Internet Draft                                  Jim Boyle
 Expiration: July September 1998                          MCI
 File: draft-ietf-rap-cops-00.txt draft-ietf-rap-cops-01.txt                Ron Cohen
                                                     Class Data Systems
                                                 David Durham
                                                 Shai Herzog
                                                 Raju Rajan
                                                 Arun Sastry

             The COPS (Common Open Policy Service) Protocol

                    Last Updated: January 20, March 12, 1998

Status of this 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.

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   A revised version of this draft document will be submitted to the
   RFC editor as a Proposed Standard for the Internet Community.
   Discussion and suggestions for improvement are requested.  This
   document will expire before June September 1998. Distribution of this
   draft is unlimited.


   This document describes a simple client/server model for supporting
   policy control over QoS Signaling Protocols with similar properties
   as ReSerVation Protocol (RSVP). It is designed to be extensible so
   that other kinds of policy clients may be supported in the future.
   The model does not make any assumptions about the decision methods
   of the policy server, but is based on the server returning responses
   to policy requests.

1. Introduction

   This document describes a simple query and response protocol that
   can be used to exchange policy information between a policy server
   (Policy Decision Point or PDP) and its clients (Policy Enforcement
   Points or PEPs).  One policy client is expected to be RSVP routers
   that must exercise policy-based admission control over RSVP usage
   [RSVP].  We assume that at least one policy server exists in each
   controlled administrative domain. The basic model of interaction
   between a policy server and its clients is compatible with
   the framework document for policy based admission control [WRK].

   A chief objective of our proposal is to begin with a simple but
   extensible design. The main characteristics of the proposed protocol

       1. The protocol employs a client/server model where the PEP
       sends requests, updates, and retractions deletes to the remote PDP and the
       PDP returns decisions back to the PEP.

       2. The protocol uses TCP as its transport protocol for reliable
       exchange of messages between policy clients and a server.
       Therefore, no additional mechanisms are necessary for reliable
       communication between a server and its clients.

       3. The protocol is extensible in that it is designed to leverage
       off self-identifying objects and can support diverse client
       specific information. Thus, even though the protocol was created
       for the administration and enforcement of policies in
       conjunction with RSVP, the protocol may be extended for
       administration of other (signaling) protocols such as multicast
       access and network security.

       4. The protocol relies on existing protocols for security.
       Namely IPSEC [IPSEC] can be used to authenticate and secure the
       channel between the PEP and the server.

       5. The protocol is stateful in two main aspects:
       (1) Request/Response state is shared between client and server
       and (2) State from various events (Request/Response pairs) may
       be inter-associated. By (1) we mean that requests from the
       client PEP are installed or remembered by the remote PDP until
       they are explicitly deleted by the PEP. At the same time,
       Responses from the remote PDP can be generated asynchronously at
       any time for a currently installed request state. By (2) we mean
       that the server may respond to new queries differently because
       of previously installed, related Request/Response state (e.g.,
       for RSVP, the server may associate state from incoming Path and
       Resv requests).

1.1. Basic Model

       |                |
       |  Network Node  |            Policy Server
       |                |
       |   +-----+      |   COPS        +-----+
       |   | PEP |<-----|-------------->| PDP |
       |   |+----+      |               +-----+
       |    ^           |
       |    |           |
       |    \-->+-----+ |
       |        | LDP | |
       |        +-----+ |
       |                |

       Figure 1: A COPS illustration.

   Figure 1 Illustrates the layout of various policy components in a
   typical COPS example (taken from [WRK]). Here, COPS is used to
   communicate policy information between a Policy Enforcement Point
   (PEP) and a remote Policy Decision Point (PDP).

   It is assumed that each participating policy client is functionally
   consistent with a PEP [WRK]. The PEP may communicate with a policy
   server (herein referred to as a remote PDP [WRK]) to obtain policy
   decisions or directives.

   The COPS protocol uses a single persistent TCP connection between
   the PEP and a remote PDP. The remote PDP listens on a well-known
   port number (COPS=3288), and the PEP is responsible for initiating
   the connection. The location of the remote PDP can either be
   configured, or obtained via a service location mechanism [SRVLOC].
   Service discovery is outside the scope of this protocol, however.

   The PEP uses the TCP connection to send requests to and receive
   responses from the remote PDP. Communication between the PEP and
   remote PDP is mainly in the form of a stateful request/response
   exchange, though the remote PDP may occasionally send an unsolicited
   response to the PEP to force a change in a previously approved
   request state. The PEP also has the capacity to report to the remote
   PDP that it has committed to an accepted request state for purposes
   of accounting and monitoring. Finally, the PEP is responsible for
   the deletion (retraction) of a request state that is no longer
   applicable. applicable or
   updating a request state on the PDP when it likewise changes at the

   The policy protocol is designed to communicate self-identifying
   objects which contain the data necessary for identifying request
   states, establishing the context for a request, identifying the type
   of request, referencing previously installed requests, relaying
   policy decisions, reporting errors, and transferring client specific

   To distinguish between different kinds of clients, the type of
   client is identified in each message. Different types of clients may
   have different client specific data and may require different kinds
   of policy decisions. It is expected that each new client type will
   have a corresponding extensions draft specifying the specifics of
   its interaction with this policy protocol.

