RSVP Extensions for Policy Control
Status of this Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Copyright © The Internet Society (2000). All Rights Reserved.
This memo presents a set of extensions for supporting generic policy based admission control in RSVP. It should be perceived as an extension to the RSVP functional specifications [RSVP]
These extensions include the standard format of POLICY_DATA objects, and a description of RSVP's handling of policy events.
This document does not advocate particular policy control mechanisms; however, a Router/Server Policy Protocol description for these extensions can be found in [RAP, COPS, COPS-RSVP].
Table of Contents
1 Introduction.......................................................2 2 A Simple Scenario..................................................3 3 Policy Data Objects................................................3 3.1 Base Format.....................................................4 3.2 Options.........................................................4 3.3 Policy Elements.................................................7 3.4 Purging Policy State............................................7 4 Processing Rules...................................................8 4.1 Basic Signaling.................................................8 4.2 Default Handling for PIN nodes..................................8 4.3 Error Signaling.................................................9 5 IANA Considerations................................................9 6 Security Considerations............................................9 7 References........................................................10 8 Acknowledgments...................................................10 9 Author Information................................................10 Appendix A: Policy Error Codes......................................11 Appendix B: INTEGRITY computation for POLICY_DATA objects...........12 Full Copyright Statement ...........................................13
RSVP, by definition, discriminates between users, by providing some users with better service at the expense of others. Therefore, it is reasonable to expect that RSVP be accompanied by mechanisms for controlling and enforcing access and usage policies. Version 1 of the RSVP Functional Specifications [RSVP] left a placeholder for policy support in the form of POLICY_DATA object.
The current RSVP Functional Specification describes the interface to admission (traffic) control that is based "only" on resource availability. In this document we describe a set of extensions to RSVP for supporting policy based admission control as well. The scope of this document is limited to these extensions and does not advocate specific architectures for policy based controls.
For the purpose of this document we do not differentiate between Policy Decision Point (PDP) and Local Decision Point (LDPs) as described in [RAP]. The term PDP should be assumed to include LDP as well.
2 A Simple Scenario
It is generally assumed that policy enforcement (at least in its initial stages) is likely to concentrate on border nodes between autonomous systems.
Figure 1 illustrates a simple autonomous domain with two boundary nodes (A, C) which represent PEPs controlled by PDPs. A core node (B) represents an RSVP capable policy ignorant node (PIN) with capabilities limited to default policy handling (Section 4.2).
PDP1 PDP2 | | | | +---+ +---+ +---+ | A +---------+ B +---------+ C | +---+ +---+ +---+ PEP2 PIN PEP2
Figure 1: Autonomous Domain scenario
Here, policy objects transmitted across the domain traverse an intermediate PIN node (B) that is allowed to process RSVP message but considered non-trusted for handling policy information.
This document describes processing rules for both PEP as well as PIN nodes.
3 Policy Data Objects
POLICY_DATA objects are carried by RSVP messages and contain policy information. All policy-capable nodes (at any location in the network) can generate, modify, or remove policy objects, even when senders or receivers do not provide, and may not even be aware of policy data objects.
The exchange of POLICY_DATA objects between policy-capable nodes along the data path, supports the generation of consistent end-to-end policies. Furthermore, such policies can be successfully deployed across multiple administrative domains when border nodes manipulate and translate POLICY_DATA objects according to established sets of bilateral agreements.
The following extends section A.13 in [RSVP].
3.1 Base Format
POLICY_DATA class=14 o Type 1 POLICY_DATA object: Class=14, C-Type=1 +-------------+-------------+-------------+-------------+ | Length | POLICY_DATA | 1 | +---------------------------+-------------+-------------+ | Data Offset | 0 (reserved) | +---------------------------+-------------+-------------+ | | // Option List // | | +-------------------------------------------------------+ | | // Policy Element List // | | +-------------------------------------------------------+
Data Offset: 16 bits
The offset in bytes of the data portion (from the first byte of the object header).
Option List: Variable length
The list of options and their usage is defined in Section 3.2.
Policy Element List: Variable length
The contents of policy elements is opaque to RSVP. See more details in Section 3.3.
This section describes a set of options that may appear in POLICY_DATA objects. All policy options appear as RSVP objects but their semantic is modified when used as policy data options.
