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Network Working Group                                           F. BakerRequest for Comments: 3175                                  C. IturraldeCategory: Standards Track                                 F. Le Faucheur                                                                B. Davie                                                           Cisco Systems                                                          September 2001Aggregation of RSVP for IPv4 and IPv6 ReservationsStatus 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 Notice   Copyright (C) The Internet Society (2001).  All Rights Reserved.Abstract   This document describes the use of a single RSVP (Resource   ReSerVation Protocol) reservation to aggregate other RSVP   reservations across a transit routing region, in a manner   conceptually similar to the use of Virtual Paths in an ATM   (Asynchronous Transfer Mode) network.  It proposes a way to   dynamically create the aggregate reservation, classify the traffic   for which the aggregate reservation applies, determine how much   bandwidth is needed to achieve the requirement, and recover the   bandwidth when the sub-reservations are no longer required.  It also   contains recommendations concerning algorithms and policies for   predictive reservations.1.  Introduction   A key problem in the design of RSVP version 1 [RSVP] is, as noted in   its applicability statement, that it lacks facilities for aggregation   of individual reserved sessions into a common class.  The use of such   aggregation is recommended in [CSZ], and required for scalability.   The problem of aggregation may be addressed in a variety of ways.   For example, it may sometimes be sufficient simply to mark reserved   traffic with a suitable DSCP (e.g., EF), thus enabling aggregation of   scheduling and classification state.  It may also be desirable to   install one or more aggregate reservations from ingress to egress ofBaker, et al.               Standards Track                     [Page 1]

RFC 3175              RSVP Reservation Aggregation        September 2001   an "aggregation region" (defined below) where each aggregate   reservation carries similarly marked packets from a large number of   flows.  This is to provide high levels of assurance that the end-to-   end requirements of reserved flows will be met, while at the same   time enabling reservation state to be aggregated.   Throughout, we will talk about "Aggregator" and "Deaggregator",   referring to the routers at the ingress and egress edges of an   aggregation region.  Exactly how a router determines whether it   should perform the role of aggregator or deaggregator is described   below.   We will refer to the individual reserved sessions (the sessions we   are attempting to aggregate) as "end-to-end" reservations ("E2E" for   short), and to their respective Path/Resv messages as E2E Path/Resv   messages.  We refer to the the larger reservation (that which   represents many E2E reservations) as an "aggregate" reservation, and   its respective Path/Resv messages as "aggregate Path/Resv messages".1.1.  Problem Statement: Aggregation Of E2E Reservations   The problem of many small reservations has been extensively   discussed, and may be summarized in the observation that each   reservation requires a non-trivial amount of message exchange,   computation, and memory resources in each router along the way.  It   would be nice to reduce this to a more manageable level where the   load is heaviest and aggregation is possible.   Aggregation, however, brings its own challenges.  In particular, it   reduces the level of isolation between individual flows, implying   that one flow may suffer delay from the bursts of another.   Synchronization of bursts from different flows may occur.  However,   there is evidence [CSZ] to suggest that aggregation of flows has no   negative effect on the mean delay of the flows, and actually leads to   a reduction of delay in the "tail" of the delay distribution (e.g.,   99% percentile delay) for the flows.  These benefits of aggregation   to some extent offset the loss of strict isolation.1.2.  Proposed Solution   The solution we propose involves the aggregation of several E2E   reservations that cross an "aggregation region" and share common   ingress and egress routers into one larger reservation from ingress   to egress.  We define an "aggregation region" as a contiguous set of   systems capable of performing RSVP aggregation (as defined following)   along any possible route through this contiguous set.Baker, et al.               Standards Track                     [Page 2]

RFC 3175              RSVP Reservation Aggregation        September 2001   Communication interfaces fall into two categories with respect to an   aggregation region; they are "exterior" to an aggregation region, or   they are "interior" to it.  Routers that have at least one interface   in the region fall into one of three categories with respect to a   given RSVP session; they aggregate, they deaggregate, or they are   between an aggregator and a deaggregator.   Aggregation depends on being able to hide E2E RSVP messages from   RSVP-capable routers inside the aggregation region.  To achieve this   end, the IP Protocol Number in the E2E reservation's Path, PathTear,   and ResvConf messages is changed from RSVP (46) to RSVP-E2E-IGNORE   (134) upon entering the aggregation region, and restored to RSVP at   the deaggregator point.  These messages are ignored (no state is   stored and the message is forwarded as a normal IP datagram) by each   router within the aggregation region whenever they are forwarded to   an interior interface.  Since the deaggregating router perceives the   previous RSVP hop on such messages to be the aggregating router, Resv   and other messages do not require this modification; they are unicast   from RSVP hop to RSVP hop anyway.   The token buckets (SENDER_TSPECs and FLOWSPECS) of E2E reservations   are summed into the corresponding information elements in aggregate   Path and Resv messages.  Aggregate Path messages are sent from the   aggregator to the deaggregator(s) using RSVP's normal IP Protocol   Number.  Aggregate Resv messages are sent back from the deaggregator   to the aggregator, thus establishing an aggregate reservation on   behalf of the set of E2E flows that use this aggregator and   deaggregator.   Such establishment of a smaller number of aggregate reservations on   behalf of a larger number of E2E reservations yields the   corresponding reduction in the amount of state to be stored and   amount of signalling messages exchanged in the aggregation region.   By using Differentiated Services mechanisms for classification and   scheduling of traffic supported by aggregate reservations (rather   than performing per aggregate reservation classification and   scheduling), the amount of classification and scheduling state in the   aggregation region is even further reduced.  It is not only   independent of the number of E2E reservations, it is also independent   of the number of aggregate reservations in the aggregation region.   One or more Diff-Serv DSCPs are used to identify traffic covered by   aggregate reservations and one or more Diff-Serv PHBs are used to   offer the required forwarding treatment to this traffic.  There may   be more than one aggregate reservation between the same pair of   routers, each representing different classes of traffic and each   using a different DSCP and a different PHB.Baker, et al.               Standards Track                     [Page 3]

RFC 3175              RSVP Reservation Aggregation        September 20011.3.  Definitions   We define an "aggregation region" as a set of RSVP-capable routers   for which E2E RSVP messages arriving on an exterior interface of one   router in the set would traverse one or more interior interfaces (of   this and possibly of other routers in the set) before finally   traversing an exterior interface.   Such an E2E RSVP message is said to have crossed the aggregation   region.   We define the "aggregating" router for this E2E flow as the first   router that processes the E2E Path message as it enters the   aggregation region (i.e., the one which forwards the message from an   exterior interface to an interior interface).   We define the "deaggregating" router for this E2E flow as the last   router to process the E2E Path as it leaves the aggregation region   (i.e., the one which forwards the message from an interior interface   to an exterior interface).   We define an "interior" router for this E2E flow as any router in the   aggregation region which receives this message on an interior   interface and forwards it to another interior interface.  Interior   routers perform neither aggregation nor deaggregation for this flow.   Note that by these definitions a single router with a mix of interior   and exterior interfaces may have the capability to act as an   aggregator on some E2E flows, a deaggregator on other E2E flows, and   an interior router on yet other flows.1.4.  Detailed Aspects of Proposed Solution   A number of issues jump to mind in considering this model.1.4.1.  Traffic Classification Within The Aggregation Region   One of the reasons that RSVP Version 1 did not identify a way to   aggregate sessions was that there was not a clear way to classify the   aggregate.  With the development of the Differentiated Services   architecture, this is at least partially resolved; traffic of a   particular class can be marked with a given DSCP and so classified.   We presume this model.   We presume that on each link en route, a queue, WDM color, or similar   management component is set aside for all aggregated traffic of the   same class, and that sufficient bandwidth is made available to carryBaker, et al.               Standards Track                     [Page 4]

