechanism specified in this document needs some configuration
   effort in order to work properly.

5.1.  Reverse DNS Lookup

   Especially the domain name retrieved through the reverse DNS lookup
   (PTR records) and the U-NAPTR entry need to be coordinated.  In this
   section we discuss this configuration for different scenarios.

5.1.1.  Private customers or very small businesses

   For private customers and very small businesses that are DSL or cable
   customers often a dynamically assigned IP address is provisioned.
   Here, the reverse DNS lookup (PTR records) are controlled by the ISP
   and they point to the ISP's domain, e.g.:

      p5B203EA1.dip.t-dialin.net.

      dslb-084-056-144-100.pools.arcor-ip.net.

      187-4-222-157.bnut3700.dsl.brasiltelecom.net.br.

      65-154-39-69.ispnetbilling.com.

      197-151-94-178.pool.ukrtel.net.

   In this case, it would be the responsibility of the respective ISP to
   provide U-NAPTR entries for the DNS suffix without the endhost part,
   e.g.:

      dip.t-dialin.net.

      pools.arcor-ip.net.

      bnut3700.dsl.brasiltelecom.net.br.

      ispnetbilling.com.

      pool.ukrtel.net.

5.1.2.  Medium-size customer networks

   The second class of customers have their own DNS domain but only one
   single upstream ISP, e.g.:





Kiesel, et al.           Expires March 17, 2012                [Page 15]

Internet-Draft            ALTO Server Discovery           September 2011


   (1)  ISP my-isp.net assigns an IP address a.b.c.d to its customer

   (2)  The customer decides that reverse mapping for a.b.c.d should be
        whatever.customerdomain.com

   (3)  If the customer wants to support ALTO, he has to ask the ISP for
        the URI of the ISP's ALTO server which can give guidance to
        a.b.c.d.  Assume that ISP replies it is
        http://altoserver.my-isp.net

   (4)  The customer establishes a U-NAPTR entry for his domain

       customerdomain.com.   IN NAPTR 200  10   "u"    "ALTO:http"
            "!.*!http://altoserver.my-isp.net!"  ""

5.1.3.  Large Customers

   For very large customers with multiple upstream connections we assume
   that they have their very own traffic optimization policies and thus
   run their own ALTO server anyway.  In this case they need to manage
   their DNS entries accordingly.

5.2.  DHCP option for DNS Suffix

   Section 3.1.2 describes the usage of a DHCP option which allows the
   network operator of the network where the ALTO client is attached to,
   to provide a DNS suffix.  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 unkown DHCP options are not passed
   through some home gateways, effectively eliminating the DHCP option.

   Another well-known issues is the usage of home gateway specific DNS
   suffixes which "override" the DNS suffix provided by the network
   operator.  For instance, a host behind a home gateway may receive a
   DNS suffix ".local" instead of "example.com".  This suffix is not
   usuable for the server discovery procedure.

   [Editor's note: This section needs references about the well-known
   issues with home gateways and it relates to the FUN activity on home
   gateways which needs to be explored further.




Kiesel, et al.           Expires March 17, 2012                [Page 16]

Internet-Draft            ALTO Server Discovery           September 2011


6.  IANA Considerations

   This document registers the following U-NAPTR application service
   tag:



      Application Service Tag:  ALTO

      Defining Publication:  The specification contained within this
         document.

   This document registers the following U-NAPTR application protocol
   tags:

   o  Application Protocol Tag: http

      Defining Publication: RFC 2616 [RFC2616]

   o  Application Protocol Tag: https

      Defining Publication: RFC 2818 [RFC2818]





























Kiesel, et al.           Expires March 17, 2012                [Page 17]

Internet-Draft            ALTO Server Discovery           September 2011


7.  Security Considerations

7.1.  General

   This is still to be done in later revision of this draft, as the
   draft evolves heavily right now.

7.2.  For U-NAPTR

   The address of an ALTO server is usually well-known within an access
   network; therefore, interception of messages does not introduce any
   specific concerns.

   The primary attack against the methods described in this document is
   one that would lead to impersonation of an ALTO server since a device
   does not necessarily have a prior relationship with an ALTO server.

   An attacker could attempt to compromise ALTO discovery at any of
   three stages:

   1.  providing a falsified domain name to be used as input to U-NAPTR

   2.  altering the DNS records used in U-NAPTR resolution

   3.  impersonation of the ALTO server

   This document focuses on the U-NAPTR resolution process and hence
   this section discusses the security considerations related to the DNS
   handling.  The security aspects of obtaining the domain name that is
   used for input to the U-NAPTR process is described in respective
   documents, such as [RFC5986].

   The domain name that is used to authenticated the ALTO server is the
   domain name in the URI that is the result of the U-NAPTR resolution.
   Therefore, 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 an
   invalid 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].

   An "https:" URI is authenticated using the method described in
   Section 3.1 of [RFC2818].  The domain name used for this
   authentication is the domain name in the URI resulting from U-NAPTR
   resolution, not the input domain name as in [RFC3958].  Using the
   domain name in the URI is more compatible with existing HTTP client
   software, which authenticate servers based on the domain name in the
   URI.



