Internet Draft                                          Jim Boyle
Expiration: Apr. 1999                                       Level3
File: draft-ietf-rap-cops-rsvp-01.txt                   Ron Cohen
                                                        David Durham
                                                        Shai Herzog
                                                        Raju Rajan
                                                        Arun Sastry

                          COPS usage for RSVP

                     Last Updated: November 18, 1998

Status of this Memo

   This document is an Internet Draft.  Internet Drafts are working
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   A revised version of this draft document will be submitted to the
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   Discussion and suggestions for improvement are requested.  This
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   Distribution of this draft is unlimited.


   This document describes usage directives for supporting COPS policy
   services in RSVP environments.

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Table of Contents

Table of Contents....................................................2
2.RSVP values for COPS objects.......................................3
2.1.Context Object (Context).........................................3
2.2.Client Specific Information (ClientSI)...........................4
2.3.Decision Object (Decision).......................................4
3.Operation of COPS for Policy Control Over RSVP.....................5
3.1.RSVP flows.......................................................5
3.2.Expected Associations for RSVP Requests..........................5
3.3.RSVP's Capacity Admission Control: Commit and Delete.............6
3.4.Policy Control Over PathTear and ResvTear........................6
3.5.PEP Caching COPS Decisions.......................................6
3.6.Using Multiple Context Flags in a single query...................7
3.7.Trusted zones and secure policy tunneling........................7
4.Illustrative Examples, Using COPS for RSVP.........................8
4.1.Unicast Flow Example.............................................8
4.2.Shared Multicast Flows...........................................9
6.Author Information and Acknowledgments............................13

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1. Introduction

   The Common Open Policy Service (COPS) protocol is a query response
   protocol used to exchange policy information between a network
   policy server and a set of clients [COPS]. COPS is being developed
   within the RSVP Admission Policy Working Group (RAP WG) of the IETF,
   primarily for use as a mechanism for providing policy-based
   admission control over requests for network resources [RAP].

   This document is based on and assumes prior knowledge of RAP
   framework [RAP] and the basic COPS [COPS] protocol. It provides
   specific usage directives for using COPS in outsourcing policy
   control decisions by RSVP clients (PEPs) to policy servers (PDPs).

   Given the COPS protocol design, client specific functionality is
   mainly limited to interoperability usage guidelines as well as
   client specific examples.

2. RSVP values for COPS objects

   The format and usage of several COPS objects is affected when used
   for client type RSVP. This section describes these objects and the

  2.1. Context Object (Context)

   The semantics of the Context object for RSVP is as follows:

   R-Type (Request Type Flag)

   0x01 = Incoming-Message request
          The arrival of an incoming RSVP message

          Allows processing of incoming policy information as well as
          the decision whether to accept an incoming message. If It is
          rejected, the message is treated as if it never Arrived.

   0x02 = Resource-Allocation request
          Applies only for Resv messages.

          The decision whether to admit a reservation and commit local
          resources to it is performed for the merge of all
          reservations that arrived on a particular interface
          (potentially from several RSVP Next-Hops).

   0x04 = Outgoing-Message request
          The forwarding of an outgoing RSVP message.

          The Decision whether to allow the forwarding of an outgoing
          RSVP message as well as providing the relevant outgoing
          policy information.

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   M-Type (Message Type)

   The M-Type field in the Context Object may have one of the
   Following values that correspond to supported RSVP messages
   In COPS:

   1 = Path
   2 = Resv
   3 = PathErr
   4 = ResvErr

   Note: The PathTear, ResvTear, and the Resv Confirm message types are
   not supported.

  2.2. Client Specific Information (ClientSI)

   All objects that were received within an RSVP message that are
   associated with the RSVP flow are encapsulated inside the Client
   Specific Information Object without alteration. (See Section 3.1. on
   multiple flows packed in a single RSVP message). These RSVP objects
   are simply contained within a single Signaled Client Specific
   Information Object (RSVP ClientSI) exchanged between the PEP and
   remote PDP.

