MPLS Working Group Bilel Jamoussi, Editor
Internet Draft Nortel Networks Corp.
Expiration Date: March 2000
September 1999
Constraint-Based LSP Setup using LDP
draft-ietf-mpls-cr-ldp-03.txt
Status of this Memo
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Abstract
Label Distribution Protocol (LDP) is defined in [1] for distribution
of labels inside one MPLS domain. One of the most important
services that may be offered using MPLS in general and LDP in
particular is support for constraint-based routing of traffic across
the routed network. Constraint-based routing offers the opportunity
to extend the information used to setup paths beyond what is
available for the routing protocol. For instance, an LSP can be
setup based on explicit route constraints, QoS constraints, and
other constraints. Constraint-based routing (CR) is a mechanism used
to meet Traffic Engineering requirements that have been proposed by
[2], [3] and [4]. These requirements may be met by extending LDP for
support of constraint-based routed label switched paths (CR-LSPs).
Other uses for CR-LSPs include MPLS-based VPNs.
This draft specifies mechanisms and TLVs for support of CR-LSPs
using LDP.
Jamoussi, et. al. draft-ietf-mpls-crldp-03.txt 1 Internet Draft Constraint-Based LSP Setup using LDP September, 1999
Table of Contents
1. Introduction....................................................3
2. Constraint-based Routing Overview...............................3
2.1 Strict and Loose Explicit Routes...............................4
2.2 Traffic Characteristics........................................4
2.3 Pre-emption....................................................5
2.4 Route Pinning..................................................5
2.5 Resource Class.................................................5
3. Solution Overview...............................................6
3.1 Required Messages and TLVs.....................................7
3.2 Label Request Message..........................................7
3.3 Label Mapping Message..........................................8
3.4 Notification Message...........................................8
3.5 Release , Withdraw, and Abort Messages.........................9
4. Protocol Specification..........................................9
4.1 Explicit Route TLV (ER-TLV)...................................10
4.2 Explicit Route Hop TLV (ER-Hop TLV)...........................10
4.3 Traffic Parameters TLV........................................11
4.3.1 Semantics...................................................13
4.3.1.1 Frequency.................................................13
4.3.1.2 Peak Rate.................................................13
4.3.1.3 Committed Rate............................................14
4.3.1.4 Excess Burst Size.........................................14
4.3.1.5 Peak Rate Token Bucket....................................14
4.3.1.6 Committed Data Rate Token Bucket..........................14
4.3.1.7 Weight....................................................15
4.3.2 Procedures..................................................15
4.3.2.1 Label Request Message.....................................15
4.3.2.2 Label Mapping Message.....................................16
4.3.2.3 Notification Message......................................16
4.4 Preemption TLV................................................16
4.5 LSPID TLV.....................................................17
4.6 Resource Class (Color) TLV....................................18
4.7 ER-Hop semantics..............................................19
4.7.1. ER-Hop 1: The IPv4 prefix..................................19
4.7.2. ER-Hop 2: The IPv6 address.................................20
4.7.3. ER-Hop 3: The autonomous system number....................20
4.7.4. ER-Hop 4: LSPID............................................21
4.8. Processing of the Explicit Route TLV.........................22
4.8.1. Selection of the next hop..................................22
4.8.2. Adding ER-Hops to the explicit route TLV...................23
4.9 Route Pinning TLV.............................................24
4.10 CR-LSP FEC Element...........................................24
4.11 Error subcodes...............................................25
5. Security.......................................................25
6. Acknowledgments................................................25
7. Intellectual Property Consideration............................26
8. References.....................................................26
9. Author's Addresses.............................................26
Appendix A: CR-LSP Establishment Examples.........................29
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A.1 Strict Explicit Route Example.................................29
A.2 Node Groups and Specific Nodes Example........................30
Appendix B. QoS Service Examples..................................33
B.1 Service Examples..............................................33
B.2 Establishing CR-LSP Supporting Real-Time Applications.........34
B.3 Establishing CR-LSP Supporting Delay Insensitive Applications.35
Appendix C. LSP Modification Using CR-LDP.........................36
C.1 Introduction..................................................36
C.2 Basic Procedure...............................................37
C.3 Priority Handling.............................................38
C.4 Modification Failure Case Handling............................39
1. Introduction
The need for constraint-based routing (CR) in MPLS has been explored
elsewhere [3], [2], and [4]. Explicit routing is a subset of the
more general constraint-based routing function. At the MPLS WG
meeting held during the Washington IETF (December 1997) there was
consensus that LDP should support explicit routing of LSPs with
provision for indication of associated (forwarding) priority. In
the Chicago meeting (August 1998), a decision was made that support
for explicit path setup in LDP will be moved to a separate document.
This document provides that support and it has been accepted as a
working document in the Orlando meeting (December 1998).
This specification proposes an end-to-end setup mechanism of a
constraint-based routed LSP (CR-LSP) initiated by the ingress LSR.
We also specify mechanisms to provide means for reservation of
resources using LDP.
This document introduce TLVs and procedures that provide support
for:
- Strict and Loose Explicit Routing
- Specification of Traffic Parameters
- Route Pinning
- CR-LSP Pre-emption though setup/holding priorities
- Handling Failures
- LSPID
- Resource Class
Section 2 introduces the various constraints defined in this
specification. Section 3 outlines the CR-LDP solution. Section 4
defines the TLVs and procedures used to setup constraint-based
routed label switched paths. Appendix A provides several examples
of CR-LSP path setup. Appendix B provides Service Definition
Examples.
