Internet Draft                                  Jim Boyle
 Expiration: February 1999                           Level 3
 File: draft-ietf-rap-cops-02.txt                Ron Cohen
                                                 David Durham
                                                 Shai Herzog
                                                 Raju Rajan
                                                 Arun Sastry

             The COPS (Common Open Policy Service) Protocol

                    Last Updated: August 6, 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,
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   Discussion and suggestions for improvement are requested.  This
   document will expire before February 1999. Distribution of this
   draft is unlimited.

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   This document describes a simple client/server model for supporting
   policy control over QoS Signaling Protocols and provisioned QoS
   resource management. 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 methods of the policy
   server, but is based on the server returning decisions to policy

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 example of a policy client is 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 policy control protocol is to begin with a
   simple but extensible design. The main characteristics of the COPS
   protocol include:

       1. The protocol employs a client/server model where the PEP
       sends requests, updates, and 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 without requiring modifications to the COPS
       protocol itself. The protocol was created for the general
       administration, configuration, and enforcement of policies
       whether signaled or provisioned. The protocol may be extended
       for the administration of a variety of signaling protocols as
       well as policy configuration on a device.

       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.

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       5. The protocol is stateful in two main aspects:
       (1) Request/Decision state is shared between client and server
       and (2) State from various events (Request/Decision 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,
       Decisions 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 Request/Decision state(s) that are

       6. Additionally, the protocol is stateful in that it allows the
       server to push configuration information to the client, and then
       allows the server to remove such state from the client when it
       is no longer applicable.

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) within the context of
   a particular type of client.

   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 PEP uses a TCP connection to send requests to and receive
   decisions from the remote PDP. Communication between the PEP and
   remote PDP is mainly in the form of a stateful request/decision
   exchange, though the remote PDP may occasionally send unsolicited
   decisions to the PEP to force changes in previously approved request

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   states. 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. The PEP is responsible for notifying the
   PDP when a request state has changed on the PEP. Finally, the PEP is
   responsible for the deletion of any state that is no longer
   applicable due to events at the client or decisions issued by the

   When the PEP sends a configuration request, it expects the PDP to
   continuously send named units of configuration data to the PEP via
   decision messages as applicable for the configuration request. When
   a unit of named configuration data is successfully installed on the
   PEP, the PEP should send a report message to the PDP confirming the
   installation. The server may then update or remove the named
   configuration information via a new decision message. When the PDP
   sends a decision to remove named configuration data from the PEP,
   the PEP will delete the specified configuration and send a report
   message to the PDP as confirmation.

   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/name space information.

   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 usage draft specifying the specifics of its
   interaction with this policy protocol.

   The context of each request corresponds to the type of event that
   triggered it. COPS identifies three types of outsourcing 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 available to describe the type of message that
   triggered the policy event. The content of a COPS request/decision
   message depends on the context. A forth type of request is useful
   for types of clients that wish to receive configuration information
   from the PDP. This allows a PEP to issue a configuration request for
   a specific named device or module that requires configuration
   information to be installed.

   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 the
   relevant local decision information must 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

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   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 a new/alternative PDP. While disconnected,
   the PEP should revert to making local decisions. Once a connection
   is reestablished, the PEP is expected to notify the PDP of any
   events that passed local admission control after the connection was
   lost. Additionally, 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, typically in the order of minutes.
   (Discussions of specific provisions for such a mechanism are outside
   of the scope of this draft, and are left to client specific

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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 = Decision                (DEC)
              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              (KA)
              10= Client-Close            (CC)
              11= Synchronize Complete    (SSC)

       Client-type: 16 bits

       The Client-type identifies the policy client. Interpretation of
       all encapsulated objects is relative to the client-type. Client-
       types that set the most significant bit in the client-type field
       are enterprise specific (these are client-types 0x8000 -
       0xFFFF). (See the specific client usage documents for particular
       client-type IDs).

       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.

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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)                   //
       |                                                       |

   The length is a two-octet value that describes the number of octets
   (including the header) that compose the object. If the length in
   octets does not fall on a 32-bit word boundary, padding must be
   added to the end of the object so that it is aligned to the next 32-
   bit boundary before the object can be sent on the wire. On the
   receiving side, a subsequent object boundary can be found by simply
   rounding up the previous stated object length to the first 32-bit

   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
               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)

   The Handle Object encapsulates a unique value that identifies an
   installed state. This identification is used by most COPS

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   operations. A state corresponding to a handle must be explicitly
   deleted when it is no longer applicable.

           C-Num = 1

           C-Type = 1, Client Handle.

