PCP Working Group                                           M. Boucadair
Internet-Draft                                            France Telecom
Updates: 6887 (if approved)                                     R. Penno
Intended status: Standards Track                                 D. Wing
Expires: November 23, 2013                                      P. Patil
                                                                T. Reddy
                                                                   Cisco
                                                            May 22, 2013


                          PCP Server Selection
                   draft-ietf-pcp-server-selection-01

Abstract

   This document specifies the behavior to be followed by the PCP client
   to contact its PCP server(s) when one or several PCP server names are
   configured.  Multiple names may be configured to a PCP client in some
   deployment contexts such as multi-homing.

   This document updates RFC6887.

Requirements Language

   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].

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 November 23, 2013.

Copyright Notice





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   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Name Resolution . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  IP Address Selection  . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Serial Queries  . . . . . . . . . . . . . . . . . . . . .   4
   5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Example 1 . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.2.  Example 2 . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.3.  Example 3 . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Appendix A.  Multi-homing . . . . . . . . . . . . . . . . . . . .   7
     A.1.  IPv6 Multi-homing . . . . . . . . . . . . . . . . . . . .   7
     A.2.  IPv4 Multi-homing . . . . . . . . . . . . . . . . . . . .   8
     A.3.  Multiple interfaces and Servers . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   This document specifies the behavior to be followed by the PCP client
   [RFC6887] to contact its PCP server(s) [RFC6887] when receiving one
   or several PCP server names (e.g., using DHCP [I-D.ietf-pcp-dhcp]).
   This document is not specific to DHCP; any other mechanism can be
   used to configure PCP server names.

   Multiple names may be configured to a PCP client in some deployment
   contexts such as multi-homing (see Appendix A).  It is out of scope
   of this document to enumerate all deployment scenarios which require
   multiple names to be configured.



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   This document assumes appropriate name resolution means (e.g.,
   Section 6.1.1 of [RFC1123]) are available on the host client.

2.  Terminology

   This document makes use of the following terms:

   o  PCP server denotes a functional element which receives and
      processes PCP requests from a PCP client.  A PCP server can be co-
      located with or be separated from the function (e.g., Network
      Address Translation (NAT), firewall) it controls.  Refer to
      [RFC6887].
   o  PCP client denotes a PCP software instance responsible for issuing
      PCP requests to a PCP server.  Refer to [RFC6887].
   o  Name is a string that can be passed to getaddrinfo (Section 6.1 of
      [RFC3493]), such as a DNS name, address literals, etc.  A name may
      be a fully qualified domain name (e.g., "myservice.example.com."),
      IPv4 address in dotted-decimal form (e.g., 192.0.2.33) or textual
      representation of an IPv6 address (e.g., 2001:db8::1).

3.  Name Resolution

   Each configured name is passed to the name resolution library (e.g.,
   Section 6.1.1 of [RFC1123] or [RFC6055]) to retrieve the
   corresponding IP address(es) (IPv4 or IPv6).  Then, the PCP client
   follows the procedure specified in Section 4 to contact its PCP
   server(s).

   A host may have multiple network interfaces (e.g, 3G, IEEE 802.11,
   etc.); each configured differently.  Each PCP server learned MUST be
   associated with the interface via which it was learned.

4.  IP Address Selection

   This section specifies the behavior to be followed by the PCP client
   to contact its PCP server(s) when receiving one or several PCP server
   names:

   1.  If only one PCP server name is configured: if a list of IP
       addresses is returned as a result of resolving the PCP server
       name, the PCP client follows the procedure specified in
       Section 4.1.









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   2.  If several PCP server names are configured: each name is treated
       as a separate PCP server.  Moreover, each name may be resolved
       into one IP address or a list of IP addresses.  The PCP client
       contacts in parallel the first IP address of each name and
       follows the procedure specified in Section 4.1 for the list of IP
       addresses returned for each name.  Section 5 provides some
       examples to illustrate this procedure.

   This procedure does not require any knowledge of the capabilities of
   the PCP-controlled device(s).  Instead, the PCP client assumes each
   configured name refer to a separate PCP server.

   This procedure may result in a PCP client instantiating multiple
   mappings maintained by distinct PCP servers.  The decision to use all
   these mappings or delete some of them is deployment-specific.  Only
   the PCP client can decide whether all the mappings are needed or only
   a subset of them.

4.1.  Serial Queries

   The PCP client initializes its Maximum Retransmission Count (MRC) to
   4.

