As per Relevance of the word explicit, we have this rfc below:
Network Working Group D.
Request for Comments: 3209 Movaz Networks, Inc
Category: Standards Track L.
D.
Juniper Networks, Inc
T.
Procket Networks, Inc
V.
Cosine Communications, Inc
G.
Cisco Systems, Inc
December 2001
RSVP-TE: Extensions to RSVP for LSP
Status of this
This document specifies an Internet standards track protocol for
Internet community, and requests discussion and suggestions
improvements. Please refer to the current edition of the "
Official Protocol Standards" (STD 1) for the standardization
and status of this protocol. Distribution of this memo is unlimited
Copyright
Copyright (C) The Internet Society (2001). All Rights Reserved
This document describes the use of RSVP (Resource
Protocol), including all the necessary extensions, to
label-switched paths (LSPs) in MPLS (Multi-Protocol Label Switching).
Since the flow along an LSP is completely identified by the
applied at the ingress node of the path, these paths may be
as tunnels. A key application of LSP tunnels is traffic
with MPLS as specified in RFC 2702.
We propose several additional objects that extend RSVP, allowing
establishment of explicitly routed label switched paths using RSVP
a signaling protocol. The result is the instantiation of label
switched tunnels which can be automatically routed away from
failures, congestion, and bottlenecks
Awduche, et al. Standards Track [Page 1]
RFC 3209 Extensions to RSVP for LSP Tunnels December 2001
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.
Section 2.9 of the MPLS architecture [2] defines a label
protocol as a set of procedures by which one Label Switched
(LSR) informs another of the meaning of labels used to
traffic between and through them. The MPLS architecture does
assume a single label distribution protocol. This document is
specification of extensions to RSVP for establishing label
paths (LSPs) in MPLS networks
Several of the new features described in this document were
by the requirements for traffic engineering over MPLS (see [3]).
particular, the extended RSVP protocol supports the instantiation
explicitly routed LSPs, with or without resource reservations.
also supports smooth rerouting of LSPs, preemption, and
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
traffic trunk are distinct though closely related concepts.
example, two LSPs between the same source and destination could
load shared to carry a single traffic trunk. Conversely
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,
LSP were capable of carrying several service classes.
applicability of these extensions is discussed further in [10].
Since the traffic that flows along a label-switched path is
by the label applied at the ingress node of the LSP, these paths
be treated as tunnels, tunneling below normal IP routing
filtering mechanisms. When an LSP is used in this way we refer to
as an LSP tunnel
LSP tunnels allow the implementation of a variety of policies
to network performance optimization. For example, LSP tunnels can
automatically or manually routed away from network failures
congestion, and bottlenecks. Furthermore, multiple parallel
tunnels can be established between two nodes, and traffic between
two nodes can be mapped onto the LSP tunnels according to
policy. Although traffic engineering (that is,
optimization of operational networks) is expected to be an
application of this specification, the extended RSVP protocol can
used in a much wider context
The purpose of this document is to describe the use of RSVP
establish LSP tunnels. The intent is to fully describe all
objects, packet formats, and procedures required to
interoperable implementations. A few new objects are also
that enhance management and diagnostics of LSP tunnels
The document also describes a means of rapid node failure
via a new HELLO message
All objects and messages described in this specification are
with respect to RSVP. This document discusses what happens when
object described here is not supported by a node
Throughout this document, the discussion will be restricted
unicast label switched paths. Multicast LSPs are left for
study
1.1.
Hosts and routers that support both RSVP [1] and Multi-Protocol
Switching [2] can associate labels with RSVP flows. When MPLS
RSVP are combined, the definition of a flow can be made
flexible. Once a label switched path (LSP) is established,
traffic through the path is defined by the label applied at
ingress node of the LSP. The mapping of label to traffic can
accomplished using a number of different criteria. The set
packets that are assigned the same label value by a specific node
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) (
[2]), and effectively define the "RSVP flow." When traffic is
onto a label-switched path in this way, we call the LSP an "
Tunnel". When labels are associated with traffic flows, it
possible for a router to identify the appropriate reservation
for a packet based on the packet's label value
The signaling protocol model uses downstream-on-demand
distribution. A request to bind labels to a specific LSP tunnel
initiated by an ingress node through the RSVP Path message. For
purpose, the RSVP Path message is augmented with a LABEL_
object. Labels are allocated downstream and distributed (
upstream) by means of the RSVP Resv message. For this purpose,
RSVP Resv message is extended with a special LABEL object.
