DNSOP Working Group                                               X.Deng
Internet Draft                                               M.Boucadair
Intended status: Informational                            France Telecom
Expires: July 12, 2014                                            Q.Zhao
                                                       February 11, 2014

                     Using PCP to update dynamic DNS


  This document focuses on the problems encountered when using dynamic
  DNS in address sharing contexts (e.g., DS-Lite, NAT64) during IPv6
  transition. Issues and possible solutions are documented in this memo.

Status of this Memo

  This Internet-Draft is submitted in full conformance with the
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  Internet-Drafts are working documents of the Internet Engineering
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  This Internet-Draft will expire on April 16, 2013.

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  Copyright (c) 2012 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
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  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. Problem Statement ........................................... 2
  2. Solution Space .............................................. 4
     2.1. Locate a Service Port................................... 4
     2.2. Detect Changes ......................................... 4
  3. Possible Solutions .......................................... 6
     3.1. Topology ............................................... 6
     3.2. For Web Service ........................................ 7
     3.3. For Non-web Service .................................... 8
  4. Additional Authors' Addresses............................... 10
  5. Acknowledgments ............................................ 10
  6. References ................................................. 10
     6.1. Normative References................................... 10
     6.2. Informative References................................. 11
  7. Authors' Addresses ......................................... 12

1. Problem Statement

  Dynamic DNS (DDNS) is a widely deployed service to facilitate hosting
  servers (e.g., to host webcam and http server) at premises. There are
  a number of providers who offer a DDNS service, working in a client
  and server mode, which mostly use a web-form based communication.
  DDNS clients are generally implemented in the user's router or
  computer, which once detects changes to its IP address it
  automatically sends an update message to the DDNS server. The
  communication between the client and the server is not standardized,
  varying from one provider to another, although a few standard web-
  based methods of updating emerged over time.

  When the network architecture evolves towards an IPv4 sharing
  architecture during IPv6 transition, the DDNS Client will have to not
  only inform the IP address updates if any, but also to notify the
  changes of external port on which the service is listening, because
  well known port numbers, e.g. port 80 will no longer be available to
  every web server. It will also require the ability to configure
  corresponding port forwarding on CGN devices, so that incoming
  communications initiated from outside can be routed to the
  appropriate server behind the CGN.

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  This document focuses on the problems encountered when using dynamic
  DNS in address sharing contexts (e.g., DS-Lite, NAT64). Below are
  listed the main challenges:

  (1)      The DDNS service MUST be able to maintain an alternative port
  number instead of the default port number.

  (2)      Appropriate means to instantiate port mapping in the address
  sharing device MUST be supported.

  (3)      DDNS client MUST be triggered by the change of the external IP
  address and the port number. Concretely, upon change of the external
  IP address, the DDNS client MUST refresh the DNS records otherwise
  the server won't be reachable from outside. This issue is exacerbated
  in the DS-Lite context because no public IPv4 address is assigned to
  the CPE.

  This document describes solutions to resolve issues listed above in
  the particular case of DS-Lite.

  Note DDNS may be considered as an implementation of the Rendezvous
  service mentioned in [RFC6887].

  After creating a mapping for incoming connections, it is necessary to
  inform remote computers about the IP address, protocol, and port for
  the incoming connection to reach the services hosted behind a DS-Lite
  CGN.  This is usually done in an application-specific manner.  For
  example, a computer game might use a rendezvous server specific to
  that game (or specific to that game developer), a SIP phone would use
  a SIP proxy, and a client using DNS-Based Service Discovery [RFC6763]
  would use DNS Update [RFC2136][RFC3007].  PCP does not provide this
  rendezvous function. RFC6281 shows an good example of how to use the
  DNS-Based Service Discovery to make the service announcement
  available, in an application manner. The rendezvous function may
  support IPv4, IPv6, or both.  Depending on that support and the
  application's support of IPv4 or IPv6, the PCP client may need an
  IPv4 mapping, an IPv6 mapping, or both. In the solution section, it
  gives an example how the DDNS server may implement such a service
  notification functionality if necessary.