FILTER_SPEC object (list) or SCOPE object
These objects describe the set of senders associated with the POLICY_DATA object. If none is provided, the policy information is assumed to be associated with all the flows of the session. These two types of objects are mutually exclusive, and cannot be mixed.
In Packed FF Resv messages, this FILTER_SPEC option provides association between a reserved flow and its POLICY_DATA objects.
In WF or SE styles, this option preserves the original flow/POLICY_DATA association as formed by PDPs, even across RSVP capable PINs. Such preservation is required since PIN nodes may change the list of reserved flows on a per-hop basis, irrespective of legitimate Edge-to-Edge PDP policy considerations.
Last, the SCOPE object should be used to prevent "policy loops" in a manner similar to the one described in [RSVP], Section 3.4. When PIN nodes are part of a WF reservation path, the RSVP SCOPE object is unable to prevent policy loops and the separate policy SCOPE object is required.
Note: using the SCOPE option may have significant impact on scaling and size of POLICY_DATA objects.
The RSVP_HOP object identifies the neighbor/peer policy-capable node that constructed the policy object. When policy is enforced at border nodes, peer policy nodes may be several RSVP hops away from each other and the originating RSVP_HOP is the basis for the mechanism that allows them to recognize each other and communicate safely and directly.
If no RSVP_HOP object is present, the policy data is implicitly assumed to have been constructed by the RSVP_HOP indicated in the RSVP message itself (i.e., the neighboring RSVP node is policy- capable).
A second RSVP_HOP object may follow the originating RSVP_HOP object. This second RSVP_HOP identifies the destination policy node. This is used to ensure the POLICY_DATA object is delivered to targeted policy nodes. It may be used to emulate unicast delivery in multicast Path messages. It may also help prevent using a policy object in other parts of the network (replay attack).
On the receiving side, a policy node should ignore any POLICY_DATA that includes a destination RSVP_HOP that doesn't match its own IP address.
Figure 1 (Section 2) provides an example where POLICY_DATA objects are transmitted between boundary nodes while traversing non-secure PIN nodes. In this scenario, the RSVP integrity mechanism becomes ineffective since it places policy trust with intermediate PIN nodes (which are trusted to perform RSVP signaling but not to perform policy decisions or manipulations).
The INTEGRITY object option inside POLICY_DATA object creates direct secure communications between non-neighboring PEPs (and their controlling PDPs) without involving PIN nodes.
This option can be used at the discretion of PDPs, and is computed in a manner described in Appendix B.
Policy Refresh TIME_VALUES (PRT)
The Policy Refresh TIME_VALUES (PRT) option is used to slow policy refresh frequency for policies that have looser timing constraints relative to RSVP. If the PRT option is present, policy refreshes can be withheld as long as at least one refresh is sent before the policy refresh timer expires. A minimal value for PRT is R; lower values are assumed to be R (neither error nor warning should be triggered).
To simplify RSVP processing, time values are not based directly on the PRT value, but on a Policy Refresh Multiplier N computed as N=Floor(PRT/R). Refresh and cleanup rules are derived from [RSVP] Section 3.7 assuming the refresh period for PRT POLICY DATA is R' computed as R'=N*R. In effect, both the refresh and the state cleanup are slowed by a factor of N).
The refresh multiplier applies to no-change periodic refreshes only (rather than updates). For example, a policy being refreshed at time T, T+N, T+2N,... may encounter a route change detected at T+X. In this case, the event would force an immediate policy update and would reset srfresh times to T+X+N, T+X+2N,...
When network nodes restart, RSVP messages between PRT policy refreshes may be rejected since they arrive without necessary POLICY_DATA objects. This error situation would clear with the next periodic policy refresh or with a policy update triggered by ResvErr or PathErr messages.
This option is especially useful to combine strong (high overhead) and weak (low overhead) authentication certificates as policy data. In such schemes the weak certificate can support admitting a reservation only for a limited time, after which the strong certificate is required.
This approach may reduce the overhead of POLICY_DATA processing. Strong certificates could be transmitted less frequently, while weak certificates are included in every RSVP refresh.
3.3 Policy Elements
The content of policy elements is opaque to RSVP; their internal format is understood by policy peers e.g. an RSVP Local Decision Point (LDP) or a Policy Decision Point (PDP) [RAP]. A registry of policy element codepoints and their meaning is maintained by [IANA- CONSIDERATIONS] (also see Section 5).