   The context of each request corresponds to the policy event that
   triggered it. COPS identifies three types of controlled events: (1)
   the arrival of an incoming message (2) allocation of local
   resources, and (3) the forwarding of an outgoing message.
   Each of these events may require different decisions to be made.
   Context sub types are also defined according to the type of message
   that triggered the policy event. In RSVP, this subtype is used to
   define the RSVP signaling message type (e.g., Path, Resv, etc.). The
   content of a COPS request/response message depends on the context.

   The PEP may also have the capability to make a local policy decision
   via its Local Decision Point (LDP) [WRK], however, the PDP remains
   the authoritative decision point at all times. This means that
   any local decision information must always be relayed to the PDP.
   That is, the PDP must be granted access to all relevant information
   to make a final policy decision. To facilitate this functionality,
   the PEP must send its local decision information to the remote PDP
   via a LDP decision object. The PEP must then abide by the PDP's
   decision as it is absolute.

   Finally, fault tolerance is a required capability for this protocol,
   particularly due to the fact it is associated with the security and
   service management of distributed network devices. Fault tolerance
   is achieved by having both the PEP and remote PDP constantly verify
   their connection to each other via keep-alive messages. When a
   failure is detected, the PEP must try to reconnect to the remote PDP
   or attempt to connect to an a new/alternative PDP. Once a connection is
   reestablished, the remote PDP may request that all the PEP's
   internal state be resynchronized (all previously installed requests
   are to be reissued). After failure and before the new connection is
   fully functional, disruption of service can be minimized if the PEP
   caches previously communicated decisions and continues to use them
   for some limited amount of time. (Discussions of specific provisions
   for such a mechanism are outside of the scope of this draft, and are
   left to client specific implementations).

2. The Protocol

   This section describes the message formats and objects exchanged
   between the PEP and remote PDP.

2.1 Common Header

   Each COPS message consists of the COPS header followed by a number
   of typed objects.

              0              1              2              3
       |Version| //// |    Op Code   |       Client Type           |
       |                      Message Length                       |

   Global note: //// implies field is reserved, set to 0.

       The fields in the header are:
         Version: 4 bits
             COPS version number. Current version is 1.

       Op Code: 8 bits
            The COPS operations:
              1 = Request                 (REQ)
              2 = Response                (RES)
              3 = Unsolicited Response    (USR)
              4 = Report State            (RPT)
              5 = Delete Request State    (DRQ)
              6 = Synchronize State Req   (SSQ)
              7 = Client-Open             (OPN)
              8 = Client-Accept           (CAT)
              9 = Keep Alive Keep-Alive              (KA)
              10= Client-Close            (CC)

       Client Type: 16 bits

       The Client Type identifies the policy client. Interpretation of
       all encapsulated objects is relative to the client type.
       (See Appendix A for the RSVPv1 client type ID).

       Message Length: 32 bits
       Size of message in octets, which includes the standard COPS
       header and all encapsulated objects. Messages must be aligned on
       4 octet intervals.

2.2 COPS Specific Object Formats

   All the objects follow the same object format; each object consists
   of one or more 32-bit words with a four octet header, using the
   following format:

              0             1              2             3
       |       Length (octets)     |    C-Num    |   C-Type    |
       |                                                       |
       //                  (Object contents)                   //
       |                                                       |

   Typically, C-Num identifies the class of information contained in
   the object, and the C-Type identifies the subtype or version of the
   information contained in the object.

      C-num: 8 bits

               1  = Handle
               2  = Handle Reference.
               3  = Context
               4  = In Interface
               5  = Out Interface
               6  = Reason code
               7  = Decision
               8  = LDP Decision
               9  = Protocol Error
               10 = Client Specific Info
               11 = Timer
               12 = PEP Identification
               13 = Report Type
               14 = PDP Address

      C-type: 8 bits
               Values defined per C-num.

2.2.1 Handle Object (Handle)

   Unique value that identifies an installed request state. This
   identification is used by most COPS operations. The request state
   corresponding to this handle must be explicitly deleted by the
   client when no longer applicable.

   The handle value is set by the PEP and is opaque to the PDP. The PDP
   performs a byte-wise comparison on the value in this object with
   respect to the handle object values for other currently installed

           C-Num = 1, C-Type = 1

   Variable-length field, no implied format.

2.2.2 Handle Reference Object (HandleRef)

   Same C-Type formats as the handle object. This object may appear in
   requests and is used to associate the current request to previously
   installed request states. The presence of a reference handle in a
   request message tells the PDP that it should also consider
   information in the referenced installed state when making a policy
   decision for the current request. Handle References are only used
   for the specific client types that mandate them.

           C-num = 2, C-Type = (same as handle object)

2.2.3 Context Object (Context)

   Specifies the type of event(s) that triggered the query. Required
   for request messages.

           C-num = 3, C-Type = 1
              0             1               2               3
       |            R-Type           |            M-Type           |

           R-Type (Request Type Flag)

               0x01 = Incoming-Message/Admission Control request
               0x02 = Resource-Allocation request
               0x04 = Outgoing-Message request
               0x08 = Configuration request

           M-Type (Message Type)

               Client Specific 16 bit values of protocol message types

2.2.4 In-Interface Object (IN-Int)

   The In-Interface Object is used to identify the incoming interface
   on which a particular request/response applies. For flows or
   messages generated from the PEP's local host, the loop back address
   is used.

   Note: In-Interface is typically relative to the flow of the
   underlying protocol messages. That is, the In-Interface is the
   interface on which the protocol message was received.

