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rfc:rfc3209

Network Working Group D. Awduche Request for Comments: 3209 Movaz Networks, Inc. Category: Standards Track L. Berger

                                                                D. Gan
                                                Juniper Networks, Inc.
                                                                 T. Li
                                                Procket Networks, Inc.
                                                         V. Srinivasan
                                           Cosine Communications, Inc.
                                                            G. Swallow
                                                   Cisco Systems, Inc.
                                                         December 2001
            RSVP-TE: Extensions to RSVP for LSP Tunnels

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 Notice

 Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

 This document describes the use of RSVP (Resource Reservation
 Protocol), including all the necessary extensions, to establish
 label-switched paths (LSPs) in MPLS (Multi-Protocol Label Switching).
 Since the flow along an LSP is completely identified by the label
 applied at the ingress node of the path, these paths may be treated
 as tunnels.  A key application of LSP tunnels is traffic engineering
 with MPLS as specified in RFC 2702.
 We propose several additional objects that extend RSVP, allowing the
 establishment of explicitly routed label switched paths using RSVP as
 a signaling protocol.  The result is the instantiation of label-
 switched tunnels which can be automatically routed away from network
 failures, congestion, and bottlenecks.

Awduche, et al. Standards Track [Page 1] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

Contents

 1      Introduction   ..........................................   3
 1.1    Background  .............................................   4
 1.2    Terminology  ............................................   6
 2      Overview   ..............................................   7
 2.1    LSP Tunnels and Traffic Engineered Tunnels  .............   7
 2.2    Operation of LSP Tunnels  ...............................   8
 2.3    Service Classes  ........................................  10
 2.4    Reservation Styles  .....................................  10
 2.4.1  Fixed Filter (FF) Style  ................................  10
 2.4.2  Wildcard Filter (WF) Style  .............................  11
 2.4.3  Shared Explicit (SE) Style  .............................  11
 2.5    Rerouting Traffic Engineered Tunnels  ...................  12
 2.6    Path MTU  ...............................................  13
 3      LSP Tunnel related Message Formats  .....................  15
 3.1    Path Message  ...........................................  15
 3.2    Resv Message  ...........................................  16
 4      LSP Tunnel related Objects  .............................  17
 4.1    Label Object  ...........................................  17
 4.1.1  Handling Label Objects in Resv messages  ................  17
 4.1.2  Non-support of the Label Object  ........................  19
 4.2    Label Request Object  ...................................  19
 4.2.1  Label Request without Label Range  ......................  19
 4.2.2  Label Request with ATM Label Range  .....................  20
 4.2.3  Label Request with Frame Relay Label Range  .............  21
 4.2.4  Handling of LABEL_REQUEST  ..............................  22
 4.2.5  Non-support of the Label Request Object  ................  23
 4.3    Explicit Route Object  ..................................  23
 4.3.1  Applicability  ..........................................  24
 4.3.2  Semantics of the Explicit Route Object  .................  24
 4.3.3  Subobjects  .............................................  25
 4.3.4  Processing of the Explicit Route Object  ................  28
 4.3.5  Loops  ..................................................  30
 4.3.6  Forward Compatibility  ..................................  30
 4.3.7  Non-support of the Explicit Route Object  ...............  31
 4.4    Record Route Object  ....................................  31
 4.4.1  Subobjects  .............................................  31
 4.4.2  Applicability  ..........................................  34
 4.4.3  Processing RRO  .........................................  35
 4.4.4  Loop Detection  .........................................  36
 4.4.5  Forward Compatibility  ..................................  37
 4.4.6  Non-support of RRO  .....................................  37
 4.5    Error Codes for ERO and RRO  ............................  37
 4.6    Session, Sender Template, and Filter Spec Objects  ......  38
 4.6.1  Session Object  .........................................  39
 4.6.2  Sender Template Object  .................................  40
 4.6.3  Filter Specification Object  ............................  42

Awduche, et al. Standards Track [Page 2] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 4.6.4  Reroute and Bandwidth Increase Procedure  ...............  42
 4.7    Session Attribute Object  ...............................  43
 4.7.1  Format without resource affinities  .....................  43
 4.7.2  Format with resource affinities  ........................  45
 4.7.3  Procedures applying to both C-Types  ....................  46
 4.7.4  Resource Affinity Procedures   ..........................  48
 5      Hello Extension  ........................................  49
 5.1    Hello Message Format  ...................................  50
 5.2    HELLO Object formats  ...................................  51
 5.2.1  HELLO REQUEST object  ...................................  51
 5.2.2  HELLO ACK object  .......................................  51
 5.3    Hello Message Usage  ....................................  52
 5.4    Multi-Link Considerations  ..............................  53
 5.5    Compatibility  ..........................................  54
 6      Security Considerations  ................................  54
 7      IANA Considerations  ....................................  54
 7.1    Message Types  ..........................................  55
 7.2    Class Numbers and C-Types  ..............................  55
 7.3    Error Codes and Globally-Defined Error Value Sub-Codes  .  57
 7.4    Subobject Definitions  ..................................  57
 8      Intellectual Property Considerations  ...................  58
 9      Acknowledgments  ........................................  58
 10     References  .............................................  58
 11     Authors' Addresses  .....................................  60
 12     Full Copyright Statement  ...............................  61

1. Introduction

 Section 2.9 of the MPLS architecture [2] defines a label distribution
 protocol as a set of procedures by which one Label Switched Router
 (LSR) informs another of the meaning of labels used to forward
 traffic between and through them.  The MPLS architecture does not
 assume a single label distribution protocol.  This document is a
 specification of extensions to RSVP for establishing label switched
 paths (LSPs) in MPLS networks.
 Several of the new features described in this document were motivated
 by the requirements for traffic engineering over MPLS (see [3]).  In
 particular, the extended RSVP protocol supports the instantiation of
 explicitly routed LSPs, with or without resource reservations.  It
 also supports smooth rerouting of LSPs, preemption, and loop
 detection.
 The LSPs created with RSVP can be used to carry the "Traffic Trunks"
 described in [3].  The LSP which carries a traffic trunk and a
 traffic trunk are distinct though closely related concepts.  For
 example, two LSPs between the same source and destination could be
 load shared to carry a single traffic trunk.  Conversely several

Awduche, et al. Standards Track [Page 3] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 traffic trunks could be carried in the same LSP if, for instance, the
 LSP were capable of carrying several service classes.  The
 applicability of these extensions is discussed further in [10].
 Since the traffic that flows along a label-switched path is defined
 by the label applied at the ingress node of the LSP, these paths can
 be treated as tunnels, tunneling below normal IP routing and
 filtering mechanisms.  When an LSP is used in this way we refer to it
 as an LSP tunnel.
 LSP tunnels allow the implementation of a variety of policies related
 to network performance optimization.  For example, LSP tunnels can be
 automatically or manually routed away from network failures,
 congestion, and bottlenecks.  Furthermore, multiple parallel LSP
 tunnels can be established between two nodes, and traffic between the
 two nodes can be mapped onto the LSP tunnels according to local
 policy.  Although traffic engineering (that is, performance
 optimization of operational networks) is expected to be an important
 application of this specification, the extended RSVP protocol can be
 used in a much wider context.
 The purpose of this document is to describe the use of RSVP to
 establish LSP tunnels.  The intent is to fully describe all the
 objects, packet formats, and procedures required to realize
 interoperable implementations.  A few new objects are also defined
 that enhance management and diagnostics of LSP tunnels.
 The document also describes a means of rapid node failure detection
 via a new HELLO message.
 All objects and messages described in this specification are optional
 with respect to RSVP.  This document discusses what happens when an
 object described here is not supported by a node.
 Throughout this document, the discussion will be restricted to
 unicast label switched paths.  Multicast LSPs are left for further
 study.

1.1. Background

 Hosts and routers that support both RSVP [1] and Multi-Protocol Label
 Switching [2] can associate labels with RSVP flows.  When MPLS and
 RSVP are combined, the definition of a flow can be made more
 flexible.  Once a label switched path (LSP) is established, the
 traffic through the path is defined by the label applied at the
 ingress node of the LSP.  The mapping of label to traffic can be
 accomplished using a number of different criteria.  The set of
 packets that are assigned the same label value by a specific node are

Awduche, et al. Standards Track [Page 4] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 said to belong to the same forwarding equivalence class (FEC) (see
 [2]), and effectively define the "RSVP flow."  When traffic is mapped
 onto a label-switched path in this way, we call the LSP an "LSP
 Tunnel".  When labels are associated with traffic flows, it becomes
 possible for a router to identify the appropriate reservation state
 for a packet based on the packet's label value.
 The signaling protocol model uses downstream-on-demand label
 distribution.  A request to bind labels to a specific LSP tunnel is
 initiated by an ingress node through the RSVP Path message.  For this
 purpose, the RSVP Path message is augmented with a LABEL_REQUEST
 object.  Labels are allocated downstream and distributed (propagated
 upstream) by means of the RSVP Resv message.  For this purpose, the
 RSVP Resv message is extended with a special LABEL object.  The
 procedures for label allocation, distribution, binding, and stacking
 are described in subsequent sections of this document.
 The signaling protocol model also supports explicit routing
 capability.  This is accomplished by incorporating a simple
 EXPLICIT_ROUTE object into RSVP Path messages.  The EXPLICIT_ROUTE
 object encapsulates a concatenation of hops which constitutes the
 explicitly routed path.  Using this object, the paths taken by
 label-switched RSVP-MPLS flows can be pre-determined, independent of
 conventional IP routing.  The explicitly routed path can be
 administratively specified, or automatically computed by a suitable
 entity based on QoS and policy requirements, taking into
 consideration the prevailing network state.  In general, path
 computation can be control-driven or data-driven.  The mechanisms,
 processes, and algorithms used to compute explicitly routed paths are
 beyond the scope of this specification.
 One useful application of explicit routing is traffic engineering.
 Using explicitly routed LSPs, a node at the ingress edge of an MPLS
 domain can control the path through which traffic traverses from
 itself, through the MPLS network, to an egress node.  Explicit
 routing can be used to optimize the utilization of network resources
 and enhance traffic oriented performance characteristics.
 The concept of explicitly routed label switched paths can be
 generalized through the notion of abstract nodes.  An abstract node
 is a group of nodes whose internal topology is opaque to the ingress
 node of the LSP.  An abstract node is said to be simple if it
 contains only one physical node.  Using this concept of abstraction,
 an explicitly routed LSP can be specified as a sequence of IP
 prefixes or a sequence of Autonomous Systems.

Awduche, et al. Standards Track [Page 5] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 The signaling protocol model supports the specification of an
 explicit path as a sequence of strict and loose routes.  The
 combination of abstract nodes, and strict and loose routes
 significantly enhances the flexibility of path definitions.
 An advantage of using RSVP to establish LSP tunnels is that it
 enables the allocation of resources along the path.  For example,
 bandwidth can be allocated to an LSP tunnel using standard RSVP
 reservations and Integrated Services service classes [4].
 While resource reservations are useful, they are not mandatory.
 Indeed, an LSP can be instantiated without any resource reservations
 whatsoever.  Such LSPs without resource reservations can be used, for
 example, to carry best effort traffic.  They can also be used in many
 other contexts, including implementation of fall-back and recovery
 policies under fault conditions, and so forth.

1.2. Terminology

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC2119 [6].
 The reader is assumed to be familiar with the terminology in [1], [2]
 and [3].
 Abstract Node
    A group of nodes whose internal topology is opaque to the ingress
    node of the LSP.  An abstract node is said to be simple if it
    contains only one physical node.
 Explicitly Routed LSP
    An LSP whose path is established by a means other than normal IP
    routing.
 Label Switched Path
    The path created by the concatenation of one or more label
    switched hops, allowing a packet to be forwarded by swapping
    labels from an MPLS node to another MPLS node.  For a more precise
    definition see [2].
 LSP
    A Label Switched Path

Awduche, et al. Standards Track [Page 6] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 LSP Tunnel
    An LSP which is used to tunnel below normal IP routing and/or
    filtering mechanisms.
 Traffic Engineered Tunnel (TE Tunnel)
    A set of one or more LSP Tunnels which carries a traffic trunk.
 Traffic Trunk
    A set of flows aggregated by their service class and then placed
    on an LSP or set of LSPs called a traffic engineered tunnel.  For
    further discussion see [3].