Policy Elements have the following format:
+-------------+-------------+-------------+-------------+ | Length | P-Type | +---------------------------+---------------------------+ | | // Policy information (Opaque to RSVP) // | | +-------------------------------------------------------+
3.4 Purging Policy State
Policy state expires in the granularity of Policy Elements (POLICY_DATA objects are mere containers and do not expire as such).
Policy elements expire in the exact manner and time as the RSVP state received in the same message (see [RSVP] Section 3.7). PRT controlled state expires N times slower (see Section 3.2).
Only one policy element of a certain P-Type can be active at any given time. Therefore, policy elements are instantaneously replaced when another policy element of the same P-Type is received from the same PDP (previous or next policy RSVP_HOP). An empty policy element of a certain P-Type is used to delete (rather than a replace) all policy state of the same P-Type.
4 Processing Rules
These sections describe the minimal required policy processing rules for RSVP.
4.1 Basic Signaling
This memo mandates enforcing policy control for Path, Resv, PathErr, and ResvErr messages only. PathTear and ResvTear are assumed not to require policy control based on two main presumptions. First, that Integrity verification [MD5] guarantee that the Tear is received from the same node that sent the installed reservation, and second, that it is functionally equivalent to that node holding-off refreshes for this reservation.
4.2 Default Handling for PIN nodes
Figure 1 illustrates an example of where policy data objects traverse PIN nodes in transit from one PEP to another.
A PIN node is required at a minimum to forward the received POLICY_DATA objects in the appropriate outgoing messages according to the following rules:
o POLICY_DATA objects are to be forwarded as is, without any modifications. o Multicast merging (splitting) nodes:
In the upstream direction:
When multiple POLICY_DATA objects arrive from downstream, the RSVP node should concatenate all of them (as a list of the original POLICY_DATA objects) and forward them with the outgoing (upstream) message.
On the downstream direction:
When a single incoming POLICY_DATA object arrives from upstream, it should be forwarded (copied) to all downstream branches of the multicast tree.
The same rules apply to unrecognized policies (sub-objects) within the POLICY_DATA object. However, since this can only occur in a policy-capable node, it is the responsibility of the PDP and not RSVP.
4.3 Error Signaling
Policy errors are reported by either ResvErr or PathErr messages with a policy failure error code in the ERROR_SPEC object. Policy error message must include a POLICY_DATA object; the object contains details of the error type and reason in a P-Type specific format (See Section 3.3).
If a multicast reservation fails due to policy reasons, RSVP should not attempt to discover which reservation caused the failure (as it would do for Blockade State). Instead, it should attempt to deliver the policy ResvErr to ALL downstream hops, and have the PDP (or LDP) decide where messages should be sent. This mechanism allows the PDP to limit the error distribution by deciding which "culprit" next-hops should be informed. It also allows the PDP to prevent further distribution of ResvErr or PathErr messages by performing local repair (e.g. substituting the failed POLICY_DATA object with a different one).
Error codes are described in Appendix Appendix A.
5 IANA Considerations
RSVP Policy Elements (P-Types)
Following the policies outlined in [IANA-CONSIDERATIONS],numbers 0-49151 are allocated as standard policy elements by IETF Consensus action, numbers in the range 49152-53247 are allocated as vendor specific (one per vendor) by First Come First Serve, and numbers 53248-65535 are reserved for private use and are not assigned by IANA.
6 Security Considerations
This memo describes the use of POLICY_DATA objects to carry policy- related information between RSVP nodes. Two security mechanisms can be optionally used to ensure the integrity of the carried information. The first mechanism relies on RSVP integrity [MD5] to provide a chain of trust when all RSVP nodes are policy capable. The second mechanism relies on the INTEGRITY object within the POLICY_DATA object to guarantee integrity between non-neighboring RSVP PEPs (see Sections 2 and 3.2).