           C-Num = 4

           C-Type = 1, IPv4 Address
               0             1              2             3
       |                   IPv4 Address format                     |

           C-Type = 2, IPv6 Address
               0             1              2             3
       |                                                           |
       +                                                           +
       |                                                           |
       +                    IPv6 Address format                    +
       |                                                           |
       +                                                           +
       |                                                           |

           C-Type = 3, Ifindex value
                   0             1              2             3
       |                          ifindex                          |

   Ifindex may be used to differ between sub-interfaces and unnumbered
   interfaces (see RSVP's LIH for an example). When appropriate, this
   ifindex integer should correspond to the same integer value for the
   interface in the SNMP MIB-II interface index table.

2.2.5 Out-Interface Object (OUT-Int)

   The Out-Interface is used to identify the outgoing interface to
   which a specific request/response applies. It has the same format as
   the In-Interface Object.

           C-Num = 5, C-Type = (same C-Type as for In-Interface)

   Note: In-Interface is typically relative to the flow of the
   underlying protocol messages. That is, the Out-Interface is the one
   on which a protocol message is about to be forwarded.

2.2.6 Reason Object (Reason)

   This object specifies the reason why the request state was deleted.
   It should appear in the delete request (DRQ) message.

           C-Num = 6, C-Type = 1
               0             1              2             3
       |         Reason-Code         |       Reason Sub-code       |

           Reason Code:
               1 = Unknown
               2 = Management
               3 = Preempted
               4 = Tear
               5 = Timeout
               6 = Route Change
               7 = Insufficient Resources
               8 = PDP's Directive
               9 = Client Specific (details in sub-code)
               10= Synchronize Handle Unknown

2.2.7 Decision Object (Decision)

   Decision made by the PDP. Must appear in replies. The specific
   decision objects required in a response to a particular request
   depend on the type of client.
       C-Num = 7

       CType = 1, Decision Flags (mandatory!)

       A flag bit set to 1 implies a negative decision for that flag.
       Flags not applicable to a given request type should be ignored.

               0             1              2             3
       |                           Flags                           |

               0x01 = Reject Incoming (Reject if set)
               0x02 = Do Not Allocate Resources (Reject if set)
               0x04 = Drop Outgoing (do not forward message if set)
               0x08 = Trigger Error (Trigger error message if set)

       Ctype = 2, Resource Allocation Data (optional)

       It is expected that PEPs would be able to configure simple
       stateless policy information to be processed locally in their
       LDP. As this set is well known and implemented ubiquitously,
       PDPs are aware of it as well (either universally, through
       configuration, or using the Client-Open message). The PDP may
       also include this information in its response, and the PEP
       should apply it to the resource allocation event that generated
       the request.

       Examples of resource allocation information that can be found in
       other documents are:

       Preemption Priority

       Priority is used by PEP to decide which of the flows should be
       preempted, when not enough resources are available on the
       interface. For RSVP, when preemption is supported, a higher
       priority reservation can preempt an installed reservation with
       lower priority.

       CType = 3, Replacement Data (Optional)

       This object is typically applicable as a response for an
       outgoing request. Format includes a list of client specific data
       that is to be used in place of information specified in the
       request. Use of this decision type is optional. For RSVP, this
       decision is used to change objects carried in RSVP messages. For
       example, replacing the policy data objects when forwarding a
       Resv message upstream is possible due to this decision type. If
       this decision doesn't appear in a response, all objects are
       passed as if the PDP was not there. To remove an object the
       decision should carry an empty object of length 4 (header only).
       Appendix A specifies the list of RSVP objects that can be

       CType = 4, Client Specific Decision Data (Optional)

       Proprietary decision types can be introduced using the Client
       Data Decision Object. Like the Replacement Data object, client
       specific information is encapsulated within the Client Data

2.2.8 LDP Decision Object (LDPDecision)

   Decision made by the PEP's local decision point (LDP). May appear in
   requests. These objects correspond to and are formatted the same as
   the client specific decision objects defined above.

           C-Num = 8

           CType = (same C-Type as for Decision object)

2.2.9 Error Object (Error)

   This object is used to identify a particular COPS protocol error.

            C-Num 9, C-Type = 1

               0             1              2             3
       |          Error-Code         |        Error Sub-code       |

               1 = Bad handle
               2 = Invalid handle reference
               3 = Bad message format
               4 = Unable to process (server gives up on query)
               5 = Mandatory client-specific info missing
               6 = Unsupported client type
               7 = Mandatory COPS object missing
               8 = Client Failure
               9 = Communication Failure
               10= Client Specific (details in sub-code)

2.2.10 Client Specific Information Object (ClientSI)

   All objects objects/attributes specific to a client's signaling protocol
   must be encapsulated within one or more Client Information Objects.
   The various types of this object are required for requests, and used
   in reports and opens when required. Additional ClientSI encapsulated
   data unknown to the PDP can be safely ignored by the PDP.

   Class-Num = 10,

   C-Type = 1 1, Request ClientSI.

   Variable-length field. The format of the data encapsulated in the
   ClientSI object is determined by the client type. Used in request

   C-Type = 2, Report ClientSI.

   Variable-length field. The format of the data encapsulated in the
   ClientSI object is determined by the client type. Used in COPS
   report messages when required.

   C-Type = 3, Client-Open ClientSI.

   Variable-length field. The format of the data encapsulated in the
   ClientSI object is determined by the client type. Used in COPS
   clientSI messages for feature negotiation, etc. when required.

