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Versions: 00                                                            
Internet Draft                                               Shai Herzog
Expiration: December 1996                                        USC/ISI
File: draft-ietf-rsvp-policy-lpm-00.txt

                     Local Policy Modules (LPM):

         Policy Enforcement for Resource Reservation Protocols

                             June 12, 1996

Status of Memo

   This document is an Internet-Draft.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
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   To learn the current status of any Internet-Draft, please check the
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   This memo describes a set of building blocks for policy based
   admission control in RSVP and similar resource reservation protocols.
   We describe an interface between RSVP and Local Policy Modules (LPM);
   this interface provides RSVP with policy related information, and
   allows local policy modules to support various accounting and access
   control policies.

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1. Introduction

   The current admission process in RSVP uses resource (capacity) based
   admission control; we expand this model to include policy based
   admission control as well, in one atomic operation. Policy admission
   control is enforced at border/policy nodes by Local Policy Modules
   (LPMs). LPMs based their admission decision, among other factors, on
   the contents of POLICY_DATA objects that are carried inside RSVP
   messages. LPMs are responsible for receiving, processing, and
   forwarding POLICY_DATA objects. Subject to the applicable bilateral
   agreements, and local policies, LPMs may also rewrite and modify the
   POLICY_DATA objects as the pass through policy nodes.

   In this document, we describe the range of policies that can be
   supported, however, we recommend that you read this document along
   side with its policy reference document~[HER96b].  This document
   describes a generic framework for policy enforcement; we do not
   advocate any specific access control policies since we believe that
   standardization of policies (as opposed to the framework) may require
   significantly more research and better understanding of the

   Section  provides a general description of the RSVP/LPM interface,
   Section~ specified the internal representation of POLICY_ELEMENT
   objects, Section~ describes the detailed interface between RSVP and
   the LPM, and Section~ provides a peek into some of the more important
   LPM implementation internals.

2. The RSVP/LPM interface

   Unless we are willing to declare a single monolithic access policy we
   need to accommodate varying, independent access control mechanisms in
   RSVP (e.g., over different regions of the Internet, internal
   accounting vs. inter-provider accounting, quota vs.  advanced
   reservations, etc.). Each mechanism can have its own, type-specific
   internal format, can be configured for local needs (e.g., policy data
   rewrite (conversion) table, etc.), and can be added and removed from
   nodes with little or no impact on other mechanisms.

   2.1 POLICY_DATA objects

      RSVP messages may carry optional POLICY_DATA objects. Policy data
      objects are a general container for policy related information
      that could assist local RSVP nodes along the reserved path in
      their policy decisions.  Policy information may originate from
      end-users, however, it can also be created or converted at the
      core of the network.  POLICY_DATA objects contain an optional list
      of FILTER_SPEC objects which identify the flows it is associated

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      with: we expect that some access control mechanisms to use session
      POLICY_DATA objects (with wildcard FILTER_SPEC) while others may
      require the full power of per-flow object semantics. Generally, we
      assume that POLICY_DATA objects can be carried by any RSVP
      message, (e.g., Path, Resv, ResvErr, etc.).

   2.2 Modular Context

      Before RSVP accepts a reservation it must check for access
      authorization.  This is where local policy modules take effect,
      verifying access rights to local resources (i.e. links, clouds,
      etc.). Figure  illustrates the context for the proposed design:
      RSVP interfaces to the LPM to handle input and output of
      POLICY_DATA objects and to check the status of reservations.
      Conceptually, a reservation must be accepted both physically and
      administratively; physically, by traditional admission control
      (based on congestion) and administratively by the local access
      policy enforced by the LPM. This dual admission must be atomic and
      this atomicity is represented by the "accept/reject" module. In
      this document, we concentrate only on the highlighted modules: the
      RSVP and the LPM interfaces. The RSVP interface is defined by
      describing the functionality that is expected from RSVP in order
      to support access control.  It includes the handling of incoming
      messages, scheduling outgoing messages, and performing status
      checks.  The LPM interface describes the services the LPM
      provides, through a set of LPM functions. However, we do not
      define how RSVP should check the status of reservations (it could
      be done by calling the LPM directly, through an accept/reject
      module, or in other ways).  [Note 1]