RFC 3175              RSVP Reservation Aggregation        September 2001   the traffic that has been assigned to it.  This bandwidth may be   adjusted based on the total amount of aggregated reservation traffic   assigned to the same class.   There are numerous options for exactly which Diff-serv PHBs might be   used for different classes of traffic as it crosses the aggregation   region.  This is the "service mapping" problem described in   [RFC2998], and is applicable to situations broader than those   described in this document.  Arguments can be made for using either   EF or one or more AF PHBs for aggregated traffic.  For example, since   controlled load requires non-TSpec-conformant (policed) traffic to be   forwarded as best effort traffic rather than dropped, it may be   appropriate to use an AF class for controlled load, using the higher   drop preference for non-conformant packets.   In conventional (unaggregated) RSVP operation, a session is   identified by a destination address and optionally a protocol port.   Since data belonging to an aggregated reservation is identified by a   DSCP, the session is defined by the destination address and DSCP.   For those cases where two DSCPs are used (for conformant and non-   conformant packets, as noted above), the session is identified by the   DSCP of conformant packets.  In general we will talk about mapping   aggregated traffic onto a DSCP (even if a second DSCP may be used for   non-conformant traffic).   Whichever PHB or PHBs are used to carry aggregated reservations, care   needs to be take in an environment where provisioned Diff-Serv and   aggregated RSVP are used in the same network, to ensure that the   total admitted load for a single PHB does not exceed the link   capacity allocated to that PHB.  One solution to this is to reserve   one PHB (or more) strictly for the aggregated reservation traffic   (e.g., AF1 Class) while using other PHBs for provisioned Diff-Serv   (e.g., AF2, AF3 and AF4 Classes).   Inside the aggregation region, some RSVP reservation state is   maintained per aggregate reservation, while classification and   scheduling state (e.g., DSCPs used for classifying traffic) is   maintained on a per aggregate reservation class basis (rather than   per aggregate reservation).  For example, if Guaranteed Service   reservations are mapped to the EF DSCP throughout the aggregation   region, there may be a reservation for each aggregator/deaggregator   pair in each router, but only the EF DSCP needs to be inspected at   each interior interface, and only a single queue is used for all EF   traffic.Baker, et al.               Standards Track                     [Page 5]

RFC 3175              RSVP Reservation Aggregation        September 20011.4.2.  Deaggregator Determination   The first question is "How do we determine the   Aggregator/Deaggregator pair that are responsible for aggregating a   particular E2E flow through the aggregation region?"   Determination of the aggregator is trivial: we know that an E2E flow   has arrived at an aggregator when its Path message arrives at a   router on an exterior interface and must be forwarded on an interior   interface.   Determination of the deaggregator is more involved.  If an SPF   routing protocol, such as OSPF or IS-IS, is in use, and if it has   been extended to advertise information on Deaggregation roles, it can   tell us the set of routers from which the deaggregator will be   chosen.  In principle, if the aggregator and deaggregator are in the   same area, then the identity of the deaggregator could be determined   from the link state database.  However, this approach would not work   in multi-area environments or for distance vector protocols.   One method for Deaggregator determination is manual configuration.   With this method the network operator would configure the Aggregator   and the Deaggregator with the necessary information.   Another method allows automatic Deaggregator determination and   corresponding Aggregator notification.  When the E2E RSVP Path   message transits from an interior interface to an exterior interface,   the deaggregating router must advise the aggregating router of the   correlation between itself and the flow.  This has the nice attribute   of not being specific to the routing protocol.  It also has the   property of automatically adjusting to route changes.  For instance,   if because of a topology change, another Deaggregator is now on the   shortest path, this method will automatically identify the new   Deaggregator and swap to it.1.4.3.  Mapping E2E Reservations Onto Aggregate Reservations   As discussed above, there may be multiple Aggregate Reservations   between the same Aggregator/Deaggregator pair.  The rules for mapping   E2E reservations onto aggregate reservations are policy decisions   which depend on the network environment and network administrator's   objectives.  Such a policy is outside the scope of this specification   and we simply assume that such a policy is defined by the network   administrator.  We also assume that such a policy is somehow   accessible to the Aggregators/Deaggregators but the details of how   this policy is made accessible to Aggregators/Deaggregators (Local   Configuration, COPS, LDAP, etc.) is outside the scope of this   specification.Baker, et al.               Standards Track                     [Page 6]

RFC 3175              RSVP Reservation Aggregation        September 2001   An example of very simple policy would be that all the E2E   reservations are mapped onto a single Aggregate Reservation (i.e.,   single DSCP) between a given pair of Aggregator/Deaggregator.   Another example of policy, which takes into account the Int-Serv   service type requested by the receiver (and signalled in the E2E   Resv), would be where Guaranteed Service E2E reservations are mapped   onto one DSCP in the aggregation region and where Controlled Load E2E   reservations are mapped onto another DSCP.   A third example of policy would be one where the mapping of E2E   reservations onto Aggregate Reservations take into account Policy   Objects (such as information authenticating the end user) which may   be included by the sender in the E2E path and/or by the receiver in   the E2E Resv.   Regardless of the actual policy, a range of options are conceivable   for where the decision to map an E2E reservation onto an aggregate   reservation is taken and how this decision is communicated between   Aggregator and Deaggregator.  Both Aggregator and Deaggregator could   be assumed to make such a decision independently.  However, this   would either require definition of additional procedures to solve   inconsistent mapping decisions (i.e., Aggregator and Deaggregator   decide to map a given E2E reservation onto different Aggregate   Reservations) or would result in possible undetected misbehavior in   the case of inconsistent decisions.   For simplicity and reliability, we assign the responsibility of the   mapping decision entirely to the Deaggregator.  The Aggregator is   notified of the selected mapping by the Deaggregator and follows this   decision.  The Deaggregator was chosen rather than the Aggregator   because the Deaggregator is the first to have access to all the   information required to make such a decision (in particular receipt   of the E2E Resv which indicates the requested Int-Serv service type   and includes information signalled by the receiver).  This allows   faster operations such as set-up or size adjustment of an Aggregate   Reservation in a number of situations resulting in faster E2E   reservation establishment.1.4.4.  Size of Aggregate Reservations   A range of options exist for determining the size of the aggregate   reservation, presenting a tradeoff between simplicity and   scalability.  Simplistically, the size of the aggregate reservation   needs to be greater than or equal to the sum of the bandwidth of the   E2E reservations it aggregates, and its burst capacity must be   greater than or equal to the sum of their burst capacities.  However,   if followed religiously, this leads us to change the bandwidth of theBaker, et al.               Standards Track                     [Page 7]

RFC 3175              RSVP Reservation Aggregation        September 2001   aggregate reservation each time an underlying E2E reservation   changes, which loses one of the key benefits of aggregation, the   reduction of message processing cost in the aggregation region.   We assume, therefore, that there is some policy, not defined in this   specification (although sample policies are suggested which have the   necessary characteristics).  This policy maintains the amount of   bandwidth required on a given aggregate reservation by taking account   of the sum of the bandwidths of its underlying E2E reservations,   while endeavoring to change it infrequently.  This may require some   level of trend analysis.  If there is a significant probability that   in the next interval of time the current aggregate reservation will   be exhausted, the router must predict the necessary bandwidth and   request it.  If the router has a significant amount of bandwidth   reserved but has very little probability of using it, the policy may   be to predict the amount of bandwidth required and release the   excess.   This policy is likely to benefit from introduction of some hysteresis   (i.e., ensure that the trigger condition for aggregate reservation   size increase is sufficiently different from the trigger condition   for aggregate reservation size decrease) to avoid oscillation in   stable conditions.   Clearly, the definition and operation of such policies are as much   business issues as they are technical, and are out of the scope of   this document.1.4.5.  E2E Path ADSPEC update   As described above, E2E RSVP messages are hidden from the Interior   routers inside the aggregation region.  Consequently, the ADSPECs of   E2E Path messages are not updated as they travel through the   aggregation region.  Therefore, the Deaggregator for a flow is   responsible for updating the ADSPEC in the corresponding E2E Path to   reflect the impact of the aggregation region on the QoS that may be   achieved end-to-end.  The Deaggregator should update the ADSPEC of   the E2E Path as accurately as possible.   Since Aggregate Path messages are processed inside the aggregation   region, their ADSPEC is updated by Interior routers to reflect the   impact of the aggregation region on the QoS that may be achieved   within the interior region.  Consequently, the Deaggregator should   make use of the information included in the ADSPEC from an Aggregate   Path where available.  The Deaggregator may elect to wait until such   information is available before forwarding the E2E Path in order to   accurately update its ADSPEC.Baker, et al.               Standards Track                     [Page 8]