2.2.11 Timer Object (Timer)

   Times are encoded as 32-bit 2 octet integer values and are in units of
   seconds.  The time value is treated as a delta.

           Class-Num = 11, C-Type = 1 (keep-alive 1, Keep-alive timer value) value

                0             1              2             3
       |        //////////////       |        KA Timer Value       |

2.2.12 PEP Identification Object (PEPID)

   The PEP Identification Object is used to identify the PEP client to
   the remote PDP. It is required for Client-Open messages.

           C-Num = 12, C-Type = 1

   Variable-length field (zero padded ASCII symbolic name) configured
   by local administrators for the PEP. For example, it can be the
   PEP's main IP address (not to be confused with the actual IP address
   used in the persistent TCP connection). It may also be the PEP's DNS
   name, or any other symbol that uniquely identifies each PEP within
   the policy domain. The choice of configuration bears no significance
   to the COPS protocol. By default, at least the primary IP address of
   the PEP represented as a string is expected in the PEPID.

2.2.13 Report-Type Object (Report-Type)

   The Type of Report on the request state associated with a handle:

   C-Num = 13, C-Type = 1

               0             1              2             3
       |         Report-Type         |        XXXXXXXXXXXXX        /////////////        |

               1 = Commit    : State was installed on client (PEP) PEP's local resources now allocated
               2 = Accounting: Accounting update for an installed state
               3 = No Commit : PEP's resource allocation failure

2.2.14 PDP Address (PDPAddr)

   A PDP when closing a PEP session for a particular client type may
   optionally use this object to redirect the PEP to another PDP server
   via this object:

   C-Num = 14,

   C-Type = 1, IPv4 Address
               0             1              2             3
       |                   IPv4 Address format                     |

   C-Type = 2, IPv6 Address (16 octets, as shown for In-interface)

3. Message Content

   This section describes the basic messages exchanged between a PEP
   and a remote PDP as well as their contents.

3.1 Request (REQ)  PEP -> PDP

   The PEP establishes a request state handle for which the remote PDP
   may maintain a state. The remote PDP then uses this handle to refer
   to the exchanged information and decisions.

   Once a stateful handle is established for a new request, any
   subsequent modifications of the request can be made using the REQ
   message specifying the previously installed handle. The format of the Request message PEP is as follows:

                 <Request> ::= <Common Header>
   responsible for notifying the PDP whenever its local state changes
   so the PDP's state will mirror the PEP's state.

   The format of the Request message is as follows:

                 <Request> ::= <Common Header>
                               [<list of HandleRefs>]

   The context object is used to determine the context within which all
   the other objects are to be interpreted. It also is used to
   determine the kind of response to be returned from the policy
   server. This response might be related to admission control,
   resource allocation, or object forwarding and substitution.

   The interface objects are used to determine the corresponding
   interface on which a signaling protocol message was received or is
   about to be sent. They are only used if the client is participating
   along the path of a signaling protocol.


   ClientSI (C-Type = 1), the client specific information object holds
   the client type specific data for which a policy decision needs to
   be made.

   The handle reference objects are used to refer to state information
   currently installed on the PDP that is associated with the current

   Finally, LDPDecision object holds information regarding the local
   decision made by the LDP.

3.2 Response (RES)  PDP -> PEP

   The PDP responds to the REQ with a RES message that includes the
   associated handle and the decision. If there was a protocol error an
   error object is returned instead.

   In order to avoid the issue of keeping track of which Request a
   particular response belongs to, it is important that, for a given
   handle, there be at most one outstanding response per query.  This
   essentially means that the PEP should not issue more than one
   REQ(for a given handle) before it receives a corresponding RES. To
   avoid deadlock, the client can always timeout after issuing a
   request. It can then delete the timed-out handle, and try again
   using a different (new) one. handle.

   The format of the Response message is as follows:

               <Response> ::= <Common Header>
                              <Decision(s)> || <Error>

   The response may include either an Error object or one or more
   object(s). objects. COPS protocol problems are reported in the Error
   object (e.g. an error with the format of the original request).
   Decision object(s) depend on the context of the associated request
   and the type of client.

3.3 Unsolicited Response (USR)  PDP -> PEP

   The remote PDP can also send an unsolicited response to a PEP to
   report a different response than the one previously communicated.
   For example, the PDP may admit a new flow and change its mind to
   reject it sometime later. The change of mind is communicated using
   the USR message.

   The format for an USR is the same as that for a RES and similarly,
   it dependents on the context of the original request.

3.4 Report State (RPT)  PEP -> PDP

   This message is used by the PEP to communicate the a change in the
   status of a previously installed request state to the server. A
   commit or no commit report indicates to the PDP that a particular
   policy directive has or has not been acted upon. upon as is relevant for
   accounting purposes. (In RSVP this would mean that the a reservation
   passed or failed local capacity admission control).

   The Report State may also be used to provide periodic updates of
   client specific information for accounting and state monitoring
   purposes depending on the type of the client. In such cases the
   accounting report type should be specified utilizing the client
   specific information object. object (C-Type = 2).

              <Report State> ::== <Common Header>
                                  [ <Client Specific Information> ]

3.5 Delete Request State (DRQ)  PEP -> PDP

   This message indicates to the remote PDP that the request state is
   no longer available in the PEP and must be deleted. This will be
   used by the remote PDP to initiate the appropriate housekeeping
   actions. The reason code object is interpreted with respect to the
   client type.