  This document requires no changes to PCP protocol or dynamic updates
  in the standard domain name system [RFC2136], but is rather an
  operational document to make the current DDNS service providers be
  aware of the impacts and issues that the IPv6 transitioning and IPv4
  address sharing will bring to them, and gives solutions address the

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  forthcoming issues. The current DDNS service providers usually
  employs a web-based form to maintain DDNS service registration and
  updates. For DNS-based Service Discovery, or DNS-SD and updates,
  [RFC6763] intensively describes how to use DNS resource records and
  standard DNS queries to facilitate service discovery, and [RFC6281]
  elaborates an implementation of it with an Apple's Back to My Mac
  (BTMM) Service.

2. Solution Space

2.1. Locate a Service Port

  At least two solutions can be used to associate a port number with a
  service identified:

  (1) Use service URIs (e.g., FTP, SIP, HTTP) which embed an explicit
     port number. Indeed, Uniform Resource Identifier (URI) defined in
     [RFC3986] allows to carry port number in the syntax (e.g.,

  (2) Use SRV records. Unfortunately, the majority of browsers do not
     support this record type.

  DDNS client and server are to be updated so that an alternative port
  number is also signaled and stored by the server. Requesting remote
  hosts will be then notified with the IP address and port number to
  reach the server.

2.2. Detect Changes

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                                    |  DDNS Server    |
                                    |                 |
                                              |3. DDNS updates
                                              |  (if any)
+---------------+                   +-----------------+
|DDNS Client    |1. PCP MAP request | CGN/PCP Server  |
|PCP Client/IWF |------------------>| (PCP mapping for|80:8080 +------+
|ON CPE or      |2. PCP MAP response| port forwarding)|<-------|Client|
|the host itself|<------------------|                 |        |      |
|               |3. DDNS updates    |                 |        +------+
|               |     (if any)      |                 |
|               |------------------>|                 |
+---------------+                   +-----------------+

                          Figure 1 : Flow Chart

  First of all, PCP MUST be used to install the appropriate mapping in
  the CGN so that incoming packets can be delivered to the appropriate

  In a network described in figure 1, DDNS Client/ PCP Client can
  either be running on a Customer Premise Equipment (CPE) or be running
  on the host that is hosting some services itself.  There are several
  possible ways to address the problems stated in section 1.

  (1) If the DDNS client is enabled, the host issues periodically (e.g.,
  1h) PCP MAP requests (e.g., messages 1 and 2 in Figure 1) with short
  lifetime (e.g., 30s) for the purpose of enquiring external IP address
  and setting. If the purpose is to detect any change of external port,
  the host must issues a PCP mapping to install a mapping for the
  internal server. Upon change of the external IP address, the DDNS
  client updates the records (e.g., message 3 in Figure 1).

  (2) If the DDNS client is enabled, it checks the local mapping table
  maintained by the PCP client. This process is repeated periodically
  (e.g., 5mn, 30mn, 1h). If there is no PCP mapping created by PCP
  client, it issues a PCP MAP request (e.g., messages 1 and 2 in Figure

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  1) for the purpose of enquiring external IP address and setting up
  port forwarding mappings for incoming connections. Upon change of the
  external IP address, the DDNS client updates the records in the DDNS
  server, e.g., message 3 in Figure 1.

3. Possible Solutions

3.1. Topology

+--------------+   +--------+    +---------+   +--------+   +-------+
| Service      |   |  DDNS  |    |  CGN&   |   | PCP    |   |Servers|
| User         |---|  Server|----|  PCP    |---| Client |---|       |
|              |   |        |    |  Server |   | /DDNS  |   |       |
|              |   |        |    |         |   | client |   |       |
+--------------+   +--------+    +---------+   +--------+   +-------+
A user             DDNS Server      AFTR          B4(CPE)   A host
From Internet                                               behind B4

                   Figure 2 : Implementation Topology

  Servers: Servers that are deployed in the DS-Lite network, or more
  generally, an IP address sharing environment. They are usually
  running on a host that has been assigned with a private IPv4 address.
  Having created a proper mapping via PCP in AFTR, these services have
  been made available to the internet users. The services may provide
  Web, FTP, SIP and other services though these ones may not be able to
  been seen as using a well known port from the outside anymore, in the
  IP address sharing context.