procedures for label allocation, distribution, binding, and
are described in subsequent sections of this document
The signaling protocol model also supports explicit
capability. This is accomplished by incorporating a
EXPLICIT_ROUTE object into RSVP Path messages. The EXPLICIT_
object encapsulates a concatenation of hops which constitutes
explicitly routed path. Using this object, the paths taken
label-switched RSVP-MPLS flows can be pre-determined, independent
conventional IP routing. The explicitly routed path can
administratively specified, or automatically computed by a
entity based on QoS and policy requirements, taking
consideration the prevailing network state. In general,
computation can be control-driven or data-driven. The mechanisms
processes, and algorithms used to compute explicitly routed paths
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
domain can control the path through which traffic traverses
itself, through the MPLS network, to an egress node.
routing can be used to optimize the utilization of network
and enhance traffic oriented performance characteristics
The concept of explicitly routed label switched paths can
generalized through the notion of abstract nodes. An abstract
is a group of nodes whose internal topology is opaque to the
node of the LSP. An abstract node is said to be simple if
contains only one physical node. Using this concept of abstraction
an explicitly routed LSP can be specified as a sequence of
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
explicit path as a sequence of strict and loose routes.
combination of abstract nodes, and strict and loose
significantly enhances the flexibility of path definitions
An advantage of using RSVP to establish LSP tunnels is that
enables the allocation of resources along the path. For example
bandwidth can be allocated to an LSP tunnel using standard
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
whatsoever. Such LSPs without resource reservations can be used,
example, to carry best effort traffic. They can also be used in
other contexts, including implementation of fall-back and
policies under fault conditions, and so forth
1.2.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
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
A group of nodes whose internal topology is opaque to the
node of the LSP. An abstract node is said to be simple if
contains only one physical node
Explicitly Routed
An LSP whose path is established by a means other than normal
routing
Label Switched
The path created by the concatenation of one or more
switched hops, allowing a packet to be forwarded by
labels from an MPLS node to another MPLS node. For a more
definition see [2].
A Label Switched
Awduche, et al. Standards Track [Page 6]
RFC 3209 Extensions to RSVP for LSP Tunnels December 2001
LSP
An LSP which is used to tunnel below normal IP routing and/
filtering mechanisms
Traffic Engineered Tunnel (TE Tunnel
A set of one or more LSP Tunnels which carries a traffic trunk
Traffic
A set of flows aggregated by their service class and then
on an LSP or set of LSPs called a traffic engineered tunnel.
further discussion see [3].
2.
2.1. LSP Tunnels and Traffic Engineered
According to [1], "RSVP defines a 'session' to be a data flow with
particular destination and transport-layer protocol." However,
RSVP and MPLS are combined, a flow or session can be defined
greater flexibility and generality. The ingress node of an LSP
use a variety of means to determine which packets are assigned
particular label. Once a label is assigned to a set of packets,
label effectively defines the "flow" through the LSP. We refer
such an LSP as an "LSP tunnel" because the traffic through it
opaque to intermediate nodes along the label switched path
New RSVP SESSION, SENDER_TEMPLATE, and FILTER_SPEC objects,
LSP_TUNNEL_IPv4 and LSP_TUNNEL_IPv6 have been defined to support
LSP tunnel feature. The semantics of these objects, from
perspective of a node along the label switched path, is that
belonging to the LSP tunnel is identified solely on the basis
packets arriving from the PHOP or "previous hop" (see [1]) with
particular label value(s) assigned by this node to upstream
to the session. In fact, the IPv4(v6) that appears in the
name only denotes that the destination address is an IPv4(v6)
address. When we refer to these objects generically, we use
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
trunk over multiple paths. In the traffic engineering
such sets are called traffic engineered tunnels (TE tunnels).
enable the identification and association of such LSP tunnels,
identifiers are carried. A tunnel ID is part of the SESSION object
The SESSION object uniquely defines a traffic engineered tunnel.
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.