[Note 1] The RSVP admission process is unidirectional and does not
include upcalls to RSVP, e.g., there is no upcall to notify RSVP that a
previously made reservation was canceled or preempted.  We do however
anticipate that once the initial access control architecture is in
place, later changes to the RSVP spec, would define an "accept/reject"
module, and associated status update upcalls to RSVP.

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                         |       RSVP         |
                            /|\          /|\
                Resv. status |            | In/Outgoing objects
                            \|/          \|/
                +---------------+      +---------------+
                | Accept/Reject |<---->|      LPM      |
                +---------------+      +---------------+
                | Ad. Control   |
               Figure 1: The modular context of access control

   2.3 Local Policy Modules

      Local Policy Modules (LPMs) can be configured locally, to a
      particular access policy. LPMs have three basic functions: first,
      to receive incoming policy data objects, second, to update the
      access/accounting status of reservations, and third, to build
      accounting/policy data objects for outgoing RSVP messages (The LPM
      message flow outline is illustrated in figure ).  LPMs maintain
      local access state for supporting the LPM operations, and this
      state must remain consistent with RSVP's state.

      2.3.1 Processing incoming messages

         RSVP calls the LPM for object processing each time it receives
         a POLICY_DATA object. The LPM processes, stores the object's
         information, and returns a status code to RSVP. The status code
         reports the success/failure of object processing, but does not
         reflect the acceptance of the reservation. The status of a
         reservation must be checked separately (see Section  for more

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              | RSVP                                         |
              |                                              |
          **************        ************************************>
         <=============*========*========       =====================
              |        *        *       ||      ||           |
              |        *        *    ***||******||******************>
              |        *        *   *   ||      ||    ===============
                       *        * *     ||      ||    ||
                      \*/       **      ||     \||/  \||/
              |        **********       +==============+
              |       LPM: Common Layer                      |
                   /|\               /|\              /|\
                    |                 |                |
                   \|/               \|/              \|/
              +-----------+     +-----------+     +-----------+
              | Handler 0 |     | Handler 1 |<----+ Handler 2 |
              +-----------+     +-----------+     +-----------+
                  Figure 2: LPM and RSVP: message flow outline

      2.3.2 Processing outgoing messages

         When RSVP generates an outgoing message it calls the LPM. The
         LPM assembles the outgoing policy data objects and hands them
         to RSVP for placing inside the outgoing message.

      2.3.3 Reservation status updates

         The concept of access control assumes that even previously
         admitted reservations are conditional, in a sense that changes
         in access status may trigger some action against the associated
         reservation (i.e., cancel it, allow its preemption, etc.).
         Therefore, the access control mechanism must periodically check
         for reservation status changes (like quota exhaustion) and take
         the appropriate measures.  Reservation status should also be
         checked when system events require it, (e.g., the arrival of a
         new policy data object with updated information).  Status
         checks may be limited to the scope of the change (e.g., only
         the interface from which the new RSVP message arrived).

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      2.3.4 Optional debiting for Reservations

         The simplest form of access control performs a binary task:
         accept or reject a reservation. More advanced policies may
         require the LPM to perform book keeping (i.e., usage quota
         enforcement or even cost recovery). To achieve such tasks, the
         LPM can be configured to perform debiting.  Debiting is not
         part of the LPM interface, and can be configured as an option
         into the status update: when RSVP queries the LPM about the
         status of a reservation, the LPM may perform debiting, and
         update the status of the reservation according to the debiting
         result.  The debiting process is based on two separate
         functions: determining "cost", and actual debiting. These two
         functions can be fully independent from each other, and most
         likely be carried out by different handlers.