   The format of the Delete Request State message is as follows:

              <Delete Request>  ::= <Common Header>

   Given the stateful nature of COPS, it is important that when a
   request state is finally removed from the PEP, a DRQ message for
   this request state is sent to the PDP so the corresponding state may
   likewise be removed on the PDP. Request states not explicitly
   deleted by the PEP will be maintained by the PDP until either the
   client session is closed or the connection is terminated.

3.6 Synchronize State Request (SSQ)  PDP -> PEP

   The format of the Synchronize State Query message is as follows:

              <Synchronize State> ::= <Common Header>

   This message indicates that the remote PDP wishes the client (which
   appears in the common header) to re-send its state. If the optional
   Handle is present, only the state associated with this handle is
   synchronized. Otherwise, If the client does not recognize the requested handle,
   it should immediately send a DRQ message to the PDP for the handle
   that was specified in the SSQ message. If no handle is specified in
   the SSQ message, all the active client state should be synchronized
   with the PDP.

   The client performs state synchronization by re-issuing request
   queries of the specified client type for the existing state in the

3.7 Client-Open (OPN)  PEP -> PDP

   The Client-Open message can be used by the PEP to specify to provide the characteristics
   of PDP
   the client types the connection, suggested PEP can support, a *suggested* time intervals interval
   for the keep-alive messages, or client specific feature negotiation. A
   Client-Open message can be sent to the PDP at any time and information on multiple
   Client-Open messages for the locally known policy elements. same client type are allowed (in case
   of global state changes).

        <Client-Open>  ::= <Common Header>

   The PEPID is a symbolic, variable length name that identifies the
   specific client to the PDP. Values for the PEPID are configurable by
   administrators of administrative domains and are of direct
   significance to the COPS protocol. By default, the PEPID specifies
   the primary IP address in the form of a string for the PEP in

   If included, the timer corresponds to PEP's preference for the
   maximum intermediate time between the generation of messages for
   connection verification.

   Finally, a ClientSI (C-Type = 3) object can be included for relaying
   global information about the PEP to the PDP when required (as
   specified in the appropriate extensions document).

3.8 Client-Accept (CAT)  PDP -> PEP

   The Client-Accept message is used to positively respond to the
   Client-Open message. This message will return to the PEP either a timer
   object indicating the expected time interval between keep-alive messages,
   or an error object indicating that an error occurred (e.g. requested
   client type is not supported by the remote PDP).

              <Client-Accept>  ::= <Common Header>
                                   <Timer> || <Error>

   If the PDP refuses the client, it will return an Error object to
   describe the reason. instead issue a Client-Close

   The timer corresponds to maximum acceptable intermediate time
   between the generation of messages by the PDP and PEP. The timer
   value is determined by the PDP taking into account the client's
   preference established with the OPN message. A timer value of
   implies no secondary connection verification is necessary.

3.9 Keep-Alive (KA)  PEP -> PDP, PDP -> PEP

   The keep-alive message only needs to be transmitted when there has
   been no activity between the client and server for a period
   approaching half that of the minimum of all timer value values negotiated
   with the OPN & CAT messages. It is a validation for each side that
   the other connection is still functioning.

   Note: The client type in the header should always be set to 0 as the
   KA is used for connection verification (not per client session

               <Keep-Alive>  ::= <Common Header>

   Both client and server may assume the connection is insufficient for
   the client type with the minimum time value (specified in the CAT
   message) if no communication activity is detected for a period
   exceeding the timer period. For the PEP, such detection implies the
   remote PDP or connection is down and the PEP should now attempt to
   use an alternative/backup PDP.

3.10 Client-Close (CC)  PEP -> PDP, PDP -> PEP

   The Client-Close message can be issued by either the PDP or PEP to
   notify the other that a particular type of client is no longer being

               <Client-Close>  ::= <Common Header>

   An Error object is optionally included to describe the reason for
   the close due to an error condition (e.g. requested client type is
   not supported by the remote PDP or client failure).

   A PDP may optionally include a PDP-Address object in order to inform
   the PEP of the alternate PDP it should use for the client type
   specified in the common header.

4. Common Operation

   This section describes the typical exchanges between remote PDP
   servers and PEP clients.


   Sometime after a connection is established between the PEP and a
   remote PDP, the PEP will send one or more Client-Open messages to
   the remote PDP, at least one for each client type supported by the
   PEP. The open message should contain the common header noting one
   client type supported by the PEP. The remote PDP will then respond
   with a Client-Accept message echoing back each of the client types
   the PEP supports that it can support as well. If a specific client
   type is not supported by the PDP, the corresponding Client-Accept message sent back to the
   PEP PDP will include an error object instead respond with
   a Client-Close specifying the client type is not
   supported. The supported, and
   possibly suggesting an alternate PDP address. Otherwise, the PDP
   will include specify the timer interval between keep-
   alive keep-alive messages in its Client-Accept.
   Client-Accept and the PEP can begin issuing requests to the PDP.

   When the PEP receives an event that requires a new policy decision
   it sends a request message to the remote PDP. The remote PDP then
   makes a decision and sends a response back to the PEP. Since the
   request is stateful, the request will be remembered, or installed,
   on the remote PDP. The unique handle, specified in both the request
   and its corresponding response identifies this request state. The
   PEP is responsible for deleting this request state once the request
   is no longer applicable.