SENDER_TEMPLATE (or FILTER_SPEC) object together with the
object uniquely identifies an LSP
2.2. Operation of LSP
This section summarizes some of the features supported by RSVP
extended by this document related to the operation of LSP tunnels
These include: (1) the capability to establish LSP tunnels with
without QoS requirements, (2) the capability to dynamically
an established LSP tunnel, (3) the capability to observe the
route traversed by an established LSP tunnel, (4) the capability
identify and diagnose LSP tunnels, (5) the capability to preempt
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,
features are briefly described. More detailed descriptions can
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
message with a session type of LSP_TUNNEL_IPv4 or LSP_TUNNEL_IPv6
inserts a LABEL_REQUEST object into the Path message.
LABEL_REQUEST object indicates that a label binding for this path
requested and also provides an indication of the network
protocol that is to be carried over this path. The reason for
is that the network layer protocol sent down an LSP cannot be
to be IP and cannot be deduced from the L2 header, which
identifies the higher layer protocol as MPLS
If the sender node has knowledge of a route that has high
of meeting the tunnel's QoS requirements, or that makes efficient
of network resources, or that satisfies some policy criteria,
node can decide to use the route for some or all of its sessions.
do this, the sender node adds an EXPLICIT_ROUTE object to the
Path message. The EXPLICIT_ROUTE object specifies the route as
sequence of abstract nodes
If, after a session has been successfully established, the
node discovers a better route, the sender can dynamically reroute
session by simply changing the EXPLICIT_ROUTE object. If
are encountered with an EXPLICIT_ROUTE object, either because
causes a routing loop or because some intermediate routers do
support it, the sender node is notified
By adding a RECORD_ROUTE object to the Path message, the sender
can receive information about the actual route that the LSP
traverses. The sender node can also use this object to
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
be used for loop detection
Finally, a SESSION_ATTRIBUTE object can be added to Path messages
aid in session identification and diagnostics. Additional
information, such as setup and hold priorities, resource
(see [3]), and local-protection, are also included in this object
Routers along the path may use the setup and hold priorities
with SENDER_TSPEC and any POLICY_DATA objects contained in
messages as input to policy control. For instance, in the
engineering application, it is very useful to use the Path message
a means of verifying that bandwidth exists at a particular
along an entire path before preempting any lower
reservations. If a Path message is allowed to progress when
are insufficient resources, then there is a danger that
priority reservations downstream of this point will unnecessarily
preempted in a futile attempt to service this request
When the EXPLICIT_ROUTE object (ERO) is present, the Path message
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.
this case the modified ERO SHOULD be stored in the path state
in addition to the received ERO
The LABEL_REQUEST object requests intermediate routers and
nodes to provide a label binding for the session. If a node
incapable of providing a label binding, it sends a PathErr
with an "unknown object class" error. If the LABEL_REQUEST object
not supported end to end, the sender node will be notified by
first node which does not provide this support
The destination node of a label-switched path responds to
LABEL_REQUEST by including a LABEL object in its response RSVP
message. The LABEL object is inserted in the filter spec
immediately following the filter spec to which it pertains
The Resv message is sent back upstream towards the sender,
the path state created by the Path message, in reverse order.
that if the path state was created by use of an ERO, then the
message will follow the reverse path of the ERO
Each node that receives a Resv message containing a LABEL object
that label for outgoing traffic associated with this LSP tunnel.
the node is not the sender, it allocates a new label and places
label in the corresponding LABEL object of the Resv message which
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
object is the label which this node will use to identify
traffic associated with this LSP tunnel. This label also serves
shorthand for the Filter Spec. The node can now update its "
Label Map" (ILM), which is used to map incoming labeled packets to
"Next Hop Label Forwarding Entry" (NHLFE), see [2].
When the Resv message propagates upstream to the sender node,
label-switched path is effectively established
2.3. Service
This document does not restrict the type of Integrated
requests for reservations. However, an implementation SHOULD
the Controlled-Load service [4] and the Null Service [16].
2.4. Reservation
The receiver node can select from among a set of possible
styles for each session, and each RSVP session must have a
style. Senders have no influence on the choice of reservation style
The receiver can choose different reservation styles for
LSPs
An RSVP session can result in one or more LSPs, depending on
reservation style chosen
Some reservation styles, such as FF, dedicate a
reservation to an individual sender node. Other reservation styles
such as WF and SE, can share a reservation among several
nodes. The following sections discuss the different
styles and their advantages and disadvantages. A more
discussion of reservation styles can be found in [1].
