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PCP Working Group                                           M. Boucadair
Internet-Draft                                            France Telecom
Intended status: Informational                                  R. Penno
Expires: November 17, 2013                                         Cisco
                                                            May 16, 2013


       Analysis of Port Control Protocol (PCP) Failure Scenarios
                     draft-boucadair-pcp-failure-06

Abstract

   This document identifies and analyzes several PCP failure scenarios.
   Identifying these failure scenarios is useful to assess the
   efficiency of the protocol and also to decide whether new PCP
   extensions are needed.

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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   This Internet-Draft will expire on November 17, 2013.

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

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  PCP Client Failure Scenarios  . . . . . . . . . . . . . . . .   2
     2.1.  Change of the IP Address of The PCP Server  . . . . . . .   2
     2.2.  Application Crash . . . . . . . . . . . . . . . . . . . .   3
     2.3.  PCP Client Crash  . . . . . . . . . . . . . . . . . . . .   4
     2.4.  Change of the Internal IP Address . . . . . . . . . . . .   4
     2.5.  Change of the CPE WAN IP Address  . . . . . . . . . . . .   5
     2.6.  UPnP IGD/PCP IWF  . . . . . . . . . . . . . . . . . . . .   6
   3.  Restart or Failure of the PCP Server  . . . . . . . . . . . .   6
     3.1.  Basic Rule  . . . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  Clear PCP Mappings  . . . . . . . . . . . . . . . . . . .   7
     3.3.  State Redundancy is Enabled . . . . . . . . . . . . . . .   7
     3.4.  Cold-Standby without State Redundancy . . . . . . . . . .   7
     3.5.  Anycast Redundancy Mode . . . . . . . . . . . . . . . . .   7
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Appendix A.  PCP State Synchronization: Overview  . . . . . . . .   9
   Appendix B.  GET/NEXT Operation . . . . . . . . . . . . . . . . .   9
     B.1.  OpCode Format . . . . . . . . . . . . . . . . . . . . . .   9
     B.2.  OpCode-Specific Result Code . . . . . . . . . . . . . . .  11
     B.3.  Ordering and Equality . . . . . . . . . . . . . . . . . .  11
     B.4.  NEXT Option . . . . . . . . . . . . . . . . . . . . . . .  11
     B.5.  GET/NEXT PCP Client Theory of Operation . . . . . . . . .  14
     B.6.  GET/NEXT PCP Server Theory of Operation . . . . . . . . .  14
     B.7.  Flow Examples . . . . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18


1.  Introduction

   This document discusses several failure scenarios that may occur when
   deploying PCP [RFC6887].

2.  PCP Client Failure Scenarios

2.1.  Change of the IP Address of The PCP Server

   When a new IP address is used to reach its PCP Server, the PCP Client
   must re-create all of its explicit dynamic mappings using the newly
   discovered IP address.





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   The PCP Client must undertake the same process as per refreshing an
   existing explicit dynamic mapping (see [RFC6887]); the only
   difference is the PCP requests are sent to a distinct IP address.  No
   specific behavior is required from the PCP Server for handling these
   requests.

      Proposed Action: No particular extension is required to be added
      to the base specification to mitigate this failure scenario.

2.2.  Application Crash

   When a fatal error is encountered by an application relying on PCP to
   open explicit dynamic mappings on an upstream device, and upon the
   restart of that application, the PCP Client should issue appropriate
   requests to refresh the explicit dynamic mappings of that application
   (e.g., clear old mappings and install new ones using the new port
   number used by the application).

   If the same port number is used but a distinct Mapping Nonce is
   generated, the request will be rejected with a NOT_AUTHORIZED error
   with the Lifetime of the error indicating duration of that existing
   mapping (see Section 2.7 of [I-D.boucadair-pcp-flow-examples]).

      Proposed Action: A solution to recover the Mapping Nonce used when
      instantiating the mapping may be envisaged; this solution may not
      be viable if PCP authentication is not in use.  Mapping Nonce
      recovery in the simple PCP threat model (especially when Mapping
      Check validation is enabled) induces the same security threated as
      those discussed in [RFC6887].