2. Constraint-based Routing Overview
Constraint-based routing is a mechanism that supports the Traffic
Engineering requirements defined in [4]. Explicit Routing is a
subset of the more general constraint-based routing where the
Jamoussi, et. al. draft-ietf-mpls-crldp-03.txt 3 Internet Draft Constraint-Based LSP Setup using LDP September, 1999
constraint is the explicit route (ER). Other constraints are defined
to provide a network operator with control over the path taken by an
LSP. This section is an overview of the various constraints
supported by this specification.
2.1 Strict and Loose Explicit Routes
Like any other LSP a CR-LSP is a path through an MPLS network. The
difference is that while other paths are setup solely based on
information in routing tables or from a management system, the
constraint-based route is calculated at one point at the edge of
network based on criteria, including but not limited to routing
information. The intention is that this functionality shall give
desired special characteristics to the LSP in order to better
support the traffic sent over the LSP. The reason for setting up CR-
LSPs might be that one wants to assign certain bandwidth or other
Service Class characteristics to the LSP, or that one wants to make
sure that alternative routes use physically separate paths through
the network.
An explicit route is represented in a Label Request Message as a
list of nodes or groups of nodes along the constraint-based route.
When the CR-LSP is established, all or a subset of the nodes in a
group may be traversed by the LSP. Certain operations to be
performed along the path can also be encoded in the constraint-based
route.
The capability to specify, in addition to specified nodes, groups of
nodes, of which a subset will be traversed by the CR-LSP, allows the
system a significant amount of local flexibility in fulfilling a
request for a constraint-based route. This allows the generator of
the constraint-based route to have some degree of imperfect
information about the details of the path.
The constraint-based route is encoded as a series of ER-Hops
contained in a constraint-based route TLV. Each ER-Hop may identify
a group of nodes in the constraint-based route. A constraint-based
route is then a path including all of the identified groups of nodes
in the order in which they appear in the TLV.
To simplify the discussion, we call each group of nodes an abstract
node. Thus, we can also say that a constraint-based route is a path
including all of the abstract nodes, with the specified operations
occurring along that path.
2.2 Traffic Characteristics
The traffic characteristics of a path are described in the Traffic
Parameters TLV in terms of a peak rate, committed rate, and service
granularity. The peak and committed rates describe the bandwidth
constraints of a path while the service granularity can be used to
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specify a constraint on the delay variation that the CR-LDP MPLS
domain may introduce to a path's traffic.
2.3 Pre-emption
CR-LDP signals the resources required by a path on each hop of the
route. If a route with sufficient resources can not be found,
existing paths may be rerouted to reallocate resources to the new
path. This is the process of path pre-emption. Setup and holding
priorities are used to rank existing paths (holding priority) and
the new path (setup priority) to determine if the new path can pre-
empt an existing path.
The setupPriority of a new CR-LSP and the holdingPriority attributes
of the existing CR-LSP are used to specify priorities. Signaling a
higher holding priority express that the path, once it has been
established, should have a lower chance of being pre-empted.
Signaling a higher setup priority expresses the expectation that, in
the case that resource are unavailable, the path is more likely to
pre-empt other paths. The exact rules determining bumping are an
aspect of network policy.
The allocation of setup and holding priority values to paths is an
aspect of network policy.
The setup and holding priority values range from zero (0) to seven
(7). The value zero (0) is the priority assigned to the most
important path. It is referred to as the highest priority. Seven (7)
is the priority for the least important path. The use of default
priority values is an aspect of network policy.
The setupPriority of a CR-LSP should not be higher (numerically
less) than its holdingPriority since it might bump an LSP and be
bumped by the next _equivalent_ request.
2.4 Route Pinning
Route pinning is applicable to segments of an LSP that are loosely
routed - i.e. those segments which are specified with a next hop
with the `L' bit set or where the next hop is an _abstract node_. A
CR-LSP may be setup using route pinning if it is undesirable to
change the path used by an LSP even when a better next hop becomes
available at some LSR along the loosely routed portion of the LSP.
2.5 Resource Class
The network operator may classify network resources in various ways.
These classes are also known as _colors_ or _administrative groups_.
When a CR-LSP is being established, it's necessary to indicate which
resource classes the CR-LSP can draw from.
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3. Solution Overview
CR-LSP over LDP Specification is designed with the following goals:
1. Meet the requirements outlined in [4] for performing traffic
engineering and provide a solid foundation for performing
more general constraint-based routing.
2. Build on already specified functionality that meets the
requirements whenever possible. Hence, this specification is
based on [1].
3. Keep the solution simple.
In this document, support for unidirectional point-to-point CR-LSPs
is specified. Support for point-to-multipoint, multipoint-to-point,
is for further study (FFS).
Support for constraint-based routed LSPs in this specification
depends on the following minimal LDP behaviors as specified in [1]:
- Use of Basic and/or Extended Discovery Mechanisms.
- Use of the Label Request Message defined in [1] in downstream
on demand label advertisement mode with ordered control.
- Use of the Label Mapping Message defined in [1] in downstream
on demand mode with ordered control.
- Use of the Notification Message defined in [1].
- Use of the Withdraw and Release Messages defined in [1].
- Use of the Loop Detection (in the case of loosely routed
segments of a CR-LSP) mechanisms defined in [1].
In addition, the following functionality is added to what's defined
in [1]:
- The Label Request Message used to setup a CR-LSP includes one
or more CR-TLVs defined in Section 4. For instance, the Label
Request Message may include the ER-TLV.