2. Overview

2.1. LSP Tunnels and Traffic Engineered Tunnels

 According to [1], "RSVP defines a 'session' to be a data flow with a
 particular destination and transport-layer protocol." However, when
 RSVP and MPLS are combined, a flow or session can be defined with
 greater flexibility and generality.  The ingress node of an LSP can
 use a variety of means to determine which packets are assigned a
 particular label.  Once a label is assigned to a set of packets, the
 label effectively defines the "flow" through the LSP.  We refer to
 such an LSP as an "LSP tunnel" because the traffic through it is
 opaque to intermediate nodes along the label switched path.
 New RSVP SESSION, SENDER_TEMPLATE, and FILTER_SPEC objects, called
 LSP_TUNNEL_IPv4 and LSP_TUNNEL_IPv6 have been defined to support the
 LSP tunnel feature.  The semantics of these objects, from the
 perspective of a node along the label switched path, is that traffic
 belonging to the LSP tunnel is identified solely on the basis of
 packets arriving from the PHOP or "previous hop" (see [1]) with the
 particular label value(s) assigned by this node to upstream senders
 to the session.  In fact, the IPv4(v6) that appears in the object
 name only denotes that the destination address is an IPv4(v6)
 address.  When we refer to these objects generically, we use the
 qualifier LSP_TUNNEL.
 In some applications it is useful to associate sets of LSP tunnels.
 This can be useful during reroute operations or to spread a traffic
 trunk over multiple paths.  In the traffic engineering application
 such sets are called traffic engineered tunnels (TE tunnels).  To
 enable the identification and association of such LSP tunnels, two
 identifiers are carried.  A tunnel ID is part of the SESSION object.
 The SESSION object uniquely defines a traffic engineered tunnel.  The

Awduche, et al. Standards Track [Page 7] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 SENDER_TEMPLATE and FILTER_SPEC objects carry an LSP ID.  The
 SENDER_TEMPLATE (or FILTER_SPEC) object together with the SESSION
 object uniquely identifies an LSP tunnel

2.2. Operation of LSP Tunnels

 This section summarizes some of the features supported by RSVP as
 extended by this document related to the operation of LSP tunnels.
 These include: (1) the capability to establish LSP tunnels with or
 without QoS requirements, (2) the capability to dynamically reroute
 an established LSP tunnel, (3) the capability to observe the actual
 route traversed by an established LSP tunnel, (4) the capability to
 identify and diagnose LSP tunnels, (5) the capability to preempt an
 established LSP tunnel under administrative policy control, and (6)
 the capability to perform downstream-on-demand label allocation,
 distribution, and binding.  In the following paragraphs, these
 features are briefly described.  More detailed descriptions can be
 found in subsequent sections of this document.
 To create an LSP tunnel, the first MPLS node on the path -- that is,
 the sender node with respect to the path -- creates an RSVP Path
 message with a session type of LSP_TUNNEL_IPv4 or LSP_TUNNEL_IPv6 and
 inserts a LABEL_REQUEST object into the Path message.  The
 LABEL_REQUEST object indicates that a label binding for this path is
 requested and also provides an indication of the network layer
 protocol that is to be carried over this path.  The reason for this
 is that the network layer protocol sent down an LSP cannot be assumed
 to be IP and cannot be deduced from the L2 header, which simply
 identifies the higher layer protocol as MPLS.
 If the sender node has knowledge of a route that has high likelihood
 of meeting the tunnel's QoS requirements, or that makes efficient use
 of network resources, or that satisfies some policy criteria, the
 node can decide to use the route for some or all of its sessions.  To
 do this, the sender node adds an EXPLICIT_ROUTE object to the RSVP
 Path message.  The EXPLICIT_ROUTE object specifies the route as a
 sequence of abstract nodes.
 If, after a session has been successfully established, the sender
 node discovers a better route, the sender can dynamically reroute the
 session by simply changing the EXPLICIT_ROUTE object.  If problems
 are encountered with an EXPLICIT_ROUTE object, either because it
 causes a routing loop or because some intermediate routers do not
 support it, the sender node is notified.
 By adding a RECORD_ROUTE object to the Path message, the sender node
 can receive information about the actual route that the LSP tunnel
 traverses.  The sender node can also use this object to request

Awduche, et al. Standards Track [Page 8] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 notification from the network concerning changes to the routing path.
 The RECORD_ROUTE object is analogous to a path vector, and hence can
 be used for loop detection.
 Finally, a SESSION_ATTRIBUTE object can be added to Path messages to
 aid in session identification and diagnostics.  Additional control
 information, such as setup and hold priorities, resource affinities
 (see [3]), and local-protection, are also included in this object.
 Routers along the path may use the setup and hold priorities along
 with SENDER_TSPEC and any POLICY_DATA objects contained in Path
 messages as input to policy control.  For instance, in the traffic
 engineering application, it is very useful to use the Path message as
 a means of verifying that bandwidth exists at a particular priority
 along an entire path before preempting any lower priority
 reservations.  If a Path message is allowed to progress when there
 are insufficient resources, then there is a danger that lower
 priority reservations downstream of this point will unnecessarily be
 preempted in a futile attempt to service this request.
 When the EXPLICIT_ROUTE object (ERO) is present, the Path message is
 forwarded towards its destination along a path specified by the ERO.
 Each node along the path records the ERO in its path state block.
 Nodes may also modify the ERO before forwarding the Path message.  In
 this case the modified ERO SHOULD be stored in the path state block
 in addition to the received ERO.
 The LABEL_REQUEST object requests intermediate routers and receiver
 nodes to provide a label binding for the session.  If a node is
 incapable of providing a label binding, it sends a PathErr message
 with an "unknown object class" error.  If the LABEL_REQUEST object is
 not supported end to end, the sender node will be notified by the
 first node which does not provide this support.
 The destination node of a label-switched path responds to a
 LABEL_REQUEST by including a LABEL object in its response RSVP Resv
 message.  The LABEL object is inserted in the filter spec list
 immediately following the filter spec to which it pertains.
 The Resv message is sent back upstream towards the sender, following
 the path state created by the Path message, in reverse order.  Note
 that if the path state was created by use of an ERO, then the Resv
 message will follow the reverse path of the ERO.
 Each node that receives a Resv message containing a LABEL object uses
 that label for outgoing traffic associated with this LSP tunnel.  If
 the node is not the sender, it allocates a new label and places that
 label in the corresponding LABEL object of the Resv message which it

Awduche, et al. Standards Track [Page 9] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 sends upstream to the PHOP.  The label sent upstream in the LABEL
 object is the label which this node will use to identify incoming
 traffic associated with this LSP tunnel.  This label also serves as
 shorthand for the Filter Spec.  The node can now update its "Incoming
 Label Map" (ILM), which is used to map incoming labeled packets to a
 "Next Hop Label Forwarding Entry" (NHLFE), see [2].
 When the Resv message propagates upstream to the sender node, a
 label-switched path is effectively established.

2.3. Service Classes

 This document does not restrict the type of Integrated Service
 requests for reservations.  However, an implementation SHOULD support
 the Controlled-Load service [4] and the Null Service [16].

2.4. Reservation Styles

 The receiver node can select from among a set of possible reservation
 styles for each session, and each RSVP session must have a particular
 style.  Senders have no influence on the choice of reservation style.
 The receiver can choose different reservation styles for different
 LSPs.
 An RSVP session can result in one or more LSPs, depending on the
 reservation style chosen.
 Some reservation styles, such as FF, dedicate a particular
 reservation to an individual sender node.  Other reservation styles,
 such as WF and SE, can share a reservation among several sender
 nodes.  The following sections discuss the different reservation
 styles and their advantages and disadvantages.  A more detailed
 discussion of reservation styles can be found in [1].

2.4.1. Fixed Filter (FF) Style

 The Fixed Filter (FF) reservation style creates a distinct
 reservation for traffic from each sender that is not shared by other
 senders.  This style is common for applications in which traffic from
 each sender is likely to be concurrent and independent.  The total
 amount of reserved bandwidth on a link for sessions using FF is the
 sum of the reservations for the individual senders.
 Because each sender has its own reservation, a unique label is
 assigned to each sender.  This can result in a point-to-point LSP
 between every sender/receiver pair.

Awduche, et al. Standards Track [Page 10] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

2.4.2. Wildcard Filter (WF) Style

 With the Wildcard Filter (WF) reservation style, a single shared
 reservation is used for all senders to a session.  The total
 reservation on a link remains the same regardless of the number of
 senders.
 A single multipoint-to-point label-switched-path is created for all
 senders to the session.  On links that senders to the session share,
 a single label value is allocated to the session.  If there is only
 one sender, the LSP looks like a normal point-to-point connection.
 When multiple senders are present, a multipoint-to-point LSP (a
 reversed tree) is created.
 This style is useful for applications in which not all senders send
 traffic at the same time.  A phone conference, for example, is an
 application where not all speakers talk at the same time.  If,
 however, all senders send simultaneously, then there is no means of
 getting the proper reservations made.  Either the reserved bandwidth
 on links close to the destination will be less than what is required
 or then the reserved bandwidth on links close to some senders will be
 greater than what is required.  This restricts the applicability of
 WF for traffic engineering purposes.
 Furthermore, because of the merging rules of WF, EXPLICIT_ROUTE
 objects cannot be used with WF reservations.  As a result of this
 issue and the lack of applicability to traffic engineering, use of WF
 is not considered in this document.

2.4.3. Shared Explicit (SE) Style

 The Shared Explicit (SE) style allows a receiver to explicitly
 specify the senders to be included in a reservation.  There is a
 single reservation on a link for all the senders listed.  Because
 each sender is explicitly listed in the Resv message, different
 labels may be assigned to different senders, thereby creating
 separate LSPs.
 SE style reservations can be provided using multipoint-to-point
 label-switched-path or LSP per sender.  Multipoint-to-point LSPs may
 be used when path messages do not carry the EXPLICIT_ROUTE object, or
 when Path messages have identical EXPLICIT_ROUTE objects.  In either
 of these cases a common label may be assigned.

Awduche, et al. Standards Track [Page 11] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 Path messages from different senders can each carry their own ERO,
 and the paths taken by the senders can converge and diverge at any
 point in the network topology.  When Path messages have differing
 EXPLICIT_ROUTE objects, separate LSPs for each EXPLICIT_ROUTE object
 must be established.

2.5. Rerouting Traffic Engineered Tunnels

 One of the requirements for Traffic Engineering is the capability to
 reroute an established TE tunnel under a number of conditions, based
 on administrative policy.  For example, in some contexts, an
 administrative policy may dictate that a given TE tunnel is to be
 rerouted when a more "optimal" route becomes available.  Another
 important context when TE tunnel reroute is usually required is upon
 failure of a resource along the TE tunnel's established path.  Under
 some policies, it may also be necessary to return the TE tunnel to
 its original path when the failed resource becomes re-activated.
 In general, it is highly desirable not to disrupt traffic, or
 adversely impact network operations while TE tunnel rerouting is in
 progress.  This adaptive and smooth rerouting requirement
 necessitates establishing a new LSP tunnel and transferring traffic
 from the old LSP tunnel onto it before tearing down the old LSP
 tunnel.  This concept is called "make-before-break." A problem can
 arise because the old and new LSP tunnels might compete with each
 other for resources on network segments which they have in common.
 Depending on availability of resources, this competition can cause
 Admission Control to prevent the new LSP tunnel from being
 established.  An advantage of using RSVP to establish LSP tunnels is
 that it solves this problem very elegantly.
 To support make-before-break in a smooth fashion, it is necessary
 that on links that are common to the old and new LSPs, resources used
 by the old LSP tunnel should not be released before traffic is
 transitioned to the new LSP tunnel, and reservations should not be
 counted twice because this might cause Admission Control to reject
 the new LSP tunnel.
 A similar situation can arise when one wants to increase the
 bandwidth of a TE tunnel.  The new reservation will be for the full
 amount needed, but the actual allocation needed is only the delta
 between the new and old bandwidth.  If policy is being applied to
 PATH messages by intermediate nodes, then a PATH message requesting
 too much bandwidth will be rejected.  In this situation simply
 increasing the bandwidth request without changing the
 SENDER_TEMPLATE, could result in a tunnel being torn down, depending
 upon local policy.