  2.3. Decision Object (Decision)

   COPS allows PDP to control RSVP’s response to messages. Beyond
   traditional accept/deny, PDPs may use the Trigger Error flag to
   allow a request yet trigger a warning at the same time. To allow
   resource allocation yet deny forwarding of a message, etc.

   Decision Flags

   The following decision flags apply to RSVP:

   0x01 = Signaled (RSVP) accept (deny if set)

          This flag should be interpreted with the decision context
          flag to figure out what it applies to.

   0x08 = Trigger Error (PathErr for Path query, or ResvErr for Resv)

   Client Specific Policy Information

   This object may include one or more policy elements (as specified
   for the RSVP Policy Data object [RSVP-EXT] which are assumed to be
   well understood by the client’s LDP. The PEP should consider these
   as if they arrived in the message Policy Data object.

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   For example: Given Policy Elements that specify a flow’s preemption
   priority, these elements may be included in an incoming Resv message
   or may be also be provided by the PDP responding to a query.

   Replacement Data

   The Replacement object may contain multiple RSVP objects to be
   replaced (from the original RSVP request). Typical replacement is
   performed on the “Forward Outgoing” request (for instance, replacing
   outgoing Policy Data), but is not limited, and can also be performed
   on other contexts (such as “Allocate Resources”). Other examples,
   may require replacement of the RSVP FlowSpec object for controlling
   resources across a trusted zone (with PIN nodes).
   Currently, RSVP clients are only required to allow replacement of
   two objects: Policy Data and FlowSpec.

   Replacement is performed in the following manner:
   If Replacement Data decision doesn't appear in a decision message,
   all signaled objects are passed as if the PDP was not there. When an
   object of a certain C-Num appears it replaces ALL the instances of
   C-Num objects in the RSVP message. If it appears empty (with a
   length of 4) it simply removes all instances of C-Num objects
   without adding a thing.

3. Operation of COPS for Policy Control Over RSVP

  3.1. RSVP flows

   Policy Control is performed per RSVP flow. An RSVP flow corresponds
   to an atomic unit of reservation as identified by RSVP (TC
   reservation). It should be noted that RSVP allows multiple flows to
   be packed (which is different from merged) into a single FF Resv
   message. To support such messages a separate COPS request must be
   issued for each of the packed flows as if they were individual RSVP

  3.2. Expected Associations for RSVP Requests

   RSVP signaling requires the participation of both senders and
   receivers. RSVP processing rules define what is the subset of the
   Path state that matches each Resv state. In the common unicast case,
   the RSVP session includes one Path state and one Resv state. In
   multicast cases the correspondence might be many to many. Since the
   decision to admit a reservation for a session may depend on
   information carried both in Path and Resv messages, we term the Path
   States that match with a single Resv state as its associated states.
   It is assumed that the PDP is capable of determining these
   associations based on the RSVP message processing rules given the
   RSVP objects expressed in the COPS Client Specific Information

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   For example, the PDP should be able to recognize activation and
   deactivation of RSVP blockade state following discrete events like
   the arrival of a ResvErr message (activate the blockade state) as
   well as the change in the outgoing Resv message.

  3.3. RSVP's Capacity Admission Control: Commit and Delete

   In RSVP, the admission of a new reservation requires both an
   administrative approval (policy control) and capacity admission
   control. Once local admission control accepts the reservation, the
   PEP notifies the remote PDP by sending a report message specifying
   the Commit type. The Commit type report message is to be used to
   signify when billing should effectively begin, and performing
   heavier operations (e.g., debiting a credit card) is permissible.

   If instead a reservation approved by the PDP fails admission due to
   lack of resources, the PEP must issue a no-commit report and fold
   back and send an updated request to its previous state (previously
   installed reservation). If no state was previously installed, the
   PEP should issue a delete.

  3.4. Policy Control Over PathTear and ResvTear

   PathTear and ResvTear messages are not controlled by this policy
   architecture. This relies on two assumptions: First, that MD-5
   authentication verifies that the Tear is received from the same node
   that sent the initial reservation, and second, that it is
   functionally equivalent to that node holding-off refreshes for this
   reservation. When a ResvTear or PathTear is received at the PEP, all
   affected states installed on the PDP should either be deleted or
   updated by the PEP.