   If a distinct port number is used by the application to bound its
   service (i.e., a new internal port number is to be signaled in PCP),
   the PCP Server may honor the refresh requests if the per-subscriber
   quota is not exceeded.  A distinct external port number would be
   assigned by the PCP Server due to the presence of "stale" explicit
   dynamic mapping(s) associated with the "old" port number.

      Proposed Action: To avoid this inconvenience induced by stale
      explicit dynamic mappings, the PCP Client may clear the "old"
      mappings before issuing the refresh requests; but this would
      require the PCP Client to store the information about the "old"
      port number.  This can be easy to solve if the PCP Client is
      embedded in the application.  In some scenarios, this is not so
      easy because the PCP Client may handle PCP requests on behalf of
      several applications and no means to identify the requesting
      application may be supported.  Means to identify the application
      may be envisaged.




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      [RFC6887] does not allow a PCP Client to issue a request to delete
      all the explicit dynamic mappings associated with an internal IP
      address.  If a PCP Client is allowed to clear all mappings bound
      to the same IP address, this would have negative impact on other
      applications and PCP Client(s) which may use the same internal IP
      address to instruct their explicit dynamic mappings in the PCP
      Server.

2.3.  PCP Client Crash

   The PCP Client may encounter a fatal error leading to its restart.
   In such case, the internal IP address and port numbers used by
   requesting applications are not impacted.  Therefore, the explicit
   dynamic mappings as maintained by the PCP Server are accurate and
   there is no need to refresh them.

   On the PCP Client side, a new UDP port should be assigned to issue
   PCP requests.  As a consequence, if outstanding requests have been
   sent to the PCP Server, the responses are likely to be lost.

   If the PCP Client stores its explicit dynamic mappings in a
   persistent memory, there is no need to retrieve the list of active
   mappings from the PCP Server.

      Proposed Action: If several PCP Clients are co-located on the same
      host, related PCP mapping tables should be uniquely distinguished
      (e.g., a PCP Client does not delete explicit dynamic mappings
      instructed by another PCP Client).

   If the PCP Client does not store the explicit dynamic mappings and
   new Mapping Nonces are assigned, the PCP Server will reject to
   refresh these mappings.

      Proposed Action: This issue can be solved if the PCP Client uses
      GET OpCode (Appendix B) to recover the mapping nonces used when
      instantiating the mappings if PCP authentication is used or
      Mapping Nonce validation check is disabled.

2.4.  Change of the Internal IP Address

   When a new IP address is assigned to a host embedding a PCP Client,
   the PCP Client must install on the PCP Server all the explicit
   dynamic mappings it manages, using the new assigned IP address as the
   internal IP address.  The hinted external port number won't be
   assigned by the PCP Server since a "stale" mapping is already
   instantiated by the PCP Server (but it is associated with a distinct
   internal IP address).




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   For a host configured with several addresses, the PCP Client must
   maintain a record about the target IP address it used when issuing
   its PCP requests.  If no record is maintained and upon a change of
   the IP address or de-activation of an interface, the PCP-instructed
   explicit dynamic mappings are broken and inbound communications will
   fail to be delivered.

   Depending on the configured policies, the PCP Server may honor all or
   part of the requests received from the PCP Client.  Upon receipt of
   the response from the PCP Server, the PCP Client must update its
   local PCP state with the new assigned port numbers and external IP
   address.

      Proposed Action: Because of the possible negative impact if the
      quota is exceed due to the presence of stale mappings (see the
      example in Section 2.14 of [I-D.boucadair-pcp-flow-examples]), a
      procedure to clear stale mappings may have some benefits.

   A PCP Client may be used to manage explicit dynamic mappings on
   behalf of a third party (i.e., the PCP Client and the third party are
   not co-located on the same host).  If a new internal IP address is
   assigned to that third party (e.g., webcam), the PCP Client should be
   instructed to delete the old mapping(s) and create new one(s) using
   the new assigned internal IP address.  When the PCP Client is co-
   located with the DHCP server (e.g., PCP Proxy [I-D.ietf-pcp-proxy],
   IWF in the CP router [I-D.ietf-pcp-upnp-igd-interworking]), the state
   can be updated using the state of the local DHCP server.  Otherwise,
   it is safe to recommend the use of static internal IP addresses if
   PCP is used to configure third-party explicit dynamic mappings.