- An LSR implicitly infers ordered control from the existence of
one or more CR-TLVs in the Label Request Message. This means
that the LSR can still be configured for independent control
for LSPs established as a result of dynamic routing. However,
when a Label Request Message includes one or more of the CR-
TLVs, then ordered control is used to setup the CR-LSP. Note
that this is also true for the loosely routed parts of a CR-
LSP.
- New status codes are defined to handle error notification for
failure of established paths specified in the CR-TLVs.
Optional TLVs are not required in the CR-LDP messages for the
messages to be compliant with the protocol. Optional parameters MAY
be required for a particular operation to work (or work correctly),
however.
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Examples of CR-LSP establishment are given in Appendix A to
illustrate how the mechanisms described in this draft work.
3.1 Required Messages and TLVs
Any Messages, TLVs, and procedures not defined explicitly in this
document are defined in the LDP Specification [1]. The state
transitions, which relate to CR-LDP messages, can be found in [5].
The following subsections are meant as a cross-reference to the [1]
document and indication of additional functionality beyond what's
defined in [1] where necessary.
3.2 Label Request Message
The Label Request Message is as defined in 3.5.8 of [1] with the
following modifications (required only if any of the CR-TLVs is
included in the Label Request Message):
- Only a single FEC-TLV may be included in the Label Request
Message. The CR-LSP FEC TLV should be used.
- The Optional Parameters TLV includes the definition of any of
the Constraint-based TLVs specified in Section 4.
- The Procedures to handle the Label Request Message are
augmented by the procedures for processing of the CR-TLVs as
defined in Section 4.
The encoding for the CR-LDP Label Request Message is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Request (0x0401) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSPID TLV (CR-LDP, mandatory) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ER-TLV (CR-LDP, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic TLV (CR-LDP, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pinning TLV (CR-LDP, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Resource Class TLV (CR-LDP, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pre-emption TLV (CR-LDP, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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3.3 Label Mapping Message
The Label Mapping Message is as defined in 3.5.7 of [1] with the
following modifications:
- Only a single Label-TLV may be included in the Label Mapping
Message.
- The Label Mapping Message Procedures are limited to downstream
on demand ordered control mode.
A Mapping message is transmitted by a downstream LSR to an upstream
LSR under one of the following conditions:
1. The LSR is the egress end of the CR-LSP and an upstream
mapping has been requested.
2. The LSR received a mapping from its downstream next hop LSR
for an CR-LSP for which an upstream request is still
pending.
The encoding for the CR-LDP Label Mapping Message is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Mapping (0x0400) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Request Message ID TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSPID TLV (CR-LDP, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic TLV (CR-LDP, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.4 Notification Message
The Notification Message is as defined in Section 3.5.1 of [1] and
the Status TLV encoding is as defined in Section 3.4.6 of [1].
Establishment of an CR-LSP may fail for a variety of reasons. All
such failures are considered advisory conditions and they are
signaled by the Notification Message.
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Notification Messages carry Status TLVs to specify events being
signaled. New status codes are defined in Section 4.11 to signal
error notifications associated with the establishment of a CR-LSP
and the processing of the CR-TLV.
The Notification Message may carry the LSPID TLV of the
corresponding CR-LSP.
Notification Messages MUST be forwarded toward the LSR originating
the Label Request at each hop and at any time that procedures in
this specification - or in [1] - specify sending of a Notification
Message in response to a Label Request Message.
The encoding of the notification message is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Notification (0x0001) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status (TLV) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.5 Release , Withdraw, and Abort Messages
The Label Release , Label Withdraw, and Label Abort Request Messages
are used as specified in [1]. These messages may also carry the
LSPID TLV.
4. Protocol Specification
The Label Request Message defined in [1] optionally carries one or
more of the optional Constraint-based Routing TLVs (CR-TLVs) defined
in this section. If needed, other constraints can be supported later
through the definition of new TLVs. In this specification, the
following TLVs are defined:
- Explicit Route TLV
- Explicit Route Hop TLV
- Traffic Parameters TLV
- Preemption TLV
- LSPID TLV
- Route Pinning TLV
- Resource Class TLV
- CR-LSP FEC TLV
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4.1 Explicit Route TLV (ER-TLV)
The ER-TLV is an object that specifies the path to be taken by the
LSP being established. It is composed of one or more Explicit Route
Hop TLVs (ER-Hop TLVs) defined in Section 4.2.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| ER-TLV (0x0800) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ER-Hop TLV 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ER-Hop TLV 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ............ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ER-Hop TLV n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
A two-byte field carrying the value of the ER-TLV type whichis
0x800.
Length
Specifies the length of the value field in bytes.
ER-Hop TLVs
One or more ER-Hop TLVs defined in Section 4.2.
4.2 Explicit Route Hop TLV (ER-Hop TLV)
The contents of an ER-TLV are a series of variable length ER-Hop
TLVs.
A node receiving a label request message including an ER-Hop type
that is not supported should not progress the label request message
to the downstream LSR and should send back a _No Route_ Notification
Message.
Each ER-Hop TLV has the form:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| ER-Hop-Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Content // |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
ER-Hop Type
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A fourteen-bit field indicating the type of contents of the ER-
Hop. Currently defined values are:
Value Type
----- ------------------------
0x801 IPv4 prefix
0x802 IPv6 prefix
0x803 Autonomous system number
0x804 LSPID
Length
Specifies the length of the value field in bytes.