RFC 3175              RSVP Reservation Aggregation        September 2001   To maximize the information made available to the Deaggregator,   whenever the Aggregator signals an Aggregate Path,  the Aggregator   should include an ADSPEC with fragments for all service types   supported in the aggregation region (even if the Aggregate Path   corresponds to an Aggregate Reservation that only supports a subset   of those service types).  Providing this information to the   Deaggregator for every possible service type facilitates accurate and   timely update of the E2E ADSPEC by the Deaggregator.   Depending on the environment and on the policy for mapping E2E   reservations onto Aggregate Reservations, to accurately update the   E2E Path ADSPEC, the Deaggregator may for example:   -  update all the E2E Path ADSPEC segments (Default General      Parameters Fragment, Guaranteed Service Fragment, Controlled-Load      Service Fragment) based on the ADSPEC of a single Aggregate Path,      or   -  update the E2E Path ADSPEC by taking into account the ADSPEC from      multiple Aggregate Path messages (e.g.,.  update the Default      General Parameters Fragment using the "worst" value for each      parameter across all the Aggregate Paths' ADSPECs, update the      Guaranteed Service Fragment using the Guaranteed Service Fragment      from the ADSPEC of the Aggregate Path for the reservation used for      Guaranteed Services).   By taking into account the information contained in the ADSPEC of   Aggregate Path(s) as mentioned above, the Deaggregator should be able   to accurately update the E2E Path ADSPEC in most situations.   However, we note that there may be particular situations where the   E2E Path ADSPEC update cannot be made entirely accurately by the   Deaggregator.  This is most likely to happen when the path taken   across the aggregation region depends on the service requested in the   E2E Resv, which is yet to arrive.  Such a situation could arise if,   for example:   -  The service mapping policy for the aggregation region is such that      E2E reservations requesting Guaranteed Service are mapped to a      different PHB that those requesting Controlled Load service.   -  Diff-Serv aware routing is used in the aggregation region, so that      packets with different DSCPs follow different paths (sending them      over different MPLS label switched paths, for example).   As a result, the ADSPEC for the aggregate reservation that supports   guaranteed service may differ from the ADSPEC for the aggregate   reservation that supports controlled load.Baker, et al.               Standards Track                     [Page 9]

RFC 3175              RSVP Reservation Aggregation        September 2001   Assume that the sender sends an E2E Path with an ADSPEC containing   segments for both Guaranteed Services and Controlled Load.  Then, at   the time of updating the E2E ADSPEC, the Deaggregator does not know   which service type will actually be requested by the receiver and   therefore cannot know which PHB will be used to transport this E2E   flow and, in turn, cannot pick the right parameter values to factor   in when updating the Default General Parameters Fragment.  As   mentioned above, in this particular case, a conservative approach   would be to always take into account the worst value for every   parameter.  Regardless of whether this conservative approach is   followed or some simpler approach such as taking into account one of   the two Aggregate Path ADSPEC, the E2E Path ADSPEC will be inaccurate   (over-optimistic or over-pessimistic) for at least one service type   actually requested by the destination.   Recognizing that entirely accurate update of E2E Path ADSPEC may not   be possible in all situations, we recommend that a conservative   approach be taken in such situations (over-pessimistic rather than   over-optimistic) and that the E2E Path ADSPEC be corrected as soon as   possible.  In the example described above, this would mean that as   soon as the Deaggregator receives the E2E Resv from the receiver, the   Deaggregator should generate another E2E Path with an accurately   updated ADSPEC based on the knowledge of which aggregate reservation   will actually carry the E2E flow.1.4.6.  Intra-domain Routes   RSVP directly handles route changes, in that reservations follow the   routes that their data follow.  This follows from the property that   Path messages contain the same IP source and destination address as   the data flow for which a reservation is to be established.  However,   since we are now making aggregate reservations by sending a Path   message from an aggregating to a deaggregating router, the reserved   (E2E) data packets no longer carry the same IP addresses as the   relevant (aggregate) Path message.  The issue becomes one of making   sure that data packets for reserved flows follow the same path as the   Path message that established Path state for the aggregate   reservation.  Several approaches are viable.   First, the data may be tunneled from aggregator to deaggregator,   using technologies such as IP-in-IP tunnels, GRE tunnels, MPLS   label-switched paths, and so on.  These each have particular   advantages, especially MPLS, which allows traffic engineering.  They   each also have some cost in link overhead and configuration   complexity.Baker, et al.               Standards Track                    [Page 10]

RFC 3175              RSVP Reservation Aggregation        September 2001   If data is not tunneled, then we are depending on a characteristic of   IP best metric routing , which is that if the route from A to Z   includes the path from H to L, and the best metric route was chosen   all along the way, then the best metric route was chosen from H to L.   Therefore, an aggregate path message which crosses a given aggregator   and deaggregator will of necessity use the best path between them.   If this is a single path, the problem is solved.  If it is a multi-   path route, and the paths are of equal cost, then we are forced to   determine, perhaps by measurement, what proportion of the traffic for   a given E2E reservation is passing along each of the paths, and   assure ourselves of sufficient bandwidth for the present use.  A   simple, though wasteful, way of doing this is to reserve the total   capacity of the aggregate route down each path.   For this reason, we believe it is advantageous to use one of the   above-mentioned tunneling mechanisms in cases where multiple equal-   cost paths may exist.1.4.7.  Inter-domain Routes   The case of inter-domain routes differs somewhat from the intra-   domain case just described.  Specifically, best-path considerations   do not apply, as routing is by a combination of routing policy and   shortest AS path rather than simple best metric.   In the case of inter-domain routes, data traffic belonging to   different E2E sessions (but the same aggregate session) may not enter   an aggregation region via the same aggregator interface, and/or may   not leave via the same deaggregator interface.  It is possible that   we could identify this occurrence in some central system which sees   the reservation information for both of the apparent sessions, but it   is not clear that we could determine a priori how much traffic went   one way or the other apart from measurement.   We simply note that this problem can occur and needs to be allowed   for in the implementation.  We recommend that each such E2E   reservation be summed into its appropriate aggregate reservation,   even though this involves over-reservation.1.4.8.  Reservations for Multicast Sessions   Aggregating reservations for multicast sessions is significantly more   complex than for unicast sessions.  The first challenge is to   construct a multicast tree for distribution of the aggregate Path   messages which follows the same path as will be followed by the data   packets for which the aggregate reservation is to be made.  This is   complicated by the fact that the path taken by a data packet mayBaker, et al.               Standards Track                    [Page 11]

RFC 3175              RSVP Reservation Aggregation        September 2001   depend on many factors such as its source address, the choice of   shared trees or source-specific trees, and the location of a   rendezvous point for the tree.   Once the problem of distributing aggregate Path messages is solved,   there are considerable problems in determining the correct amount of   resources to reserve at each link along the multicast tree.  Because   of the amount of heterogeneity that may exist in an aggregate   multicast reservation, it appears that it would be necessary to   retain information about individual E2E reservations within the   aggregation region to allocate resources correctly.  Thus, we may end   up with a complex set of procedures for forming aggregate   reservations that do not actually reduce the amount of stored state   significantly for multicast sessions.   As noted above, there are several aspects to RSVP state, and our   approach for unicast aggregates all forms of state:  classification,   scheduling, and reservation state.  One possible approach to   multicast is to focus only on aggregation of classification and   scheduling state, which are arguably the most important because of   their impact on the forwarding path.  That approach is the one   described in the current draft.1.4.9.  Multi-level Aggregation   Ideally, an aggregation scheme should be able to accommodate   recursive aggregation, with aggregate reservations being themselves   aggregated.  Multi-level aggregation can be accomplished using the   procedures described here and a simple extension to the protocol   number swapping process.   We can consider E2E RSVP reservations to be at aggregation level 0.   When we aggregate these reservations, we produce reservations at   aggregation level 1.  In general, level n reservations may be   aggregated to form reservations at level n+1.   When an aggregating router receives an E2E Path, it swaps the   protocol number from RSVP to RSVP-E2E-IGNORE.  In addition, it should   write the aggregation level (1, in this case) in the 2 byte field   that is present (and currently unused) in the router alert option.   In general, a router which aggregates reservations at level n to   create reservations at level n+1 will write the number n+1 in the   router alert field.  A router which deaggregates level n+1   reservations will examine all messages with IP protocol number RSVP-   E2E-IGNORE but will process the message and swap the protocol number   back to RSVP only in the case where the router alert field carries   the number n+1.  For any other value, the message is forwarded   unchanged.  Interior routers ignore all messages with IP protocolBaker, et al.               Standards Track                    [Page 12]