  B4 (CPE): An endpoint of IPv4-in-v6 tunnel. A PCP client together
  with a DDNS client are running on it. After PCP client establishes a
  mapping on the AFTR, an end user may register its domain name and its
  external IPv4 address plus port number to its DDNS service provider
  (DDNS server), manually or automatically by DDNS client. Later,
  likewise, end users may manually or let DDNS client on behalf of it,
  to automatically announce IP and port changes to the DDNS server.

  AFTR: Responsible for maintaining mappings between internal IPv4
  Address plus port and external IPv4 address plus port.

  DDNS server: Maintains a table linking a registered domain name and a
  pair of registered host's external IPv4 address plus port number.
  When being notified IP address and port number changes from DDNS

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  client, DDNS server then announces the updates to DNS servers on
  behalf of end user. RFC 2136 and RFC 2137 may be used by DDNS server
  to send updates to DNS servers. In many current practices, DDNS
  server provider usually announce its own IP address as the registered
  Domain names of end users. When Http requests reach the DDNS server,
  they may employ URL Forwarding or HTTP 301 redirection to redirect
  the request to a proper registered end user by looking up the
  maintained link table.

  Service users: Users who want to access services behind an IP address
  sharing network. They send out standard DNS requests to locate the
  services, which will lead them to a DDNS server, provided that the
  requested services have been registered to a DDNS service provider.
  Then the DDNS server will handle the rest in the way as described

3.2. For Web Service

  Current DDNS server implementations typically assume that the end
  servers host web server on the default 80 port. In the DS-Lite
  context, they will have to take into account that external port
  assigned by AFTR may be any number other than 80, in order to
  maintain proper mapping between domain names and external IP plus
  port. By doing such changes to implementation, the HTTP request would
  be redirected to the AFTR which servers the specific end host that
  are running servers. The following chart shows how the messages reach
  the right server.

Web Visitor        DDNS server         AFTR      B4(CPE)     Web Server
                                                  behind b4
| HTTP Get*             |                |          |               |
|---------------------->|                |          |               |
| ip_DDNS_server        |--------------->|          |               |
|                       | HTTP 301       |          |               |
|                       |<---------------|          |               |
| HTTP Get* ip_aftr:8001                 |          |               |
|--------------------------------------->|                          |
|                                        | HTTP Get* ip_websrv:8000 |
|                                        |------------------------->|
|                                        |                          |
|                       HTTP response    | HTTP response            |

                     Figure 3 Http Service Messages

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  When a web user sends out a HTTP GET message to DDNS server after a
  standard DNS query, DDNS server redirects the request to a registered
  web server, in this case, by responding with a HTTP 301 message. Then
  the HTTP GET message will be sent out to the AFTR, which will in turn
  finds the proper hosts behind it. For simplicity, messages among AFTR,
  B4 and web server behind b4 are not shown completely; for
  communications among those nodes, please refer to [RFC6333].

3.3. For Non-web Service

  For non-web services, as mentioned in Section 2, other means will be
  needed to inform the users about the service information.

  [RFC6763] shows an good example of DNS based solution to do so, in
  which case an application running in the end user's device will
  retrieve service information via DNS SRV/TXT records, and list
  available services. In a scenario where such application is not
  applicable, following provides another means for a third party, e.g.
  DDNS service provider, to disclose services to the Internet users.

  A web portal can be used to list available services. DDNS server
  maintains a web portal for each user FQDN, which provides a users
  service links. In the figure below, it assumes websrv.myip.org is a
  user's FQDN provided by a DDNS service provider.