   The PCP client sends its PCP message to the PCP server following the
   retransmission procedure specified in Section 8.1.1 of [RFC6887].  If
   no response is received after MRC attempts, the PCP client tries with
   the next IP address in its list of PCP server addresses.  If it has
   exhausted its list, the procedure is repeated every fifteen minutes
   until the PCP request is successfully answered.  If, when sending PCP
   requests the PCP client receives an ICMP error (e.g., port
   unreachable, network unreachable) it SHOULD immediately try the next
   IP address in the list.  Once the PCP client has successfully
   received a response from a PCP server address on that interface, it
   sends subsequent PCP requests to that same server address until that
   PCP server becomes non-responsive, which causes the PCP client to
   attempt to re-iterate the procedure starting with the first PCP
   server address on its list.

5.  Examples

   The following sub-sections provide three examples to illustrate the
   procedure.

   For all these examples, let's suppose pcpserver-x, pcpserver-y and
   pcpserver-z are configured as PCP server names.

5.1.  Example 1




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   Let's also suppose:

   * IPx1 and IPx2 are returned for pcpserver-x; IPx1 is not reachable.
   * IPy1 and IPy2 are returned for pcpserver-y; IPy1 is reachable
   * IPz1 and IPz2 are returned for pcpserver-z; IPz1 is reachable


   The procedure to contact the PCP servers is as follows:

   * Send PCP requests to all servers: IPx1, IPy1 and IPz1
   * Responses are received from IPy1 and IPz1 but not from IPx1
     - The request is re-sent to IPx1
     - If no response is received after four attempts, the request
       is sent to IPx2


5.2.  Example 2

   Now, if the following conditions are made:

   * IPx1 and IPx2 are returned for pcpserver-x; IPx1 is not reachable.
   * IPy1 and IPy2 are returned for pcpserver-y; IPy1 is reachable
   * IPz1 and IPz2 are returned for pcpserver-z; IPz1 is not reachable


   The procedure to contact the PCP servers lead to the following:

   * Send PCP requests to all servers: IPx1, IPy1 and IPz1
   * A response is received from IPy1 but not from IPx1 and IPz1
     - the requests are re-sent to IPx1 and IPz1
     - If no response is received after four attempts, the request
       is then sent to IPx2 and IPz2


5.3.  Example 3

   Let's suppose now that:

   * IPx1 and IPx2 are returned for pcpserver-x; IPx1 is not reachable.
   * IPy1 and IPy2 are returned for pcpserver-y; IPy1 is not reachable
   * IPz1 and IPz2 are returned for pcpserver-z; IPz1 is not reachable


   The procedure to contact the PCP servers is as follows:

   * Send PCP requests to all servers: IPx1, IPy1 and IPz1
   * No answer is received for all requests
     - the requests are re-sent to IPx1, IPy1 and IPz1



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     - If no response is received after four attempts, the request
       is then sent to IPx2, IPy2 and IPz2


6.  Security Considerations

   PCP-related security considerations are discussed in [RFC6887].

   This document does not specify how PCP server names are provisioned
   to the PCP client.  It is the responsibility of PCP server
   provisioning document(s) to elaborate on the security considerations
   to discover a legitimate PCP server.

7.  IANA Considerations

   This document does not request any action from IANA.

8.  Acknowledgements

   Many thanks to D.  Thaler for the review and comments.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC6887]  Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)", RFC 6887, April
              2013.

9.2.  Informative References

   [I-D.ietf-pcp-dhcp]
              Boucadair, M., Penno, R., and D. Wing, "DHCP Options for
              the Port Control Protocol (PCP)", draft-ietf-pcp-dhcp-07
              (work in progress), March 2013.

   [RFC1123]  Braden, R., "Requirements for Internet Hosts - Application
              and Support", STD 3, RFC 1123, October 1989.

   [RFC3493]  Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
              Stevens, "Basic Socket Interface Extensions for IPv6", RFC
              3493, February 2003.






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   [RFC4116]  Abley, J., Lindqvist, K., Davies, E., Black, B., and V.
              Gill, "IPv4 Multihoming Practices and Limitations", RFC
              4116, July 2005.

   [RFC6055]  Thaler, D., Klensin, J., and S. Cheshire, "IAB Thoughts on
              Encodings for Internationalized Domain Names", RFC 6055,
              February 2011.