         In multicast environments, with upstream merging, it is very
         likely that a reservation will be debited against multiple
         network entities that represent the aggregated credentials of
         the downstream receivers. This raises the issue of the "sharing
         model".  The sharing model defines how the reservation is
         shared among the different policy data objects. [Note 2]

         The sharing model, and the selection of cost allocation and
         actual debiting mechanisms is an issue of LPM local
         configuration, and is not discussed in this document.

      2.3.5 Security issues

         Hop-by-hop authentication mechanism:

              The RSVP security mechanism proposed in [BAK96] relies on hop-
              by-hop authentication. This form of authentication creates
              a chain of trust that is only as strong as its weakest
              element (in our case, the weakest router). As long as we
              believe that all RSVP nodes are policy nodes as well, then
              RSVP security is sufficient for the entire RSVP message,
              including POLICY_DATA objects.  This however is not the
              case when policy is only enforced at boundary nodes.
[Note 2] Sharing model examples: (1) Each policy object is allocated the
full cost, (2) The cost is divided equally between the different objects
(3) The cost is attributed to an arbitrary object (4) The cost allocated
relative to some criteria like the number of downstream receivers, the
size of the organization, the amount of pre-purchased capacity
(remaining quota), etc.

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         Security over clouds:

              If policies are only enforced at cloud entry and exit
              points, then RSVP's security is insufficient to protect
              policy objects, since from a policy enforcement
              perspective, the in-cloud nodes are unsecured.  We propose
              a "policy data tunneling" approach, where the logical
              policy topology is discovered automatically, and security
              is enforced over the logical topology.  When policy
              objects are created at border routers, they are
              encapsulated in a security envelope (described in Sections
               and ref security-issues).  The envelop is forwarded as-is
              over the cloud, and is only removed by the cloud border
              (exit) node.

   2.4 Default handling of policy data objects

      Because we do not expect (or desire) that every RSVP node will be
      capable of processing all types of policy data objects, it is
      essential that RSVP define default handling of such unrecognized
      objects, and that this default handling be required from any
      RSVP/LPM implementation.  The general concept is that RSVP play
      the role of a repeater (or a tunnel) by forwarding the received
      objects without modification.  Implementation details are an part
      of the internal LPM architecture, described in Section .

3. POLICY_ELEMENT objects: internal representation

   The contents of the POLICY_ELEMENT is opaque to RSVP; the format we
   describe here is only visible to the LPM.  POLICY_ELEMENT objects are
   made of a list of policy particles. Policy particles have a length, a
   policy type (PType) and a type specific format.

        |     Length                |      20     |    CType    |
        |     Policy Particles (list)                           |

   Individual policy particle has the following format

        |     Length                |      PType                |
        |     Ptype specific format                             |

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4. LPM calls

   The LPM maintains access control state per flow. This state is
   complementary to the RSVP state, and both are semantically attached
   by flow handles, for all the LPM calls.

   4.1 Success codes

      All the LPM calls report success/failure status. This report is
      made of three components: (1) a return code of the lpm function,
      that reports the general success of the call (2) a global variable
      "lpm_errno" that reports specific reason code (similar to the
      errno in Unix), and (3) a global variable "lpm_eflgs" used for
      flags set by the LPM call.

   4.2 Flow handles (fh)

      The LPM uses Flow Handles (fh) to associate RSVP flows with LPM
      state.  RSVP obtains flow handles by calling "lpm_open()", which
      is called only once for each session or flow, upon the first
      arrival of a POLICY_DATA object associated with that flow or
      session.  RSVP obtains the flow handle and stores it in the flow's
      data structures, for future lpm calls.

      When an RSVP message is fragmented, POLICY_DATA objects may be out
      of order, and may reside in separate packets.  The responsibility
      of associating a POLICY_DATA object with a particular flow (and
      its flow handles (fh)) lies "always" with RSVP. The FILTER_SPEC
      object inside the POLICY_DATA object is visible to RSVP, and
      should be used by it to aid in this classification. [Note 3]

      It is important to note that under no circumstances should this
      classification be left to the LPM.