   Variable-length field, no implied format other than it is unique
   from other client handles. It is always initially chosen by the PEP
   and then deleted by the PEP when no longer applicable. The client
   handle is used to refer to a request state initiated by the PEP and
   installed at the PDP. A PEP will specify a client handle in its
   Request messages, Report messages and Delete messages sent to the
   PDP. In all cases, the client handle is used to uniquely identify
   the PEP request.

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

2.2.2 Context Object (Context)

   Specifies the type of event(s) that triggered the query. Required
   for request messages. Admission control, resource allocation, and
   forwarding requests are all amenable to client-types that outsource
   their decision making facility to the PDP. For applicable client-
   types a PEP can also make a request to receive named configuration
   information from the PDP. This named configuration data may be in a
   form useful for setting system attributes on a PEP, or it may be in
   the form of policy rules that are to be directly verified by the

   Multiple flags can be set for the same request. This is only
   allowed, however, if the set of client specific information in the
   combined request is identical to the client specific information
   that would be specified if individual requests were made for each
   specified flag.

           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

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           M-Type (Message Type)

               Client Specific 16 bit values of protocol message types

2.2.3 In-Interface Object (IN-Int)

   The In-Interface Object is used to identify the incoming interface
   on which a particular request/decision 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.

2.2.4 Out-Interface Object (OUT-Int)

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

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

   Note: Out-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.

2.2.5 Reason Object (Reason)

   This object specifies the reason why the request state was deleted.
   It should appear in the delete request (DRQ) message. The Reason
   Sub-code field is reserved for more detailed client-specific reason
   codes defined in the corresponding documents.

           C-Num = 6, C-Type = 1

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

           Reason Code:
               1 = Unspecified
               2 = Management
               3 = Preempted
               4 = Tear
               5 = Timeout
               6 = Route Change
               7 = Insufficient Resources
               8 = PDP's Directive
               9 = Unsupported decision
               10= Synchronize Handle Unknown
               11= Transient Handle (stateless event)

2.2.6 Decision Object (Decision)

   Decision made by the PDP. Must appear in replies. The specific non-
   mandatory decision objects required in a decision 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.
       Not setting any flags generally implies a positive decision.
       Flag values not applicable to a given request type MUST be
       ignored by the PEP.

               0             1              2             3
       |                           Flags                           |

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               0x01 = Allow Incoming (Reject if set)
               0x02 = Allocate Resources (Reject if set)
               0x04 = Forward Outgoing (do not forward if set)
               0x08 = Trigger Error (Trigger error message if set)
               0x10 = NULL Configuration (No configuration data if set)
               0x20 = Install Configuration (Nothing to install if set)
               0x40 = Remove Configuration (Nothing to remove if set)
               0x80 = Enable Configuration (Nothing to enable if set)
               0x100= Disable Configuration (Nothing to disable if set)
               0x200= Solicited Decision
                  (Initial decision after a new/updated request if set)

              Ctype = 2, Resource Allocation Data

       It is expected that even outsourcing PEPs will be able to make
       some simple stateless policy decisions 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 decision, and the PEP should apply it to the
       resource allocation event that generated the request.

       As an example, reservations may be admitted by a PDP contingent
       on some type of per-session preemption priority. A RSVP PEP
       could have a set of stateless policy rules for when to preempt
       other reservations in favor of a new one (e.g. higher-priority
       pre-empts any of lower priority). The PDP would need to include
       appropriate priority information for each reservation in its
       decisions that the PEP can use to apply its rules.

               CType = 3, Replacement Data

       This object is typically applicable as a decision 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 decision message, all signaled
       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).

               CType = 4, Client Specific Decision Data

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

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               Ctype = 5, Named Decision Data

       Named configuration information should be encapsulated in this
       version of the decision object in response to configuration

2.2.7 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 objects)

2.2.8 Error Object (Error)

   This object is used to identify a particular COPS protocol error.
   The error sub-code field contains additional detailed client
   specific error codes.

            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= Unspecified
               11= Shutting down

2.2.9 Client Specific Information Object (ClientSI)

   The various types of this object are required for requests, and used
   in reports and opens when required. It contains client-related

           C-Num = 10,

           C-Type = 1, Signaled ClientSI.

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   Variable-length field. All objects/attributes specific to a client's
   signaling protocol or internal state must be encapsulated within one
   or more signaled Client Specific Information Objects. The format of
   the data encapsulated in the ClientSI object is determined by the

           C-Type = 2, Named ClientSI.

   Variable-length field. Contains named configuration information
   useful for relaying specific information about the PEP, a request,
   or configured state to the server.

2.2.10 Timer Object (Timer)

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

           C-Num = 11,

           C-Type = 1, Keep-alive timer value

   Timer object used to specify the maximum time interval over which a
   COPS message must be sent or received. The value of zero implies

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

           C-Type = 2, Accounting timer value

   Optional timer value used to determine the minimum interval between
   periodic accounting type reports. The value of zero implies

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

2.2.11 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

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   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
   for the COPS protocol, but does for policy at the PDP that may need
   to uniquely identify individual PEPs. By default, at least the
   primary IP address of the PEP represented as a string is expected in
   the PEPID.