L bit
The L bit in the ER-Hop 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 ER-Hop attribute is loose then it is a
_loose ER-Hop._ Otherwise, it's a _strict ER-Hop._ Further,
we say that the abstract node of a strict or loose ER-Hop 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 prior node MUST include
only network nodes from the strict node and its prior abstract
node.
The path between a loose node and its prior node MAY include
other network nodes, which are not part of the strict node or
its prior abstract node.
Contents
A variable length field containing a node or abstract node
which is one of the consecutive nodes that make up the
explicitly routed LSP.
4.3 Traffic Parameters TLV
The following sections describe the CR-LSP Traffic Parameters. The
required characteristics of a CR-LSP are expressed by the Traffic
Parameter values.
A Traffic Parameters TLV, is used to signal the Traffic Parameter
values. The Traffic Parameters are defined in the subsequent
sections.
The Traffic Parameters TLV contains a Flags field, a Frequency, a
Weight, and the five Traffic Parameters PDR, PBS, CDR, CBS, EBS.
The Traffic Parameters TLV is shown below:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Traf. Param. TLV (0x0810)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Frequency | Reserved | Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Peak Data Rate (PDR) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Peak Burst Size (PBS) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Committed Data Rate (CDR) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Committed Burst Size (CBS) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Excess Burst Size (EBS) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
A fourteen-bit field carrying the value of the ER-TLV type
which is 0x810.
Length
Specifies the length of the value field in bytes.
Flags
The Flags field is shown below:
+--+--+--+--+--+--+--+--+
| Res |F6|F5|F4|F3|F2|F1|
+--+--+--+--+--+--+--+--+
Res - These bits are reserved.
Zero on transmission.
Ignored on receipt.
F1 - Corresponds to the PDR.
F2 - Corresponds to the PBS.
F3 - Corresponds to the CDR.
F4 - Corresponds to the CBS.
F5 - Corresponds to the EBS.
F6 - Corresponds to the Weight.
Each flag Fi is a Negotiable Flag corresponding to a Traffic
Parameter. The Negotiable Flag value zero denotes NotNegotiable
and value one denotes Negotiable.
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Frequency
The Frequency field is coded as an 8 bit unsigned integer with
the following code points defined:
0- Unspecified
1- Frequent
2- VeryFrequent
3-255 - Reserved
Reserved - Zero on transmission. Ignored on receipt.
Weight
An 8 bit unsigned integer indicating the weight of the CR-LSP.
Valid weight values are from 1 to 255. The value 0 means that
weight is not applicable for the CR-LSP.
Traffic Parameters
Each Traffic Parameter is encoded as a 32-bit IEEE single-
precision floating-point number. A value of positive infinity
is represented as an IEEE single-precision floating-point
number with an exponent of all ones (255) and a sign and
mantissa of all zeros. The values PDR and CDR are in units of
bytes per second. The values PBS, CBS and EBS are in units of
bytes.
The value of PDR MUST be greater than or equal to the value of
CDR in a correctly encoded Traffic Parameters TLV.
4.3.1 Semantics
4.3.1.1 Frequency
The Frequency specifies at what granularity the CDR allocated to the
CR-LSP is made available. The value VeryFrequent means that the
available rate should average at least the CDR when measured over
any time interval equal to or longer than the shortest packet time
at the CDR. The value Frequent means that the available rate should
average at least the CDR when measured over any time interval equal
to or longer than a small number of shortest packet times at the
CDR.
The value Unspecified means that the CDR MAY be provided at any
granularity.
4.3.1.2 Peak Rate
The Peak Rate defines the maximum rate at which traffic SHOULD be
sent to the CR-LSP. The Peak Rate is useful for the purpose of
resource allocation. If resource allocation within the MPLS domain
depends on the Peak Rate value then it should be enforced at the
ingress to the MPLS domain.
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The Peak Rate is defined in terms of the two Traffic Parameters PDR
and PBS, see section 4.3.1.5 below.
4.3.1.3 Committed Rate
The Committed Rate defines the rate that the MPLS domain commits to
be available to the CR-LSP.
The Committed Rate is defined in terms of the two Traffic Parameters
CDR and CBS, see section 4.3.1.6 below.
4.3.1.4 Excess Burst Size
The Excess Burst Size may be used at the edge of an MPLS domain for
the purpose of traffic conditioning. The EBS MAY be used to measure
the extent by which the traffic sent on a CR-LSP exceeds the
committed rate.
The possible traffic conditioning actions, such as passing, marking
or dropping, are specific to the MPLS domain.
The Excess Burst Size is defined together with the Committed Rate,
see section 4.3.1.6 below.
4.3.1.5 Peak Rate Token Bucket
The Peak Rate of a CR-LSP is specified in terms of a token bucket P
with token rate PDR and maximum token bucket size PBS.
The token bucket P is initially (at time 0) full, i.e., the token
count Tp(0) = PBS. Thereafter, the token count Tp, if less than
PBS, is incremented by one PDR times per second. When a packet of
size B bytes arrives at time t, the following happens:
- If Tp(t)-B >= 0, the packet is not in excess of the peak rate
and Tp is decremented by B down to the minimum value of 0, else
- the packet is in excess of the peak rate and Tp is not
decremented.
Note that according to the above definition, a positive infinite
value of either PDR or PBS implies that arriving packets are never
in excess of the peak rate.
The actual implementation of an LSR doesn't need to be modeled
according to the above formal token bucket specification.