   The PEP may can update a previously installed request state by reissuing
   a request for the previously installed handle. The remote PDP is
   then expected to make new decisions and send a response back to the
   PEP. Likewise, the server may change a previously issued decision on
   any currently installed request state at any time by issuing an
   asynchronous response. At all times the PEP module is expected to
   abide by the PDP's decisions. decisions and notify the PDP on state changes.

   The PEP may also notify the remote PDP of the local status of an
   installed request using the report message where appropriate. The
   report message is to be used to signify when billing should
   effectively begin, or to produce periodic updates for monitoring and
   accounting purposes depending on the client. This message can carry
   client specific information when needed.

   Finally, to

   To validate the connection between the client and server is still
   functioning, the keep-alive message is used. If no COPS message is
   generated within one half the minimum timer value interval, a keep-alive keep-
   alive message needs to be generated. Both the PEP and remote PDP are
   expected to follow this procedure.

   Finally, Client-Close messages are used to negate the affects of the
   corresponding Client-Open messages, notifying the other side that
   the specified client type is no longer supported/active.

5. Security

   The security of RSVP messages is provided by inter-router MD5
   authentication [MD5].  This assumes a chain-of-trust model for inter
   PEP authentication.  Security between the client (PEP) and server
   (PDP) is provided by IPSEC [IPSEC].

   To ensure the client (PEP) is communicating with the correct policy
   server (PDP) involves two issues: authentication of the policy
   client and server using a shared secret, and consistent proof that
   the connection remains valid. The shared secret requires manual
   configuration of keys, which is a maintenance issue. IPSEC AH may be
   used for the validation of the connection; IPSEC ESP may be used to
   provide both validation and secrecy.

6. Open issues

   6.1 Bi-directional Connection Establishment:

   Currently, only the PEP is supposed to connect with the PDP. It
   might be useful to have the PDP proactive in establishing
   connections with its PEPs. PEPs (via a separate COPS PEP port). Such would
   potentially simplify PEP configuration and allow a primary PDP that
   has failed to notify its clients that it is functional again.

   6.2 Client Type Close/Redirect:

   Is there a need for a Close message per client type so the PEP and
   PDP can notify each other Such
   functionality will be specified in case of a capability change? If there
   is a close, should the PDP be able to tell appropriate COPS Extensions
   document. In the PEP which PDP server
   it meantime, PEPs should now use (redirect)?

   6.3 Division of Labor Negotiation:

   How can (and is there a need for) the PEP at least be locally
   configured to notify the remote PDP
   of its LDP's capabilities (e.g. the LDP can directly authenticate
   user information)?

   6.4 Group ID:

   Is there a need for a Group ID for identifying the group a client
   belongs akin connect to how the PEPID identifies an individual client?

   6.5 their appropriate Primary PDP/Backup PDP.

   6.2 RSVP Object Replacement:

   Should the PDP be capable of directing the RSVP PEP to replace other
   objects than the Policy Data object (e.g. FlowSpec)? If so, which
   RSVP objects and for which request types?


   6.3 RSVP Policy Data Priority Element Definition (other work). Definition.

   The object format of the Policy Data Element for Priority
   representation will be described in another document.

7. References

   [RSVP]  Braden, R. ed. et al., "Resource ReSerVation Protocol (RSVP)
           Version 1 - Functional Specification", RFC 2205, September

   [WRK]   Yavatkar, R. et al., "A Framework for Policy-Based Admission
           Control", Internet-Draft, draft-ietf-rap-framework-00.txt,
           November 1997.

   [SRVLOC]Guttman, E. et al., "Service Location Protocol", Internet-
           Draft,  draft-ietf-svrloc-protocol-v2-01.txt, October 1997.

   [INSCH] Shenker, S., Wroclawski, J., "General Characterization
           Parameters for Integrated Service Network Elements", RFC
           2215, September 1997.

   [IPSEC] Atkinson, R., "Security Architecture for the Internet
           Protocol", RFC1825, August 1995.

   [MD5]   Baker, F., "RSVP Cryptographic Authentication", Internet-
           Draft, draft-ietf-rsvp-md5-05.txt, August 1997.

   [RSVPPR]Braden, R., Zhang, L., "Resource ReSerVation Protocol (RSVP)
           - Version 1 Message Processing Rules", RFC 2209, September

   [UserID]Yadav, S., Pabbati, R., Ford, P., Herzog, S., "User Identity
           Representation for RSVP", Internet-Draft, draft-ietf-rap-
           user-identity-00.txt, March 1998.

8. 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
       MCI                              Class Data Systems
       2100 Reston Parkway              13 Hasadna St.
       Reston, VA 20191                 Ra'anana 43650 Israel
       703.715.7006                     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
       2055 Gateway Pl., Suite 400      506210 W Tasman Drive
       San Jose, CA 95110               San Jose, CA 95134
       408.390.3045                     408.526.7685   
          Appendix A. COPS Extensions for Use with RSVP

A.1 Overview of COPS extensions for RSVP

   Building on the foundations described in the previous sections this
   section describes the specific functionality required for this
   protocol to support policy control over RSVP.

   Setting the client type in the COPS common header to 1 indicates an
   RSVP client capable of performing admission control and policy data
   substitution using RSVP V1 objects.

A.2 COPS objects for use with RSVP

   The COPS objects defined in section 2.2 are applicable to RSVP
   policy control, and their use is described in the text that follows.

   The message type information found in the RSVP message header is
   represented by the M-Type in the COPS Context Object.