RFC 3175              RSVP Reservation Aggregation        September 2001   number RSVP-E2E-IGNORE.  Note that only a few bits of the 2 byte   field in the option would be needed, given the likely number of   levels of aggregation.   For IPv6, certain values of the router alert "value" field are   reserved.  This specification requires IANA assignment of a small   number of consecutive values for the purpose of recording the   aggregation level.1.4.10.  Reliability Issues   There are a variety of issues that arise in the context of   aggregation that would benefit from some form of explicit   acknowledgment mechanism for RSVP messages.  For example, it is   possible to configure a set of routers such that an E2E Path of   protocol type RSVP-E2E-IGNORE would be effectively "black-holed", if   it never reached a router which was appropriately configured to act   as a deaggregator.  It could then travel all the way to its   destination where it would probably be ignored due to its non-   standard protocol number.  This situation is not easy to detect.  The   aggregator can be sure this problem has not occurred if an aggregate   PathErr message is received from the deaggregator (as described in   detail below).  It can also be sure there is no problem if an E2E   Resv is received.  However, the fact that neither of these events has   happened may only mean that no receiver wishes to reserve resources   for this session, or that an RSVP message loss occurred, or it may   mean that the Path was black-holed.  However, if a neighbor-to-   neighbor acknowledgment mechanism existed, the aggregator would   expect to receive an acknowledgment of the E2E Path from the   deaggregator, and would interpret the lack of a response as an   indication that a problem of configuration existed.  It could then   refrain from aggregating this particular session.  We note that such   a reliability mechanism has been proposed for RSVP in [RFC291] and   propose that it be used here.1.4.11.  Message Integrity and Node Authentication   [RSVP] defines a hop-by-hop authentication and integrity check.  The   present specification allows use of this check on Aggregate RSVP   messages and also preserves this check on E2E RSVP messages for E2E   RSVP messages.   Outside the Aggregation Region, any E2E RSVP message may contain an   INTEGRITY object using a keyed cryptographic digest technique which   assumes that RSVP neighbors share a secret.  Because E2E RSVP   messages are not processed by routers in the Aggregation Region, the   Aggregator and Deaggregator appear as logical RSVP neighbors of each   other.  The Deaggregator is the Aggregator's Next Hop for E2E RSVPBaker, et al.               Standards Track                    [Page 13]

RFC 3175              RSVP Reservation Aggregation        September 2001   messages while the Aggregator is the Deaggregator's Previous Hop.   Consequently, INTEGRITY objects which may appear in E2E RSVP messages   traversing the Aggregation Region are exchanged directly between the   Aggregator and Deaggregator in a manner which is entirely transparent   to the Interior routers.  Thus, hop-by-hop integrity checking for E2E   messages over the Aggregation Region requires that the Aggregator and   Deaggregator share a secret.  Techniques for establishing that secret   are described in [INTEGRITY].   Inside the Aggregation Region, any Aggregate RSVP message may contain   an INTEGRITY object which assumes that the corresponding RSVP   neighbors inside the Aggregation Region (e.g., Aggregator and   Interior Router, two Interior Routers, Interior Router and   Deaggregator) share a secret.1.4.12.  Aggregated reservations without E2E reservations   Up to this point we have assumed that the aggregate reservation is   established as a result of the establishment of E2E reservations from   outside the aggregation region.  It should be clear that alternative   triggers are possible.  As discussed in [RFC2998], an aggregate RSVP   reservation can be used to manage bandwidth in a diff-serv cloud even   if RSVP is not used end-to-end.   The simplest example of an alternative configuration is the static   configuration of an aggregated reservation for a certain amount for   traffic from an ingress (aggregator) router to an egress (de-   aggregator) router.  This would have to be configured in at least the   system originating the aggregate PATH message (the aggregator).  The   deaggregator could detect that the PATH message is directed to it,   and could be configured to "turn around" such messages, i.e., it   responds with a RESV back to the aggregator.  Alternatively,   configuration of the aggregate reservation could be performed at both   the aggregator and the deaggregator.  As before, an aggregate   reservation is associated with a DSCP for the traffic that will use   the reserved capacity.   In the absence of E2E microflow reservations, the aggregator can use   a variety of policies to set the DSCP of packets passing into the   aggregation region, thus determining whether they gain access to the   resources reserved by the aggregate reservation.  These policies are   a matter of local configuration, as usual for a device at the edge of   a diffserv cloud.Baker, et al.               Standards Track                    [Page 14]

RFC 3175              RSVP Reservation Aggregation        September 2001   Note that the "aggregator" could even be a device such as a PSTN   gateway which makes an aggregate reservation for the set of calls to   another PSTN gateway (the deaggregator) across an intervening diff-   serv region.  In this case the reservation may be established in   response to call signalling.   From the perspective of RSVP signalling and the handling of data   packets in the aggregation region, these cases are equivalent to the   case of aggregating E2E RSVP reservations.  The only difference is   that E2E RSVP signalling does not take place and cannot therefore be   used as a trigger, so some additional knowledge is required in   setting up the aggregate reservation.2.  Elements of Procedure   To implement aggregation, we define a number of elements of   procedure.2.1.  Receipt of E2E Path Message By Aggregating Router   The very first event is the arrival of the E2E Path message at an   exterior interface of an aggregator.  Standard RSVP procedures [RSVP]   are followed for this, including onto what set of interfaces the   message should be forwarded.  These interfaces comprise zero or more   exterior interfaces and zero or more interior interfaces.  (If the   number of interior interfaces is zero, the router is not acting as an   aggregator for this E2E flow.)   Service on exterior interfaces is handled as defined in [RSVP].   Service on interior interfaces is complicated by the fact that the   message needs to be included in some aggregate reservation, but at   this point it is not known which one, because the deaggregator is not   known.  Therefore, the E2E Path message is forwarded on the interior   interface(s) using the IP Protocol number RSVP-E2E-IGNORE, but in   every other respect identically to the way it would be sent by an   RSVP router that was not performing aggregation.2.2.  Handling Of E2E Path Message By Interior Routers   At this point, the E2E Path message traverses zero or more interior   routers.  Interior routers receive the E2E Path message on an   interior interface and forward it on another interior interface.  The   Router Alert IP Option alerts interior routers to check internally,   but they find that the IP Protocol is RSVP-E2E-IGNORE and the next   hop interface is interior.  As such, they simply forward it as a   normal IP datagram.Baker, et al.               Standards Track                    [Page 15]

RFC 3175              RSVP Reservation Aggregation        September 20012.3.  Receipt of E2E Path Message By Deaggregating Router   The E2E Path message finally arrives at a deaggregating router, which   receives it on an interior interface and forwards it on an exterior   interface.  Again, the Router Alert IP Option alerts it to intercept   the message, but this time the IP Protocol is RSVP-E2E-IGNORE and the   next hop interface is an exterior interface.   Before forwarding the E2E Path towards the receiver, the Deaggregator   should update its ADSPEC.  This update is to reflect the impact of   the aggregation region onto the QoS to be achieved E2E by the flow.   Such information can be collected by the ADSPEC of Aggregate Path   messages travelling from the Aggregator to the Deaggregator.  Thus,   to enable correct updating of the ADSPEC, a deaggregating router may   wait as described below for the arrival of an aggregate Path before   forwarding the E2E Path.   When receiving the E2E Path, depending on the policy for mapping E2E   reservation onto Aggregate Reservations, the Deaggregator may or may   not be in a position to decide which DSCP the E2E flow for the   processed E2E Path is going to be mapped onto, as described above.   If the Deaggregator is in a position to know the mapping at this   point, then the Deaggregator first checks that there is an Aggregate   Path in place for the corresponding DSCP.  If so, then the   Deaggregator uses the ADSPEC of this Aggregate Path to update the   ADSPEC of the E2E Path and then forwards the E2E Path towards the   receiver.  If not, then the Deaggregator requests establishment of   the corresponding Aggregate Path by sending an E2E PathErr message   with an error code of NEW-AGGREGATE-NEEDED and the desired DSCP   encoded in the DCLASS Object.  The Deaggregator may also at the same   time request establishment of an aggregate reservation for other   DSCPs.  When receiving the Aggregate Path for the desired DSCP, the   Deaggregator then uses the ADSPEC of this Aggregate Path to update   the ADSPEC of the E2E Path.   If the Deaggregator is not in a position to know the mapping at this   point, then the Deaggregator uses the information contained in the   ADSPEC of one Aggregate Path or of multiple Aggregate Paths to update   the E2E Path ADSPEC.  Similarly, if one or more of the necessary   Aggregate Paths is not yet established, the Deaggregator requests   establishment of the corresponding Aggregate Path by sending an E2E   PathErr message with an error code of NEW-AGGREGATE-NEEDED and the   desired DSCP encoded in the respective DCLASS Object.  When receiving   the Aggregate Path for the desired DSCP, the Deaggregator then uses   the ADSPEC of this Aggregate Path to update the ADSPEC of the E2E   Path.Baker, et al.               Standards Track                    [Page 16]