4.3.1.6 Committed Data Rate Token Bucket
The committed rate of a CR-LSP is specified in terms of a token
bucket C with rate CDR. The extent by which the offered rate
exceeds the committed rate MAY be measured in terms of another token
Jamoussi, et. al. draft-ietf-mpls-crldp-03.txt 14 Internet Draft Constraint-Based LSP Setup using LDP September, 1999
bucket E, which also operates at rate CDR. The maximum size of the
token bucket C is CBS and the maximum size of the token bucket E is
EBS.
The token buckets C and E are initially (at time 0) full, i.e., the
token count Tc(0) = CBS and the token count Te(0) = EBS.
Thereafter, the token counts Tc and Te are updated CDR times per
second as follows:
- If Tc is less than CBS, Tc is incremented by one, else
- if Te is less then EBS, Te is incremented by one, else
- neither Tc nor Te is incremented.
When a packet of size B bytes arrives at time t, the following
happens:
- If Tc(t)-B >= 0, the packet is not in excess of the Committed
Rate and Tc is decremented by B down to the minimum value of 0,
else
- if Te(t)-B >= 0, the packet is in excess of the Committed rate
but is not in excess of the EBS and Te is decremented by B down
to the minimum value of 0, else
- the packet is in excess of both the Committed Rate and the EBS
and neither Tc nor Te is decremented.
Note that according to the above specification, a CDR value of
positive infinity implies that arriving packets are never in excess
of either the Committed Rate or EBS. A positive infinite value of
either CBS or EBS implies that the respective limit cannot be
exceeded.
The actual implementation of an LSR doesn't need to be modeled
according to the above formal specification.
4.3.1.7 Weight
The weight determines the CR-LSP's relative share of the possible
excess bandwidth above its committed rate. The definition of
_relative share_ is MPLS domain specific.
4.3.2 Procedures
4.3.2.1 Label Request Message
If an LSR receives an incorrectly encoded Traffic Parameters TLV in
which the value of PDR is less than the value of CDR then it MUST
send a Notification Message including the Status code _Traffic
Parameters Unavailable_ to the upstream LSR from which it received
the erroneous message.
Jamoussi, et. al. draft-ietf-mpls-crldp-03.txt 15 Internet Draft Constraint-Based LSP Setup using LDP September, 1999
If a Traffic Parameter is indicated as Negotiable in the Label
Request Message by the corresponding Negotiable Flag then an LSR MAY
replace the Traffic Parameter value with a smaller value.
If the Weight is indicated as Negotiable in the Label Request
Message by the corresponding Negotiable Flag then an LSR may replace
the Weight value with a lower value (down to 0).
If, after possible Traffic Parameter negotiation, an LSR can support
the CR-LSP Traffic Parameters then the LSR MUST reserve the
corresponding resources for the CR-LSP.
If, after possible Traffic Parameter negotiation, an LSR cannot
support the CR-LSP Traffic Parameters then the LSR MUST send a
Notification Message that contains the _Resource Unavailable_ status
code.
4.3.2.2 Label Mapping Message
If an LSR receives an incorrectly encoded Traffic Parameters TLV in
which the value of PDR is less than the value of CDR then it MUST
send a Label Release message containing the Status code _Traffic
Parameters Unavailable_ to the LSR from which it received the
erroneous message. In addition, the LSP should send a Notification
Message upstream with the status code _Label Request Aborted_.
If the negotiation flag was set in the label request message, the
egress LSR MUST include the (possibly negotiated) Traffic Parameters
and Weight in the Label Mapping message.
The Traffic Parameters and the Weight in a Label Mapping message
MUST be forwarded unchanged.
An LSR SHOULD adjust the resources that it reserved for a CR-LSP
when it receives a Label Mapping Message if the Traffic Parameters
differ from those in the corresponding Label Request Message.
4.3.2.3 Notification Message
If an LSR receives a Notification Message for a CR-LSP, it SHOULD
release any resources that it possibly had reserved for the CR-LSP.
In addition, on receiving a Notification Message from a Downstream
LSR that is associated with a Label Request from an upstream LSR,
the local LSR MUST propagate the Notification message using the
procedures in [1].
4.4 Preemption TLV
The defualt value of the setup and holding priorities should be in
the middle of the range (e.g., 4) so that this feature can be turned
on gradually in an operational network by increasing or decerasing
the priority starting at the middle of the range.
Jamoussi, et. al. draft-ietf-mpls-crldp-03.txt 16 Internet Draft Constraint-Based LSP Setup using LDP September, 1999
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Preemption-TLV (0x0820) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SetPrio | HoldPrio | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
A fourteen-bit field carrying the value of the Preemption-TLV
type which is 0x820.
Length
Specifies the length of the value field in bytes.
Reserved
Zero on transmission. Ignored on receipt.
SetPrio
A SetupPriority of value zero (0) is the priority assigned to
the most important path. It is referred to as the highest
priority. Seven (7) is the priority for the least important
path. The higher the setup priority, the more paths CR-LDP can
bump to set up the path. The default value should be 4.
HoldPrio
A HoldingPriority of value zero (0) is the priority assigned to
the most important path. It is referred to as the highest
priority. Seven (7) is the priority for the least important
path. The default value should be 4.
The higher the holding priority, the less likely it is for CR-
LDP to reallocate its bandwidth to a new path.
4.5 LSPID TLV
LSPID is a unique identifier of a CR-LSP within an MPLS network.
The LSPID is composed of the ingress LSR Router ID (or any of its
own Ipv4 addresses) and a Locally unique CR-LSP ID to that LSR.
The LSPID is useful in network management, in CR-LSP repair, and in
using an already established CR-LSP as a hop in an ER-TLV.