Awduche, et al. Standards Track [Page 12] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 The combination of the LSP_TUNNEL SESSION object and the SE
 reservation style naturally accommodates smooth transitions in
 bandwidth and routing.  The idea is that the old and new LSP tunnels
 share resources along links which they have in common.  The
 LSP_TUNNEL SESSION object is used to narrow the scope of the RSVP
 session to the particular TE tunnel in question.  To uniquely
 identify a TE tunnel, we use the combination of the destination IP
 address (an address of the node which is the egress of the tunnel), a
 Tunnel ID, and the tunnel ingress node's IP address, which is placed
 in the Extended Tunnel ID field.
 During the reroute or bandwidth-increase operation, the tunnel
 ingress needs to appear as two different senders to the RSVP session.
 This is achieved by the inclusion of the "LSP ID", which is carried
 in the SENDER_TEMPLATE and FILTER_SPEC objects.  Since the semantics
 of these objects are changed, a new C-Types are assigned.
 To effect a reroute, the ingress node picks a new LSP ID and forms a
 new SENDER_TEMPLATE.  The ingress node then creates a new ERO to
 define the new path.  Thereafter the node sends a new Path Message
 using the original SESSION object and the new SENDER_TEMPLATE and
 ERO.  It continues to use the old LSP and refresh the old Path
 message.  On links that are not held in common, the new Path message
 is treated as a conventional new LSP tunnel setup.  On links held in
 common, the shared SESSION object and SE style allow the LSP to be
 established sharing resources with the old LSP.  Once the ingress
 node receives a Resv message for the new LSP, it can transition
 traffic to it and tear down the old LSP.
 To effect a bandwidth-increase, a new Path Message with a new LSP_ID
 can be used to attempt a larger bandwidth reservation while the
 current LSP_ID continues to be refreshed to ensure that the
 reservation is not lost if the larger reservation fails.

2.6. Path MTU

 Standard RSVP [1] and Int-Serv [11] provide the RSVP sender with the
 minimum MTU available between the sender and the receiver.  This path
 MTU identification capability is also provided for LSPs established
 via RSVP.
 Path MTU information is carried, depending on which is present, in
 the Integrated Services or Null Service objects.  When using
 Integrated Services objects, path MTU is provided based on the
 procedures defined in [11].  Path MTU identification when using Null
 Service objects is defined in [16].

Awduche, et al. Standards Track [Page 13] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 With standard RSVP, the path MTU information is used by the sender to
 check which IP packets exceed the path MTU.  For packets that exceed
 the path MTU, the sender either fragments the packets or, when the IP
 datagram has the "Don't Fragment" bit set, issues an ICMP destination
 unreachable message.  This path MTU related handling is also required
 for LSPs established via RSVP.
 The following algorithm applies to all unlabeled IP datagrams and to
 any labeled packets which the node knows to be IP datagrams, to which
 labels need to be added before forwarding.  For labeled packets the
 bottom of stack is found, the IP header examined.
 Using the terminology defined in [5], an LSR MUST execute the
 following algorithm:
 1. Let N be the number of bytes in the label stack (i.e, 4 times the
    number of label stack entries) including labels to be added by
    this node.
 2. Let M be the smaller of the "Maximum Initially Labeled IP Datagram
    Size" or of (Path MTU - N).
 When the size of an IPv4 datagram (without labels) exceeds the value
    of M,
    If the DF bit is not set in the IPv4 header, then
       (a) the datagram MUST be broken into fragments, each of whose
           size is no greater than M, and
       (b) each fragment MUST be labeled and then forwarded.
    If the DF bit is set in the IPv4 header, then
       (a) the datagram MUST NOT be forwarded
       (b) Create an ICMP Destination Unreachable Message:
            i. set its Code field [12] to "Fragmentation Required and
               DF Set",
           ii. set its Next-Hop MTU field [13] to M
       (c) If possible, transmit the ICMP Destination Unreachable
           Message to the source of the of the discarded datagram.
    When the size of an IPv6 datagram (without labels) exceeds the
           value of M,

Awduche, et al. Standards Track [Page 14] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

       (a) the datagram MUST NOT be forwarded
       (b) Create an ICMP Packet too Big Message with the Next-Hop
           link MTU field [14] set to M
       (c) If possible, transmit the ICMP Packet too Big Message to
           the source of the of the discarded datagram.

3. LSP Tunnel related Message Formats

 Five new objects are defined in this section:
    Object name          Applicable RSVP messages
    ---------------      ------------------------
    LABEL_REQUEST          Path
    LABEL                  Resv
    EXPLICIT_ROUTE         Path
    RECORD_ROUTE           Path, Resv
    SESSION_ATTRIBUTE      Path
 New C-Types are also assigned for the SESSION, SENDER_TEMPLATE, and
 FILTER_SPEC, objects.
 Detailed descriptions of the new objects are given in later sections.
 All new objects are OPTIONAL with respect to RSVP.  An implementation
 can choose to support a subset of objects.  However, the
 LABEL_REQUEST and LABEL objects are mandatory with respect to this
 specification.
 The LABEL and RECORD_ROUTE objects, are sender specific.  In Resv
 messages they MUST appear after the associated FILTER_SPEC and prior
 to any subsequent FILTER_SPEC.
 The relative placement of EXPLICIT_ROUTE, LABEL_REQUEST, and
 SESSION_ATTRIBUTE objects is simply a recommendation.  The ordering
 of these objects is not important, so an implementation MUST be
 prepared to accept objects in any order.

3.1. Path Message

 The format of the Path message is as follows:
    <Path Message> ::=       <Common Header> [ <INTEGRITY> ]
                             <SESSION> <RSVP_HOP>
                             <TIME_VALUES>
                             [ <EXPLICIT_ROUTE> ]
                             <LABEL_REQUEST>
                             [ <SESSION_ATTRIBUTE> ]

Awduche, et al. Standards Track [Page 15] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

                             [ <POLICY_DATA> ... ]
                             <sender descriptor>
    <sender descriptor> ::=  <SENDER_TEMPLATE> <SENDER_TSPEC>
                             [ <ADSPEC> ]
                             [ <RECORD_ROUTE> ]

3.2. Resv Message

 The format of the Resv message is as follows:
    <Resv Message> ::=       <Common Header> [ <INTEGRITY> ]
                             <SESSION>  <RSVP_HOP>
                             <TIME_VALUES>
                             [ <RESV_CONFIRM> ]  [ <SCOPE> ]
                             [ <POLICY_DATA> ... ]
                             <STYLE> <flow descriptor list>
    <flow descriptor list> ::= <FF flow descriptor list>
                             | <SE flow descriptor>
    <FF flow descriptor list> ::= <FLOWSPEC> <FILTER_SPEC>
                             <LABEL> [ <RECORD_ROUTE> ]
                             | <FF flow descriptor list>
                             <FF flow descriptor>
    <FF flow descriptor> ::= [ <FLOWSPEC> ] <FILTER_SPEC> <LABEL>
                             [ <RECORD_ROUTE> ]
    <SE flow descriptor> ::= <FLOWSPEC> <SE filter spec list>
    <SE filter spec list> ::= <SE filter spec>
                             | <SE filter spec list> <SE filter spec>
    <SE filter spec> ::=     <FILTER_SPEC> <LABEL> [ <RECORD_ROUTE> ]
    Note:  LABEL and RECORD_ROUTE (if present), are bound to the
           preceding FILTER_SPEC.  No more than one LABEL and/or
           RECORD_ROUTE may follow each FILTER_SPEC.

Awduche, et al. Standards Track [Page 16] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

4. LSP Tunnel related Objects

4.1. Label Object

 Labels MAY be carried in Resv messages.  For the FF and SE styles, a
 label is associated with each sender.  The label for a sender MUST
 immediately follow the FILTER_SPEC for that sender in the Resv
 message.
 The LABEL object has the following format:
 LABEL class = 16, C_Type = 1
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           (top label)                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The contents of a LABEL is a single label, encoded in 4 octets.  Each
 generic MPLS label is an unsigned integer in the range 0 through
 1048575.  Generic MPLS labels and FR labels are encoded right aligned
 in 4 octets.  ATM labels are encoded with the VPI right justified in
 bits 0-15 and the VCI right justified in bits 16-31.

4.1.1. Handling Label Objects in Resv messages

 In MPLS a node may support multiple label spaces, perhaps associating
 a unique space with each incoming interface.  For the purposes of the
 following discussion, the term "same label" means the identical label
 value drawn from the identical label space.  Further, the following
 applies only to unicast sessions.
 Labels received in Resv messages on different interfaces are always
 considered to be different even if the label value is the same.

4.1.1.1. Downstream

 The downstream node selects a label to represent the flow.  If a
 label range has been specified in the label request, the label MUST
 be drawn from that range.  If no label is available the node sends a
 PathErr message with an error code of "routing problem" and an error
 value of "label allocation failure".
 If a node receives a Resv message that has assigned the same label
 value to multiple senders, then that node MAY also assign a single
 value to those same senders or to any subset of those senders.  Note

Awduche, et al. Standards Track [Page 17] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 that if a node intends to police individual senders to a session, it
 MUST assign unique labels to those senders.
 In the case of ATM, one further condition applies.  Some ATM nodes
 are not capable of merging streams.  These nodes MAY indicate this by
 setting a bit in the label request to zero.  The M-bit in the
 LABEL_REQUEST object of C-Type 2, label request with ATM label range,
 serves this purpose.  The M-bit SHOULD be set by nodes which are
 merge capable.  If for any senders the M-bit is not set, the
 downstream node MUST assign unique labels to those senders.
 Once a label is allocated, the node formats a new LABEL object.  The
 node then sends the new LABEL object as part of the Resv message to
 the previous hop.  The node SHOULD be prepared to forward packets
 carrying the assigned label prior to sending the Resv message.  The
 LABEL object SHOULD be kept in the Reservation State Block.  It is
 then used in the next Resv refresh event for formatting the Resv
 message.
 A node is expected to send a Resv message before its refresh timers
 expire if the contents of the LABEL object change.

4.1.1.2. Upstream

 A node uses the label carried in the LABEL object as the outgoing
 label associated with the sender.  The router allocates a new label
 and binds it to the incoming interface of this session/sender.  This
 is the same interface that the router uses to forward Resv messages
 to the previous hops.
 Several circumstance can lead to an unacceptable label.
    1. the node is a merge incapable ATM switch but the downstream
       node has assigned the same label to two senders
    2. The implicit null label was assigned, but the node is not
       capable of doing a penultimate pop for the associated L3PID
    3. The assigned label is outside the requested label range
 In any of these events the node send a ResvErr message with an error
 code of "routing problem" and an error value of "unacceptable label
 value".

Awduche, et al. Standards Track [Page 18] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

4.1.2. Non-support of the Label Object

 Under normal circumstances, a node should never receive a LABEL
 object in a Resv message unless it had included a LABEL_REQUEST
 object in the corresponding Path message.  However, an RSVP router
 that does not recognize the LABEL object sends a ResvErr with the
 error code "Unknown object class" toward the receiver.  This causes
 the reservation to fail.

4.2. Label Request Object

 The Label Request Class is 19.  Currently there are three possible
 C_Types.  Type 1 is a Label Request without label range.  Type 2 is a
 label request with an ATM label range.  Type 3 is a label request
 with a Frame Relay label range.  The LABEL_REQUEST object formats are
 shown below.

4.2.1. Label Request without Label Range

 Class = 19, C_Type = 1
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |           Reserved            |             L3PID             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Reserved
       This field is reserved.  It MUST be set to zero on transmission
       and MUST be ignored on receipt.
    L3PID
       an identifier of the layer 3 protocol using this path.
       Standard Ethertype values are used.

