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Versions: (draft-bpw-pcp-proxy) 00 01 02 03 04 05

PCP Working Group                                           M. Boucadair
Internet-Draft                                            France Telecom
Intended status: Standards Track                                R. Penno
Expires: August 17, 2013                                         D. Wing
                                                                   Cisco
                                                       February 13, 2013


               Port Control Protocol (PCP) Proxy Function
                        draft-ietf-pcp-proxy-02

Abstract

   This document specifies a new PCP functional element denoted as PCP
   Proxy.  The PCP Proxy relays PCP requests received from PCP Clients
   to upstream PCP Server(s).  This function is mandatory when PCP
   Clients can not be configured with the address of the PCP Server
   located more than one hop.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on August 17, 2013.

Copyright Notice

   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
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   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements Language  . . . . . . . . . . . . . . . . . . . .  3
   3.  PCP Server Discovery and Provisioning  . . . . . . . . . . . .  4
   4.  PCP Proxy as a PCP Server  . . . . . . . . . . . . . . . . . .  4
   5.  Control of the Firewall  . . . . . . . . . . . . . . . . . . .  4
   6.  No NAT is Co-located with the PCP Proxy  . . . . . . . . . . .  4
   7.  PCP Proxy Co-located with a NAT Function . . . . . . . . . . .  5
   8.  MAP/PEER Handling  . . . . . . . . . . . . . . . . . . . . . .  6
   9.  Mapping Repair . . . . . . . . . . . . . . . . . . . . . . . .  7
   10. Advanced Functions . . . . . . . . . . . . . . . . . . . . . .  8
     10.1.  Multiple PCP Servers  . . . . . . . . . . . . . . . . . .  8
     10.2.  Epoch Handling  . . . . . . . . . . . . . . . . . . . . .  8
     10.3.  Request/Response Caching  . . . . . . . . . . . . . . . .  9
     10.4.  Retransmission Handling . . . . . . . . . . . . . . . . .  9
     10.5.  Full State  . . . . . . . . . . . . . . . . . . . . . . .  9
   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   12. Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     14.1.  Normative References  . . . . . . . . . . . . . . . . . . 10
     14.2.  Informative References  . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11























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1.  Introduction

   This document defines a new PCP [I-D.ietf-pcp-base] function element,
   called PCP Proxy, which is meant to facilitate the communication
   between a PCP Client and upstream PCP Server(s).  The PCP Proxy acts
   as a PCP Server receiving PCP requests on internal interfaces, and as
   a PCP Client forwarding accepted PCP requests on an external
   interface to a PCP Server.  The PCP Server in turn sends PCP
   responses to the PCP Proxy external interface which are finally
   forwarded to PCP Clients.  A reference architecture is depicted in
   Figure 1.

   A PCP Proxy can be for instance embedded in a CP (Customer Premises)
   router while the PCP Server is located in a network operated by an
   ISP (Internet Service Provider).  It is out of scope of this document
   to list all deployment scenarios requiring a PCP Proxy to be
   involved.

   The PCP Proxy can be simple (i.e., a single-homed entity which
   implement as transparent/minimal processing as possible) or it can
   support advanced features (see Section 10).  A Proxy can be co-
   located with UPnP IGD [I-D.ietf-pcp-upnp-igd-interworking] or/and
   NAT-PMP [I-D.bpw-pcp-nat-pmp-interworking] Interworking Function
   (IWF).


            +------------+
            | PCP Client |-----+
            +--(Host 1)--+     |   +-----------+       +----------+
                               +---|           |       |          |
                                   | PCP Proxy |-------|PCP Server|
                               +---|           |       |          |
            +------------+     |   +-----------+       +----------+
            | PCP Client |-----+
            +--(Host 2)--+

          Internal PCP Clients


                     Figure 1: Reference Architecture


2.  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].




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3.  PCP Server Discovery and Provisioning

   The PCP Proxy MUST follow the procedure defined in Section 8.1 of
   [I-D.ietf-pcp-base] to discover its PCP Server.

   The address of the PCP Proxy is provisioned to internal PCP Clients
   (see Figure 1) as their default PCP Server: If the PCP DHCP option
   [I-D.ietf-pcp-dhcp] is supported by an internal PCP Client, it will
   retrieve the PCP Server IP address to use from its local DHCP server;
   otherwise internal PCP Clients will assume their default router being
   the PCP Server.