  +-------------+    +-------------+    +----------+ Internet +-------+
  |DDNS client /|----|DDNS server /|----|DNS server|----------|Visitor|
  |  Web Server |    | web portal  |    |          |          |       |
  +-------------+    +-------------+    +----------+          +-------+
      |      register       |                 |                    |
      |<------------------> |                 |                    |
      |   websrv.myip.org   |  update DNS     |                    |
      |    | <-------------> |                    |
      |                     | websrv.myip.org |                    |
      |                     |   portal's IP   |                    |
      |              +-------------+          |                    |
      |              |update portal|          |                    |
      |              +-------------+          |  DNS resolve for   |
      |                     |                 | <----------------> |
      |                     |                 |  websrv.myip.org   |
      |                     |                 |  get portal's IP   |
      |                     |                 |                    |
      |                     |   visit portal of websrv.myip.org    |
      |                     | <----------------------------------> |
      |                     |                 |                    |
      |                  visit               |
      | <--------------------------------------------------------> |

                       Figure 4 Update Web Portal

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  The DDNS client registers the servers' information to the DDNS server,
  including public IP address and port obtained via PCP, user's FQDN
  and other necessary information. The DDNS server also works as portal
  server, it registers its IP address and user's FQDN to the DNS system,
  so that visitors can visit the web portal.

  DDNS server also maintains a web portal for each user's FQDN, update
  the portal according to registered information from DDNS client. When
  a visitor visits websrv.myip.org, DNS query will resolve to portal
  server's address, and the visitor will see the portal and the
  available services.

  |                                                             |
  |              Portal of websrv.myip.org                      |
  |                                                             |
  |    Service1: web server                                     |
  |    Link:                          |
  |                                                             |
  |    Service2: video                                          |
  |    Link:     rtsp://                 |
  |                                                             |
  |    ......                                                   |
  |                                                             |

                    Figure 5 An Example of Web Portal

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  The web portal in the above figure shows service links that are
  available to be accessed. Multiple services is accessible per user's
  FQDN. Some applications which are not http based can also be
  supported via this solution. When user click a link, the registered
  application in the client OS will be invoked to handle the link. How
  this can be achieved is out of the scope of this document.

4. Additional Authors' Addresses

  This work is made available also from additional authors'
  contribution and work.

  Xiaohong Huang

  Beijing University of Posts and Telecommunications, China
  Email: huangxh@bupt.edu.cn

  Yan Ma

  Beijing University of Posts and Telecommunications, China
  Email: mayan@bupt.edu.cn

5. Acknowledgments

  Thanks to Stuart Cheshire for bringing up DNS-Based Service Discovery
  and RFC6281 where covers DNS-based SD scenario and gives a good
  example of how the application means of solution to address dynamic
  DNS update, in this case, apple' BTMM, can be achieved.

6. References

6.1. Normative References


            P. Vixie, et. al." Dynamic Updates in the Domain Name
            System (DNS UPDATE)", April 1997.


            B. Wellington, " Secure Domain Name System (DNS) Dynamic
            Update", November 2000.


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            T. Berners-Lee, et. al. " Uniform Resource Identifier (URI):
            Generic Syntax", January 2005.


            S. Cheshire, et. Al. " Understanding Apple's Back to My Mac
            (BTMM) Service", June 2011.


            A. Durand, et. Al. " Dual-Stack Lite Broadband Deployments
            Following IPv4 Exhaustion", August 2011.

6.2. Informative References


             D. Wing, et. al. " Port Control Protocol (PCP)", April 2013.


           S. Cheshire, et. al. " DNS-Based Service Discovery ",
           February 2013

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7. Authors' Addresses

   Xiaohong Deng
   France Telecom
   Rennes,35000 France
   Email: dxhbupt@gmail.com

   Mohamed BOUCADAIR
   France Telecom
   Rennes,35000 France

   Email: mohamed.boucadair@orange.com

   Qin Zhao
   Beijing University of Posts and Telecommunications, China
   Email: zhaoqin.bupt@gmail.com

   James Huang
   Huawei Technologies
   Email: james.huang@huawei.com

  Cathy Zhou
  Huawei Technologies
  Email: cathy.zhou@huawei.com

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