Awduche, et al. Standards Track [Page 19] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

4.2.2. Label Request with ATM Label Range

 Class = 19, C_Type = 2
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |           Reserved            |             L3PID             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |M| Res |    Minimum VPI        |      Minimum VCI              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Res  |    Maximum VPI        |      Maximum VCI              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Reserved (Res)
       This field is reserved.  It MUST be set to zero on transmission
       and MUST be ignored on receipt.
    L3PID
       an identifier of the layer 3 protocol using this path.
       Standard Ethertype values are used.
    M
       Setting this bit to one indicates that the node is capable of
       merging in the data plane
    Minimum VPI (12 bits)
       This 12 bit field specifies the lower bound of a block of
       Virtual Path Identifiers that is supported on the originating
       switch.  If the VPI is less than 12-bits it MUST be right
       justified in this field and preceding bits MUST be set to zero.
    Minimum VCI (16 bits)
       This 16 bit field specifies the lower bound of a block of
       Virtual Connection Identifiers that is supported on the
       originating switch.  If the VCI is less than 16-bits it MUST be
       right justified in this field and preceding bits MUST be set to
       zero.

Awduche, et al. Standards Track [Page 20] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

    Maximum VPI (12 bits)
       This 12 bit field specifies the upper bound of a block of
       Virtual Path Identifiers that is supported on the originating
       switch.  If the VPI is less than 12-bits it MUST be right
       justified in this field and preceding bits MUST be set to zero.
    Maximum VCI (16 bits)
       This 16 bit field specifies the upper bound of a block of
       Virtual Connection Identifiers that is supported on the
       originating switch.  If the VCI is less than 16-bits it MUST be
       right justified in this field and preceding bits MUST be set to
       zero.

4.2.3. Label Request with Frame Relay Label Range

 Class = 19, C_Type = 3
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |           Reserved            |             L3PID             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Reserved    |DLI|                     Minimum DLCI            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Reserved        |                     Maximum DLCI            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Reserved
       This field is reserved.  It MUST be set to zero on transmission
       and ignored on receipt.
    L3PID
       an identifier of the layer 3 protocol using this path.
       Standard Ethertype values are used.
    DLI
       DLCI Length Indicator.  The number of bits in the DLCI.  The
       following values are supported:
                 Len    DLCI bits
                  0        10
                  2        23

Awduche, et al. Standards Track [Page 21] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

    Minimum DLCI
       This 23-bit field specifies the lower bound of a block of Data
       Link Connection Identifiers (DLCIs) that is supported on the
       originating switch.  The DLCI MUST be right justified in this
       field and unused bits MUST be set to 0.
    Maximum DLCI
       This 23-bit field specifies the upper bound of a block of Data
       Link Connection Identifiers (DLCIs) that is supported on the
       originating switch.  The DLCI MUST be right justified in this
       field and unused bits MUST be set to 0.

4.2.4. Handling of LABEL_REQUEST

 To establish an LSP tunnel the sender creates a Path message with a
 LABEL_REQUEST object.  The LABEL_REQUEST object indicates that a
 label binding for this path is requested and provides an indication
 of the network layer protocol that is to be carried over this path.
 This permits non-IP network layer protocols to be sent down an LSP.
 This information can also be useful in actual label allocation,
 because some reserved labels are protocol specific, see [5].
 The LABEL_REQUEST SHOULD be stored in the Path State Block, so that
 Path refresh messages will also contain the LABEL_REQUEST object.
 When the Path message reaches the receiver, the presence of the
 LABEL_REQUEST object triggers the receiver to allocate a label and to
 place the label in the LABEL object for the corresponding Resv
 message.  If a label range was specified, the label MUST be allocated
 from that range.  A receiver that accepts a LABEL_REQUEST object MUST
 include a LABEL object in Resv messages pertaining to that Path
 message.  If a LABEL_REQUEST object was not present in the Path
 message, a node MUST NOT include a LABEL object in a Resv message for
 that Path message's session and PHOP.
 A node that sends a LABEL_REQUEST object MUST be ready to accept and
 correctly process a LABEL object in the corresponding Resv messages.
 A node that recognizes a LABEL_REQUEST object, but that is unable to
 support it (possibly because of a failure to allocate labels) SHOULD
 send a PathErr with the error code "Routing problem" and the error
 value "MPLS label allocation failure."  This includes the case where
 a label range has been specified and a label cannot be allocated from
 that range.

Awduche, et al. Standards Track [Page 22] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 A node which receives and forwards a Path message each with a
 LABEL_REQUEST object, MUST copy the L3PID from the received
 LABEL_REQUEST object to the forwarded LABEL_REQUEST object.
 If the receiver cannot support the protocol L3PID, it SHOULD send a
 PathErr with the error code "Routing problem" and the error value
 "Unsupported L3PID."  This causes the RSVP session to fail.

4.2.5. Non-support of the Label Request Object

 An RSVP router that does not recognize the LABEL_REQUEST object sends
 a PathErr with the error code "Unknown object class" toward the
 sender.  An RSVP router that recognizes the LABEL_REQUEST object but
 does not recognize the C_Type sends a PathErr with the error code
 "Unknown object C_Type" toward the sender.  This causes the path
 setup to fail.  The sender should notify management that a LSP cannot
 be established and possibly take action to continue the reservation
 without the LABEL_REQUEST.
 RSVP is designed to cope gracefully with non-RSVP routers anywhere
 between senders and receivers.  However, obviously, non-RSVP routers
 cannot convey labels via RSVP.  This means that if a router has a
 neighbor that is known to not be RSVP capable, the router MUST NOT
 advertise the LABEL_REQUEST object when sending messages that pass
 through the non-RSVP routers.  The router SHOULD send a PathErr back
 to the sender, with the error code "Routing problem" and the error
 value "MPLS being negotiated, but a non-RSVP capable router stands in
 the path."  This same message SHOULD be sent, if a router receives a
 LABEL_REQUEST object in a message from a non-RSVP capable router.
 See [1] for a description of how a downstream router can determine
 the presence of non-RSVP routers.

4.3. Explicit Route Object

 Explicit routes are specified via the EXPLICIT_ROUTE object (ERO).
 The Explicit Route Class is 20.  Currently one C_Type is defined,
 Type 1 Explicit Route.  The EXPLICIT_ROUTE object has the following
 format:

Awduche, et al. Standards Track [Page 23] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 Class = 20, C_Type = 1
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 //                        (Subobjects)                          //
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Subobjects
 The contents of an EXPLICIT_ROUTE object are a series of variable-
 length data items called subobjects.  The subobjects are defined in
 section 4.3.3 below.
 If a Path message contains multiple EXPLICIT_ROUTE objects, only the
 first object is meaningful.  Subsequent EXPLICIT_ROUTE objects MAY be
 ignored and SHOULD NOT be propagated.

4.3.1. Applicability

 The EXPLICIT_ROUTE object is intended to be used only for unicast
 situations.  Applications of explicit routing to multicast are a
 topic for further research.
 The EXPLICIT_ROUTE object is to be used only when all routers along
 the explicit route support RSVP and the EXPLICIT_ROUTE object.  The
 EXPLICIT_ROUTE object is assigned a class value of the form 0bbbbbbb.
 RSVP routers that do not support the object will therefore respond
 with an "Unknown Object Class" error.

4.3.2. Semantics of the Explicit Route Object

 An explicit route is a particular path in the network topology.
 Typically, the explicit route is determined by a node, with the
 intent of directing traffic along that path.
 An explicit route is described as a list of groups of nodes along the
 explicit route.  In addition to the ability to identify specific
 nodes along the path, an explicit route can identify a group of nodes
 that must be traversed along the path.  This capability allows the
 routing system a significant amount of local flexibility in
 fulfilling a request for an explicit route.  This capability allows
 the generator of the explicit route to have imperfect information
 about the details of the path.

Awduche, et al. Standards Track [Page 24] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 The explicit route is encoded as a series of subobjects contained in
 an EXPLICIT_ROUTE object.  Each subobject identifies a group of nodes
 in the explicit route.  An explicit route is thus a specification of
 groups of nodes to be traversed.
 To formalize the discussion, we call each group of nodes an abstract
 node.  Thus, we say that an explicit route is a specification of a
 set of abstract nodes to be traversed.  If an abstract node consists
 of only one node, we refer to it as a simple abstract node.
 As an example of the concept of abstract nodes, consider an explicit
 route that consists solely of Autonomous System number subobjects.
 Each subobject corresponds to an Autonomous System in the global
 topology.  In this case, each Autonomous System is an abstract node,
 and the explicit route is a path that includes each of the specified
 Autonomous Systems.  There may be multiple hops within each
 Autonomous System, but these are opaque to the source node for the
 explicit route.

4.3.3. Subobjects

 The contents of an EXPLICIT_ROUTE object are a series of variable-
 length data items called subobjects.  Each subobject has the form:
  0                   1
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------//----------------+
 |L|    Type     |     Length    | (Subobject contents)          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------//----------------+
    L
       The L bit is an attribute of the subobject.  The L bit is set
       if the subobject represents a loose hop in the explicit route.
       If the bit is not set, the subobject represents a strict hop in
       the explicit route.
    Type
       The Type indicates the type of contents of the subobject.
       Currently defined values are:
                 1   IPv4 prefix
                 2   IPv6 prefix
                32   Autonomous system number

Awduche, et al. Standards Track [Page 25] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

    Length
       The Length contains the total length of the subobject in bytes,
       including the L, Type and Length fields.  The Length MUST be at
       least 4, and MUST be a multiple of 4.

4.3.3.1. Strict and Loose Subobjects

 The L bit in the subobject is a one-bit attribute.  If the L bit is
 set, then the value of the attribute is 'loose.'  Otherwise, the
 value of the attribute is 'strict.'  For brevity, we say that if the
 value of the subobject attribute is 'loose' then it is a 'loose
 subobject.'  Otherwise, it's a 'strict subobject.'  Further, we say
 that the abstract node of a strict or loose subobject is a strict or
 a loose node, respectively.  Loose and strict nodes are always
 interpreted relative to their prior abstract nodes.
 The path between a strict node and its preceding node MUST include
 only network nodes from the strict node and its preceding abstract
 node.
 The path between a loose node and its preceding node MAY include
 other network nodes that are not part of the strict node or its
 preceding abstract node.

4.3.3.2. Subobject 1: IPv4 prefix

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |L|    Type     |     Length    | IPv4 address (4 bytes)        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IPv4 address (continued)      | Prefix Length |      Resvd    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    L
       The L bit is an attribute of the subobject.  The L bit is set
       if the subobject represents a loose hop in the explicit route.
       If the bit is not set, the subobject represents a strict hop in
       the explicit route.
    Type
       0x01  IPv4 address

Awduche, et al. Standards Track [Page 26] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

    Length
       The Length contains the total length of the subobject in bytes,
       including the Type and Length fields.  The Length is always 8.
    IPv4 address
       An IPv4 address.  This address is treated as a prefix based on
       the prefix length value below.  Bits beyond the prefix are
       ignored on receipt and SHOULD be set to zero on transmission.
    Prefix length
       Length in bits of the IPv4 prefix
    Padding
       Zero on transmission.  Ignored on receipt.
 The contents of an IPv4 prefix subobject are a 4-octet IPv4 address,
 a 1-octet prefix length, and a 1-octet pad.  The abstract node
 represented by this subobject is the set of nodes that have an IP
 address which lies within this prefix.  Note that a prefix length of
 32 indicates a single IPv4 node.

4.3.3.3. Subobject 2: IPv6 Prefix

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |L|    Type     |     Length    | IPv6 address (16 bytes)       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IPv6 address (continued)                                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IPv6 address (continued)                                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IPv6 address (continued)                                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IPv6 address (continued)      | Prefix Length |      Resvd    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    L
       The L bit is an attribute of the subobject.  The L bit is set
       if the subobject represents a loose hop in the explicit route.
       If the bit is not set, the subobject represents a strict hop in
       the explicit route.