An _action indicator flag_ is carried in the LSPID TLV. This _action
indicator flag_ indicates explicitly the action that should be taken
if the LSP already exists on the LSR receiving the message.
After a CR-LSP is set up, its bandwidth reservation may need to be
changed by the network operator, due to the new requirements for the
traffic carried on that CR-LSP. The _action indicator flag_ is used
Jamoussi, et. al. draft-ietf-mpls-crldp-03.txt 17 Internet Draft Constraint-Based LSP Setup using LDP September, 1999
indicate the need to modify the bandwidth and possibly other
parameters of an established CR-LSP without service interruption.
This feature has application in dynamic network resources management
where traffic of different priorities and service classes is
involved.
The procedure for the code point _modify_ is defined in Appendix C.
The procedures for other flags are FFS.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| LSPID-TLV (0x0821) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |ActFlg | Local CR-LSP ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ingress LSR Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
A fourteen-bit field carrying the value of the LSPID-TLV type
which is 0x821.
Length
Specifies the length of the value field in bytes.
ActFlg
Action Indicator Flag: A 4-bit field that indicates explicitly
the action that should be taken if the LSP already exists on
the LSR receiving the message. A set of indicator code points
is proposed as follows:
0000: indicates initial LSP setup
0001: indicates modify LSP
Reserved
Zero on transmission. Ignored on receipt.
Local CR-LSP ID
The Local LSP ID is an identifier of the CR-LSP locally unique
within the Ingress LSR originating the CR-LSP.
Ingress LSR Router ID
An LSR may use any of its own IPv4 addresses in this field.
4.6 Resource Class (Color) TLV
The Resource Class as defined in [4] is used to specify which links
are acceptable by this CR-LSP. This information allows for the
network's topology to be pruned.
Jamoussi, et. al. draft-ietf-mpls-crldp-03.txt 18 Internet Draft Constraint-Based LSP Setup using LDP September, 1999
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| ResCls-TLV (0x0822) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RsCls |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
A fourteen-bit field carrying the value of the ResCls-TLV type
which is 0x822.
Length
Specifies the length of the value field in bytes.
RsCls
The Resource Class bit mask indicating which of the 32
_administrative groups_ or _colors_ of links the CR-LSP can
traverse.
4.7 ER-Hop semantics
4.7.1. ER-Hop 1: The IPv4 prefix
The abstract node represented by this ER-Hop is the set of nodes,
which have an IP address, which lies within this prefix. Note that
a prefix length of 32 indicates a single IPv4 node.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| 0x801 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Reserved | PreLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
IPv4 Address 0x801
Length
Specifies the length of the value field in bytes.
L Bit
Set to indicate Loose hop.
Cleared to indicate a strict hop.
Reserved
Zero on transmission. Ignored on receipt.
PreLen
Jamoussi, et. al. draft-ietf-mpls-crldp-03.txt 19 Internet Draft Constraint-Based LSP Setup using LDP September, 1999
Prefix Length 1-32
IP Address
A four-byte field indicating the IP Address.
4.7.2. ER-Hop 2: The 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| 0x802 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Reserved | PreLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV6 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV6 address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV6 address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV6 address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
0x802 IPv6 address
Length
Specifies the length of the value field in bytes.
L Bit
Set to indicate Loose hop.
Cleared to indicate a strict hop.
Reserved
Zero on transmission. Ignored on receipt.
PreLen
Prefix Length 1-128
IPv6 address
A 128-bit unicast host address.
4.7.3. ER-Hop 3: The autonomous system number
The abstract node represented by this ER-Hop is the set of nodes
belonging to the autonomous system.
Jamoussi, et. al. draft-ietf-mpls-crldp-03.txt 20 Internet Draft Constraint-Based LSP Setup using LDP September, 1999
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| 0x803 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Reserved | AS Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
AS Number 0x803
Length
Specifies the length of the value field in bytes.
L Bit
Set to indicate Loose hop.
Cleared to indicate a strict hop.
Reserved
Zero on transmission. Ignored on receipt.
AS Number
Autonomous System number
4.7.4. ER-Hop 4: LSPID
The LSPID is used to identify the tunnel ingress point as the next
hop in the ER. This ER-Hop allows for stacking new CR-LSPs within an
already established CR-LSP. It also allows for splicing the CR-LSP
being established with an existing CR-LSP.
If an LSPID Hop is the last ER-Hop in an ER-TLV, than the LSR may
splice the CR-LSP of the incoming Label Request to the CR-LSP that
currently exists with this LSPID. This is useful, for example, at
the point at which a Label Request used for local repair arrives at
the next ER-Hop after the loosely specified CR-LSP segment. Use of
the LSPID Hop in this scenario eliminates the need for ER-Hops to
keep the entire remaining ER-TLV at each LSR that is at either
(upstream or downstream) end of a loosely specified CR-LSP segment
as part of its state information. This is due to the fact that the
upstream LSR needs only to keep the next ER-Hop and the LSPID and
the downstream LSR needs only to keep the LSPID in order for each
end to be able to recognize that the same LSP is being identified.
If the LSPID Hop is not the last hop in an ER-TLV, the LSR must
forward the remaining ER-TLV in a Label Request message, using the
CR-LSP specified by the LSPID, to the LSR that is the CR-LSP's
egress. That LSR will continue processing of the CR-LSP Label
Request Message. The result is a tunneled, or stacked, CR-LSP.
Jamoussi, et. al. draft-ietf-mpls-crldp-03.txt 21 Internet Draft Constraint-Based LSP Setup using LDP September, 1999
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| 0x804 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Reserved | Local LSPID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ingress LSR Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
LSPID 0x804
Length
Specifies the length of the value field in bytes.