   4.3 Associating source and receiver objects

      The access status of a reservation may depend on policy data
      objects originating from the source, receivers or both.  For
      instance, a lecture can be sponsored by the source that would
      provide the necessary credentials. If the LPM architecture is to
      support source based policies, it must be able to associate source
      objects with reservation state. Some associations are trivial
[Note 3] The FILTER_SPEC object is opaque to the LPM and the only reason
it is included inside the POLICY_DATA object is to allow RSVP to
associate the object with its corresponding flow.

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      (like in the case of fixed filter (FF) reservation style) but some
      are more complicated (as in WF reservations).  Since the LPM
      architecture associates flow handles with individual source state,
      it is the responsibility of RSVP to map reservations to their list
      of associated sources. The list takes the form of a list of flow
      handles, and can be passed on to LPM functions through a pair of
      parameters, "int fh_num" and "int *fn_vec").

   4.4 LPM calls format

      lpm_open (int *fh)

      When RSVP first encounters POLICY_DATA objects, it calls the LPM's
      "lpm_open" routine. The LPM builds internal control blocks and
      places the flow handle value in fh, for future reference.

      All incoming POLICY_DATA objects are passed by RSVP to the LPM:

      lpm_in (int fh_num, int *fh_vec, int vif, RSVP_HOP *hop, int
           mtype, POLICY_DATA *polp, int ttd)

      Parameter "vif" describes the input virtual interface [Note 4]
       from which the RSVP message was received, "hop" describes the
      node that sent the RSVP message (previous hop/next hop), and
      "mtype" describes the type (and implicitly, the direction) of the
      RSVP message (i.e., Path, Resv etc.).  Parameter "polp" points to
      the policy data object, and "ttd" provides a timeout (time to die)
      value for the policy data object.

      When RSVP is ready for output, it queries the LPM:

      lpm_out (int fh_num, int *fh_vec, int vif, RSVP_HOP *hop, int
           mtype, POLICY_DATA **polp)

      The parameters are similar to those for "lpm_in". A successful
      call places a pointer to the outgoing POLICY_DATA object in
      "polp"; Notice that the output process is performed separately for
      each outgoing RSVP message, but is required to maintain
[Note 4] The term Virtual Interface (vif) is borrowed from DVMRP
terminology, although, for LPM purposes it can be any integer index that
RSVP associates with specific interfaces, independently from any routing

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      consistency and atomicity even if some LPM status had changed in
      between outputs of different outgoing RSVP messages.  Notice that
      there is no formal limit on the size of the resulting POLICY_DATA
      object. If the resulting object is too large to be sent in a
      single RSVP message it is RSVP's responsibility to perform
      semantic fragmentation because it has the unique knowledge about
      available message space.  An alternative solution would be to
      provide an lpm_fragment() service to help RSVP in this task.

      Checking the status of an existing reservation is done by calling:

      lpm_status (int fh_session, int fh_num, int *fh_vec, int vif, int
           cur_time, int phy_resv_handle, Object_header
           *phy_resv_flwspec, int ind)

      Status is checked individually for each outgoing (reserved) link.
      Parameter "fh_session" specifies the flow handle associated with
      the session, "phy_resv_handle" identifies the physical reservation
      (e.g., ISPS, etc.), and "phy_resv_flwspec" describes the current,
      merged FlowSpec of the reservation. The value of "cur_time"
      describe the current RSVP time, which allows the LPM to timeout
      old state (state with earlier time to die values).  Parameter
      "ind" is used to have different flavors of status checks:
      "LPM_STATF_AGE": setting this flag ages (and times
      out) LPM state associated with the specified fh. Status checks may
      be periodic or event driven; this flag is set only for periodic
      status checks.  "LPM_STATF_RECALC": Status checks may involve
      calculations over multiple outgoing interfaces, and thus need only
      be done once for all interfaces before individual per-interface
      status is reported.  This bit is set on for the first vif checked
      and is reset for the rest. [Note 5]

      Status checks with "ind" set to 0 simply report values that were
      already calculated before and do not age the LPM state.