Appendix A.  Multi-homing

   The main problem of a PCP multi-homing situation can be succinctly
   described as 'one PCP client, multiple PCP servers'.  As described in
   Section 4, if a PCP client discovers multiple PCP server names, it
   should send requests to all of them in parallel with the following
   assumptions:

   o  There is no requirement that multiple PCP servers have the same
      capabilities.

   o  PCP requests to different servers are independent, the result of a
      PCP request to one server does not influence another.

   o  If PCP servers provide NAT, it is out of scope how the client
      manages ports across PCP servers.  For example, whether PCP client
      requires all external ports to be the same or whether there are
      ports available at all.

   The following sub-sections describe multi-homing examples to
   illustrate PCP client behavior.

A.1.  IPv6 Multi-homing

   In this example of an IPv6 multi-homed network, two or more routers
   co-located with firewalls are present on a single link shared with
   the host(s).  Each router is in turn connected to a different service
   provider network and the host in this environment would be offered
   multiple prefixes and advertised multiple DNS/NTP servers.  Consider
   a scenario in which firewalls within an IPv6 multi-homing environment
   also implement a PCP server.  PCP client learns of the available PCP
   servers using DHCP [I-D.ietf-pcp-dhcp] or any other PCP server
   discovery technique defined in future specifications.  The PCP client
   will send PCP requests in parallel to each of the PCP servers.

                       ==================
                       |    Internet    |
                       ==================
                          |          |
                          |          |



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                     +----+-+      +-+----+
                     | ISP1 |      | ISP2 |
                     +----+-+      +-+----+      ISP Network
                          |          |
    .........................................................
                          |          |
                          |          |        Subscriber Network
                  +-------+---+ +----+------+
                  | rtr1 with | | rtr2 with |
                  |   FW1     | |    FW2    |
                  +-------+---+ +----+------+
                          |          |
                          |          |
                          |          |
                   -----+-+-----+------
                          |
                        +-+-----+
                        | Hosts |
                        +-------+

                        Figure 1: IPv6 Multihoming

A.2.  IPv4 Multi-homing

   In this example an IPv4 multi-homed network described in 'NAT- or
   RFC2260-based multi-homing' (Section 3.3 of[RFC4116]), the gateway
   router is connected to different service provider networks.  This
   method uses PA addresses assigned by each transit provider to which
   the site is connected.  The site uses NAT to translate the various
   provider addresses into a single set of private-use addresses within
   the site.  In such a case, two PCP servers have to be present to
   control NAT to each of the transit providers.  PCP client learns of
   the available PCP servers using DHCP [I-D.ietf-pcp-dhcp] or any other
   PCP server discovery technique defined in future specifications.  The
   PCP client will send PCP requests in parallel to each of the PCP
   servers.

                     ====================
                     |    Internet       |
                     =====================
                        |              |
                        |              |
                   +----+--------+   +-+------------+
                   | ISP1        |   | ISP2         |
                   |             |   |              |
                   +----+--------+   +-+------------+ ISP Network
                        |              |
                        |              |



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      ..............................................................
                        |              |
                        | Port1        | Port2    Subscriber Network
                        |              |
                   +----+-----------------+
                   |   NAT & PCP servers  |
                   |       GW Router      |
                   +----+-----------------+
                        |
                        |
                        |
                   -----+-+-----+------
                        |
                      +-+-----+
                      | Hosts |  (private address space)
                      +-------+

                        Figure 2: IPv4 Multihoming

A.3.  Multiple interfaces and Servers

   In case for multi-homing when an end host such as a mobile terminal
   has multiple interfaces concurrently active (e.g., IEEE 802.11 and
   3G), a PCP client would discover different PCP servers over different
   interfaces.  Although multiple interfaces are available, an
   application might choose to use just one based on, for example, cost
   and bandwidth requirements, and therefore would need to send PCP
   requests to just one PCP server.

Authors' Addresses

   Mohamed Boucadair
   France Telecom
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com


   Reinaldo Penno
   Cisco
   USA

   Email: repenno@cisco.com







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   Dan Wing
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, California  95134
   USA

   Email: dwing@cisco.com


   Prashanth Patil
   Cisco Systems, Inc.
   Bangalore
   India

   Email: praspati@cisco.com


   Tirumaleswar Reddy
   Cisco Systems, Inc.
   Cessna Business Park, Varthur Hobli
   Sarjapur Marathalli Outer Ring Road
   Bangalore, Karnataka  560103
   India

   Email: tireddy@cisco.com

























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