L Bit
Set to indicate Loose hop.
Cleared to indicate a strict hop.
Reserved
Zero on transmission. Ignored on receipt.
Local LSPID
A 2 byte field indicating the LSPID which is unique with
reference to its Ingress LSR.
Ingress LSR Router ID
An LSR may use any of its own IPv4 addresses in this field.
4.8. Processing of the Explicit Route TLV
4.8.1. Selection of the next hop
A Label Request Message containing an explicit route TLV must
determine the next hop for this path. Selection of this next hop
may involve a selection from a set of possible alternatives. The
mechanism for making a selection from this set is implementation
dependent and is outside of the scope of this specification.
Selection of particular paths is also outside of the scope of this
specification, but it is assumed that each node will make a best
effort attempt to determine a loop-free path. Note that such best
efforts may be overridden by local policy.
To determine the next hop for the path, a node performs the
following steps:
1. The node receiving the Label Request Message must first
evaluate the first ER-Hop. If the L bit is not set in the
first ER-Hop and if the node is not part of the abstract node
described by the first ER-Hop, it has received the message in
Jamoussi, et. al. draft-ietf-mpls-crldp-03.txt 22 Internet Draft Constraint-Based LSP Setup using LDP September, 1999
error, and should return a _Bad Initial ER-Hop_ error. If the
L bit is set and the local node is not part of the abstract
node described by the first ER-Hop, the node selects a next
hop that is along the path to the abstract node described by
the first ER-Hop. If there is no first ER-Hop, the message is
also in error and the system should return a _Bad Explicit
Routing TLV_ error using a Notification Message sent upstream.
2. If there is no second ER-Hop, this indicates the end of the
explicit route. The explicit route TLV should be removed from
the Label Request Message. This node may or may not be the
end of the LSP. Processing continues with section 4.8.2,
where a new explicit route TLV may be added to the Label
Request Message.
3. If the node is also a part of the abstract node described by
the second ER-Hop, then the node deletes the first ER-Hop and
continues processing with step 2, above. Note that this makes
the second ER-Hop into the first ER-Hop of the next iteration.
4. The node determines if it is topologically adjacent to the
abstract node described by the second ER-Hop. If so, the node
selects a particular next hop which is a member of the
abstract node. The node then deletes the first ER-Hop and
continues processing with section 4.8.2.
5. Next, the node selects a next hop within the abstract node of
the first ER-Hop that is along the path to the abstract node
of the second ER-Hop. If no such path exists then there are
two cases:
5.a If the second ER-Hop is a strict ER-Hop, then there is
an error and the node should return a _Bad Strict Node_
error.
5.b Otherwise, if the second ER-Hop is a loose ER-Hop, then
the node selects any next hop that is along the path to the
next abstract node. If no path exists within the MPLS
domain, then there is an error, and the node should return a
_Bad loose node_ error.
6. Finally, the node replaces the first ER-Hop with any ER-Hop
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.
7. Progress the Label Request Message to the next hop.
4.8.2. Adding ER-Hops to the explicit route TLV
After selecting a next hop, the node may alter the explicit route in
the following ways.
Jamoussi, et. al. draft-ietf-mpls-crldp-03.txt 23 Internet Draft Constraint-Based LSP Setup using LDP September, 1999
If, as part of executing the algorithm in section 4.8.1, the
explicit route TLV is removed, the node may add a new explicit route
TLV.
Otherwise, if the node is a member of the abstract node for the
first ER-Hop, then a series of ER-Hops may be inserted before the
first ER-Hop or may replace the first ER-Hop. Each ER-Hop in this
series must denote an abstract node that is a subset of the current
abstract node.
Alternately, if the first ER-Hop is a loose ER-Hop, an arbitrary
series of ER-Hops may be inserted prior to the first ER-Hop.
4.9 Route Pinning TLV
Section 2.4 describes the use of route pinning. The encoding of the
Route Pinning TLV is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| 0x823 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
Pinning-TLV type 0x823
Length
Specifies the length of the value field in bytes.
P Bit
The P bit is set to 1 to indicate that route pinning is
requested.
The P bit is set to 0 to indicate that route pinning is not
requested
Reserved
Zero on transmission. Ignored on receipt.
4.10 CR-LSP FEC Element
A new FEC element is introduced in this specification to support CR-
LSPs. This new FEC element does not preclude the use of other FECs
elements (Type=0x01, 0x02, 0x03) defined in the LDP spec in CR-LDP
messages. The CR-LDP FEC Element is an opaque FEC to be used only in
Messages of CR-LSPs.
Jamoussi, et. al. draft-ietf-mpls-crldp-03.txt 24 Internet Draft Constraint-Based LSP Setup using LDP September, 1999
FEC Element Type Value
Type name
CR-LSP 0x04 No value; i.e., 0 value octets;
The CR-LSP FEC TLV encoding is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| FEC(0x0100) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CR-LSP (4) |
+-+-+-+-+-+-+-+-+
Type
FEC TLV type 0x0100
Length
Specifies the length of the value field in bytes.
CR-LSP FEC Element Type
0x04
4.11 Error subcodes
In the processing described above, certain errors need to be
reported as part of the Notification Message. This section defines
the status codes for the errors described in this specification.