      If RSVP prunes branches from the reservation tree, it must notify
      the LPM by calling:

      lpm_prune (int fh_num, int *fh_vec, int vif, RSVP_HOP *hop, int

[Note 5] This is an optimization. While useless, there should be no harm
in recalculating status parameters, for each outgoing interface.

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      (The details of this call is described in Section ).

      When RSVP deletes an entire flow state, it must notify the LPM:

      lpm_close (int fh)

      Upon this notification, the LPM finishes its accounting for this
      reservation (final debits/credits) and deletes all internal state
      associated with fh.

      Initializing the LPM is done once only, in the initialization
      phase of RSVP, by calling.

      lpm_config (void)

   4.5 State Maintenance

      LPM state must remain consistent with the corresponding RSVP
      state. State is created when POLICY_DATA objects are passed to the
      LPM and can be updated or removed through several possible
      mechanisms that correspond to RSVP's state management mechanisms:


           When new POLICY_DATA objects cease to arrive (as a result of
           either change of policy or fragmentation loss) the locally
           stored state begins to age. Each POLICY_ELEMENT/FILTER_SPEC
           pair is subject to a timer, and when the timer goes off, the
           state should be deleted.  The timer mechanism should be
           similar to that of RSVP and both should remained synchronized
           in the following way: each time RSVP hands over a policy
           object to the LPM (lpm_in()) it provides the LPM with time-
           to-die value ("current-timer + time-to-live) ".  Each time
           RSVP verifies the status of a reservation (lpm_status()), it
           provides the current timer value, forcing all pieces of
           information with an earlier timeout value to be purged.


           From a network security standpoint, creating new policy state
           requires the similar integrity protection as tearing it down.
           We propose a very simple mechanism for tearing down state:
           the state created by sending POLICY_ELEMENT Pe_i is torn down
           by sending -Pe_i (the same object marked as teardown).  In
           this case, the LPM would locate the original state, compare
           it with the teardown object, if a match is found, tear it

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           down.  We define each POLICY_ELEMENT as a pair of two CTypes,
           thus effectively splitting the CType range of POLICY_ELEMENT
           objects in two.  Given a POLICY_ELEMENT i, Pe_i represents an
           updated state, while Pe_i+1 represents teardown state of
           CType i (-Pe_i).

      Pruning When the shape of the reserved tree changes due to routing
           updates or RSVP teardown messages, RSVP purges the state of
           the pruned link, and must also call "lpm_prune()" to purge
           the corresponding LPM state.

      Closing: The call "lpm_close(fh)" purges all the state associated
           with the handle fh. Closing a flow handle is done when RSVP
           no longer maintains any state associated with that flow (a
           sender quits, the session is over, etc.).

5. LPM internals

   This section describes the current internal design of the LPM. While
   this design is not part of the mandatory specification we recommend
   following it.

   5.1 LPM configurations

      LPM configuration can be general, for all handlers, but can also
      be type/handler specific. (e.g., a specific handler's rewrite
      conversion table for policy data objects). Configuration may be
      expressed in a simple configuration file or even through a
      configuration language.

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               | RSVP                                                      |
               |        Incoming Resv:  Resv-header,LPM-header,P1,P2,P3,P4 |
               |                                         |                 |
               | LPM: Common Layer                      \|/                |
               | lpm_in()          +-------- LPM-header,P1,P2,P3,P4        |
               |                  /           /          |          \      |
               |           |   P1|     |   P2|     |   P3|     |   P4|     |
               |           |    \|/    |    \|/    |    \|/    |    \|/    |
               |           |           |           |           |           |
               | Handler 0 | Handler 1 | Handler 2 | Handler 4 | Handler 5 |
      Figure 3: Disassembly of an incoming Resv message with POLICY_DATA

   5.2 The LPM layered Design

      The internal format of POLICY_DATA objects is PType specific,
      allowing up to 65535 independent types. Our design allow each
      specific PType to be handled by a separate handler, and allow such
      handlers to be added and configured independently. Clearly,
      handlers are allowed to handler more than one PTypes.