2.2.12 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         |        /////////////        |

               1 = Commit    : PEP's local resources now allocated
               2 = Accounting: Accounting update for an installed state
               3 = No Commit : PEP's resource allocation failure
               4 = Installed : Named configuration installed
               5 = Removed   : Named configuration removed
               6 = Enabled   : Named configuration enabled
               7 = Disabled  : Named configuration disabled
               8 = Inst&Enab : Named config. installed and enabled

2.2.13 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 (4 octets, as shown for In-interface)

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

2.3 Communication

   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

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   configured, or obtained via a service location mechanism [SRVLOC].
   Service discovery is outside the scope of this protocol, however.

   It is possible a single PEP may have open connections to multiple
   PDPs. This is the case when there are physically different PDPs
   supporting different client-types as shown in figure 2.

       |                |
       |  Network Node  |            Policy Server
       |                |
       |   +-----+      | COPS Client Type 1  +-----+
       |   |PEP1 |<-----|-------------------->| PDP1|
       |   +-----+  |   | COPS Client Type 2  +-----+
       |    ^ | PEP2|<--|---------\           +-----+
       |    | +-----+   |          \----------| PDP2|
       |    \-->+-----+ |                     +-----+
       |        | LDP | |
       |        +-----+ |
       |                |

       Figure 2: Multiple PDPs illustration.

   When a TCP connection is torn down or is lost, both the PEP and PDP
   is expected to clean up any outstanding state related to any
   pervious request/decision exchanges. Additionally, the PEP should
   continuously attempt to contact the primary PDP or, if unsuccessful,
   any known backup PDPs. If a PEP is in communication with a backup
   PDP and the primary PDP becomes available, the backup PDP should
   redirect the PEP back to the primary PDP (via a close/redirect
   message for the affected client-type).

2.4 Client Handle Usage

   The client handle is used to identify a unique request state. Client
   handles are chosen by the PEP and are opaque to the PDP. The PDP
   simply uses the request handle to uniquely identify the request
   state and generically tie its decisions to a corresponding request.
   Client handles are initiated in request messages and are then used
   by subsequent request, decision, and report messages to reference
   the same request state. When the PEP is ready to remove a local
   request state, it will issue a delete message to the PDP for the
   corresponding client handle. A handle MUST be explicitly deleted by
   the PEP before it can be used to identify a new request state.
   Handles referring to different request states must be unique.

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   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 client 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 PEP is
   responsible for notifying the PDP whenever its local state changes
   so the PDP's state will be able to accurately mirror the PEP's

   The format of the Request message is as follows:

                 <Request> ::= <Common Header>
                               <Client Handle>

   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 decision to be returned from the policy
   server. This decision might be related to admission control,
   resource allocation, object forwarding and substitution, or

   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 typically used if the client is
   participating along the path of a signaling protocol or if the
   client is requesting configuration data for a particular interface.

   ClientSI, the client specific information object holds the client-
   type specific data for which a policy decision needs to be made. In
   the case of configuration, the named clientSI may include named
   information about the module, interface, or functionality to be

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

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3.2 Decision (DEC)  PDP -> PEP

   The PDP responds to the REQ with a DEC message that includes the
   associated client handle and one or more decision objects. If there
   was a protocol error an error object is returned instead.

   It is assumed that the first decision for a new/updated request will
   set the solicited decision flag. This avoids the issue of keeping
   track of which updated request (that is, a request reissued for the
   same handle) a particular decision corresponds. It is important
   that, for a given handle, there be at most one outstanding solicited
   decision per request. This essentially means that the PEP should not
   issue more than one REQ (for a given handle) before it receives a
   corresponding DEC with the solicited decision flag set.

   To avoid deadlock, the client can always timeout after issuing a
   request. It must then delete the timed-out handle, and possibly try
   again using a different (new) handle.

   The format of the Decision message is as follows:

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

   The decision may include either an Error object or one or more
   decision 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 and the type of client.

3.3 Report State (RPT)  PEP -> PDP

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

   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.

              <Report State> ::== <Common Header>
                                  <Client Handle>

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3.4 Delete Request State (DRQ)  PEP -> PDP

   When sent from the PEP this message indicates to the remote PDP that
   the state identified by the client handle is no longer
   available/relevant. This information will then be used by the remote
   PDP to initiate the appropriate housekeeping actions. The reason
   code object is interpreted with respect to the client-type and
   signifies the reason for the removal.

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

              <Delete Request>  ::= <Common Header>
                                    <Client Handle>

   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.