2.4.1. Fixed Filter (FF)
The Fixed Filter (FF) reservation style creates a
reservation for traffic from each sender that is not shared by
senders. This style is common for applications in which traffic
each sender is likely to be concurrent and independent. The
amount of reserved bandwidth on a link for sessions using FF is
sum of the reservations for the individual senders
Because each sender has its own reservation, a unique label
assigned to each sender. This can result in a point-to-point
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)
With the Wildcard Filter (WF) reservation style, a single
reservation is used for all senders to a session. The
reservation on a link remains the same regardless of the number
senders
A single multipoint-to-point label-switched-path is created for
senders to the session. On links that senders to the session share
a single label value is allocated to the session. If there is
one sender, the LSP looks like a normal point-to-point connection
When multiple senders are present, a multipoint-to-point LSP (
reversed tree) is created
This style is useful for applications in which not all senders
traffic at the same time. A phone conference, for example, is
application where not all speakers talk at the same time. If
however, all senders send simultaneously, then there is no means
getting the proper reservations made. Either the reserved
on links close to the destination will be less than what is
or then the reserved bandwidth on links close to some senders will
greater than what is required. This restricts the applicability
WF for traffic engineering purposes
Furthermore, because of the merging rules of WF, EXPLICIT_
objects cannot be used with WF reservations. As a result of
issue and the lack of applicability to traffic engineering, use of
is not considered in this document
2.4.3. Shared Explicit (SE)
The Shared Explicit (SE) style allows a receiver to
specify the senders to be included in a reservation. There is
single reservation on a link for all the senders listed.
each sender is explicitly listed in the Resv message,
labels may be assigned to different senders, thereby
separate LSPs
SE style reservations can be provided using multipoint-to-
label-switched-path or LSP per sender. Multipoint-to-point LSPs
be used when path messages do not carry the EXPLICIT_ROUTE object,
when Path messages have identical EXPLICIT_ROUTE objects. In
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
point in the network topology. When Path messages have
EXPLICIT_ROUTE objects, separate LSPs for each EXPLICIT_ROUTE
must be established
2.5. Rerouting Traffic Engineered
One of the requirements for Traffic Engineering is the capability
reroute an established TE tunnel under a number of conditions,
on administrative policy. For example, in some contexts,
administrative policy may dictate that a given TE tunnel is to
rerouted when a more "optimal" route becomes available.
important context when TE tunnel reroute is usually required is
failure of a resource along the TE tunnel's established path.
some policies, it may also be necessary to return the TE tunnel
its original path when the failed resource becomes re-activated
In general, it is highly desirable not to disrupt traffic,
adversely impact network operations while TE tunnel rerouting is
progress. This adaptive and smooth rerouting
necessitates establishing a new LSP tunnel and transferring
from the old LSP tunnel onto it before tearing down the old
tunnel. This concept is called "make-before-break." A problem
arise because the old and new LSP tunnels might compete with
other for resources on network segments which they have in common
Depending on availability of resources, this competition can
Admission Control to prevent the new LSP tunnel from
established. An advantage of using RSVP to establish LSP tunnels
that it solves this problem very elegantly
To support make-before-break in a smooth fashion, it is
that on links that are common to the old and new LSPs, resources
by the old LSP tunnel should not be released before traffic
transitioned to the new LSP tunnel, and reservations should not
counted twice because this might cause Admission Control to
the new LSP tunnel
A similar situation can arise when one wants to increase
bandwidth of a TE tunnel. The new reservation will be for the
amount needed, but the actual allocation needed is only the
between the new and old bandwidth. If policy is being applied
PATH messages by intermediate nodes, then a PATH message
too much bandwidth will be rejected. In this situation
increasing the bandwidth request without changing
SENDER_TEMPLATE, could result in a tunnel being torn down,
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
reservation style naturally accommodates smooth transitions
bandwidth and routing. The idea is that the old and new LSP
share resources along links which they have in common.