4.  PCP Proxy as a PCP Server

   The PCP Proxy acts as a PCP Server for internal hosts and accepts PCP
   requests on the interface(s) facing them.

   When the topology makes a routing loop possible, the PCP Proxy MAY
   check it is not the source of a PCP message it received.


5.  Control of the Firewall

   A security policy to accept PCP messages from the provisioned PCP
   Server(s) is to be enabled on the device embedding the PCP Proxy.
   This policy can be for instance triggered by DHCP configuration or by
   outbound PCP requests issued from the PCP Proxy to the provisioned
   PCP Server.

   In order to accept inbound and outbound traffic associated with PCP
   mappings instantiated in the upstream PCP Server, appropriate
   security policies are to be configured on the firewall.

   For instance if the firewall rules have a lifetime, PCP response can
   be snooped in order to instantiate the corresponding firewall rules
   with the same lifetime.  If they have no lifetime, an explicit
   dynamic mapping table can be kept in the PCP Proxy state in order to
   instantiate and remove corresponding firewall rules.

   FILTER Options can be installed into the local firewall, forwarded to
   the PCP Server so installed into the remote NAT/firewall or both.


6.  No NAT is Co-located with the PCP Proxy

   When no NAT is co-located with the PCP Proxy, the port numbers
   included in received PCP messages (from the PCP Server or PCP



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   Client(s)) are not altered by the PCP Proxy.  Nevertheless, the PCP
   Client IP Address MUST be changed to the address of the PCP Proxy and
   a THIRD_PARTY Option inserted to carry the IP address of the source
   PCP Client.

   Because no NAT is invoked, there is no reachability failure risk to
   relay to the PCP Server unknown Options and OpCodes which carry an IP
   address.


7.  PCP Proxy Co-located with a NAT Function

   When the PCP Proxy is co-located with a NAT function, it MUST update
   the content of received requests with the mapped port number and the
   address belonging to the external interface of the PCP Proxy (i.e.,
   after the NAT operation) and not as initially positioned by the PCP
   Client.  For the reverse path, PCP responses MUST be updated by the
   PCP Proxy to replace the internal port number to what has been
   initially positioned by the PCP Client.  For this purpose the PCP
   Proxy MUST have an access to the local NAT state maintained locally.
   Because PCP messages with an unknown OpCode or Option can carry a
   hidden internal address or internal port which will not be
   translated:

   o  a PCP Proxy co-located with a NAT SHOULD reject by an
      UNSUPP_OPCODE error response a received request with an unknown
      OpCode;

   o  a PCP Proxy co-located with a NAT SHOULD reject by an
      UNSUPP_OPTION error response a received request with a mandatory-
      to-process unknown Option;

   o  a PCP Proxy co-located with a NAT MAY remove any optional-to-
      process unknown Options from received requests before forwarding
      them.

   Rejecting unknown Options and OpCodes has the drawback of preventing
   a PCP Client to make use of new capabilities offered by the PCP
   Server but not supported by the PCP Proxy even if no IP address
   and/or port is included in the Option/OpCode.

   When a PCP request is received and accepted by the PCP Proxy the
   corresponding mapping (explicit dynamic mapping for a MAP request,
   implicit dynamic mapping for a PEER request) is looked for in the
   local NAT state and temporary created if it does not exist.
   "Temporary" means it is deleted if no SUCCESS response is received,
   either explicitly or because of its short lifetime at creation.




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   If the local NAT associates explicit dynamic mappings to a lifetime,
   the requested lifetime in MAP requests SHOULD be adjusted to be in
   the accepted range of the local NAT, and the assigned lifetime copied
   from MAP responses to the corresponding mapping in the local NAT.
   The same processing applies to implicit dynamic mappings and PEER
   requests/responses.

   Otherwise explicit dynamic mappings have an undefined lifetime in the
   local NAT and the PCP Proxy SHOULD maintain an explicit dynamic
   mapping table and SHOULD delete corresponding explicit dynamic
   mappings in the local NAT when they expire or are deleted by the MAP
   request with a zero requested lifetime.


8.  MAP/PEER Handling

   A simple PCP Proxy performs minimal modifications to PCP requests and
   responses, in particular it does not change the Nonce value in
   requests and the Epoch value in responses.  A simple PCP Proxy is
   assumed to handle only one PCP Server.