Awduche, et al. Standards Track [Page 27] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

    Type
       0x02  IPv6 address
    Length
       The Length contains the total length of the subobject in bytes,
       including the Type and Length fields.  The Length is always 20.
    IPv6 address
       An IPv6 address.  This address is treated as a prefix based on
       the prefix length value below.  Bits beyond the prefix are
       ignored on receipt and SHOULD be set to zero on transmission.
    Prefix Length
       Length in bits of the IPv6 prefix.
    Padding
       Zero on transmission.  Ignored on receipt.
 The contents of an IPv6 prefix subobject are a 16-octet IPv6 address,
 a 1-octet prefix length, and a 1-octet pad.  The abstract node
 represented by this subobject is the set of nodes that have an IP
 address which lies within this prefix.  Note that a prefix length of
 128 indicates a single IPv6 node.

4.3.3.4. Subobject 32: Autonomous System Number

 The contents of an Autonomous System (AS) number subobject are a 2-
 octet AS number.  The abstract node represented by this subobject is
 the set of nodes belonging to the autonomous system.
 The length of the AS number subobject is 4 octets.

4.3.4. Processing of the Explicit Route Object

4.3.4.1. Selection of the Next Hop

 A node receiving a Path message containing an EXPLICIT_ROUTE object
 must determine the next hop for this path.  This is necessary because
 the next abstract node along the explicit route might be an IP subnet
 or an Autonomous System.  Therefore, selection of this next hop may
 involve a decision from a set of feasible alternatives.  The criteria
 used to make a selection from feasible alternatives is implementation
 dependent and can also be impacted by local policy, and is beyond the

Awduche, et al. Standards Track [Page 28] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 scope of this specification.  However, it is assumed that each node
 will make a best effort attempt to determine a loop-free path.  Note
 that paths so determined can be overridden by local policy.
 To determine the next hop for the path, a node performs the following
 steps:
 1) The node receiving the RSVP message MUST first evaluate the first
    subobject.  If the node is not part of the abstract node described
    by the first subobject, it has received the message in error and
    SHOULD return a "Bad initial subobject" error.  If there is no
    first subobject, the message is also in error and the system
    SHOULD return a "Bad EXPLICIT_ROUTE object" error.
 2) If there is no second subobject, this indicates the end of the
    explicit route.  The EXPLICIT_ROUTE object SHOULD be removed from
    the Path message.  This node may or may not be the end of the
    path.  Processing continues with section 4.3.4.2, where a new
    EXPLICIT_ROUTE object MAY be added to the Path message.
 3) Next, the node evaluates the second subobject.  If the node is
    also a part of the abstract node described by the second
    subobject, then the node deletes the first subobject and continues
    processing with step 2, above.  Note that this makes the second
    subobject into the first subobject of the next iteration and
    allows the node to identify the next abstract node on the path of
    the message after possible repeated application(s) of steps 2 and
    3.
 4) Abstract Node Border Case: The node determines whether it is
    topologically adjacent to the abstract node described by the
    second subobject.  If so, the node selects a particular next hop
    which is a member of the abstract node.  The node then deletes the
    first subobject and continues processing with section 4.3.4.2.
 5) Interior of the Abstract Node Case: Otherwise, the node selects a
    next hop within the abstract node of the first subobject (which
    the node belongs to) that is along the path to the abstract node
    of the second subobject (which is the next abstract node).  If no
    such path exists then there are two cases:
 5a) If the second subobject is a strict subobject, there is an error
     and the node SHOULD return a "Bad strict node" error.
 5b) Otherwise, if the second subobject is a loose subobject, the node
     selects any next hop that is along the path to the next abstract
     node.  If no path exists, there is an error, and the node SHOULD
     return a "Bad loose node" error.

Awduche, et al. Standards Track [Page 29] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 6) Finally, the node replaces the first subobject with any subobject
    that denotes an abstract node containing the next hop.  This is
    necessary so that when the explicit route is received by the next
    hop, it will be accepted.

4.3.4.2. Adding subobjects to the Explicit Route Object

 After selecting a next hop, the node MAY alter the explicit route in
 the following ways.
 If, as part of executing the algorithm in section 4.3.4.1, the
 EXPLICIT_ROUTE object is removed, the node MAY add a new
 EXPLICIT_ROUTE object.
 Otherwise, if the node is a member of the abstract node for the first
 subobject, a series of subobjects MAY be inserted before the first
 subobject or MAY replace the first subobject.  Each subobject in this
 series MUST denote an abstract node that is a subset of the current
 abstract node.
 Alternately, if the first subobject is a loose subobject, an
 arbitrary series of subobjects MAY be inserted prior to the first
 subobject.

4.3.5. Loops

 While the EXPLICIT_ROUTE object is of finite length, the existence of
 loose nodes implies that it is possible to construct forwarding loops
 during transients in the underlying routing protocol.  This can be
 detected by the originator of the explicit route through the use of
 another opaque route object called the RECORD_ROUTE object.  The
 RECORD_ROUTE object is used to collect detailed path information and
 is useful for loop detection and for diagnostics.

4.3.6. Forward Compatibility

 It is anticipated that new subobjects may be defined over time.  A
 node which encounters an unrecognized subobject during its normal ERO
 processing sends a PathErr with the error code "Routing Error" and
 error value of "Bad Explicit Route Object" toward the sender.  The
 EXPLICIT_ROUTE object is included, truncated (on the left) to the
 offending subobject.  The presence of an unrecognized subobject which
 is not encountered in a node's ERO processing SHOULD be ignored.  It
 is passed forward along with the rest of the remaining ERO stack.

Awduche, et al. Standards Track [Page 30] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

4.3.7. Non-support of the Explicit Route Object

 An RSVP router that does not recognize the EXPLICIT_ROUTE object
 sends a PathErr with the error code "Unknown object class" toward the
 sender.  This causes the path setup to fail.  The sender should
 notify management that a LSP cannot be established and possibly take
 action to continue the reservation without the EXPLICIT_ROUTE or via
 a different explicit route.

4.4. Record Route Object

 Routes can be recorded via the RECORD_ROUTE object (RRO).
 Optionally, labels may also be recorded.  The Record Route Class is
 21.  Currently one C_Type is defined, Type 1 Record Route.  The
 RECORD_ROUTE object has the following format:
 Class = 21, C_Type = 1
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 //                        (Subobjects)                          //
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Subobjects
       The contents of a RECORD_ROUTE object are a series of
       variable-length data items called subobjects.  The subobjects
       are defined in section 4.4.1 below.
 The RRO can be present in both RSVP Path and Resv messages.  If a
 Path message contains multiple RROs, only the first RRO is
 meaningful.  Subsequent RROs SHOULD be ignored and SHOULD NOT be
 propagated.  Similarly, if in a Resv message multiple RROs are
 encountered following a FILTER_SPEC before another FILTER_SPEC is
 encountered, only the first RRO is meaningful.  Subsequent RROs
 SHOULD be ignored and SHOULD NOT be propagated.

4.4.1. Subobjects

 The contents of a RECORD_ROUTE object are a series of variable-length
 data items called subobjects.  Each subobject has its own Length
 field.  The length contains the total length of the subobject in
 bytes, including the Type and Length fields.  The length MUST always
 be a multiple of 4, and at least 4.

Awduche, et al. Standards Track [Page 31] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 Subobjects are organized as a last-in-first-out stack.  The first
 subobject relative to the beginning of RRO is considered the top.
 The last subobject is considered the bottom.  When a new subobject is
 added, it is always added to the top.
 An empty RRO with no subobjects is considered illegal.
 Three kinds of subobjects are currently defined.

4.4.1.1. Subobject 1: IPv4 address

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |      Type     |     Length    | IPv4 address (4 bytes)        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IPv4 address (continued)      | Prefix Length |      Flags    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Type
       0x01  IPv4 address
    Length
       The Length contains the total length of the subobject in bytes,
       including the Type and Length fields.  The Length is always 8.
    IPv4 address
       A 32-bit unicast, host address.  Any network-reachable
       interface address is allowed here.  Illegal addresses, such as
       certain loopback addresses, SHOULD NOT be used.
    Prefix length
       32
    Flags
       0x01  Local protection available
             Indicates that the link downstream of this node is
             protected via a local repair mechanism.  This flag can
             only be set if the Local protection flag was set in the
             SESSION_ATTRIBUTE object of the corresponding Path
             message.

Awduche, et al. Standards Track [Page 32] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

       0x02  Local protection in use
             Indicates that a local repair mechanism is in use to
             maintain this tunnel (usually in the face of an outage
             of the link it was previously routed over).

4.4.1.2. Subobject 2: IPv6 address

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |      Type     |     Length    | IPv6 address (16 bytes)       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IPv6 address (continued)                                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IPv6 address (continued)                                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IPv6 address (continued)                                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | IPv6 address (continued)      | Prefix Length |      Flags    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Type
       0x02  IPv6 address
    Length
       The Length contains the total length of the subobject in bytes,
       including the Type and Length fields.  The Length is always 20.
    IPv6 address
       A 128-bit unicast host address.
    Prefix length
       128
    Flags
       0x01  Local protection available
             Indicates that the link downstream of this node is
             protected via a local repair mechanism.  This flag can
             only be set if the Local protection flag was set in the
             SESSION_ATTRIBUTE object of the corresponding Path
             message.

Awduche, et al. Standards Track [Page 33] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

       0x02  Local protection in use
             Indicates that a local repair mechanism is in use to
             maintain this tunnel (usually in the face of an outage
             of the link it was previously routed over).

4.4.1.3. Subobject 3, Label

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |     Length    |    Flags      |   C-Type      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Contents of Label Object                                |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Type
       0x03  Label
    Length
       The Length contains the total length of the subobject in bytes,
       including the Type and Length fields.
    Flags
       0x01 = Global label
         This flag indicates that the label will be understood
         if received on any interface.
    C-Type
       The C-Type of the included Label Object.  Copied from the Label
       Object.
    Contents of Label Object
       The contents of the Label Object.  Copied from the Label Object

4.4.2. Applicability

 Only the procedures for use in unicast sessions are defined here.
 There are three possible uses of RRO in RSVP.  First, an RRO can
 function as a loop detection mechanism to discover L3 routing loops,
 or loops inherent in the explicit route.  The exact procedure for
 doing so is described later in this document.

Awduche, et al. Standards Track [Page 34] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 Second, an RRO collects up-to-date detailed path information hop-by-
 hop about RSVP sessions, providing valuable information to the sender
 or receiver.  Any path change (due to network topology changes) will
 be reported.
 Third, RRO syntax is designed so that, with minor changes, the whole
 object can be used as input to the EXPLICIT_ROUTE object.  This is
 useful if the sender receives RRO from the receiver in a Resv
 message, applies it to EXPLICIT_ROUTE object in the next Path message
 in order to "pin down session path".