   All objects contained within RSVP messaging are expected to be
   encapsulated in the Client Specific Information Object without
   alteration. Multiple RSVP objects may be contained within a single
   Client Specific Information Object exchanged between the PEP and
   remote PDP.

   In support of the verification integrity of incoming RSVP messages,
   the COPS protocol may optionally return a security key in the Client
   Specific Decision Data object (C-Type = 4) useful for future
   integrity checks by the PEP. Refer to the document on User Identity
   Representation for RSVP [UserID] for details on the format and
   application of this security key when supported by the PEP.

   Finally, for the COPS outgoing message responses, RSVP objects may
   be returned to the PEP from the remote PDP via the Replacement Data
   Decision Object. This object may contain multiple RSVP objects, but
   is primarily concerned with returning the Policy Data object.
   Objects included in the Replace Data Decision Object are to replace
   their corresponding object in the RSVP message (typically for
   outgoing RSVP messages).

A.3. Operation of COPS for Policy Control Over RSVP

A.3.1 RSVP values for the 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 Previous 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.

   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 = PathErr ResvErr

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

A.3.2 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

A.3.4 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

A.3.5 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 notify the PDP by issuing a delete

A.3.6 Policy Control Over Path and Resv Tear

   Path and Resv Tear 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 Resv or Path Tear is received at the PEP, all
   affected states installed on the PDP should either be deleted or
   updated by the PEP.

A.3.7 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.

A.3.8 Data Expected in Request Messages for RSVP Support

   The information required in a RSVP request for each applicable
   message type and request type combination is outlined below:

       In, Path -
           <handle><context: in, Path><in-interface>
           <client info: all objects in Path message>
       Out, Path -
           <handle><context: out, Path><out-interface>
           <client info: all objects in outgoing Path message>
       In & Out (unicast combined request), Path -
           <handle><context: in & out, Path><in-interface>
           <client info: all objects in Path message>

       In, Resv -
           <handle><context: in, Resv><in-interface>
           <client info: all objects in Resv message>
       Merge, Resv -
           <handle><context: merge, Resv><in-interface>
           <client info: all objects in merged Resv message including
            the merged FLOWSPEC object>
       Out, Resv -
           <handle><context: out, Resv><out-interface>
           <client info: all objects in outgoing Resv message>
       In & Merge (combined request, PEP can merge), Resv -
           <handle><context: in & merge, Resv><in-interface>
           <client info: all objects in Resv message>
       In & Merge & Out (unicast combined request), Resv -
           <handle><context: in & merge & out, Resv><in-interface>
           <client info: all objects in Resv message>

       In, PathErr -
           <handle><context: in, PathErr><in-interface>
           <client info: all objects in PathErr message>
       Out, PathErr -
           <handle><context: out, PathErr><out-interface>
           <client info: all objects in outgoing PathErr message>
       In & Out (unicast combined request), PathErr -
           <handle><context: in & out, PathErr><in-interface>
           <client info: all objects in PathErr message>

       In, ResvErr -
           <handle><context: in, ResvErr><in-interface>
           <client info: all objects in ResvErr message>
       Out, ResvErr -
           <handle><context: out, ResvErr><out-interface>
           <client info: all objects in outgoing ResvErr message>
       In & Out (unicast combined request), ResvErr
           <handle><context: in & out, ResvErr><in-interface>
           <client info: all objects in ResvErr message>

A.3.9 Expected Decisions for RSVP Requests

   The expected decision information relative to a request for each
   applicable message type and request type combination is outlined
   below ([optional]):

       In, Path -
           <handle><Decision Flags> Flags>[<Decision Data: Security Key>]
       Out, Path -
           <handle><Decision Flags><Decision Replacement: Flags>[<DecisionReplacement: policy data> data>]
       In & Out (combined request), Path -
           <handle><Decision Flags><Decision Replacement: Flags>[<DecisionReplacement: policy data> data>]
          [<Decision Data: Security Key>]

       In, Resv -
           <handle><Decision Flags> Flags>[<Decision Data: Security Key>]
       Merge, Resv -
           <handle><Decision Flags><Decision Priority> Flags>[<Decision Priority>]
       Out, Resv -
           <handle><Decision Flags><Decision Replacement: Flags>[<DecisionReplacement: policy data> data>]
       In & Merge (combined request, PEP can merge), Resv -
           <handle><Decision Flags><Decision Priority> Flags>[<Decision Priority>][<Decision
           Data: Security Key>]
       In & Merge & Out (unicast combined request), Resv -
           <handle><Decision Flags><Decision Priority>
           <Decision Replacement: Flags>[<Decision Priority>]
           [<DecisionReplacement: policy data> data>][<Decision Data:
           Security Key>]

       In, PathErr -
           <handle><Decision Flags>
       Out, PathErr -
           <handle><Decision Flags><Decision Replacement: Flags>[<DecisionReplacement: policy data> data>]
       In & Out (combined request), PathErr -
           <handle><Decision Flags><Decision Replacement: Flags>[<DecisionReplacement: policy data> data>]

       In, ResvErr -
           <handle><Decision Flags>
       Out, ResvErr -
           <handle><Decision Flags><Decision Replacement: Flags>[<DecisionReplacement: policy data> data>]
       In & Out (combined request), ResvErr -
           <handle><Decision Flags><Decision Replacement: Flags>[<DecisionReplacement: policy data> data>]

A.4 Illustrative Examples, Using COPS for RSVP

A.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           if3+------------ S1
                                 |       if2       |
                                         PDP (server)

                    figure 1: Unicast Example: a single router view

   The PEP router has three interfaces (1,2,3). Sender S1 sends to
   receiver R1.

