PCP Working Group                                           M. Boucadair
Internet-Draft                                            France Telecom
Updates: 6887 (if approved)                                     R. Penno
Intended status: Standards Track                                 D. Wing
Expires: July 10, 2014                                          P. Patil
                                                                T. Reddy
                                                                   Cisco
                                                        January 06, 2014


                          PCP Server Selection
                   draft-ietf-pcp-server-selection-02

Abstract

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

   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 July 10, 2014.







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Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  IP Address Selection  . . . . . . . . . . . . . . . . . . . .   3
   4.  Multiple Interfaces . . . . . . . . . . . . . . . . . . . . .   4
   5.  Example: Multiple PCP servers on a Single Interface . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  Multi-homing . . . . . . . . . . . . . . . . . . . .   8
     A.1.  IPv6 Multi-homing . . . . . . . . . . . . . . . . . . . .   8
     A.2.  IPv4 Multi-homing . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Multiple IP addresses may be configured on a PCP client in some
   deployment contexts such as multi-homing (see Appendix A).  A PCP
   server may also have multiple IP addresses associated with it.  This
   document specifies the behavior to be followed by the PCP client
   [RFC6887] to contact its PCP server(s) [RFC6887] when it receives one
   or several PCP server IP addresses (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 IP addresses.

   It is out of scope of this document to enumerate all deployment
   scenarios that require multiple IP addresses to be configured.




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2.  Terminology

   This document makes use of the following terms:

   o  PCP server denotes a functional element that 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].

3.  IP Address Selection

   These steps specify the behavior to be followed by the PCP client to
   contact a PCP server when the PCP client has multiple IP addresses
   for a single PCP server.  Additional considerations to be taken into
   account when the PCP client is multi-interfaced are specified in
   Section 4:

   1.  If the PCP client can use both address families when
       communicating to a particular PCP server, the PCP client SHOULD
       select the source address of the PCP request to be of the same IP
       address family as its requested PCP mapping (i.e., the address
       family of the Requested External IP Address).

   2.  Whenever communicating with a PCP server, the rules of Section 6
       of [RFC6724] SHOULD be followed by using the source address
       selected in the previous step as input to the destination address
       selection algorithm.

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

   4.  The PCP client sends its PCP message to the PCP server's IP
       address following the retransmission procedure specified in
       Section 8.1.1 of [RFC6887].  If no response is received after MRC
       attempts, the PCP client re-tries the procedure excluding the
       destination addresses which did not respond.  The PCP client
       SHOULD ignore any response received from an IP address after
       exhausting MRC attempts for that particular IP address.  If, when
       sending PCP requests, the PCP client receives a hard ICMP error
       [RFC1122] it SHOULD immediately try the next IP address from the
       list of PCP server' IP addresses.






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   5.  If the PCP client has exhausted all IP addresses configured for a
       given PCP server, the procedure is repeated every fifteen minutes
       until the PCP request is successfully answered.

   6.  Once the PCP client has successfully received a response from a
       PCP server's IP address, it sends subsequent PCP requests to the
       same server's IP address until that IP address becomes non-
       responsive, which causes the PCP client to follow the steps above
       to contact its PCP server.

   For efficiency, the PCP client should use the same Mapping Nonce for
   requests sent to all PCP server' IP addresses.

   If several PCP servers are configured, each with multiple IP
   addresses, the PCP client contacts all PCP servers in parallel
   following the steps described above.  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 implementation-specific and only the PCP client can decide
   whether all mappings are needed or only a subset of them.

4.  Multiple Interfaces

   When an end host has multiple interfaces concurrently active (e.g.,
   IEEE 802.11 and 3G), a PCP client would discover different PCP
   servers over different interfaces.  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.  Particularly, the PCP client relies on the
   source IP address of an outgoing PCP request to select which PCP
   server(s) to use.

   Although multiple interfaces may be available, a PCP client 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.

   Generic multi-interfaces considerations are documented in Section 8.4
   of [RFC6887]

5.  Example: Multiple PCP servers on a Single Interface

   Figure 1 depicts an example that is used to illustrate the server
   selection procedure specified in Section 3.