4.4.3. Processing RRO

 Typically, a node initiates an RSVP session by adding the RRO to the
 Path message.  The initial RRO contains only one subobject - the
 sender's IP addresses.  If the node also desires label recording, it
 sets the Label_Recording flag in the SESSION_ATTRIBUTE object.
 When a Path message containing an RRO is received by an intermediate
 router, the router stores a copy of it in the Path State Block.  The
 RRO is then used in the next Path refresh event for formatting Path
 messages.  When a new Path message is to be sent, the router adds a
 new subobject to the RRO and appends the resulting RRO to the Path
 message before transmission.
 The newly added subobject MUST be this router's IP address.  The
 address to be added SHOULD be the interface address of the outgoing
 Path messages.  If there are multiple addresses to choose from, the
 decision is a local matter.  However, it is RECOMMENDED that the same
 address be chosen consistently.
 When the Label_Recording flag is set in the SESSION_ATTRIBUTE object,
 nodes doing route recording SHOULD include a Label Record subobject.
 If the node is using a global label space, then it SHOULD set the
 Global Label flag.
 The Label Record subobject is pushed onto the RECORD_ROUTE object
 prior to pushing on the node's IP address.  A node MUST NOT push on a
 Label Record subobject without also pushing on an IPv4 or IPv6
 subobject.
 Note that on receipt of the initial Path message, a node is unlikely
 to have a label to include.  Once a label is obtained, the node
 SHOULD include the label in the RRO in the next Path refresh event.
 If the newly added subobject causes the RRO to be too big to fit in a
 Path (or Resv) message, the RRO object SHALL be dropped from the
 message and message processing continues as normal.  A PathErr (or

Awduche, et al. Standards Track [Page 35] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 ResvErr) message SHOULD be sent back to the sender (or receiver).  An
 error code of "Notify" and an error value of "RRO too large for MTU"
 is used.  If the receiver receives such a ResvErr, it SHOULD send a
 PathErr message with error code of "Notify" and an error value of
 "RRO notification".
 A sender receiving either of these error values SHOULD remove the RRO
 from the Path message.
 Nodes SHOULD resend the above PathErr or ResvErr message each n
 seconds where n is the greater of 15 and the refresh interval for the
 associated Path or RESV message.  The node MAY apply limits and/or
 back-off timers to limit the number of messages sent.
 An RSVP router can decide to send Path messages before its refresh
 time if the RRO in the next Path message is different from the
 previous one.  This can happen if the contents of the RRO received
 from the previous hop router changes or if this RRO is newly added to
 (or deleted from) the Path message.
 When the destination node of an RSVP session receives a Path message
 with an RRO, this indicates that the sender node needs route
 recording.  The destination node initiates the RRO process by adding
 an RRO to Resv messages.  The processing mirrors that of the Path
 messages.  The only difference is that the RRO in a Resv message
 records the path information in the reverse direction.
 Note that each node along the path will now have the complete route
 from source to destination.  The Path RRO will have the route from
 the source to this node; the Resv RRO will have the route from this
 node to the destination.  This is useful for network management.
 A received Path message without an RRO indicates that the sender node
 no longer needs route recording.  Subsequent Resv messages SHALL NOT
 contain an RRO.

4.4.4. Loop Detection

 As part of processing an incoming RRO, an intermediate router looks
 into all subobjects contained within the RRO.  If the router
 determines that it is already in the list, a forwarding loop exists.
 An RSVP session is loop-free if downstream nodes receive Path
 messages or upstream nodes receive Resv messages with no routing
 loops detected in the contained RRO.

Awduche, et al. Standards Track [Page 36] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 There are two broad classifications of forwarding loops.  The first
 class is the transient loop, which occurs as a normal part of
 operations as L3 routing tries to converge on a consistent forwarding
 path for all destinations.  The second class of forwarding loop is
 the permanent loop, which normally results from network mis-
 configuration.
 The action performed by a node on receipt of an RRO depends on the
 message type in which the RRO is received.
 For Path messages containing a forwarding loop, the router builds and
 sends a "Routing problem" PathErr message, with the error value "loop
 detected," and drops the Path message.  Until the loop is eliminated,
 this session is not suitable for forwarding data packets.  How the
 loop eliminated is beyond the scope of this document.
 For Resv messages containing a forwarding loop, the router simply
 drops the message.  Resv messages should not loop if Path messages do
 not loop.

4.4.5. Forward Compatibility

 New subobjects may be defined for the RRO.  When processing an RRO,
 unrecognized subobjects SHOULD be ignored and passed on.  When
 processing an RRO for loop detection, a node SHOULD parse over any
 unrecognized objects.  Loop detection works by detecting subobjects
 which were inserted by the node itself on an earlier pass of the
 object.  This ensures that the subobjects necessary for loop
 detection are always understood.

4.4.6. Non-support of RRO

 The RRO object is to be used only when all routers along the path
 support RSVP and the RRO object.  The RRO object is assigned a class
 value of the form 0bbbbbbb.  RSVP routers that do not support the
 object will therefore respond with an "Unknown Object Class" error.

4.5. Error Codes for ERO and RRO

 In the processing described above, certain errors must be reported as
 either a "Routing Problem" or "Notify".  The value of the "Routing
 Problem" error code is 24; the value of the "Notify" error code is
 25.

Awduche, et al. Standards Track [Page 37] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 The following defines error values for the Routing Problem Error
 Code:
    Value    Error:
       1     Bad EXPLICIT_ROUTE object
       2     Bad strict node
       3     Bad loose node
       4     Bad initial subobject
       5     No route available toward destination
       6     Unacceptable label value
       7     RRO indicated routing loops
       8     MPLS being negotiated, but a non-RSVP-capable router
             stands in the path
       9     MPLS label allocation failure
      10     Unsupported L3PID
 For the Notify Error Code, the 16 bits of the Error Value field are:
       ss00 cccc cccc cccc
 The high order bits are as defined under Error Code 1. (See [1]).
 When ss = 00, the following subcodes are defined:
       1    RRO too large for MTU
       2    RRO notification
       3    Tunnel locally repaired

4.6. Session, Sender Template, and Filter Spec Objects

 New C-Types are defined for the SESSION, SENDER_TEMPLATE and
 FILTER_SPEC objects.
 The LSP_TUNNEL objects have the following format:

Awduche, et al. Standards Track [Page 38] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

4.6.1. Session Object

4.6.1.1. LSP_TUNNEL_IPv4 Session Object

 Class = SESSION, LSP_TUNNEL_IPv4 C-Type = 7
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                   IPv4 tunnel end point address               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  MUST be zero                 |      Tunnel ID                |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       Extended Tunnel ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    IPv4 tunnel end point address
       IPv4 address of the egress node for the tunnel.
    Tunnel ID
       A 16-bit identifier used in the SESSION that remains constant
       over the life of the tunnel.
    Extended Tunnel ID
       A 32-bit identifier used in the SESSION that remains constant
       over the life of the tunnel.  Normally set to all zeros.
       Ingress nodes that wish to narrow the scope of a SESSION to the
       ingress-egress pair may place their IPv4 address here as a
       globally unique identifier.

Awduche, et al. Standards Track [Page 39] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

4.6.1.2. LSP_TUNNEL_IPv6 Session Object

 Class = SESSION, LSP_TUNNEL_IPv6 C_Type = 8
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 +                                                               +
 |                   IPv6 tunnel end point address               |
 +                                                               +
 |                            (16 bytes)                         |
 +                                                               +
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  MUST be zero                 |      Tunnel ID                |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 +                                                               +
 |                       Extended Tunnel ID                      |
 +                                                               +
 |                            (16 bytes)                         |
 +                                                               +
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    IPv6 tunnel end point address
       IPv6 address of the egress node for the tunnel.
    Tunnel ID
       A 16-bit identifier used in the SESSION that remains constant
       over the life of the tunnel.
    Extended Tunnel ID
       A 16-byte identifier used in the SESSION that remains constant
       over the life of the tunnel.  Normally set to all zeros.
       Ingress nodes that wish to narrow the scope of a SESSION to the
       ingress-egress pair may place their IPv6 address here as a
       globally unique identifier.

4.6.2. Sender Template Object

4.6.2.1. LSP_TUNNEL_IPv4 Sender Template Object

 Class = SENDER_TEMPLATE, LSP_TUNNEL_IPv4 C-Type = 7

Awduche, et al. Standards Track [Page 40] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                   IPv4 tunnel sender address                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  MUST be zero                 |            LSP ID             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    IPv4 tunnel sender address
       IPv4 address for a sender node
    LSP ID
       A 16-bit identifier used in the SENDER_TEMPLATE and the
       FILTER_SPEC that can be changed to allow a sender to share
       resources with itself.

4.6.2.2. LSP_TUNNEL_IPv6 Sender Template Object

 Class = SENDER_TEMPLATE, LSP_TUNNEL_IPv6 C_Type = 8
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 +                                                               +
 |                   IPv6 tunnel sender address                  |
 +                                                               +
 |                            (16 bytes)                         |
 +                                                               +
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  MUST be zero                 |            LSP ID             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    IPv6 tunnel sender address
       IPv6 address for a sender node
    LSP ID
       A 16-bit identifier used in the SENDER_TEMPLATE and the
       FILTER_SPEC that can be changed to allow a sender to share
       resources with itself.

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4.6.3. Filter Specification Object

4.6.3.1. LSP_TUNNEL_IPv4 Filter Specification Object

    Class = FILTER SPECIFICATION, LSP_TUNNEL_IPv4 C-Type = 7
 The format of the LSP_TUNNEL_IPv4 FILTER_SPEC object is identical to
 the LSP_TUNNEL_IPv4 SENDER_TEMPLATE object.

4.6.3.2. LSP_TUNNEL_IPv6 Filter Specification Object

    Class = FILTER SPECIFICATION, LSP_TUNNEL_IPv6 C_Type = 8
 The format of the LSP_TUNNEL_IPv6 FILTER_SPEC object is identical to
 the LSP_TUNNEL_IPv6 SENDER_TEMPLATE object.

4.6.4. Reroute and Bandwidth Increase Procedure

 This section describes how to setup a tunnel that is capable of
 maintaining resource reservations (without double counting) while it
 is being rerouted or while it is attempting to increase its
 bandwidth.  In the initial Path message, the ingress node forms a
 SESSION object, assigns a Tunnel_ID, and places its IPv4 address in
 the Extended_Tunnel_ID.  It also forms a SENDER_TEMPLATE and assigns
 a LSP_ID.  Tunnel setup then proceeds according to the normal
 procedure.
 On receipt of the Path message, the egress node sends a Resv message
 with the STYLE Shared Explicit toward the ingress node.
 When an ingress node with an established path wants to change that
 path, it forms a new Path message as follows.  The existing SESSION
 object is used.  In particular the Tunnel_ID and Extended_Tunnel_ID
 are unchanged.  The ingress node picks a new LSP_ID to form a new
 SENDER_TEMPLATE.  It creates an EXPLICIT_ROUTE object for the new
 route.  The new Path message is sent.  The ingress node refreshes
 both the old and new path messages.
 The egress node responds with a Resv message with an SE flow
 descriptor formatted as:
    <FLOWSPEC><old_FILTER_SPEC><old_LABEL_OBJECT><new_FILTER_SPEC>
    <new_LABEL_OBJECT>
 (Note that if the PHOPs are different, then two messages are sent
 each with the appropriate FILTER_SPEC and LABEL_OBJECT.)

Awduche, et al. Standards Track [Page 42] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 When the ingress node receives the Resv Message(s), it may begin
 using the new route.  It SHOULD send a PathTear message for the old
 route.

4.7. Session Attribute Object

 The Session Attribute Class is 207.  Two C_Types are defined,
 LSP_TUNNEL, C-Type = 7 and LSP_TUNNEL_RA, C-Type = 1.  The
 LSP_TUNNEL_RA C-Type includes all the same fields as the LSP_TUNNEL
 C-Type.  Additionally it carries resource affinity information.  The
 formats are as follows:

4.7.1. Format without resource affinities

 SESSION_ATTRIBUTE class = 207, LSP_TUNNEL C-Type = 7
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Setup Prio  | Holding Prio  |     Flags     |  Name Length  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 //          Session Name      (NULL padded display string)      //
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Setup Priority
       The priority of the session with respect to taking resources,
       in the range of 0 to 7.  The value 0 is the highest priority.
       The Setup Priority is used in deciding whether this session can
       preempt another session.
    Holding Priority
       The priority of the session with respect to holding resources,
       in the range of 0 to 7.  The value 0 is the highest priority.
       Holding Priority is used in deciding whether this session can
       be preempted by another session.

Awduche, et al. Standards Track [Page 43] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

    Flags
       0x01  Local protection desired
             This flag permits transit routers to use a local repair
             mechanism which may result in violation of the explicit
             route object.  When a fault is detected on an adjacent
             downstream link or node, a transit router can reroute
             traffic for fast service restoration.
       0x02  Label recording desired
             This flag indicates that label information should be
             included when doing a route record.
       0x04  SE Style desired
             This flag indicates that the tunnel ingress node may
             choose to reroute this tunnel without tearing it down.
             A tunnel egress node SHOULD use the SE Style when
             responding with a Resv message.
    Name Length
       The length of the display string before padding, in bytes.
    Session Name
       A null padded string of characters.