RFC 3175              RSVP Reservation Aggregation        September 2001   Generating a E2E PathErr message with an error code of NEW-   AGGREGATE-NEEDED should not result in any Path state being removed,   but should result in the aggregating router initiating the necessary   aggregate Path message, as described in the following section.   The deaggregating router changes the E2E Path message's IP Protocol   from RSVP-E2E-IGNORE to RSVP and forwards the E2E Path message   towards its intended destination.2.4.  Initiation of New Aggregate Path Message By Aggregating Router   The aggregating Router is responsible for generating a new Aggregate   Path for a DSCP when receiving a E2E PathErr message with the error   code NEW-AGGREGATE-NEEDED from the deaggregator.  The DSCP value to   include in the Aggregate Path Session is found in the DCLASS Object   of the received E2E PathErr message.  The identity of the   deaggregator itself is found in the ERROR SPECIFICATION of the E2E   PathErr message.  The destination address of the aggregate Path   message is the address of the deaggregating router, and the message   is sent with IP protocol number RSVP.   Existing RSVP procedures specify that the size of a reservation   established for a flow is set to the minimum of the Path SENDER_TSPEC   and the Resv FLOW_SPEC.  Consequently, the size of an Aggregate   Reservation cannot be larger than the SENDER_TSPEC included in the   Aggregate Path by the Aggregator.  To ensure that Aggregate   Reservations can be sized by the Deaggregator without undesired   limitations, the Aggregating router should always attempt to include   in the Aggregate Path a SENDER_TSPEC which is at least as large as   the size that would actually be required as determined by the   Deaggregator.  One method to achieve this is to use a SENDER_TSPEC   which is obviously larger than the highest load of E2E reservations   that may be supported onto this network.  Another method is for the   Aggregator to keep track of which flows are mapped onto a DSCP and   always add their E2E Path SENDER_TSPEC into the Aggregate Path   SENDER_TSPEC (and possibly also add some additional bandwidth in   anticipation of future E2E reservations).   The aggregating router is notified of the mapping from an E2E flow to   a DSCP in two ways.  First, when the aggregating router receives a   E2E PathErr with error code NEW-AGGREGATE-NEEDED, the Aggregator is   notified that the corresponding E2E flow is (at least temporarily)   mapped onto a given DSCP.  Secondly, when the aggregating router   receives an E2E Resv containing a DCLASS Object (as described further   below), the Aggregating Router is notified that the corresponding E2E   flow is mapped onto a given DSCP.Baker, et al.               Standards Track                    [Page 17]

RFC 3175              RSVP Reservation Aggregation        September 20012.5.  Handling of E2E Resv Message by Deaggregating Router   Having sent the E2E Path message on toward the destination, the   deaggregator must now expect to receive an E2E Resv for the session.   On receipt, its responsibility is to ensure that there is sufficient   bandwidth reserved within the aggregation region to support the new   E2E reservation, and if there is, then to forward the E2E Resv to the   aggregating router.   The Deaggregating router first makes the final decision of which   Aggregate Reservation (and thus which DSCP) this E2E reservation is   to be mapped onto.  This decision is made according to the policy   selected by the network administrator as described above.   If this final mapping decision is such that the Deaggregator can now   make a more accurate update of the E2E Path ADSPEC than done when   forwarding the initial E2E Path, the Deaggregator should do so and   generate a new E2E Path immediately in order to provide the accurate   ADSPEC information to the receiver as soon as possible.  Otherwise,   normal Refresh procedures should be followed for the E2E Path.   If no Aggregate Reservation currently exists from the corresponding   aggregating router with the corresponding DSCP, the Deaggregating   router will establish a new Aggregate Reservation as described in the   next section.   If the corresponding Aggregate Reservation exists but has   insufficient bandwidth reserved to accommodate the new E2E   reservation (in addition to all the existing E2E reservations   currently mapped onto it), it should follow the normal RSVP   procedures [RSVP] for a reservation being placed with insufficient   bandwidth to support the reservation.  It may also first attempt to   increase the aggregate reservation that is supplying bandwidth by   increasing the size of the FLOW_SPEC that it includes in the   aggregate Resv that it sends upstream.  As discussed in the previous   section, the Aggregating Router should ensure that the SENDER_TSPEC   it includes in the Aggregate Path is always in excess of the   FLOW_SPEC that may be requested in the Aggregate Resv by the   Deaggregator, so that the Deaggregator is not unnecessarily prevented   from effectively increasing the Aggregate Reservation bandwidth as   required.   When sufficient bandwidth is available on the corresponding aggregate   reservation, the Deaggregating Router may simply send the E2E Resv   message with IP Protocol RSVP to the aggregating router.  This   message should include the DCLASS object to indicate which DSCP the   aggregator must use for this E2E flow.  The deaggregator will alsoBaker, et al.               Standards Track                    [Page 18]

RFC 3175              RSVP Reservation Aggregation        September 2001   add the token bucket from the E2E Resv FLOWSPEC object into its   internal understanding of how much of the Aggregate reservation is in   use.   As discussed above, in order to minimize the occurrence of situations   where insufficient bandwidth is reserved on the corresponding   Aggregate Reservation at the time of processing an E2E Resv, and in   turn to avoid the delay associated with the increase of this   aggregate bandwidth, the Deaggregator MAY anticipate the current   demand and increase the Aggregate Reservations size ahead of actual   requirements by E2E reservations.2.6.  Initiation of New Aggregate Resv Message By Deaggregating Router   Upon receiving an E2E Resv message on an exterior interface, and   having determined the appropriate DSCP for the session according to   the mapping policy, the Deaggregator looks for the corresponding path   state for a session with the chosen DSCP.  If aggregate Path state   exists, but no aggregate Resv state exists, the Deaggregator creates   a new aggregate Resv.   If no aggregate Path state exists for the appropriate DSCP, this may   be because the Deaggregator could not decide earlier the final   mapping for this E2E flow and elected to not establish Aggregate Path   state for all DSCPs.  In that case, the Deaggregator should request   establishment of the corresponding Aggregate Path by sending a E2E   PathErr with error code of NEW-AGGREGATE-NEEDED and with a DCLASS   containing the required DSCP.  This will trigger the Aggregator to   establish the corresponding Aggregate Path.  Once the Deaggregator   has determined that the aggregate Path state is established, it   creates a new Aggregate Resv.   The FLOW_SPEC of the new Aggregate Resv is set to a value not smaller   than the requirement of the E2E reservation it is supporting.  The   Aggregate Resv is sent toward the aggregator (i.e., to the previous   hop), using the AGGREGATED-RSVP session and filter specifications   defined below.  Since the DSCP is in the SESSION object, no DCLASS   object is necessary.  The message should be reliably delivered using   the mechanisms in [RFC2961] or, alternatively, the CONFIRM object may   be used, to assure that the aggregate Resv does indeed arrive and is   granted.  This enables the deaggregator to determine that the   requested bandwidth is available to allocate to the E2E flows it   supports.   In order to minimize the occurrence of situations where no   corresponding Aggregate Reservation is established at the time of   processing an E2E Resv, and in turn to avoid the delay associated   with the creation of this aggregate reservation, the Deaggregator MAYBaker, et al.               Standards Track                    [Page 19]

RFC 3175              RSVP Reservation Aggregation        September 2001   anticipate the current demand and create the Aggregate Reservation   before receiving E2E Resv messages requiring bandwidth on those   aggregate reservations.2.7.  Handling of Aggregate Resv Message by Interior Routers   The aggregate Resv message is handled in essentially the same way as   defined in [RSVP].  The Session object contains the address of the   deaggregating router (or the group address for the session in the   case of multicast) and the DSCP that has been chosen for the session.   The Filterspec object identifies the aggregating router.  These   routers perform admission control and resource allocation as usual   and send the aggregate Resv on towards the aggregator.2.8.  Handling of E2E Resv Message by Aggregating Router   The receipt of the E2E Resv message with a DCLASS Object is the final   confirmation to the aggregating router of the mapping of the E2E   reservation onto an Aggregate Reservation.  Under normal   circumstances, this is the only way it will be informed of this   association.  It should now forward the E2E Resv to its previous hop,   following normal RSVP processing rules [RSVP].2.9.  Removal of E2E Reservation   E2E reservations are removed in the usual way via PathTear, ResvTear,   timeout, or as the result of an error condition.  When they are   removed, their FLOWSPEC information must also be removed from the   allocated portion of the aggregate reservation.  This same bandwidth   may be re-used for other traffic in the near future.  When E2E Path   messages are removed, their SENDER_TSPEC information must also be   removed from the aggregate Path.2.10.  Removal of Aggregate Reservation   Should an aggregate reservation go away (presumably due to a   configuration  change, route change, or policy event), the E2E   reservations it supports are no longer active.  They must be treated   accordingly.2.11.  Handling of Data On Reserved E2E Flow by Aggregating Router   Prior to establishment that a given E2E flow is part of a given   aggregate, the flow's data should be treated as traffic without a   reservation by whatever policies prevail for such.  Generally, this   will mean being given the same forwarding behavior as best effort   traffic.  However, upon establishing that the flow belongs to a given   aggregate, the aggregating router is responsible for marking anyBaker, et al.               Standards Track                    [Page 20]