      Proposed Action: No particular extension is required to be added
      to the base specification to mitigate this failure scenario.

2.5.  Change of the CPE WAN IP Address

   The change of the IP address of the WAN interface of the CPE would
   have an impact on the accuracy of the explicit dynamic mappings
   instantiated in the PCP Server:

   o  For the DS-Lite case [RFC6333]: if a new IPv6 address is used by
      the B4 element when encapsulating IPv4 packets in IPv6 ones, the
      explicit dynamic mappings should be refreshed: If the PCP Client
      is embedded in the B4, the refresh operation is triggered by the
      change of the B4 IPv6 address.  This would be more complicated
      when the PCP Client is located in a device behind the B4.  If a
      PCP Proxy is embedded in the CPE, the proxy can use ANNOUNCE
      OpCode towards internal IPv4 hosts behind the DS-Lite CPE.




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   o  For the NAT64 case [RFC6146], any change of the assigned IPv6
      prefix delegated to the CPE will be detected by the PCP Client
      (because this leads to the allocation of a new IPv6 address).  The
      PCP Client has to undertake the operation described in
      Section 2.4.

   o  For the NAT444 case, similar problems are encountered because the
      PCP Client has no reasonable way to detect the CPE's WAN address
      changed.

      Proposed Action: Means to help detecting the CPE's WAN address
      change would help in mitigating this failure scenario.

2.6.  UPnP IGD/PCP IWF

   In the event an UPnP IGD/PCP IWF [I-D.ietf-pcp-upnp-igd-interworking]
   fails to renew a mapping, there is no mechanism to inform the UPnP
   Control Point about this failure.

      Proposed Action: This issue can not be solved.

   On the reboot of the IWF, if no mapping table is maintained in a
   permanent storage, "stale" mappings will be maintained by the PCP
   Server and per-user quota will be consumed.  This is even exacerbated
   if new mapping nonces are assigned by the IWF.

      Proposed Action: This issue can be soften by synchronizing the
      mapping table owing to the invocation of the GET OpCode defined in
      Appendix B.  This procedure is supported only if Mapping Nonce
      validation checks are disabled.

3.  Restart or Failure of the PCP Server

   This section covers failure scenarios encountered by the PCP Server.

3.1.  Basic Rule

   In any situation the PCP Server loses all or part of its PCP state,
   the Epoch value must be reset when replying to received requests.
   Doing so would allow PCP Client to audit its explicit dynamic mapping
   table.

   If the state is not lost, the PCP Server must not reset the Epoch
   value returned to requesting PCP Clients.

      Proposed Action: No action is required to update the base PCP
      specification for this failure scenario.




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3.2.  Clear PCP Mappings

   When a command line or a configuration change is enforced to clear
   all or a subset of PCP explicit dynamic mappings maintained by the
   PCP Server, the PCP Server must reset its Epoch to zero value.

   In order to avoid all PCP Clients to update their explicit dynamic
   mappings, the PCP Server should reset the Epoch to zero value only
   for impacted users.

      Proposed Action: No action is required to update the base PCP
      specification for this failure scenario.

3.3.  State Redundancy is Enabled

   When state redundancy is enabled, the state is not lost during
   failure events.  Failures are therefore transparent to requesting PCP
   Clients.  When a backup device takes over, Epoch must not be reset to
   zero.

      Proposed Action: No action is required to update the base PCP
      specification for this failure scenario.

3.4.  Cold-Standby without State Redundancy

   In this section we assume that a redundancy mechanisms is configured
   between a primary PCP-controlled device and a backup one but without
   activating any state synchronization for the PCP-instructed explicit
   dynamic mappings between the backup and the primary devices.

   If the primary PCP-controlled device fails and the backup one takes
   over, the PCP Server must reset the Epoch to zero value.  Doing so
   would allow PCP Clients to detect the loss of states in the PCP
   Server and proceed to state synchronization.