  3.5. PEP Caching COPS Decisions

   Because COPS is a stateful protocol, refreshes for RSVP Path and
   Resv messages need not be constantly sent to the remote PDP. Once a
   decision has been returned for a request, the PEP can cache that
   decision and apply it to future refreshes. The PEP is only
   responsible for updating a request state if there is a change
   detected in the corresponding Resv or Path message.

   If the connection is lost between the PEP and the PDP, the cached
   RSVP state may be retained for the RSVP timeout period. If no
   connection can be reestablished with the PDP or a backup PDP after
   the timeout period, the RSVP PEP is expected to default back to
   using its LDP results. Additionally, the LDP is to be used for the
   admission control of any new RSVP messages that may have arrived
   while connectivity was lost.

   Once a connection is reestablished to a new (or the original) PDP
   the PDP may issue a SSQ request. In this case, the PEP must reissue

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   requests that correspond to the current RSVP state (as if all the
   state has been updated recently). It should also include as LDP the
   current (cached) decision regarding each such state.

  3.6. Using Multiple Context Flags in a single query

   RSVP is a store-and-forward control protocol where messages are
   processed in three distinctive steps (input, resource allocation,
   and output). Each step requires a separate policy decision as
   indicated by context flags (see Section 2.1). In many cases, setting
   multiple context flags for bundling two or three operations together
   in one request may significantly optimize protocol operations.

   The following rules apply for setting multiple Context flags:

   a. Multiple context flags can be set only in two generic cases which
      are guaranteed not to cause ambiguity and represent substantial
      portion of expected COPS transactions.

      Unicast FF:

              [Incoming + Allocation + Outgoing]

      Multicast with only one Resv message received on the interface

              [Incoming + Allocation]

   b. Context events are ordered by time since every message processing
      must first be processed as Incoming, then as Resource allocation
      and only then as Outgoing. When multiple context flags are set,
      all ClientSI objects included in the request are assumed to be
      processed to the latest flag. This rule applies both to request
      (REQ) context as well as to decision (DEC) context.

      For example: when combining Incoming + Allocation for an incoming
      Resv message, the Flowspec included in the ClientSI would be the
      one corresponding to the Resource-Allocation context (TC).

   c. Each decision is bound to a context object, which determines
      which portion of the request context it applies to. When
      different decisions apply to different sub-groups of context the
      PDP should send each group of decision objects encapsulated or
      separated by the context flags object with the context flags
      applicable to these objects set. (See the examples in Section 4).

  3.7. Trusted zones and secure policy tunneling

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  Security for RSVP messages is provided by inter-router MD5
  authentication [MD5], assuming a chain-of-trust model.
  A possible deployment scenario calls for PEPs to be deployed at the
  network edge (boundary nodes) while PINs are deployed in the core of
  the network (backbone). In this case, MD5 trust (authentication) must
  be established between boundary (non-neighboring) PEPs, which is
  achieved through internal signing of the Policy Data object. [RSVP-

4. Illustrative Examples, Using COPS for RSVP

  This section details both typical unicast and multicast scenarios.

  4.1. Unicast Flow Example

   This section details the steps in using COPS for controlling a
   Unicast RSVP flow. It details the contents of the COPS messages
   with respect to the following figure.

                                     PEP (router)
                                 |                 |
                  R1 ------------+if1           if2+------------ S1
                                 |                 |

                    Figure 1: Unicast Example: a single PEP view

   The PEP router has two interfaces (if1, if2). Sender S1 sends to
   receiver R1.