Awduche, et al. Standards Track [Page 44] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

4.7.2. Format with resource affinities

  SESSION_ATTRIBUTE class = 207, LSP_TUNNEL_RA C-Type = 1
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         Exclude-any                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         Include-any                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         Include-all                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Setup Prio  | Holding Prio  |     Flags     |  Name Length  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 //          Session Name      (NULL padded display string)      //
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Exclude-any
       A 32-bit vector representing a set of attribute filters
       associated with a tunnel any of which renders a link
       unacceptable.
    Include-any
       A 32-bit vector representing a set of attribute filters
       associated with a tunnel any of which renders a link acceptable
       (with respect to this test).  A null set (all bits set to zero)
       automatically passes.
    Include-all
       A 32-bit vector representing a set of attribute filters
       associated with a tunnel all of which must be present for a
       link to be acceptable (with respect to this test).  A null set
       (all bits set to zero) automatically passes.
    Setup Priority
       The priority of the session with respect to taking resources,
       in the range of 0 to 7.  The value 0 is the highest priority.
       The Setup Priority is used in deciding whether this session can
       preempt another session.

Awduche, et al. Standards Track [Page 45] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

    Holding Priority
       The priority of the session with respect to holding resources,
       in the range of 0 to 7.  The value 0 is the highest priority.
       Holding Priority is used in deciding whether this session can
       be preempted by another session.
    Flags
       0x01  Local protection desired
             This flag permits transit routers to use a local repair
             mechanism which may result in violation of the explicit
             route object.  When a fault is detected on an adjacent
             downstream link or node, a transit router can reroute
             traffic for fast service restoration.
       0x02  Label recording desired
             This flag indicates that label information should be
             included when doing a route record.
       0x04  SE Style desired
             This flag indicates that the tunnel ingress node may
             choose to reroute this tunnel without tearing it down.
             A tunnel egress node SHOULD use the SE Style when
             responding with a Resv message.
    Name Length
       The length of the display string before padding, in bytes.
    Session Name
       A null padded string of characters.

4.7.3. Procedures applying to both C-Types

 The support of setup and holding priorities is OPTIONAL.  A node can
 recognize this information but be unable to perform the requested
 operation.  The node SHOULD pass the information downstream
 unchanged.
 As noted above, preemption is implemented by two priorities.  The
 Setup Priority is the priority for taking resources.  The Holding
 Priority is the priority for holding a resource.  Specifically, the

Awduche, et al. Standards Track [Page 46] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 Holding Priority is the priority at which resources assigned to this
 session will be reserved.  The Setup Priority SHOULD never be higher
 than the Holding Priority for a given session.
 The setup and holding priorities are directly analogous to the
 preemption and defending priorities as defined in [9].  While the
 interaction of these two objects is ultimately a matter of policy,
 the following default interaction is RECOMMENDED.
 When both objects are present, the preemption priority policy element
 is used.  A mapping between the priority spaces is defined as
 follows.  A session attribute priority S is mapped to a preemption
 priority P by the formula P = 2^(14-2S).  The reverse mapping is
 shown in the following table.
       Preemption Priority     Session Attribute Priority
             0 - 3                         7
             4 - 15                        6
            16 - 63                        5
            64 - 255                       4
           256 - 1023                      3
          1024 - 4095                      2
          4096 - 16383                     1
         16384 - 65535                     0
 When a new Path message is considered for admission, the bandwidth
 requested is compared with the bandwidth available at the priority
 specified in the Setup Priority.
 If the requested bandwidth is not available a PathErr message is
 returned with an Error Code of 01, Admission Control Failure, and an
 Error Value of 0x0002.  The first 0 in the Error Value indicates a
 globally defined subcode and is not informational.  The 002 indicates
 "requested bandwidth unavailable".
 If the requested bandwidth is less than the unused bandwidth then
 processing is complete.  If the requested bandwidth is available, but
 is in use by lower priority sessions, then lower priority sessions
 (beginning with the lowest priority) MAY be preempted to free the
 necessary bandwidth.
 When preemption is supported, each preempted reservation triggers a
 TC_Preempt() upcall to local clients, passing a subcode that
 indicates the reason.  A ResvErr and/or PathErr with the code "Policy
 Control failure" SHOULD be sent toward the downstream receivers and
 upstream senders.

Awduche, et al. Standards Track [Page 47] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 The support of local-protection is OPTIONAL.  A node may recognize
 the local-protection Flag but may be unable to perform the requested
 operation.  In this case, the node SHOULD pass the information
 downstream unchanged.
 The recording of the Label subobject in the ROUTE_RECORD object is
 controlled by the label-recording-desired flag in the
 SESSION_ATTRIBUTE object.  Since the Label subobject is not needed
 for all applications, it is not automatically recorded.  The flag
 allows applications to request this only when needed.
 The contents of the Session Name field are a string, typically of
 display-able characters.  The Length MUST always be a multiple of 4
 and MUST be at least 8.  For an object length that is not a multiple
 of 4, the object is padded with trailing NULL characters.  The Name
 Length field contains the actual string length.

4.7.4. Resource Affinity Procedures

 Resource classes and resource class affinities are described in [3].
 In this document we use the briefer term resource affinities for the
 latter term.  Resource classes can be associated with links and
 advertised in routing protocols.  Resource class affinities are used
 by RSVP in two ways.  In order to be validated a link MUST pass the
 three tests below.  If the test fails a PathErr with the code "policy
 control failure" SHOULD be sent.
 When a new reservation is considered for admission over a strict node
 in an ERO, a node MAY validate the resource affinities with the
 resource classes of that link.  When a node is choosing links in
 order to extend a loose node of an ERO, the node MUST validate the
 resource classes of those links against the resource affinities.  If
 no acceptable links can be found to extend the ERO, the node SHOULD
 send a PathErr message with an error code of "Routing Problem" and an
 error value of "no route available toward destination".
 In order to be validated a link MUST pass the following three tests.
 To precisely describe the tests use the definitions in the object
 description above.  We also define
    Link-attr      A 32-bit vector representing attributes associated
                   with a link.

Awduche, et al. Standards Track [Page 48] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 The three tests are
    1. Exclude-any
       This test excludes a link from consideration if the link
       carries any of the attributes in the set.
       (link-attr & exclude-any) == 0
    2. Include-any
       This test accepts a link if the link carries any of the
       attributes in the set.
       (include-any == 0) | ((link-attr & include-any) != 0)
    3. Include-all
       This test accepts a link only if the link carries all of the
       attributes in the set.
       (include-all == 0) | (((link-attr & include-all) ^ include-
       all) == 0)
 For a link to be acceptable, all three tests MUST pass.  If the test
 fails, the node SHOULD send a PathErr message with an error code of
 "Routing Problem" and an error value of "no route available toward
 destination".
 If a Path message contains multiple SESSION_ATTRIBUTE objects, only
 the first SESSION_ATTRIBUTE object is meaningful.  Subsequent
 SESSION_ATTRIBUTE objects can be ignored and need not be forwarded.
 All RSVP routers, whether they support the SESSION_ATTRIBUTE object
 or not, SHALL forward the object unmodified.  The presence of non-
 RSVP routers anywhere between senders and receivers has no impact on
 this object.

5. Hello Extension

 The RSVP Hello extension enables RSVP nodes to detect when a
 neighboring node is not reachable.  The mechanism provides node to
 node failure detection.  When such a failure is detected it is
 handled much the same as a link layer communication failure.  This
 mechanism is intended to be used when notification of link layer
 failures is not available and unnumbered links are not used, or when
 the failure detection mechanisms provided by the link layer are not
 sufficient for timely node failure detection.

Awduche, et al. Standards Track [Page 49] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 It should be noted that node failure detection is not the same as a
 link failure detection mechanism, particularly in the case of
 multiple parallel unnumbered links.
 The Hello extension is specifically designed so that one side can use
 the mechanism while the other side does not.  Neighbor failure
 detection may be initiated at any time.  This includes when neighbors
 first learn about each other, or just when neighbors are sharing Resv
 or Path state.
 The Hello extension is composed of a Hello message, a HELLO REQUEST
 object and a HELLO ACK object.  Hello processing between two
 neighbors supports independent selection of, typically configured,
 failure detection intervals.  Each neighbor can autonomously issue
 HELLO REQUEST objects.  Each request is answered by an
 acknowledgment.  Hello Messages also contain enough information so
 that one neighbor can suppress issuing hello requests and still
 perform neighbor failure detection.  A Hello message may be included
 as a sub-message within a bundle message.
 Neighbor failure detection is accomplished by collecting and storing
 a neighbor's "instance" value.  If a change in value is seen or if
 the neighbor is not properly reporting the locally advertised value,
 then the neighbor is presumed to have reset.  When a neighbor's value
 is seen to change or when communication is lost with a neighbor, then
 the instance value advertised to that neighbor is also changed.  The
 HELLO objects provide a mechanism for polling for and providing an
 instance value.  A poll request also includes the sender's instance
 value.  This allows the receiver of a poll to optionally treat the
 poll as an implicit poll response.  This optional handling is an
 optimization that can reduce the total number of polls and responses
 processed by a pair of neighbors.  In all cases, when both sides
 support the optimization the result will be only one set of polls and
 responses per failure detection interval.  Depending on selected
 intervals, the same benefit can occur even when only one neighbor
 supports the optimization.

5.1. Hello Message Format

 Hello Messages are always sent between two RSVP neighbors.  The IP
 source address is the IP address of the sending node.  The IP
 destination address is the IP address of the neighbor node.
 The HELLO mechanism is intended for use between immediate neighbors.
 When HELLO messages are being the exchanged between immediate
 neighbors, the IP TTL field of all outgoing HELLO messages SHOULD be
 set to 1.

Awduche, et al. Standards Track [Page 50] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 The Hello message has a Msg Type of 20.  The Hello message format is
 as follows:
    <Hello Message> ::= <Common Header> [ <INTEGRITY> ]
                            <HELLO>

5.2. HELLO Object formats

 The HELLO Class is 22.  There are two C_Types defined.

5.2.1. HELLO REQUEST object

 Class = HELLO Class, C_Type = 1
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         Src_Instance                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         Dst_Instance                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.2.2. HELLO ACK object

 Class = HELLO Class, C_Type = 2
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         Src_Instance                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         Dst_Instance                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Src_Instance: 32 bits
    a 32 bit value that represents the sender's instance.  The
    advertiser maintains a per neighbor representation/value.  This
    value MUST change when the sender is reset, when the node reboots,
    or when communication is lost to the neighboring node and
    otherwise remains the same.  This field MUST NOT be set to zero
    (0).
    Dst_Instance: 32 bits
    The most recently received Src_Instance value received from the
    neighbor.  This field MUST be set to zero (0) when no value has
    ever been seen from the neighbor.