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                               ISP Network
                             |              |
       .........................................................
                             |              |        Subscriber Network
                     +-------+------+  +----+---------+
                     | PCP-Server-A |  | PCP-Server-B |
                     |              |  |              |
                     +-------+------+  +----+---------+
            192.0.2.1        |              |     198.51.100.1
            2001:db8:2222::1 |              |     2001:db8:3333::1
                             |              |
                             |              |
                      -------+--------------+-----------
                                     |
                                     |    203.0.113.0
                                     |    2001:db8:1111::1
                                 +---+---+
                                 | Host  |
                                 +-------+

                                 Figure 1

   The example shows the experienced behavior when a single IP address
   for one PCP server is not responsive.  The PCP client is configured
   with two PCP servers, PCP-Server-A and PCP-Server-B each having two
   IP addresses, an IPv4 address and an IPv6 address.  The PCP client
   wants an IPv4 mapping so it orders the addresses as follows:

   o  PCP-Server-A:

      *  192.0.2.1

      *  2001:db8:1111::1

   o  PCP-Server-B:

      *  198.51.100.1

      *  2001:db8:2222::1

   Suppose that:

   o  The path to reach 192.0.2.1 is broken

   o  The path to reach 2001:db8:1111::1 is working

   o  The path to reach 198.51.100.1 is working




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   o  The path to reach 2001:db8:2222::1 is working

   The PCP client sends two PCP requests at the same time, the first to
   192.0.2.1 (corresponding to PCP-Server-A) and the second to
   198.51.100.1 (corresponding to PCP-Server-B).  The path to
   198.51.100.1 is working so a PCP response is received.  Because the
   path to 192.0.2.1 is broken, no PCP response is received.  The PCP
   client retries 4 times to elicit a response from 192.0.2.1 and
   finally gives up on that address and sends a PCP message to
   2001::db8:1111:1.  That path is working, and a response is received.
   Thereafter, the PCP client should continue using that responsive IP
   address for PCP-Server-A (2001:db8:1111::1).  In this particular
   case, it will have to use THIRD_PARTY option for IPv4 mappings.

6.  Security Considerations

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

   This document does not specify how PCP server addresses are
   provisioned to the PCP client.  It is the responsibility of any 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 Dave 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.

   [RFC6724]  Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
              "Default Address Selection for Internet Protocol Version 6
              (IPv6)", RFC 6724, September 2012.

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






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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-09
              (work in progress), November 2013.

   [RFC1122]  Braden, R., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122, October 1989.

   [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.

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































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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 3, if a PCP client discovers multiple PCP servers, 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 the 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 servers.  Consider a
   scenario in which firewalls within an IPv6 multi-homing environment
   also implement a PCP server.  The PCP client learns the available PCP
   servers using DHCP [I-D.ietf-pcp-dhcp] or any other provisioning
   mechanism.  In reference to Figure 2, a typical model is to embed
   DHCP servers in rtr1 and rtr2.  A host located behind rtr1 and rtr2
   can contact these two DHCP server and retrieves from each server the
   IP address of the corresponding PCP server.

   The PCP client will send PCP requests in parallel to each of the PCP
   servers.












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                          ==================
                          |    Internet    |
                          ==================
                             |          |
                             |          |
                        +----+-+      +-+----+
                        | ISP1 |      | ISP2 |
                        +----+-+      +-+----+      ISP Network
                             |          |
       .........................................................
                             |          |
                             |          |        Subscriber Network
                     +-------+---+ +----+------+
                     | rtr1 with | | rtr2 with |
                     |   FW1     | |    FW2    |
                     +-------+---+ +----+------+
                             |          |
                             |          |
                      -------+----------+------
                                  |
                              +---+---+
                              | Host  |
                              +-------+

                        Figure 2: 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 Provider-Aggregatable (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.  The PCP client learns the available PCP servers using
   DHCP [I-D.ietf-pcp-dhcp] or any other provisioning mechanism.  In
   reference to Figure 3, a typical model is to embed the DHCP server
   and the PCP servers in rtr1.  A host located behind rtr1 can contact
   the DHCP server to obtain IP addresses of the PCP servers.  The PCP
   client will send PCP requests in parallel to each of the PCP servers.









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                        =====================
                        |    Internet       |
                        =====================
                           |              |
                           |              |
                      +----+--------+   +-+------------+
                      | ISP1        |   | ISP2         |
                      |             |   |              |
                      +----+--------+   +-+------------+ ISP Network
                           |              |
                           |              |
         ..............................................................
                           |              |
                           | Port1        | Port2    Subscriber Network
                           |              |
                      +----+-------------------+
                      |rtr1: NAT & PCP servers |
                      |       GW Router        |
                      +----+-------------------+
                           |
                           |
                           |
                      -----+--------------
                           |
                         +-+-----+
                         | Host  |  (private address space)
                         +-------+

                        Figure 3: IPv4 Multihoming

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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