[RAP] Yavatkar, R., Pendarakis, D. and R. Guerin, "A Framework for Policy Based Admission Control", RFC 2753, January 2000. [COPS] Boyle, J., Cohen, R., Durham, D., Herzog, S., Raja, R. and A. Sastry, "The COPS (Common Open Policy Service) Protocol", RFC 2748, January 2000. [COPS-RSVP] Boyle, J., Cohen, R., Durham, D., Herzog, S., Raja, R. and A. Sastry, "COPS Usage for RSVP", RFC 2749, January 2000. [RSVP] Braden, R., Ed., Zhang, L., Berson, S., Herzog, S. and S. Jamin, "Resource ReSerVation Protocol (RSVP) - Functional Specification", RFC 2205, September 1997. [MD5] Baker, F., Lindell B. and M. Talwar, "RSVP Cryptographic Authentication", RFC 2747, January 2000. [IANA-CONSIDERATIONS] Alvestrand, H. and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
This document incorporates inputs from Lou Berger, Bob Braden, Deborah Estrin, Roch Guerin, Timothy O'Malley, Dimitrios Pendarakis, Raju Rajan, Scott Shenker, Andrew Smith, Raj Yavatkar, and many others.
9 Author Information
55 New York Avenue
Framingham, MA 01701
Phone: (508) 620-1141 EMail: firstname.lastname@example.org
Appendix A: Policy Error Codes
This Appendix extends the list of error codes described in Appendix B of [RSVP].
Note that Policy Element specific errors are reported as described in Section 4.3 and cannot be reported through RSVP (using this mechanism). However, this mechanism provides a simple, less secure mechanism for reporting generic policy errors. Most likely the two would be used in concert such that a generic error code is provided by RSVP, while Policy Element specific errors are encapsulated in a return POLICY_DATA object (as in Section 4.3).
ERROR_SPEC class = 6
Error Code = 02: Policy Control failure
Error Value: 16 bit
0 = ERR_INFO : Information reporting 1 = ERR_WARN : Warning 2 = ERR_UNKNOWN : Reason unknown 3 = ERR_REJECT : Generic Policy Rejection 4 = ERR_EXCEED : Quota or Accounting violation 5 = ERR_PREEMPT : Flow was preempted 6 = ERR_EXPIRED : Previously installed policy expired (not refreshed) 7 = ERR_REPLACED: Previous policy data was replaced & caused rejection 8 = ERR_MERGE : Policies could not be merged (multicast) 9 = ERR_PDP : PDP down or non functioning 10= ERR_SERVER : Third Party Server (e.g., Kerberos) unavailable 11= ERR_PD_SYNTX: POLICY_DATA object has bad syntax 12= ERR_PD_INTGR: POLICY_DATA object failed Integrity Check 13= ERR_PE_BAD : POLICY_ELEMENT object has bad syntax 14= ERR_PD_MISS : Mandatory PE Missing (Empty PE is in the PD object) 15= ERR_NO_RSC : PEP Out of resources to handle policies. 16= ERR_RSVP : PDP encountered bad RSVP objects or syntax 17= ERR_SERVICE : Service type was rejected 18= ERR_STYLE : Reservation Style was rejected 19= ERR_FL_SPEC : FlowSpec was rejected (too large)
Values between 2^15 and 2^16-1 can be used for site and/or vendor error values.
Appendix B: INTEGRITY computation for POLICY_DATA objects
Computation of the INTEGRITY option is based on the rules set forth in [MD5], with the following modifications:
Rather than computing digest for an RSVP message, a digest is computed for a POLICY_DATA object in the following manner:
(1) The INTEGRITY object is inserted in the appropriate place in
the POLICY_DATA object, and its location in the message is remembered for later use.
(2) The PDP, at its discretion, and based on destination PEP/PDP
or other criteria, selects an Authentication Key and the hash algorithm to be used.
(3) A copy of RSVP SESSION object is temporarily appended to the
end of the PD object (for the computation purposes only, without changing the length of the POLICY_DATA object). The flags field of the SESSION object is set to 0. This concatenation is considered as the message for which a digest is to be computed.
(4) The rest of the steps in Section 4.1 ((4)..(9)) remain unchanged when computed over the concatenated message.
Note: When the computation is complete, the SESSION object is ignored and is not part of the POLICY_DATA object.
The processing of a received POLICY_DATA object as well as a challenge-response INTEGRITY object inside a POLICY_DATA object is performed in the manner described in [MD5]. This processing is subject to the modified computation algorithm as described in the beginning of this appendix (for Section 4.1 of [MD5]).
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