3.5 Synchronize State Request (SSQ)  PDP -> PEP

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

              <Synchronize State> ::= <Common Header>
                                      [<Client Handle>]

   This message indicates that the remote PDP wishes the client (which
   appears in the common header) to re-send its state. If the optional
   Client Handle is present, only the state associated with this handle
   is synchronized. If the PEP 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
   PEP. When synchronization is complete, the PEP must issue a
   synchronize state complete message to the PDP.

3.6 Client-Open (OPN)  PEP -> PDP

   The Client-Open message can be used by the PEP to specify to the PDP
   the client-types the PEP can support, a *suggested* time interval
   for keep-alive messages, and/or minimum time intervals for
   accounting updates, and/or client specific feature negotiation. A
   Client-Open message can be sent to the PDP at any time and multiple

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   Client-Open messages for the same client-type are allowed (in case
   of global state changes).

        <Client-Open>  ::= <Common Header>
                           [<KA Timer>]
                           [<ACCT Timer>]
                           [<Client ClientSI>]

   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 and/or the minimum time interval between
   periodic accounting reports.

   Finally, a named ClientSI object can be included for relaying
   additional global information about the PEP to the PDP when required
   (as specified in the appropriate extensions document for the client-

3.7 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 a timer
   object indicating the maximum time interval between keep-alive
   messages. Optionally, a timer specifying the minimum allowed
   interval between accounting report messages may be included when

              <Client-Accept>  ::= <Common Header>
                                   <KA Timer>
                                   [<ACCT Timer>]

   If the PDP refuses the client, it will instead issue a Client-Close

   The KA 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 0
   implies no secondary connection verification is necessary.

   The optional accounting timer allows the PDP to indicate to the PEP
   that periodic accounting reports should not exceed the specified

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   timer interval. This allows the PDP to control the rate at which
   accounting reports are sent by the PEP (when applicable).

3.8 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 values negotiated
   with the OPN & CAT messages. It is a validation for each side that
   the 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.

3.9 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.

3.10 Synchronize State Complete (SSC) PEP -> PDP

   The Synchronize State Complete is sent by the PEP to the PDP after
   the PDP sends a synchronize state request to the PEP and the PEP has
   finished synchronization. It is useful so that the PDP will know
   when all the old client state has been successfully re-requested
   and, thus, the PEP and PDP are completely synchronized.

         <Synchronize State Complete>  ::= <Common Header>

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   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 PDP will instead respond with
   a Client-Close specifying the client-type is not supported and will
   possibly suggest an alternate PDP address. Otherwise, the PDP will
   specify the timer interval between keep-alive messages in its
   Client-Accept and the PEP can begin issuing its requests to the PDP.

   In the outsourcing scenario, when the PEP receives an event that
   requires a new policy decision it sends a request message to the
   remote PDP. What specifically qualifies as an event for a particular
   client-type should be specified in the specific document for that
   client-type. The remote PDP then makes a decision and sends a
   decision message 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
   decision identifies this request state. The PEP is responsible for
   deleting this request state once the request is no longer

   The PEP 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 decision message back
   to the PEP. Likewise, the server may change a previously issued
   decision on any currently installed request state at any time by
   issuing another decision message. At all times the PEP module is
   expected to abide by the PDP's decisions and notify the PDP of any
   state changes.

   Likewise, in the configuration scenario, the PEP will make a
   configuration request to the PDP for a particular interface, module,
   or functionality that may be specified in the named client specific
   information object. The PDP will then send potentially several
   decisions containing named units of configuration data to the PEP.
   The PEP is expected to install and use the configuration locally. A
   particular named configuration can be updated by simply sending
   additional decision messages for the same named configuration. When
   the PDP no longer wishes the PEP to use a piece of configuration
   information, it will send a decision message specifying the named
   configuration and a decision flags object with the remove
   configuration flag set. The PEP should then proceed to remove the

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   corresponding configuration and send a report message to the PDP
   that specifies it has been deleted.

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

   The keep-alive message is used to validate the connection between
   the client and server is still functioning when there is no other
   messaging between the PEP and PDP. The PEP must generate a COPS
   message within one half the negotiated minimum timer interval or
   else a keep-alive message must be generated. Likewise, the PDP must
   either have sent a COPS message to every connected PEP within half
   the negotiated minimum timer interval or a keep-alive must be
   issued. If either side does not receive a keep-alive or any other
   COPS message within the negotiated timer interval from the other,
   the connection should be considered lost.

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

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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.

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6. Open issues

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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.

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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
       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
       2055 Gateway Pl., Suite 400      506210 W Tasman Drive
       San Jose, CA 95110               San Jose, CA 95134
       408.390.3045                     408.526.7685   

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