   A Path message arrives from S1:

       PEP --> PDP   REQ := <Handle A> <Context: in & out, Path>
                            <In-Interface if2> <Out-Interface if1>
                            <ClientSI: all objects in Path message>

       PDP --> PEP   DEC := <Handle A> <Context: in & out, Path>
                            <Decision flags: Accept>

   A Resv message arrives from R1:

       PEP --> PDP   REQ := <Handle B>
                            <Context: in & allocation & out, Resv>
                            <In-Interface if1> <Out-Interface if2>
                            <ClientSI: all objects in Resv message>

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       PDP --> PEP   DEC := <Handle B>
                            <Context: in, Resv>
                            <Decision flags: accept>
                            <Context: allocation, Resv>
                            <Decision flags: accept>
                            <Decision: ClientSI, Priority=7>
                            <Context: out, Resv>
                            <Decision flags: accept>
                            <Decision replace: POLICY-DATA1>

       PEP --> PDP   RPT := <Handle B>
                            <Report type: commit>

   Notice that the Decision was split because of the need to specify
   different decision objects for different context flags.

   Time Passes, the PDP changes its decision:

       PDP --> PEP   DEC := <Handle B>
                            <Context: allocation, Resv>
                            <Decision flags: accept>
                            <Decision: ClientSI, Priority=3>

   Because the priority is too low, the PEP preempts the flow:

       PEP --> PDP   DRQ := <Handle B>
                            <Reason Code: Preempted>

   Time Passes, the sender S1 ceases to send Path messages:

       PEP --> PDP   DRQ := <Handle A>
                            <Reason: Timeout>

  4.2. Shared Multicast Flows

   This section details the steps in using COPS for controlling a
   multicast RSVP flow. It details the contents of the COPS messages
   with respect to the following figure.

                                  PEP (router)
                              |                 |
               R1-------------+ if1         if3 +--------- S1
                              |                 |
               R2----+        |                 |
                     |        |                 |
                     +--------+ if2         if4 +--------- S2
                     |        |                 |
               R3----+        +-----------------+

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                Figure 2: Multicast example: a single PEP view

   Figure 2 shows an RSVP PEP (router) which has two senders (S1, S2)
   and three receivers (R1, R2, R3) for the same multicast session.
   Interface if2 is connected to a shared media.
   In this example, we assume that the multicast membership is already
   in place, no previous RSVP messages were received, and the first to
   arrive is a Path message on interface if3 from sender S1:

       PEP --> PDP   REQ := <Handle A> <Context: in, Path>
                            <In-interface if3>
                            <ClientSI: all objects in incoming Path>

       PDP --> PEP   DEC := <Handle A> <Context: in, Path>
                            <Decision flags: accept>

   The PEP consults its forwarding table, and finds two outgoing
   interface for the path (if1, if2). The exchange below is for
   interface if1, another exchange would likewise be completed for if2
   using the new handle B2.

       PEP --> PDP   REQ := <Handle B1> <Context: out, Path>
                            <Out-interface if1>
                            <clientSI: all objects in outgoing Path>

       PDP --> PEP   DEC := <Handle B1>
                            <Context: out, Path>
                            <Decision flags: accept>
                            <Decision Replacement: POLICY-DATA1>

   Here, the PDP decided to allow the forwarding of the Path message
   and provided the appropriate policy-data object for interface if1.

   Next, a WF Resv message from receiver R2 arrives on interface if2.

       PEP --> PDP   REQ := <Handle C> <Context: in & allocation, Resv>
                            <In-interface if2>
                            <ClientSI: all objects in Resv message
                             including RSpec1 >

       PDP --> PEP   DEC := <Handle C>
                            <Context: in, Resv>
                            <Decision flags: accept>
                            <Context: allocation, Resv>
                            <Decision flags: accept>
                            <Decision ClientSI: priority=5>

       PEP --> PDP   RPT := <handle C> <Commit>

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   Here, the PDP approves the reservation and assigned it preemption
   priority of 5. The PEP responded with a commit report.

   The PEP needs to forward the Resv message upstream toward S1:

       PEP --> PDP   REQ := <Handle E> <Context: out, Resv>
                            <out-interface if3>
                            <Client info: all objects in outgoing Resv>

       PDP --> PEP   DEC := <Handle E>
                            <Context: out, Resv>
                            <Decision flags: accept>
                            <Decision replacement: POLICY-DATA2>

   Note: The Context object is part of this DEC message even though it
   may look redundant since the REQ specified only one context flag.