      The LPM is divided into two layers: a PType specific layer and a
      common layer (figure ).  The PType specific layer provides a set
      of locally configured independent handlers, one for each PType
      supported by the local node. The common layer provides the glue
      between RSVP and the PType specific layer by multiplexing RSVP's
      lpm calls into individual, PType specific calls.

      On input, the common layer disassembles the incoming POLICY_DATA
      object, dispatches the internal objects to their PType specific
      handlers, and aggregates the return code status (figure ).  On
      output, it collects the internal objects from all active handlers,
      and assembles them into a single POLICY_DATA object (figure ).

      On status queries, the common layer queries all the active
      handlers, and combines their individual status responses into a
      single status result. We use the following rule: a reservation is
      approved by the common layer, if there is at least one handler
      that approves it, and none other rejects it. PType specific
      handlers can accept, reject or be neutral in their responses.
      [Note 6]
[Note 6] A policy data object that determines cost is a good example for

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               | RSVP                                                      |
               |        Outgoing Resv:  Resv-header,LPM-header,P1,P2,P3,P4 |
               |                                        /|\                |
               | LPM: Common Layer                       |                 |
               | lpm_out()         +-------> LPM-header,P1,P2,P3,P4        |
               |                  /           /         /|\         \      |
               |           |   P1|     |   P2|     |   P3|     |   P4|     |
               |           |     |     |     |     |     |     |     |     |
               |           |           |           |           |           |
               | Handler 0 | Handler 1 | Handler 2 | Handler 4 | Handler 5 |
      Figure 4: Assembly of POLICY_DATA objects for an outgoing Resv message

   5.3 Interaction between handlers

      It is reasonable to assume that independent PTypes may require
      some interaction between their handlers.  Consider the case where
      policy object type-1 is a credential type (defines a user
      identity) and a type-2 is an accounting type (determines cost), a
      possible interaction could be to let type-2 determine the cost,
      and let type-1 perform the actual debiting according to the user
      identity.  Such interaction has two basic requirements: order
      dependency and export capability. Order dependency is required
      because type-2 must calculate the cost before type-1. Export
      capability is needed to allow type-2 to export the calculation
      results to type-1.  Our implementation allows the ordering or
      handlers to be expressed as part of local LPM configuration. It
      also provides internal support for function calls between
      independent handlers (in order to obtain exported state).

      Consider the case where type-3 and type-4 also perform accounting.
      The proposed architecture is flexible enough to allow local
      configuration to select the handler that determines the debited
      cost: type-2, type-3 or type-4.

a neutral handler. It provide information about how much the flow costs,
but does not perform actual debiting.

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   5.4 Default handling of policy data objects

      In~[HER96c] we define the default handling of unrecognized POLICY_DATA
      objects. If an RSVP node is LPM capable, it may be more beneficial
      for the LPM to take that burden off from RSVP and perform it
      itself. We propose the use of CType 0 for default handling: In a
      policy node, only unrecognized objects would be handled by handler
      PType 0. In a non-policy node, all objects are unrecognized, and
      therefore should all are handled as PType 0, regardless of their
      actual PType. PType 0 is regarded as a reserved type.

6. Acknowledgment

   This document incorporates inputs from Deborah Estrin, Scott Shenker
   and Bob Braden and feedback from RSVP collaborators.


[BAK96]  F. Baker. RSVP Cryptographic Authentication "Internet-Draft",
    draft-ietf-rsvp-md5-02.txt, 1996.

[HER96c]  RSVP Extensions for Policy Control. "Internet-Draft", draft-

[HER96b]  Accounting and Access Control Policies for Resource
    Reservation Protocols. "Internet-Draft", draft-ietf-rsvp-policy-

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