      Proposed Action: No action is required to update the base PCP
      specification for this failure scenario.

3.5.  Anycast Redundancy Mode

   When an anycast-based mode is deployed (i.e., the same IP address is
   used to reach several PCP Servers) for redundancy reasons, the change
   of the PCP Server which handles the requests of a given PCP Client
   won't be detected by that PCP Client.

   Tweaking the Epoch (Section 8.5 of [RFC6887]) may help to detect the
   loss of state and therefore to re-create missing explicit dynamic
   mappings.



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      Proposed Action: No action is required to update the base PCP
      specification for this failure scenario.

4.  Security Considerations

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

5.  IANA Considerations

   No action is required from IANA.

6.  Acknowledgements

   Francis Dupont contributed text to this document.  Many thanks to
   him.

7.  References

7.1.  Normative References

   [I-D.ietf-pcp-proxy]
              Boucadair, M., Penno, R., and D. Wing, "Port Control
              Protocol (PCP) Proxy Function", draft-ietf-pcp-proxy-02
              (work in progress), February 2013.

   [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-10 (work in progress), April 2013.

   [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.

7.2.  Informative References

   [I-D.boucadair-pcp-flow-examples]
              Boucadair, M., "PCP Flow Examples", draft-boucadair-pcp-
              flow-examples-00 (work in progress), February 2013.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, April 2011.




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   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, August 2011.

Appendix A.  PCP State Synchronization: Overview

   The following sketches the state synchronization logic:

   o  One element (i.e., PCP Client/host/application, PCP Server, PCP
      Proxy, PCP IWF) of the chain is REQUIRED to use stable storage

   o  If the PCP Client (resp., the PCP Server) crashes and restarts it
      just have to synchronize with the PCP Server (resp., the PCP
      Client);

   o  If both crash then one has to use stable storage and we fall back
      in the previous case as soon as we know which one (the Epoch value
      gives this information);

   o  PCP Server -> PCP Client not-disruptive synchronization requires a
      GET/NEXT mechanism to retrieve the state from the PCP Server;
      without this mechanism the only way to put the PCP Server in a
      known state is for the PCP Client to send a delete all request, a
      clearly disruptive operation.

   o  PCP Client -> PCP Server synchronization is done by a re-create or
      refresh of the state.  The PCP Client MAY retrieve the PCP Server
      state in order to prevent stale explicit dynamic mappings.

Appendix B.  GET/NEXT Operation

   This section defines a new PCP OpCode called GET and its associated
   Option NEXT.

   These PCP Opcode and Option are used by the PCP Client to retrieve an
   explicit mapping or to walk through the explicit dynamic mapping
   table maintained by the PCP Server for this subscriber and retrieves
   a list of explicit dynamic mapping entries it instantiated.

   GET can also be used by a NoC to retrieve the list of mappings for a
   given subscriber.

B.1.  OpCode Format

   The GET OpCode payload contains a Filter used for explicit dynamic
   mapping matching: only the explicit dynamic mappings of the
   subscriber which match the Filter in a request are considered so
   could be returned in response.



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      Implementation Note: Some existing implementations use 98 (0x62)
      codepoint for GET OpCode, 131 for AMBIGUOUS error code, and 131
      (0x83) for NEXT Option.

   The layout of GET OpCode is shown in Figure 1.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Protocol    |                Reserved                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       :   Filter internal IP address (always 128 bits)                :
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       :   Filter external IP address (always 128 bits)                :
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Filter internal port        |   Filter external port        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                       Figure 1: GET: OpCode format

   For all fields, the value 0 in a request means wildcard filter/any
   value matches.  Of course this has to be sound: no defined port with
   protocol set to any.

   These fields are described below:

   Protocol:  Same than for MAP [RFC6887].

   Reserved:  MUST be sent as 0 and MUST be ignored when received.

   Filter internal IP address:  Conveys the internal IP address
      (including an unspecified IPv4IPv6 address).  The encoding of this
      field follows Section 5 of [RFC6887].

   Filter external IP address:  Conveys the external IP address
      (including an unspecified IPv4IPv6 address).  The encoding of this
      field follows Section 5 of [RFC6887].