Awduche, et al. Standards Track [Page 51] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

5.3. Hello Message Usage

 The Hello Message is completely OPTIONAL.  All messages may be
 ignored by nodes which do not wish to participate in Hello message
 processing.  The balance of this section is written assuming that the
 receiver as well as the sender is participating.  In particular, the
 use of MUST and SHOULD with respect to the receiver applies only to a
 node that supports Hello message processing.
 A node periodically generates a Hello message containing a HELLO
 REQUEST object for each neighbor who's status is being tracked.  The
 periodicity is governed by the hello_interval.  This value MAY be
 configured on a per neighbor basis.  The default value is 5 ms.
 When generating a message containing a HELLO REQUEST object, the
 sender fills in the Src_Instance field with a value representing it's
 per neighbor instance.  This value MUST NOT change while the agent is
 exchanging Hellos with the corresponding neighbor.  The sender also
 fills in the Dst_Instance field with the Src_Instance value most
 recently received from the neighbor.  For reference, call this
 variable Neighbor_Src_Instance.  If no value has ever been received
 from the neighbor or this node considers communication to the
 neighbor to have been lost, the Neighbor_Src_Instance is set to zero
 (0).  The generation of a message SHOULD be suppressed when a HELLO
 REQUEST object was received from the destination node within the
 prior hello_interval interval.
 On receipt of a message containing a HELLO REQUEST object, the
 receiver MUST generate a Hello message containing a HELLO ACK object.
 The receiver SHOULD also verify that the neighbor has not reset.
 This is done by comparing the sender's Src_Instance field value with
 the previously received value.  If the Neighbor_Src_Instance value is
 zero, and the Src_Instance field is non-zero, the
 Neighbor_Src_Instance is updated with the new value.  If the value
 differs or the Src_Instance field is zero, then the node MUST treat
 the neighbor as if communication has been lost.
 The receiver of a HELLO REQUEST object SHOULD also verify that the
 neighbor is reflecting back the receiver's Instance value.  This is
 done by comparing the received Dst_Instance field with the
 Src_Instance field value most recently transmitted to that neighbor.
 If the neighbor continues to advertise a wrong non-zero value after a
 configured number of intervals, then the node MUST treat the neighbor
 as if communication has been lost.
 On receipt of a message containing a HELLO ACK object, the receiver
 MUST verify that the neighbor has not reset.  This is done by
 comparing the sender's Src_Instance field value with the previously

Awduche, et al. Standards Track [Page 52] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 received value.  If the Neighbor_Src_Instance value is zero, and the
 Src_Instance field is non-zero, the Neighbor_Src_Instance is updated
 with the new value.  If the value differs or the Src_Instance field
 is zero, then the node MUST treat the neighbor as if communication
 has been lost.
 The receiver of a HELLO ACK object MUST also verify that the neighbor
 is reflecting back the receiver's Instance value.  If the neighbor
 advertises a wrong value in the Dst_Instance field, then a node MUST
 treat the neighbor as if communication has been lost.
 If no Instance values are received, via either REQUEST or ACK
 objects, from a neighbor within a configured number of
 hello_intervals, then a node MUST presume that it cannot communicate
 with the neighbor.  The default for this number is 3.5.
 When communication is lost or presumed to be lost as described above,
 a node MAY re-initiate HELLOs.  If a node does re-initiate it MUST
 use a Src_Instance value different than the one advertised in the
 previous HELLO message.  This new value MUST continue to be
 advertised to the corresponding neighbor until a reset or reboot
 occurs, or until another communication failure is detected.  If a new
 instance value has not been received from the neighbor, then the node
 MUST advertise zero in the Dst_instance value field.

5.4. Multi-Link Considerations

 As previously noted, the Hello extension is targeted at detecting
 node failures not per link failures.  When there is only one link
 between neighboring nodes or when all links between a pair of nodes
 fail, the distinction between node and link failures is not really
 meaningful and handling of such failures has already been covered.
 When there are multiple links shared between neighbors, there are
 special considerations.  When the links between neighbors are
 numbered, then Hellos MUST be run on each link and the previously
 described mechanisms apply.
 When the links are unnumbered, link failure detection MUST be
 provided by some means other than Hellos.  Each node SHOULD use a
 single Hello exchange with the neighbor.  The case where all links
 have failed, is the same as the no received value case mentioned in
 the previous section.

Awduche, et al. Standards Track [Page 53] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

5.5. Compatibility

 The Hello extension does not affect the processing of any other RSVP
 message.  The only effect is to allow a link (node) down event to be
 declared sooner than it would have been.  RSVP response to that
 condition is unchanged.
 The Hello extension is fully backwards compatible.  The Hello class
 is assigned a class value of the form 0bbbbbbb.  Depending on the
 implementation, implementations that do not support the extension
 will either silently discard Hello messages or will respond with an
 "Unknown Object Class" error.  In either case the sender will fail to
 see an acknowledgment for the issued Hello.

6. Security Considerations

 In principle these extensions to RSVP pose no security exposures over
 and above RFC 2205[1].  However, there is a slight change in the
 trust model.  Traffic sent on a normal RSVP session can be filtered
 according to source and destination addresses as well as port
 numbers.  In this specification, filtering occurs only on the basis
 of an incoming label.  For this reason an administration may wish to
 limit the domain over which LSP tunnels can be established.  This can
 be accomplished by setting filters on various ports to deny action on
 a RSVP path message with a SESSION object of type LSP_TUNNEL_IPv4 (7)
 or LSP_TUNNEL_IPv6 (8).

7. IANA Considerations

 IANA assigns values to RSVP protocol parameters.  Within the current
 document an EXPLICIT_ROUTE object and a ROUTE_RECORD object are
 defined.  Each of these objects contain subobjects.  This section
 defines the rules for the assignment of subobject numbers.  This
 section uses the terminology of BCP 26 "Guidelines for Writing an
 IANA Considerations Section in RFCs" [15].
 EXPLICIT_ROUTE Subobject Type
    EXPLICIT_ROUTE Subobject Type is a 7-bit number that identifies
    the function of the subobject.  There are no range restrictions.
    All possible values are available for assignment.
    Following the policies outlined in [15], subobject types in the
    range 0 - 63 (0x00 - 0x3F) are allocated through an IETF Consensus
    action, codes in the range 64 - 95 (0x40 - 0x5F) are allocated as
    First Come First Served, and codes in the range 96 - 127 (0x60 -
    0x7F) are reserved for Private Use.

Awduche, et al. Standards Track [Page 54] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 ROUTE_RECORD Subobject Type
    ROUTE_RECORD Subobject Type is an 8-bit number that identifies the
    function of the subobject.  There are no range restrictions.  All
    possible values are available for assignment.
    Following the policies outlined in [15], subobject types in the
    range 0 - 127 (0x00 - 0x7F) are allocated through an IETF
    Consensus action, codes in the range 128 - 191 (0x80 - 0xBF) are
    allocated as First Come First Served, and codes in the range 192 -
    255 (0xC0 - 0xFF) are reserved for Private Use.
    The following assignments are made in this document.

7.1. Message Types

 Message Message
 Number  Name
   20    Hello

7.2. Class Numbers and C-Types

 Class   Class
 Number  Name
   1     SESSION
         Class Types or C-Types:
                7       LSP Tunnel IPv4
                8       LSP Tunnel IPv6
   10    FILTER_SPEC
         Class Types or C-Types:
                7       LSP Tunnel IPv4
                8       LSP Tunnel IPv6
   11    SENDER_TEMPLATE
         Class Types or C-Types:
                7       LSP Tunnel IPv4
                8       LSP Tunnel IPv6

Awduche, et al. Standards Track [Page 55] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

   16    RSVP_LABEL
         Class Types or C-Types:
                1       Type 1 Label
   19    LABEL_REQUEST
         Class Types or C-Types:
                1       Without Label Range
                2       With ATM Label Range
                3       With Frame Relay Label Range
   20    EXPLICIT_ROUTE
         Class Types or C-Types:
                1       Type 1 Explicit Route
   21    ROUTE_RECORD
         Class Types or C-Types:
                1       Type 1 Route Record
   22    HELLO
         Class Types or C-Types:
                1       Request
                2       Acknowledgment
  207    SESSION_ATTRIBUTE
         Class Types or C-Types:
                1       LSP_TUNNEL_RA
                7       LSP Tunnel

Awduche, et al. Standards Track [Page 56] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

7.3. Error Codes and Globally-Defined Error Value Sub-Codes

 The following list extends the basic list of Error Codes and Values
 that are defined in [RFC2205].
 Error Code    Meaning
   24          Routing Problem
               This Error Code has the following globally-defined
               Error Value sub-codes:
                1       Bad EXPLICIT_ROUTE object
                2       Bad strict node
                3       Bad loose node
                4       Bad initial subobject
                5       No route available toward
                         destination
                6       Unacceptable label value
                7       RRO indicated routing loops
                8       MPLS being negotiated, but a
                        non-RSVP-capable router stands
                          in the path
                9       MPLS label allocation failure
               10       Unsupported L3PID
   25          Notify Error
              This Error Code has the following globally-defined
              Error Value sub-codes:
                1       RRO too large for MTU
                2       RRO Notification
                3       Tunnel locally repaired

7.4. Subobject Definitions

 Subobjects of the EXPLICIT_ROUTE object with C-Type 1:
        1       IPv4 prefix
        2       IPv6 prefix
       32       Autonomous system number

Awduche, et al. Standards Track [Page 57] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 Subobjects of the RECORD_ROUTE object with C-Type 1:
        1       IPv4 address
        2       IPv6 address
        3       Label

8. Intellectual Property Considerations

 The IETF has been notified of intellectual property rights claimed in
 regard to some or all of the specification contained in this
 document.  For more information consult the online list of claimed
 rights.

9. Acknowledgments

 This document contains ideas as well as text that have appeared in
 previous Internet Drafts.  The authors of the current document wish
 to thank the authors of those drafts.  They are Steven Blake, Bruce
 Davie, Roch Guerin, Sanjay Kamat, Yakov Rekhter, Eric Rosen, and Arun
 Viswanathan.  We also wish to thank Bora Akyol, Yoram Bernet and Alex
 Mondrus for their comments on this document.

10. References

 [1]  Braden, R., Zhang, L., Berson, S., Herzog, S. and S. Jamin,
      "Resource ReSerVation Protocol (RSVP) -- Version 1, Functional
      Specification", RFC 2205, September 1997.
 [2]  Rosen, E., Viswanathan, A. and R. Callon, "Multiprotocol Label
      Switching Architecture", RFC 3031, January 2001.
 [3]  Awduche, D., Malcolm, J., Agogbua, J., O'Dell and J. McManus,
      "Requirements for Traffic Engineering over MPLS", RFC 2702,
      September 1999.
 [4]  Wroclawski, J., "Specification of the Controlled-Load Network
      Element Service", RFC 2211, September 1997.
 [5]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D.,
      Li, T. and A. Conta, "MPLS Label Stack Encoding", RFC 3032,
      January 2001.
 [6]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [7]  Almquist, P., "Type of Service in the Internet Protocol Suite",
      RFC 1349, July 1992.

Awduche, et al. Standards Track [Page 58] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

 [8]  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.
 [9]  Herzog, S., "Signaled Preemption Priority Policy Element", RFC
      2751, January 2000.
 [10] Awduche, D., Hannan, A. and X. Xiao, "Applicability Statement
      for Extensions to RSVP for LSP-Tunnels", RFC 3210, December
      2001.
 [11] Wroclawski, J., "The Use of RSVP with IETF Integrated Services",
      RFC 2210, September 1997.
 [12] Postel, J., "Internet Control Message Protocol", STD 5, RFC 792,
      September 1981.
 [13] Mogul, J. and S. Deering, "Path MTU Discovery", RFC 1191,
      November 1990.
 [14] Conta, A. and S. Deering, "Internet Control Message Protocol
      (ICMPv6) for the Internet Protocol Version 6 (IPv6)", RFC 2463,
      December 1998.
 [15] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
      Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
 [16] Bernet, Y., Smiht, A. and B. Davie, "Specification of the Null
      Service Type", RFC 2997, November 2000.

Awduche, et al. Standards Track [Page 59] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

11. Authors' Addresses

 Daniel O. Awduche
 Movaz Networks, Inc.
 7926 Jones Branch Drive, Suite 615
 McLean, VA 22102
 Voice: +1 703-298-5291
 EMail: awduche@movaz.com
 Lou Berger
 Movaz Networks, Inc.
 7926 Jones Branch Drive, Suite 615
 McLean, VA 22102
 Voice: +1 703 847 1801
 EMail: lberger@movaz.com
 Der-Hwa Gan
 Juniper Networks, Inc.
 385 Ravendale Drive
 Mountain View, CA 94043
 EMail: dhg@juniper.net
 Tony Li
 Procket Networks
 3910 Freedom Circle, Ste. 102A
 Santa Clara CA 95054
 EMail: tli@procket.com
 Vijay Srinivasan
 Cosine Communications, Inc.
 1200 Bridge Parkway
 Redwood City, CA 94065
 Voice: +1 650 628 4892
 EMail: vsriniva@cosinecom.com
 George Swallow
 Cisco Systems, Inc.
 250 Apollo Drive
 Chelmsford, MA 01824
 Voice: +1 978 244 8143
 EMail: swallow@cisco.com

Awduche, et al. Standards Track [Page 60] RFC 3209 Extensions to RSVP for LSP Tunnels December 2001

12. Full 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.

Awduche, et al. Standards Track [Page 61]

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