RFC 3175              RSVP Reservation Aggregation        September 2001   related traffic with the correct DSCP and forwarding it in the manner   appropriate to traffic on that reservation.  This may imply   forwarding it to a given IP next hop, or piping it down a given link   layer circuit, tunnel, or MPLS label switched path.   The aggregator is responsible for performing per-reservation policing   on the E2E flows that it is aggregating.  The aggregator performs   metering of traffic belonging to each reservation to assess   compliance to the token bucket for the corresponding E2E reservation.   Packets which are assessed in compliance are forwarded as mentioned   above.  Packets which are assessed out of compliance must be either   dropped, reshaped or marked to a different DSCP.  The detailed   policing behavior is an aspect of the service mapping described in   [RFC2998].2.12.  Procedures for Multicast Sessions   Because of the difficulties of aggregating multicast sessions   described above, we focus on the aggregation of scheduling and   classification state in the multicast case.  The main difference   between the multicast and unicast cases is that rather than sending   an aggregate Path message to the unicast address of a single   deaggregating router, in the multicast case we send the "aggregate"   Path message to the same group address as the E2E session.  This   ensures that the aggregate Path message follows the same route as the   E2E Path.  This difference between unicast and multicast is reflected   in the Session objects defined below.  A consequence of this approach   is that we continue to have reservation state per multicast session   inside the aggregation region.   A further challenge arises in multicast sessions with heterogeneous   receivers.  Consider an interior router which must forward packets   for a multicast session on two interfaces, but has only received a   reservation request on one of those interfaces.  It receives packets   marked with the DSCP chosen for the aggregate reservation.  When   sending them out the interface which has no installed reservation, it   has the following options:   a) remark those packets to best effort before sending them out the      interface;   b) send the packets out the interface with the DSCP chosen for the      aggregate reservation.   The first approach suffers from the drawback that it requires nMF   classification at an interior router in order to recognize the flows   whose packets must be demoted.  The second approach requires over-   reservation of resources on the interface on which no reservation wasBaker, et al.               Standards Track                    [Page 21]

RFC 3175              RSVP Reservation Aggregation        September 2001   received.  In the absence of such over-reservation, the packets sent   with the "wrong" DSCP would be able to degrade the service   experienced by packets using that DSCP legitimately.   To make MF classification acceptable in an interior router, it may be   possible to treat the case of heterogeneous flows as an exception.   That is, an interior router only needs to be able to recognize those   individual microflows that have heterogeneous resource needs on the   outbound interfaces of this router.3.  Protocol Elements3.1.  IP Protocol RSVP-E2E-IGNORE   This specification requires the assignment of a protocol type RSVP-   E2E-IGNORE, whose number is at this point 134.  This is used only on   E2E messages which require a router alert (Path, PathTear, and   ResvConf), and signifies that the message must be treated one way   when destined to an interior interface, and another way when destined   to an exterior interface.  The protocol type is swapped by the   Aggregator from RSVP to RSVP-E2E-IGNORE in E2E Path, PathTear, and   ResvConf messages when they enter the Aggregation Region.  The   protocol type is swapped back by the Deaggregator from RSVP-E2E-   IGNORE to RSVP in such E2E messages when they exit the Aggregation   Region.3.2.  Path Error Code   A PathErr code NEW-AGGREGATE-NEEDED is required.  This value does not   signify that a fatal error has occurred, but that an action is   required of the aggregating router to avoid an error condition in the   near future.3.3.  SESSION Object   The SESSION object contains two values: the IP Address of the   aggregate session destination, and the DSCP that it will use on the   E2E data the reservation contains.  For unicast sessions, the session   destination address is the address of the deaggregating router.  For   multicast sessions, the session destination is the multicast address   of the E2E session (or sessions) being aggregated.  The inclusion of   the DSCP in the session allows for multiple sessions toward the same   address to be distinguished by their DSCP and queued separately.  It   also provides the means for aggregating scheduling and classification   state.  In the case where a session uses a pair of PHBs (e.g., AF11   and AF12), the DSCP used should represent the numerically smallest   PHB (e.g., AF11).  This follows the same naming convention described   in [BRIM].Baker, et al.               Standards Track                    [Page 22]

RFC 3175              RSVP Reservation Aggregation        September 2001   Session types are defined for IPv4 and IPv6 addresses.   o  IP4 SESSION object: Class = SESSION,      C-Type = RSVP-AGGREGATE-IP4        +-------------+-------------+-------------+-------------+        |              IPv4 Session Address (4 bytes)           |        +-------------+-------------+-------------+-------------+        | /////////// |    Flags    |  /////////  |     DSCP    |        +-------------+-------------+-------------+-------------+   o  IP6 SESSION object: Class = SESSION,      C-Type = RSVP-AGGREGATE-IP6        +-------------+-------------+-------------+-------------+        |                                                       |        +                                                       +        |                                                       |        +              IPv6 Session Address (16 bytes)          +        |                                                       |        +                                                       +        |                                                       |        +-------------+-------------+-------------+-------------+        | /////////// |    Flags    |  /////////  |     DSCP    |        +-------------+-------------+-------------+-------------+3.4.  SENDER_TEMPLATE Object   The SENDER_TEMPLATE object identifies the aggregating router for the   aggregate reservation.   o  IP4 SENDER_TEMPLATE object: Class = SENDER_TEMPLATE,      C-Type = RSVP-AGGREGATE-IP4        +-------------+-------------+-------------+-------------+        |                IPv4 Aggregator Address (4 bytes)      |        +-------------+-------------+-------------+-------------+Baker, et al.               Standards Track                    [Page 23]

RFC 3175              RSVP Reservation Aggregation        September 2001   o  IP6 SENDER_TEMPLATE object: Class = SENDER_TEMPLATE,      C-Type = RSVP-AGGREGATE-IP6        +-------------+-------------+-------------+-------------+        |                                                       |        +                                                       +        |                                                       |        +           IPv6 Aggregator Address (16 bytes)          +        |                                                       |        +                                                       +        |                                                       |        +-------------+-------------+-------------+-------------+3.5.  FILTER_SPEC Object   The FILTER_SPEC object identifies the aggregating router for the   aggregate reservation, and is syntactically identical to the   SENDER_TEMPLATE object.4.  Policies and Algorithms For Predictive Management Of Blocks Of    Bandwidth   The exact policies used in determining how much bandwidth should be   allocated to an aggregate reservation at any given time are beyond   the scope of this document, and may be proprietary to the service   provider in question.  However, here we explore some of the issues   and suggest approaches.   In short, the ideal condition is that the aggregate reservation   always has enough resources to allocate to any E2E reservation that   requires its support, and never takes too much.  Simply stated, but   more difficult to achieve.  Factors that come into account include   significant times in the diurnal cycle: one may find that a large   number of people start placing calls at 8:00 AM, even though the hour   from 7:00 to 8:00 is dead calm.  They also include recent history: if   more people have been  placing calls recently than have been   finishing them, a prediction of the necessary bandwidth a few moments   hence may call for more bandwidth than is currently allocated.   Likewise, at the end of a busy period, we may find that the trend   calls for declining reservation amounts.   We recommend a policy something along this line.  At any given time,   one should expect that the amount of bandwidth required for the   aggregate reservation is the larger of the following:   (a) a requirement known a priori, such as from history of the diurnal       cycle at a particular week day and time of day, andBaker, et al.               Standards Track                    [Page 24]

RFC 3175              RSVP Reservation Aggregation        September 2001   (b) the trend line over recent history, with 90 or 99% statistical       confidence.   We further expect that changes to that aggregate reservation would be   made no more often than every few minutes, and ideally perhaps on   larger granularity such as fifteen minute intervals or hourly.  The   finer the granularity, the greater the level of signaling required,   while the coarser the granularity, the greater the chance for error,   and the need to recover from that error.   In general, we expect that the aggregate reservation will not ever   add up to exactly the sum of the reservations it supports, but rather   will be an integer multiple of some block reservation size, which   exceeds that value.5.  Security Considerations   Numerous security issues pertain to this document; for example, the   loss of an aggregate reservation to an aggressor causes many calls to   operate unreserved, and the reservation of a great excess of   bandwidth may result in a denial of service.  However, these issues   are not confined to this extension: RSVP itself has them.  We believe   that the security mechanisms in RSVP address these issues as well.   One security issue specific to RSVP aggregation involves the   modification of the IP protocol number in RSVP Path messages that   traverse an aggregation region.  If that field were maliciously   modified in a Path message, it would cause the message to be ignored   by all subsequent devices on its path, preventing reservations from   being made.  It could even be possible to correct the value before it   reached the receiver, making it difficult to detect the attack.  In   theory, it might also be possible for a node to modify the IP   protocol number for non-RSVP messages as well, thus interfering with   the operation of other protocols.   One way to mitigate the risks of malicious modification of the IP   protocol number is to use an IPSEC authentication header, which would   ensure that malicious modification of the IP header is detected.   This is a desirable approach but imposes some administrative burden   in the form of key management for authentication purposes.   It is RECOMMENDED that implementations of this specification only   support modification of the IP protocol number for RSVP Path,   PathTear, and ResvConf messages.  That is, a general facility for   modification of the IP protocol number SHOULD NOT be made available.Baker, et al.               Standards Track                    [Page 25]