   Filter internal port:  The internal port (including 0).

   Filter external port:  The external port (including 0).





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   Responses include a bit-to-bit copy of the OpCode found in the
   request.

B.2.  OpCode-Specific Result Code

   This OpCode defines two new specific Result Code

   TBD:  NONEXIST_MAP, e.g., no explicit dynamic mapping matching the
      Filter was found.

   TBD:  AMBIGUOUS.  This code is returned when the PCP Server is not
      able to decide which mapping to return.  Existing implementations
      use 131 as codepoint.

B.3.  Ordering and Equality

   The PCP server is required to implement an order between matching
   explicit dynamic mappings.  The only property of this order is to be
   stable: it doesn't change (*) between two GET requests with the same
   Filter.

   (*) "change" means two mappings are not gratuitously swapped:
   expiration, renewal or creation are authorized to change the order
   but they are at least expected by the PCP client.

      [Ed.  Note: We have two proposals for the order: lexicographical
      order and lifetime order.  Both work, this should be left to the
      implementor.]

   Equality is defined by:

   o  same protocol and;
   o  same internal address and;
   o  same external address and;
   o  same internal port and;
   o  same external port.

B.4.  NEXT Option

   Formal definition:

   Name:  NEXT

   Number:  at most one in requests, any in responses.

   Purpose:  carries a Locator in requests, matching explicit dynamic
      mappings greater than the Locator in responses.




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   Is valid for OpCodes:  GET OpCode.

   Length:  variable, the minimum is 11.

   May appear in:  both requests and responses.

   Maximum occurrences:  one for requests, bounded by maximum message
      size for PCP responses [RFC6887].

   The layout of the NEXT Option is shown in Figure 2.

   Version=1
        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Protocol    |          Reserved             |  MORE/END     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       :   Mapping internal IP address (always 128 bits)               :
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       :   Mapping external IP address (always 128 bits)               :
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Mapping remaining lifetime                                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Mapping internal port       |   Mapping external port       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                       Mapping Options                         :
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Version=2

         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        :                 Mapping Nonce (96 bits)                       :
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |   Protocol    |          Reserved             |  MORE/END     |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        :   Mapping internal IP address (always 128 bits)               :
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        :   Mapping external IP address (always 128 bits)               :



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        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |   Mapping remaining lifetime                                  |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |   Mapping internal port       |   Mapping external port       |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |                       Mapping Options                         :
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                       Figure 2: NEXT: Option format

   In requests the NEXT Option carries a Locator: a position in the list
   of explicit dynamic mappings which match the Filter.  The following
   two useful forms of Locators are considered:

   o  the "Undefined" form where the Protocol, Addresses, Ports fields
      are set to zero.

   o  the "Defined" form where none of the Protocol, Addresses and Ports
      is set to zero.

   The new fields in a Locator (a.k.a., the NEXT Option in a GET
   request) are described below:

   MORE/END:  The value 0 denotes "MORE" and means the response MAY
      include multiple NEXT Options; a value other than 0 (1 is
      RECOMMENDED) denotes "END" and means the response SHALL include at
      most one NEXT Option.

   Mapping remaining lifetime:  MUST be sent as 0 and MUST be ignored
      when received.

   Mapping Options:  The Option Codes of the PCP Client wants to get in
      the response (e.g., THIRD_PARTY).  The format is the same than for
      the UNPROCESSED Option (see rev 17 of[RFC6887]).

   In responses the NEXT Options carry the returned explicit dynamic
   mappings, one per NEXT Option.  The fields are described below:

   Protocol:  The protocol of the returned mapping.

   MORE/END:  The value 0 when there are explicit dynamic mapping
      matching the Filter and greater than this returned mapping; a
      value other than 0 (1 is RECOMMENDED) when the return mapping is
      the greatest explicit dynamic mapping matching the Filter.



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   Mapping internal IP address:  the internal address of the returned
      mapping.  The encoding of this field follows Section 5 of
      [RFC6887].

   Mapping external IP address:  the external address of the returned
      mapping.  The encoding of this field follows Section 5 of
      [RFC6887].