   A Path message arrives from S1:

          PEP --> PDP   REQ := <Handle A><Context in&out, Path>
                               <In-Interface if3> <Out-Interface if1>
                               <ClientSI: all objects in Path message>

          PDP --> PEP   RES := <Handle A><Decision accept>

   A Resv message arrives from R1:

          PEP --> PDP   REQ := <Handle B><Context in&merge&out, Resv>
                               <In-Interface if1> <Out-Interface if3>
                               <ClientSI: all objects in Resv message>

          PDP --> PEP   RES := <Handle B>
                               <Decisions: accept, Priority=7,
                                Replace: POLICY.DATA1>

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

   Time Passes, the PDP changes its decision:

          PDP --> PEP   USR := <Handle B>
                               <Decisions: accept, Priority=3,
                                Replace: POLICY.DATA2>

   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>

A.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.

                     r1       |                 |
               H1-------------|i1               |      r4
                              |              o1 |---------------- S1
                     r2       |     Router      |
               H2 ------------|i2               |
                     |        |              o2 |---------------- S2
                     | r3     |                 |
                     |         -----------------

                figure 1: 2 senders and 3 receivers

   Figure 1 shows an RSVP router which has two senders and three
   receivers for the same multicast session. Interface i2 is connected
   to a shared media.

   First detailed is the request message content for a Path sent by
   sender S1, assuming that both receivers have already joined the
   multicast session, but haven't sent a Resv message as yet. Assume
   sender S2 has not yet sent a path message. The Path message arrives
   on interface o1:

       PEP -----> PDP    REQ   := <handle A><context in, Path>
                                  <in-interface o1><client info: all
                                  objects in Path message>
       PDP -----> PEP    RES   := <handle A><Decision accept>

   Here the PDP decides to allow the Path message. Next, the Router
   consults its forwarding table, and finds two outgoing  interfaces,
   i1 and i2, for the path. The exchange below is for interface i1,
   another exchange would likewise be completed for i2 using the new
   handle B2.

       PEP -----> PDP    REQ   := <handle B1><context out, Path>
                                  <out-interface i1><client info: all
                                  objects in outgoing Path message>
       PDP -----> PEP    RES   := <handle B1><Decision forward>
                                  <Decision replacement object:
                                   policy object>

   Here, the PDP decided to allow the forwarding of the Path message
   via interface i1, and determined the appropriate policy objects for
   the message going out on this interface.

   Next, the receiver r2 sends a Resv message of WF style. The Resv
   arrives on interface i2. Here the PEP queries the PDP which decides
   to accept this reservation with priority 5 as shown below.

       PEP -----> PDP    REQ   := <handle C><context in, Resv>
                                  <in-interface i2><client info: all
                                  objects in Resv message>
       PDP -----> PEP    RES   := <handle C><Decision accept>

   This assumes the PEP is not itself capable of merging priority
   information, and, thus, must make another query for the incoming
   interface merge.

       PEP -----> PDP    REQ   := <handle D><context merge, Resv>
                                  <in-interface i2><client info: all
                                  objects in merged Resv message>
       PDP -----> PEP    RES   := <handle D><Decision Priority: 5>

   After PEP successfully admitted the reservation it sends a report
   message that signals to the PDP that it can start an accounting log
   for this reservation.

       PEP -----> PDP    RPT   := <handle D>

   The reservation r2 needs to be sent upstream towards sender S1 out
   interface o1. An outgoing Resv request is made which carries the
   associated handle of the Path message for which this Resv is being

       PEP -----> PDP    REQ   := <handle E><context out,Resv>
                                  <out-interface o1><client info: all
                                  objects in outgoing Resv message>
       PDP -----> PEP    RES   := <handle E><Decision forward><Decision
                                  replacement object: policy object>

   Next, receiver H3 sends the Resv message r3. The PEP sends an
   incoming request for handle F and the PDP decides to accept the Resv
   (as before). The new reservation also requires the PEP to update the
   merged request (handle D) due to the modified flowspec. The PDP now
   gives this request priority 7. If accepted by local admission
   control, a report is again sent.

       PEP -----> PDP    REQ   := <handle D><context merge, Resv>
                                  <in-interface i2><client info: all
                                  objects in merged Resv message w/
                                  new merged FLOWSPEC>
       PDP -----> PEP    RES   := <handle D><Decision priority 7>
       PEP -----> PDP    RPT   := <handle D>

   Now the outgoing request for handle E is reissued for the merged (R2
   & R3) outgoing Resv to be sent towards sender S1 due to a modified

       PEP -----> PDP    REQ   := <handle E><context out,Resv>
                                  <out-interface o1><client info: all
                                  objects in outgoing Resv message w/
                                  new merged FLOWSPEC>
       PDP -----> PEP    RES   := <handle E><Decision forward><Decision
                                  replacement object: policy object>

   When S2 joins the session by sending a Path message, incoming and
   outgoing Path requests are issued for the new Path. The two incoming
   Resv requests may then be reissued for handle C and handle E if
   there is a change in their shared sender filter list (for SE
   filters) specifying the new sender. A new outgoing Resv request
   would then be issued for the Resv to be sent to s2 out interface o2.