RFC 3175              RSVP Reservation Aggregation        September 2001   Network operators deploying routers with RSVP aggregation capability   should be aware of the risks of inappropriate modification of the IP   protocol number and should take appropriate steps (physical security,   password protection, etc.) to reduce the risk that a router could be   configured by an attacker to perform malicious modification of the   protocol number.6.  IANA ConsiderationsSection 1.2 proposes a new protocol type, RSVP-E2E-IGNORE, which is   used to identify a message that routers in the network core will see;   further processing of such messages may or may not be required,   depending on the egress interface type, as described inSection 1.2.   The IANA assigned IP protocol number 134, in accordance with   [RFC2780], meeting the Standards Track publication criterion.Section 1.4.9 describes the manner in which the Router Alert is used   in the context of this specification, which is essentially a simple   counter of the depth of nesting of aggregation.  The IPv4 Router   Alert [RFC2113] has the option simply to ask the router to look at   the protocol type of the intercepted datagram and decide what to do   with it; the parameter is additional information to that decision.   The IPv6 Router Alert [RFC2711] turns the parameter into an option   sub-type.  As a result, the IPv6 router alert option may not be used   algorithmically in the context of the protocol in question.  The IANA   assigned a block of 32 values (3-35, "Aggregated Reservation Nesting   Level") which we may map to nesting depths 0..31, hoping that 32   levels is enough.Section 3.2 discusses a new, required path error code.  The IANA has   assigned RSVP Parameters Error Code 26 to NEW-AGGREGATE-NEEDED.   Sections3.3,3.4, and3.5 describe extensions to three object   classes: Session, Filter Specification, and Sender Template.  The   IANA has assigned two new common C-Types to be specified for the   aggregator's address.  RSVP-AGGREGATE-IP4 is C-Type 9 and RSVP-   AGGREGATE-IP6 is C-Type 10.  In adding these C-types to IANA RSVP   Class Names, Class Numbers and Class Types registry, the same   numbering for them is used in all three Classes, as is done for IPv4   and IPv6 address tuples in [RSVP].Baker, et al.               Standards Track                    [Page 26]

RFC 3175              RSVP Reservation Aggregation        September 20017.  Acknowledgments   The authors acknowledge that published documents and discussion with   several people, notably John Wroclawski, Steve Berson, and Andreas   Terzis materially contributed to this document.  The design is   influenced by the RSVP tunnels document [TERZIS].Baker, et al.               Standards Track                    [Page 27]

RFC 3175              RSVP Reservation Aggregation        September 2001APPENDIX 1: Example Signalling Flow For First E2E Flow   This Appendix does not provide additional specification.  It only   illustrates the specification detailed above through a possible flow   of RSVP signalling messages involved in the successful establishment   of a unicast E2E reservation which is the first between a given pair   of Aggregator/Deaggregator.           Aggregator                              Deaggregator    E2E Path   ---------------->                (1)                           E2E Path                     ------------------------------->                                                        (2)                      E2E PathErr(New-agg-needed, DCLASS=x)                     <-------------------------------                      E2E PathErr(New-agg-needed, DCLASS=y)                     <-------------------------------                (3)                           AggPath(DSCP=x)                     ------------------------------->                           AggPath(DSCP=y)                     ------------------------------->                                                        (4)                                                           E2E Path                                                           ----------->                                                        (5)                           AggResv (DSCP=x)                     <-------------------------------                           AggResv (DSCP=y)                     <-------------------------------               (6)                           AggResvConfirm (DSCP=x)                     ------------------------------>                           AggResvConfirm (DSCP=y)                     ------------------------------>                                                        (7)                                                           E2E Resv                                                           <----------                                                        (8)                           E2E Resv (DCLASS=x)                     <-----------------------------               (9)       E2E Resv   <---------------Baker, et al.               Standards Track                    [Page 28]

RFC 3175              RSVP Reservation Aggregation        September 2001   (1)  Aggregator forwards E2E Path into aggregation region after        modifying its IP Protocol Number to RSVP-E2E-IGNORE   (2)  Let's assume no Aggregate Path exists.  To be able to accurately        update the ADSPEC of the E2E Path, the Deaggregator needs the        ADSPEC of Aggregate PATH.  In this example the Deaggregator        elects to instruct the Aggregator to set up Aggregate Path        states for the two supported DSCPs by sending a New-Agg-Needed        PathErr code for each DSCP.   (3)  The Aggregator follows the request from the Deaggregator and        signals an Aggregate Path for both DSCPs.   (4)  The Deaggregator takes into account the information contained in        the ADSPEC from both Aggregate Path and updates the E2E Path        ADSPEC accordingly.  The Deaggregator also modifies the E2E Path        IP Protocol Number to RSVP before forwarding it.   (5)  In this example, the Deaggregator elects to immediately proceed        with establishment of Aggregate Reservations for both DSCPs.  In        effect, the Deaggregator can be seen as anticipating the actual        demand of E2E reservations so that resources are available on        Aggregate Reservations when the E2E Resv requests arrive in        order to speed up establishment of E2E reservations.  Assume        also that the Deaggregator includes the optional Resv Confirm        Request in these Aggregate Resv.   (6)  The Aggregator merely complies with the received ResvConfirm        Request and returns the corresponding Aggregate ResvConfirm.   (7)  The Deaggregator has explicit confirmation that both Aggregate        Resv are established.   (8)  On receipt of the E2E Resv, the Deaggregator applies the mapping        policy defined by the network administrator to map the E2E Resv        onto an Aggregate Reservation.  Let's assume that this policy is        such that the E2E reservation is to be mapped onto the Aggregate        Reservation with DSCP=x.  The Deaggregator knows that an        Aggregate Reservation is in place for the corresponding DSCP        since (7).  The Deaggregator performs admission control of the        E2E Resv onto the Aggregate Resv for DSCP=x.  Assuming that the        Aggregate Resv for DSCP=x had been established with sufficient        bandwidth to support the E2E Resv, the Deaggregator adjusts its        counter tracking the unused bandwidth on the Aggregate        Reservation and forwards the E2E Resv to the Aggregator        including a DCLASS object conveying the selected mapping onto        DSCP=x.Baker, et al.               Standards Track                    [Page 29]

RFC 3175              RSVP Reservation Aggregation        September 2001   (9)  The Aggregator records the mapping of the E2E Resv onto DSCP=x.        The Aggregator removes the DCLASS object and forwards the E2E        Resv towards the sender.APPENDIX 2: Example Signalling Flow For Subsequent E2E Flow Without            Reservation Resizing   This Appendix does not provide additional specification.  It only   illustrates the specification detailed above through a possible flow   of RSVP signalling messages involved in the successful establishment   of a unicast E2E reservation which follows other E2E reservations   between a given pair of Aggregator/Deaggregator.  This flow could be   imagined as following the flow of messages illustrated in Appendix 1.           Aggregator                              Deaggregator    E2E Path   ---------------->                (10)                           E2E Path                       ------------------------------->                                                      (11)                                                         E2E Path                                                         ----------->                                                          E2E Resv                                                         <-----------                                                      (12)                           E2E Resv (DCLASS=x)                     <-----------------------------                 (13)       E2E Resv   <---------------   (10) Aggregator forwards E2E Path into aggregation region after        modifying its IP Protocol Number to RSVP-E2E-IGNORE   (11) Because previous E2E reservations have been established, let's        assume that Aggregate Path exists for all supported DSCPs.  The        Deaggregator takes into account the information contained in the        ADSPEC from the Aggregate Paths and updates the E2E Path ADSPEC        accordingly.  The Deaggregator also modifies the E2E Path IP        Protocol Number to RSVP before forwarding it.   (12) On receipt of the E2E Resv, the Deaggregator applies the mapping        policy defined by the network administrator to map the E2E Resv        onto an Aggregate Reservation.  Let's assume that this policy is        such that the E2E reservation is to be mapped onto the Aggregate        Reservation with DSCP=x.  Because previous E2E reservations haveBaker, et al.               Standards Track                    [Page 30]