   Mapping remaining lifetime:  The remaining lifetime in seconds of the
      returned mapping.

   Mapping internal port:  the internal port of the returned mapping.

   Mapping external port:  the external port of the returned mapping.

   Mapping Options:  An embedded list of option values.  Each
      corresponding Option Code MUST be present in the request NEXT
      Option, each option MUST be related to the returned mapping or not
      related to any mapping.

B.5.  GET/NEXT PCP Client Theory of Operation

   GET requests without a NEXT Option have low usage but with a full
   wildcard Filter they ask the PCP Server to know if it has at least
   one explicit dynamic mapping for this subscriber.

   GET requests with an END NEXT Option are "pure" GET: they asks for
   the status and/or the remaining lifetime or options of a specific
   explicit dynamic mapping.  It is recommended to use an Undefined
   Locator and to use the Filter to identify the mapping.

   GET requests with a MORE NEXT Option are for the whole explicit
   dynamic mapping table retrieval from the PCP Server.  The initial
   request contains an Undefined Locator, other requests a Defined
   Locator filled by a copy of the last returned mapping with the
   Lifetime and Option fields reseted to the original values.  An END
   NEXT Option marks the end of the retrieval.

B.6.  GET/NEXT PCP Server Theory of Operation

   The PCP Server behavior is described below:

   o  on the reception of a valid GET request the ordered list of
      explicit dynamic mapping of the subscriber matching the given
      Filter is (conceptually) built.

   o  if the list is empty a NONEXIST_MAP error response is returned.
      It includes no NEXT Option.



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   o  the list is scanned to find the Locator using the Equality defined
      in Appendix B.3.  If it is found the mappings less than the
      Locator are removed from the list, so the result is a list which
      begins by the mapping equals to the Locator followed by greater
      mappings.

   o  if the NEXT Option in the request is an END one, the first mapping
      of the list is returned in an only NEXT option, marked END if the
      list contains only this mapping, marked MORE otherwise.

   o  if the NEXT option in the request is a MORE one, as many as can
      fit mappings are returned in order in the response, marked as MORE
      but if the whole list can be returned the last is marked END.

   "Returned" means to include required options when they are defined
   for a mapping: if the mapping M has 3 REMOTE_PEER_FILTERs and the
   REMOTE_PEER_FILTER code was in the request NEXT, the NEXT carrying M
   will get the 3 REMOTE_PEER_FILTER options embedded.

B.7.  Flow Examples

   As an illustration example, let's consider the following explicit
   dynamic mapping table is maintained by the PCP Server:

   +------+--------------+----------+-----------+----------+-----------+
   | Pro  | Internal IP  | Internal |  External | External | Remaining |
   |      |   Address    |   Port   |     IP    |   Port   |  Lifetime |
   |      |              |          |  Address  |          |           |
   +------+--------------+----------+-----------+----------+-----------+
   | UDP  | 198.51.100.1 |  25655   | 192.0.2.1 |  15659   |    1659   |
   | TCP  | 198.51.100.2 |  12354   | 192.0.2.1 |  32654   |    3600   |
   | TCP  | 198.51.100.2 |   8596   | 192.0.2.1 |  25659   |    6000   |
   | UDP  | 198.51.100.1 |  19856   | 192.0.2.1 |  42654   |    7200   |
   | TCP  | 198.51.100.1 |  15775   | 192.0.2.1 |  32652   |    9000   |
   +------+--------------+----------+-----------+----------+-----------+

                    Table 1: Excerpt of a mapping table

   As shown in Table 1, the PCP Server sorts the explicit dynamic
   mapping table using the internal IP address and the remaining
   lifetime.

   Figure 3 illustrates the exchange that occurs when a PCP Client tries
   to retrieve the information related to a non-existing explicit
   dynamic mapping.