   For handling THIRD_PARTY option, the PCP Proxy MUST follow the PCP
   Server behavior specified in Section 13.1 of [I-D.ietf-pcp-base].

   The detailed behavior at the reception of a PCP request on an
   internal interface is as follows:

   o  Check if the source IP address and the PCP Client IP Address are
      the same.

   o  Apply security controls (e.g., THIRD_PARTY filtering).

   o  If the request is rejected, build a synthetic error response and
      send it back to the PCP Client.

   o  If the request is accepted, adjust it (e.g., adding a THIRD_PARTY
      Option, updating the PCP Client IP Address and Internal Port to
      their translated values as specified in Section 7 and forward it
      on a fresh UDP socket connected to the PCP Server).

   o  Wait for the response during a reasonable delay.

   o  When the response is received from the PCP Server, adjust it back
      (e.g., removing the THIRD_PARTY Option added previously, updating
      the PCP Client IP Address and Internal Port to their initial
      values as specified in Section 7), forward it to the source PCP
      Client and close the socket to the PCP Server.




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   o  On a hard error on the UDP socket, build a synthetic ICMP error
      and send it to the source PCP Client.

   The reasonable delay minimum value is 20 seconds, request
   retransmission is handled by PCP clients.

   For each pending request, the proxy MUST maintain in a data record:

   o  the request payload

   o  the interface where the request was received

   o  the source IP address of the request

   o  the source UDP port of the request

   o  the UDP socket connected to the PCP server

   o  an expire timeout

   Receiving interfaces can be implemented by a set of servicing
   sockets, each socket bound to an address of an internal interface.
   Interface, source address and port are used to send back packets to
   the source PCP Client.  The request payload is used to generate
   synthetic ICMP.  Responses are received on the UDP socket.

   Too large requests SHOULD be forwarded to the PCP Server in order to
   relay back the error response, i.e., the PCP Proxy is not in charge
   to enforce the message size limit and in general the PCP Proxy SHOULD
   NOT generate error response for a reason other than security
   controls.  No behavior is specified in the case the PCP Proxy
   processing (e.g., adding a THIRD_PARTY Option) makes a valid request
   too large when it is sent to the PCP Server.


9.  Mapping Repair

   ANNOUNCE requests received from PCP Clients are handled locally; as
   such these requests MUST NOT be relayed to the provisioned PCP
   Server.

   Upon receipt of an unsolicited ANNOUNCE response from a PCP Server,
   the PCP Proxy proceeds to renewing the mappings and checks whether
   there are changes compared to a local cache if it is maintained by
   the PCP Proxy.  If no change is detected, no unsolicited ANNOUNCE is
   generated towards PCP Clients.  If a change is detected, the PCP
   Proxy MUST generate unsolicited ANNOUNCE message(s) to appropriate
   PCP Clients.  If the PCP Proxy does not maintain a local cache for



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   the mappings, unsolicited ANNOUNCE messages are relayed to PCP
   Clients.

   Unsolicited PCP MAP/PEER responses received from a PCP Server are
   handled as any normal MAP/PEER response.  To handle unsolicited PCP
   MAP/PEER responses, the PCP Proxy is required to maintain a local
   cache of instantiated mappings in the PCP Server (Section 10.5).

   Upon change of its external IP address, the PCP Proxy SHOULD renew
   the mappings it maintained.  If the PCP Server assigns a different
   external port, the PCP Proxy SHOULD follow the mapping repair
   procedure defined in [I-D.ietf-pcp-base].  This can be achieved only
   if a full state table is maintained by the PCP Proxy.


10.  Advanced Functions

   Below are listed a set of advanced features which may be supported by
   the PCP Proxy.

10.1.  Multiple PCP Servers

   A PCP Proxy MAY handle multiple PCP Servers at the same time, each
   PCP Server is associated to each own handled Epoch value according to
   Section 10.2.  PCP Clients are not aware of the presence of multiple
   PCP Servers.

   According to [I-D.ietf-pcp-dhcp], if several PCP Names are configured
   to the PCP Proxy, it will contact in parallel all these PCP Servers.

   In some contexts (e.g., PCP-controlled CGNs), the PCP Proxy MAY load
   balance the PCP Client among available PCP Servers.  The PCP Proxy
   MUST ensure requests of a given PCP Client are relayed to the same
   PCP Server.