RFC 3175              RSVP Reservation Aggregation        September 2001        been established, let's assume that an Aggregate Reservation is        in place for DSCP=x.  The Deaggregator performs admission        control of the E2E Resv onto the Aggregate Resv for DSCP=x.        Assuming that the Aggregate Resv for DSCP=x has sufficient        unused bandwidth to support the new E2E Resv, the Deaggregator        then adjusts its counter tracking the unused bandwidth on the        Aggregate Reservation and forwards the E2E Resv to the        Aggregator including a DCLASS object conveying the selected        mapping onto DSCP=x.   (13) The Aggregator records the mapping of the E2E Resv onto DSCP=x.        The Aggregator removes the DCLASS object and forwards the E2E        Resv towards the sender.APPENDIX 3: Example Signalling Flow For Subsequent E2E Flow With            Reservation Resizing   This Appendix does not provide additional specification.  It only   illustrates the specification detailed above through a possible flow   of RSVP signalling messages involved in the successful establishment   of a unicast E2E reservation which follows other E2E reservations   between a given pair of Aggregator/Deaggregator.  This flow could be   imagined as following the flow of messages illustrated in Appendix 2.Baker, et al.               Standards Track                    [Page 31]

RFC 3175              RSVP Reservation Aggregation        September 2001                 Aggregator                        Deaggregator    E2E Path   ---------------->                    (14)                           E2E Path                       ------------------------------->                                                       (15)                                                           E2E Path                                                           ----------->                                                           E2E Resv                                                           <-----------                                                       (16)                        AggResv (DSCP=x, increased Bw)                       <-------------------------------                   (17)                       AggResvConfirm (DSCP=x, increased Bw)                       ------------------------------>                                                       (18)                          E2E Resv (DCLASS=x)                       <-----------------------------                   (19)       E2E Resv   <---------------   (14) Aggregator forwards E2E Path into aggregation region after        modifying its IP Protocol Number to RSVP-E2E-IGNORE   (15) Because previous E2E reservations have been established, let's        assume that Aggregate Path exists for all supported DSCPs.  The        Deaggregator takes into account the information contained in the        ADSPEC from the Aggregate Paths and updates the E2E Path ADSPEC        accordingly.  The Deaggregator also modifies the E2E Path IP        Protocol Number to RSVP before forwarding it.   (16) On receipt of the E2E Resv, the Deaggregator applies the mapping        policy defined by the network administrator to map the E2E Resv        onto an Aggregate Reservation.  Let's assume that this policy is        such that the E2E reservation is to be mapped onto the Aggregate        Reservation with DSCP=x.  Because previous E2E reservations have        been established, let's assume that an Aggregate Reservation is        in place for DSCP=x.  The Deaggregator performs admission        control of the E2E Resv onto the Agg Resv for DSCP=x.  Let's        assume that the Aggregate Resv for DSCP=x does NOT have        sufficient unused bandwidth to support the new E2E Resv.  TheBaker, et al.               Standards Track                    [Page 32]

RFC 3175              RSVP Reservation Aggregation        September 2001        Deaggregator then attempts to increase the Aggregate Reservation        bandwidth for DSCP=x by sending a new Aggregate Resv with an        increased bandwidth sufficient to accommodate all the E2E        reservations already mapped onto that Aggregate reservation plus        the new E2E reservation plus possibly some additional spare        bandwidth in anticipation of additional E2E reservations to        come.  Assume also that the Deaggregator includes the optional        Resv Confirm Request in these Aggregate Resv.   (17) The Aggregator merely complies with the received ResvConfirm        Request and returns the corresponding Aggregate ResvConfirm.   (18) The Deaggregator has explicit confirmation that the Aggregate        Resv has been successfully increased.  The Deaggregator performs        again admission control of the E2E Resv onto the increased        Aggregate Reservation for DSCP=x.  Assuming that the increased        Aggregate Reservation for DSCP=x now has sufficient unused        bandwidth and resources to support the new E2E Resv, the        Deaggregator then adjusts its counter tracking the unused        bandwidth on the Aggregate Reservation and forwards the E2E Resv        to the Aggregator including a DCLASS object conveying the        selected mapping onto DSCP=x.   (19) The Aggregator records the mapping of the E2E Resv onto DSCP=x.        The Aggregator removes the DCLASS object and forwards the E2E        Resv towards the sender.References   [CSZ]        Clark, D., S. Shenker, and L. Zhang, "Supporting Real-                Time Applications in an Integrated Services Packet                Network:  Architecture and Mechanism," in Proc.                SIGCOMM'92, September 1992.   [IP]         Postel, J., "Internet Protocol", STD 5,RFC 791,                September 1981.   [HOSTREQ]    Braden, R., "Requirements for Internet hosts -                communication layers", STD 3,RFC 1122, October 1989.   [DSFIELD]    Nichols, K., Blake, S., Baker, F. and D. Black,                "Definition of the Differentiated Services Field (DS                Field) in the IPv4 and IPv6 Headers",RFC 2474, December                1998.   [PRINCIPLES] Carpenter, B., "Architectural Principles of the                Internet",RFC 1958, June 1996.Baker, et al.               Standards Track                    [Page 33]

RFC 3175              RSVP Reservation Aggregation        September 2001   [ASSURED]    Heinanen, J, Baker, F., Weiss, W. and J. Wroclawski,                "Assured Forwarding PHB Group",RFC 2597, June 1999.   [BROKER]     Jacobson, V., Nichols K. and L. Zhang, "A Two-bit                Differentiated Services Architecture for the Internet",RFC 2638, June 1999.   [BRIM]       Brim, S., Carpenter, B. and F. LeFaucheur, "Per Hop                Behavior Identification Codes",RFC 2836, May 2000.   [RSVP]       Braden, R., Zhang, L., Berson, S., Herzog, S. and S.                Jamin, "Resource Reservation Protocol (RSVP) Version 1                Functional Specification",RFC 2205, September 1997.   [TERZIS]     Terzis, A., Krawczyk, J., Wroclawski, J. and L. Zhang,                "RSVP Operation Over IP Tunnels",RFC 2746, January                2000.   [DCLASS]     Bernet, Y., "Format of the RSVP DCLASS Object",RFC2996, November 2000.   [INTEGRITY]  Baker, F., Lindell, B. and M. Talwar, "RSVP                Cryptographic Authentication",RFC 2747, January 2000.   [RFC2998]    Bernet Y., Ford, P., Yavatkar, R., Baker, F., Zhang, L.,                Speer, M., Braden, R., Davie, B., Wroclawski, J. and E.                Felstaine, "Integrated Services Operation Over Diffserv                Networks",RFC 2998, November 2000.   [RFC2961]    Berger, L., Gan, D., Swallow, G., Pan, P. and F.                Tommasi, "RSVP Refresh Reduction Extensions",RFC 2961,                April 2001.   [RFC2780]    Bradner, S. and V. Paxson, "IANA Allocation Guidelines                For Values In the Internet Protocol and Related                Headers",RFC 2780, March 2000.   [RFC2711]    Partridge, C. and A. Jackson, "IPv6 Router Alert                Option",RFC 2711, October 1999.   [RFC2113]    Katz, D. "IP Router Alert Option",RFC 2113, February                1997.Baker, et al.               Standards Track                    [Page 34]

RFC 3175              RSVP Reservation Aggregation        September 2001Authors' Addresses   Fred Baker   Cisco Systems   1121 Via Del Rey   Santa Barbara, CA, 93117  USA   Phone: (408) 526-4257   EMail: fred@cisco.com   Carol Iturralde   Cisco Systems   250 Apollo Drive   Chelmsford MA, 01824 USA   Phone: 978-244-8532   EMail: cei@cisco.com   Francois Le Faucheur   Cisco Systems   Domaine Green Side   400, Avenue de Roumanille   06410 Biot - Sophia Antipolis   France   Phone: +33.4.97.23.26.19   EMail: flefauch@cisco.com   Bruce Davie   Cisco Systems   250 Apollo Drive   Chelmsford MA,01824 USA   Phone: 978-244-8921   EMail: bdavie@cisco.comBaker, et al.               Standards Track                    [Page 35]

RFC 3175              RSVP Reservation Aggregation        September 2001Full Copyright Statement   Copyright (C) The Internet Society (2001).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Baker, et al.               Standards Track                    [Page 36]