                    +------+                           +------+
                    | PCP  |                           | PCP  |



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                    |Client|                           |Server|
                    +------+                           +------+
                       |       (1) PCP GET Request         |
                       |           protocol= TCP           |
                       | internal-ip-address= 198.51.100.1 |
                       |        internal-port= 59864       |
                       |         Undefined Locator         |
                       |---------------------------------->|
                       |                                   |
                       |        (2) PCP GET Response       |
                       |       error= NONEXIST_MAP         |
                       |<----------------------------------|
                       |                                   |


                Figure 3: Example of a failed GET operation

   Figure 4 shows an example of a PCP Client which retrieves
   successfully an existing mapping from the PCP Server.

                    +------+                           +------+
                    | PCP  |                           | PCP  |
                    |Client|                           |Server|
                    +------+                           +------+
                       |       (1) PCP GET Request         |
                       |           protocol= TCP           |
                       | internal-ip-address= 198.51.100.1 |
                       |        internal-port= 25655       |
                       |         Undefined Locator         |
                       |---------------------------------->|
                       |                                   |
                       |      (2) PCP GET Response         |
                       |             END                   |
                       |           protocol= TCP           |
                       | internal-ip-address= 198.51.100.1 |
                       |        internal-port= 25655       |
                       |   external-ip-address= 192.0.2.1  |
                       |        external-port= 15659       |
                       |       remaining-lifetime= 1659    |
                       |<----------------------------------|
                       |                                   |
                       |      (3) PCP MAP4 Request         |
                       |           protocol= TCP           |
                       | internal-ip-address= 198.51.100.1 |
                       |        internal-port= 25655       |
                       |   external-ip-address= 192.0.2.1  |
                       |        external-port= 15659       |
                       |       requested-lifetime= 0       |



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                       |---------------------------------->|
                       |                                   |

              Figure 4: Example of a successful GET operation

   In reference to Figure 5, the PCP Server returns the explicit dynamic
   mappings having the internal address equal to 192.0.2.1 ordered by
   increasing remaining lifetime.

                    +------+                           +------+
                    | PCP  |                           | PCP  |
                    |Client|                           |Server|
                    +------+                           +------+
                       |       (1) PCP GET Request         |
                       | internal-ip-address= 198.51.100.2 |
                       |         Undefined Locator         |
                       |---------------------------------->|
                       |                                   |
                       |       (2) PCP GET Response        |
                       |               MORE                |
                       |           protocol= TCP           |
                       | internal-ip-address= 198.51.100.2 |
                       |        internal-port= 12354       |
                       |   external-ip-address= 192.0.2.1  |
                       |        external-port= 32654       |
                       |       remaining-lifetime= 3600    |
                       |               END                 |
                       |           protocol= TCP           |
                       | internal-ip-address= 198.51.100.2 |
                       |        internal-port= 8596        |
                       |   external-ip-address= 192.0.2.1  |
                       |        external-port= 25659       |
                       |       remaining-lifetime= 6000    |
                       |<----------------------------------|
                       |                                   |

                    Figure 5: Flow example of GET/NEXT

   In reference to Figure 6, the PCP Server returns the explicit dynamic
   mappings having the internal address equal to 192.0.2.2 ordered by
   increasing remaining lifetime.  In this example, the same internal
   port is used for TCP and UDP.

                    +------+                           +------+
                    | PCP  |                           | PCP  |
                    |Client|                           |Server|
                    +------+                           +------+
                       |       (1) PCP GET Request         |



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                       | internal-ip-address= 198.51.100.1 |
                       |        internal-port= 25655       |
                       |         Undefined Locator         |
                       |---------------------------------->|
                       |                                   |
                       |       (2) PCP GET Response        |
                       |               MORE                |
                       |           protocol= UDP           |
                       | internal-ip-address= 198.51.100.1 |
                       |        internal-port= 25655       |
                       |   external-ip-address= 192.0.2.1  |
                       |        external-port= 15659       |
                       |       remaining-lifetime= 1659    |
                       |                END                |
                       |           protocol= TCP           |
                       | internal-ip-address= 198.51.100.1 |
                       |        internal-port= 25655       |
                       |   external-ip-address= 192.0.2.1  |
                       |        external-port= 32652       |
                       |       remaining-lifetime= 9000    |
                       |<----------------------------------|
                       |                                   |

       Figure 6: Flow example of GET/NEXT: same internal port number

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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