   In other deployment scenarios (e.g., presence of multiple PCP-
   controlled firewalls), the PCP Proxy MUST relay PCP requests to all
   these PCP Servers.

   The PCP Proxy MAY rely on some fields (e.g., Zone ID
   [I-D.penno-pcp-zones]) in the PCP request to redirect the request to
   a given PCP Server.

10.2.  Epoch Handling

   A PCP Proxy MAY use its own internal timers and not blindly copy them
   from PCP responses.  There should be no advantages to have more than
   one managed Epoch per PCP Server.



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   The Epoch MUST be reset when explicit dynamic mappings are lost,
   i.e.:

   o  at startup if the PCP Proxy can't recover the state.

   o  when the WAN address is changed or any similar events which show
      any previous state is no longer valid.

   o  when the Epoch value in a PCP response is too small (cf. Epoch
      value validation rules in [I-D.ietf-pcp-base]).

   o  when the External IP Address has changed.

   The last two rules are per PCP Server, a PCP Proxy MAY check these
   conditions in all received responses for a PCP Server.

10.3.  Request/Response Caching

   A PCP Proxy providing request/response caching checks each time it
   receives a PCP request if it has already seen the same request
   recently and got the corresponding PCP response.  In this case, it
   sends back directly the cached response with the proper Epoch value
   and not forward the request to the PCP Server.

10.4.  Retransmission Handling

   An extension of the previous service is to manage the retransmission
   of pending requests to the PCP Server internally, i.e., no longer
   driven by the PCP Client.  A cache entry SHOULD be expired after a
   delay short enough to keep it easy to distinguish it from a replay.

10.5.  Full State

   A PCP Proxy MAY keep the full state, i.e., an image of all active
   explicit dynamic mappings is kept in memory.  When this service is
   supported the state SHOULD be recovered in case of failures (e.g.,
   according to [I-D.boucadair-pcp-failure]).


11.  IANA Considerations

   This document makes no request of IANA.


12.  Security Considerations

   The PCP Proxy MUST follow the security considerations elaborated in
   [I-D.ietf-pcp-base] for both the client and server side.



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   A received request carrying an unknown OpCode or Option SHOULD be
   dropped (or in the case of an unknown Option which is not mandatory-
   to-process the Option be removed) if it is not a priori compatible
   with security controls or correct processing.

   The device embedding the PCP Proxy MAY block PCP requests directly
   sent to the PCP Server.  This can be enforced using access control
   lists (ACLs).


13.  Acknowledgements

   Many thanks to C. Zhou and T. Reddy for their review and comments.

   Special thanks to F. Dupont who contributed to this document.


14.  References

14.1.  Normative References

   [I-D.ietf-pcp-base]
              Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)",
              draft-ietf-pcp-base-29 (work in progress), November 2012.

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

14.2.  Informative References

   [I-D.boucadair-pcp-failure]
              Boucadair, M., Dupont, F., and R. Penno, "Port Control
              Protocol (PCP) Failure Scenarios",
              draft-boucadair-pcp-failure-04 (work in progress),
              August 2012.

   [I-D.bpw-pcp-nat-pmp-interworking]
              Boucadair, M., Penno, R., Wing, D., and F. Dupont, "Port
              Control Protocol (PCP) NAT-PMP Interworking Function",
              draft-bpw-pcp-nat-pmp-interworking-00 (work in progress),
              March 2011.

   [I-D.ietf-pcp-dhcp]
              Boucadair, M., Penno, R., and D. Wing, "DHCP Options for
              the Port Control Protocol (PCP)", draft-ietf-pcp-dhcp-05
              (work in progress), September 2012.




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   [I-D.ietf-pcp-upnp-igd-interworking]
              Boucadair, M., Penno, R., and D. Wing, "Universal Plug and
              Play (UPnP) Internet Gateway Device (IGD)-Port Control
              Protocol (PCP) Interworking Function",
              draft-ietf-pcp-upnp-igd-interworking-06 (work in
              progress), December 2012.

   [I-D.penno-pcp-zones]
              Penno, R., "PCP Support for Multi-Zone Environments",
              draft-penno-pcp-zones-01 (work in progress), October 2011.


Authors' Addresses

   Mohamed Boucadair
   France Telecom
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com


   Reinaldo Penno
   Cisco
   USA

   Email: repenno@cisco.com


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

   Email: dwing@cisco.com















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