   Next, a new WF Resv message from receiver R3 arrives on interface
   if2 with a higher RSpec (Rspec2). Given two reservations arrived on
   if2, it cannot perform a request with multiple context flags, and
   must issue them separately.

   The PEP re-issues an updated handle C REQ with a new context object
   <Context: in , Resv>, and receives a DEC for handle C.

       PEP --> PDP   REQ := <Handle F> <Context: in , Resv>
                            <In-interface if2>
                            <ClientSI: all objects in Resv message
                             including RSpec2 >

       PDP --> PEP   DEC := <Handle F> <Context: in , Resv>
                            <Decision flags: accept>

       PEP --> PDP   REQ := <Handle G> <Context: allocation, Resv>
                            <In-interface if2>
                            <ClientSI: all objects in merged Resv
                             including RSpec2 >

       PDP --> PEP   DEC := <Handle G>
                            <Context: allocation, Resv>
                            <Decision flags: accept>
                            <Decision ClientSI: priority=5>

       PEP --> PDP   RPT := <handle G> <Commit>

   Given the change in incoming reservations, the PEP needs to forward
   a new outgoing Resv message upstream toward S1. This repeats exactly
   the previous interaction of Handle E, except that the ClientSI
   objects now reflect the merging of two reservations.

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   If an ResvErr arrives from S1, the PEP maps it to R3 only (because
   it has a higher flowspec: Rspec2) the following takes place:

       PEP --> PDP   REQ := <Handle H> <Context: in, ResvErr>
                            <In-interface if3>
                            <ClientSI: all objects in incoming ResvErr>

       PDP --> PEP   DEC := <Handle H> <Context: in, ResvErr>
                            <Decision flags: accept>

       PEP --> PDP   REQ := <Handle I> <Context: out, ResvErr>
                            <Out-interface if2>
                            <clientSI: all objects in outgoing ResvErr>

       PDP --> PEP   DEC := <Handle I>
                            <Context: out, ResvErr>
                            <Decision flags: accept>
                            <Decision Replacement: POLICY-DATA3>

   When S2 joins the session by sending a Path message, incoming and
   outgoing Path requests are issued for the new Path. A new outgoing
   Resv request would be sent to S2.

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5. References

  [RSVP-EXT]  Herzog, S. "RSVP Extensions for Policy Control",
         Internet-Draft, draft-ietf-rap-rsvp-ext-00.txt, Apr. 1998.

  [RAP]  Yavatkar, R., et al., "A Framework for Policy Based Admission
         Control",IETF <draft-ietf-rap-framework-00.txt>, November,

  [COPS] Boyle, J., Cohen, R., Durham, D., Herzog, S., Raja,n R.,
         Sastry, A., "The COPS (Common Open Policy Service) Protocol",
         IETF <draft-ietf-rap-cops-02.txt>, Aug. 1998.

  [RSVP] Braden, R., Zhang, L., Berson, S., Herzog, S., and Jamin, S.,
         "Resource Reservation Protocol (RSVP) Version 1 Functional
         Specification", IETF RFC 2205, Proposed Standard, September

6. Author Information and Acknowledgments

   Special thanks to Timothy O'Malley our WG Chair, Raj Yavatkar,
   Russell Fenger, Fred Baker, Laura Cunningham, Roch Guerin, Ping Pan,
   and Dimitrios Pendarakis for their valuable contributions.

       Jim Boyle                        Ron Cohen
       Level 3 Communications           CISCO Systems
       1450 Infinite Drive13            Hasadna St.
       Louisville, CO 80027             Ra'anana 43650 Israel
       303.926.3100                     972.9.7462020

       David Durham                     Raju Rajan
       Intel                            IBM T.J. Watson Research Cntr
       2111 NE 25th Avenue              P.O. Box 704
       Hillsboro, OR 97124              Yorktown Heights, NY 10598
       503.264.6232                     914.784.7260

       Shai Herzog                      Arun Sastry
       IPHighway                        Cisco Systems
       400 Kelby St., Suite 1500         506210 W Tasman Drive
       Fort-Lee, NJ 07024               San Jose, CA 95134
       201.585.0800                     408.526.7685   

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