LSP_TUNNEL SESSION object is used to narrow the scope of the
session to the particular TE tunnel in question. To
identify a TE tunnel, we use the combination of the destination
address (an address of the node which is the egress of the tunnel),
Tunnel ID, and the tunnel ingress node's IP address, which is
in the Extended Tunnel ID field
During the reroute or bandwidth-increase operation, the
ingress needs to appear as two different senders to the RSVP session
This is achieved by the inclusion of the "LSP ID", which is
in the SENDER_TEMPLATE and FILTER_SPEC objects. Since the
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
new SENDER_TEMPLATE. The ingress node then creates a new ERO
define the new path. Thereafter the node sends a new Path
using the original SESSION object and the new SENDER_TEMPLATE
ERO. It continues to use the old LSP and refresh the old
message. On links that are not held in common, the new Path
is treated as a conventional new LSP tunnel setup. On links held
common, the shared SESSION object and SE style allow the LSP to
established sharing resources with the old LSP. Once the
node receives a Resv message for the new LSP, it can
traffic to it and tear down the old LSP
To effect a bandwidth-increase, a new Path Message with a new LSP_
can be used to attempt a larger bandwidth reservation while
current LSP_ID continues to be refreshed to ensure that
reservation is not lost if the larger reservation fails
2.6. Path
Standard RSVP [1] and Int-Serv [11] provide the RSVP sender with
minimum MTU available between the sender and the receiver. This
MTU identification capability is also provided for LSPs
via RSVP
Path MTU information is carried, depending on which is present,
the Integrated Services or Null Service objects. When
Integrated Services objects, path MTU is provided based on
procedures defined in [11]. Path MTU identification when using
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
check which IP packets exceed the path MTU. For packets that
the path MTU, the sender either fragments the packets or, when the
datagram has the "Don't Fragment" bit set, issues an ICMP
unreachable message. This path MTU related handling is also
for LSPs established via RSVP
The following algorithm applies to all unlabeled IP datagrams and
any labeled packets which the node knows to be IP datagrams, to
labels need to be added before forwarding. For labeled packets
bottom of stack is found, the IP header examined
Using the terminology defined in [5], an LSR MUST execute
following algorithm
1. Let N be the number of bytes in the label stack (i.e, 4 times
number of label stack entries) including labels to be added
this node
2. Let M be the smaller of the "Maximum Initially Labeled IP
Size" or of (Path MTU - N).
When the size of an IPv4 datagram (without labels) exceeds the
of M
If the DF bit is not set in the IPv4 header,
(a) the datagram MUST be broken into fragments, each of
size is no greater than M,
(b) each fragment MUST be labeled and then forwarded
If the DF bit is set in the IPv4 header,
(a) the datagram MUST NOT be
(b) Create an ICMP Destination Unreachable Message
i. set its Code field [12] to "Fragmentation Required
DF Set",
ii. set its Next-Hop MTU field [13] to
(c) If possible, transmit the ICMP Destination
Message to the source of the of the discarded datagram
When the size of an IPv6 datagram (without labels) exceeds
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
(b) Create an ICMP Packet too Big Message with the Next-
link MTU field [14] set to
(c) If possible, transmit the ICMP Packet too Big Message
the source of the of the discarded datagram
3. LSP Tunnel related Message
Five new objects are defined in this section
Object name Applicable RSVP
--------------- ------------------------
LABEL_REQUEST
LABEL
EXPLICIT_ROUTE
RECORD_ROUTE Path,
SESSION_ATTRIBUTE
New C-Types are also assigned for the SESSION, SENDER_TEMPLATE,
FILTER_SPEC, objects
Detailed descriptions of the new objects are given in later sections
All new objects are OPTIONAL with respect to RSVP. An
can choose to support a subset of objects. However,
LABEL_REQUEST and LABEL objects are mandatory with respect to
specification
The LABEL and RECORD_ROUTE objects, are sender specific. In
messages they MUST appear after the associated FILTER_SPEC and
to any subsequent FILTER_SPEC
The relative placement of EXPLICIT_ROUTE, LABEL_REQUEST,
SESSION_ATTRIBUTE objects is simply a recommendation. The
of these objects is not important, so an implementation MUST
prepared to accept objects in any order
3.1. Path
The format of the Path message is as follows
::= [ <INTEGRITY> ]
[ <EXPLICIT_ROUTE> ]
[ ATTRIBUTE> ]
Awduche, et al. Standards Track [Page 15]
RFC 3209 Extensions to RSVP for LSP Tunnels December 2001
[ ... ]
descriptor
descriptor> ::= TEMPLATE>
[ ]
[ ]
3.2. Resv
The format of the Resv message is as follows
::= [ <INTEGRITY> ]
[ ] [ ]
[ ... ]