Kiesel, et al.           Expires March 17, 2012                [Page 18]

Internet-Draft            ALTO Server Discovery           September 2011


   An ALTO server that is identified by an "http:" URI cannot be
   authenticated.  If an "http:" URI is the product of the ALTO
   discovery, this leaves devices vulnerable to several attacks.  Lower
   layer protections, such as layer 2 traffic separation might be used
   to provide some guarantees.














































Kiesel, et al.           Expires March 17, 2012                [Page 19]

Internet-Draft            ALTO Server Discovery           September 2011


8.  Open Issues

   Here are a few open issues to be clarified:

   Handling of reverse DNS lookups for IPv6:  Refer to [RFC4472] for a
      discussion about the issues.

   Missing reverse DNS entries for an IP address:  There may be cases
      where the reverse DNS lookup does not yield any result.  However,
      this will leave the ALTO client with no choice, other than giving
      up.  This needs better documentation.

   How to handled multiple results:  For instance, a host behind a NAT
      that yields an ALTO server in the private IP address domain and
      one in the public IP address domain.  Whom to ask?

   Normative Language  The current version of this memo lacks the proper
      normative language in many places.

































Kiesel, et al.           Expires March 17, 2012                [Page 20]

Internet-Draft            ALTO Server Discovery           September 2011


9.  Conclusion

   This document describes a general ALTO server discovery process and
   discusses how the process can be applied in different deployment
   scenarios, including the resouce consumer discovery as well as the
   third party discovery.













































Kiesel, et al.           Expires March 17, 2012                [Page 21]

Internet-Draft            ALTO Server Discovery           September 2011


10.  References

10.1.  Normative References

   [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.

   [RFC3958]  Daigle, L. and A. Newton, "Domain-Based Application
              Service Location Using SRV RRs and the Dynamic Delegation
              Discovery Service (DDDS)", RFC 3958, January 2005.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, March 2005.

   [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
              "Session Traversal Utilities for NAT (STUN)", RFC 5389,
              October 2008.

10.2.  Informative References

   [I-D.cheshire-nat-pmp]
              Cheshire, S., "NAT Port Mapping Protocol (NAT-PMP)",
              draft-cheshire-nat-pmp-03 (work in progress), April 2008.

   [I-D.ietf-alto-deployments]
              Stiemerling, M. and S. Kiesel, "ALTO Deployment
              Considerations", draft-ietf-alto-deployments-02 (work in
              progress), July 2011.

   [I-D.ietf-alto-protocol]
              Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
              draft-ietf-alto-protocol-09 (work in progress), June 2011.

   [I-D.ietf-alto-reqs]
              Kiesel, S., Previdi, S., Stiemerling, M., Woundy, R., and
              Y. Yang, "Application-Layer Traffic Optimization (ALTO)
              Requirements", draft-ietf-alto-reqs-11 (work in progress),
              July 2011.

   [RFC4472]  Durand, A., Ihren, J., and P. Savola, "Operational
              Considerations and Issues with IPv6 DNS", RFC 4472,
              April 2006.

   [RFC4848]  Daigle, L., "Domain-Based Application Service Location



Kiesel, et al.           Expires March 17, 2012                [Page 22]

Internet-Draft            ALTO Server Discovery           September 2011


              Using URIs and the Dynamic Delegation Discovery Service
              (DDDS)", RFC 4848, April 2007.

   [RFC5693]  Seedorf, J. and E. Burger, "Application-Layer Traffic
              Optimization (ALTO) Problem Statement", RFC 5693,
              October 2009.

   [RFC5986]  Thomson, M. and J. Winterbottom, "Discovering the Local
              Location Information Server (LIS)", RFC 5986,
              September 2010.

   [UPnP-IGD-WANIPConnection1]
              UPnP Forum, "Internet Gateway Device (IGD) Standardized
              Device Control Protocol V 1.0: WANIPConnection:1 Service
              Template Version 1.01 For UPnP Version 1.0", DCP 05-001,
              November 2001.

   [bep24]    Harrison, D., "Tracker Returns External IP",
              BEP http://bittorrent.org/beps/bep_0024.html.
































Kiesel, et al.           Expires March 17, 2012                [Page 23]

Internet-Draft            ALTO Server Discovery           September 2011


Appendix A.  Contributors List and Acknowledgments

   The initial version of this document was co-authored by Marco Tomsu
   <marco.tomsu@alcatel-lucent.com>.

   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.

   Marco Tomsu and Nico Schwan are partially supported by the ENVISION
   project (http://www.envision-project.org), a research project
   supported by the European Commission under its 7th Framework Program
   (contract no. 248565).  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 ENVISION project or the European Commission.

   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 COAST project
   (COntent Aware Searching, retrieval and sTreaming,
   http://www.coast-fp7.eu), a research project supported by the
   European Commission under its 7th Framework Program (contract no.
   248036).  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 COAST project or the European Commission.
















Kiesel, et al.           Expires March 17, 2012                [Page 24]

Internet-Draft            ALTO Server Discovery           September 2011


Authors' Addresses

   Sebastian Kiesel
   University of Stuttgart Computing Center
   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: martin.stiemerling@neclab.eu
   URI:   http://ietf.stiemerling.org


   Nico Schwan
   Alcatel-Lucent Bell Labs
   Lorenzstrasse 10
   Stuttgart  70435
   Germany

   Email: nico.schwan@alcatel-lucent.com
   URI:   www.alcatel-lucent.com/bell-labs


   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




Kiesel, et al.           Expires March 17, 2012                [Page 25]


Html markup produced by rfcmarkup 1.107, available from http://tools.ietf.org/tools/rfcmarkup/