Status Code Type
-------------------------------------- ----------
Bad Explicit Routing TLV Error 0x44000001
Bad Strict Node Error 0x44000002
Bad Loose Node Error 0x44000003
Bad Initial ER-Hop Error 0x44000004
Resource Unavailable 0x44000005
Traffic Parameters Unavailable 0x44000006
Setup Abort (Label Request Aborted in [1]) 0x04000015
Modify Request Not Supported 0x44000008
5. Security
Pre-emption has to be controlled by the MPLS domain.
Resource reservation requires the LSRs to have an LSP admission
control function.
Traffic Engineered LSPs can bypass normal routing.
6. Acknowledgments
Jamoussi, et. al. draft-ietf-mpls-crldp-03.txt 25 Internet Draft Constraint-Based LSP Setup using LDP September, 1999
The messages used to signal the CR-LSP setup are based on the work
done by the [1] team.
The authors would also like to acknowledge the careful review and
comments of Ken Hayward, Greg Wright, Geetha Brown, Brian Williams,
Paul Beaubien, Matthew Yuen, Liam Casey, Ankur Anand, Adrian Farrel.
7. Intellectual Property Consideration
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.
8. References
1 Andersson et al, "Label Distribution Protocol Specification"
work in progress (draft-ietf-mpls-ldp-05), June 1999.
2 Callon et al, "Framework for Multiprotocol Label Switching",
work in progress (draft-ietf-mpls-framework-05), September 1999.
3 Rosen et al, "Multiprotocol Label Switching Architecture",
work in progress (draft-ietf-mpls-arch-06), September 1999.
4 Awduche et al, "Requirements for Traffic Engineering Over
MPLS", RFC 2702, September 1999.
5 L. Wu, et. al., "LDP State Machine" work in progress
(draft-ietf-mpls-ldp-state-00), Feb 1999.
9. Author's Addresses
Osama S. Aboul-Magd Loa Andersson
Nortel Networks Nortel Networks
P O Box 3511 Station C S:t Eriksgatan 115
Ottawa, ON K1Y 4H7 PO Box 6701
Canada 113 85 Stockholm
Phone: +1 613 763-5827 Tel: +46 8 508 835 00
Osama@nortelnetworks.com Fax: +46 8 508 835 01
Loa_andersson@nortelnetworks.com
Peter Ashwood-Smith Ross Callon
Nortel Networks IronBridge Networks
P O Box 3511 Station C 55 Hayden Avenue,
Ottawa, ON K1Y 4H7 Lexington, MA 02173
Canada Phone: +1-781-402-8017
Phone: +1 613 763-4534 Rcallon@ironbridgenetworks.com
Petera@nortelnetworks.com
Ram Dantu Paul Doolan
Alcatel USA Inc. Ennovate Networks
Jamoussi, et. al. draft-ietf-mpls-crldp-03.txt 26 Internet Draft Constraint-Based LSP Setup using LDP August, 1999
IP Competence Center 330 Codman Hill Rd
1201 E. Campbell Road.,446-315 Marlborough MA 01719
Richadson, TX USA., 75081-2206 Phone: 978-263-2002
Phone: 972 996 2938 Pdoolan@ennovatenetworks.com
Fax: 972 996 5902
Ram.dantu@alcatel.com
Nancy Feldman Andre Fredette
IBM Corp. Nortel Networks
17 Skyline Drive 600 Technology Park Drive
Hawthorne NY 10532 Billerica, MA 01821
Phone: 914-784-3254 978-288-8524
Nkf@us.ibm.com Fredette@nortelnetworks.com
Eric Gray Joel M. Halpern
Lucent Technologies, Inc Institutional Venture Partners
1600 Osgood St. 650-926-5633
North Andover, MA 01847 Joel@mcquillan.com
Phone: 603-659-3386
Ewgray@lucent.com
Juha Heinanen Fiffi Hellstrand
Telia Finland, Inc. Ericsson Telecom AB
Myyrmaentie 2 S-126 25 STOCKHOLM
01600 VANTAA Sweden
Finland Tel: +46 8 719 4933
Tel: +358 41 500 4808 Etxfiff@etxb.ericsson.se
Jh@telia.fi
Bilel Jamoussi Timothy E. Kilty
Nortel Networks Corp. Northchurch Communications
600 Technology Park Drive 5 Corporate Drive,
Billerica, MA 01821 Andover, MA 018110
USA phone: 978 691-4656
Phone: +1 978 288-4506 Tkilty@northc.com
Jamoussi@nortelnetworks.com
Andrew G. Malis Muckai K Girish
Ascend Communications, Inc. SBC Technology Resources,
1 Robbins Road 4698 Willow Road
Westford, MA 01886 Pleasanton, CA 94588
Phone: 978 952-7414 Phone: (925) 598-1263
fax: 978 392-2074 Fax: (925) 598-1321
Malis@ascend.com Mgirish@tri.sbc.com
Kenneth Sundell Pasi Vaananen
Nortel Networks Nokia Telecommunications
S:t Eriksgatan 115 3 Burlington Woods Drive,
PO Box 6701 Burlington, MA 01803
113 85 Stockholm Phone: +1-781-238-4981
Tel: +46 8 508 835 00 Pasi.vaanenen@ntc.nokia.com
Fax: +46 8 508 835 01
Jamoussi, et. al. draft-ietf-mpls-cr-ldp-03.txt 27 Internet Draft Constraint-Based LSP Setup using LDP August, 1999
Ksundell@nortelnetworks.com
Tom Worster Liwen Wu
Nokia Alcatel U.S.A
3 Burlington Woods Dr. 44983 Knoll Square
Suite 250 Ashburn, Va. 20147
Burlington MA 01803 USA Phone: (703) 724-2619
+1 617 247 2624 FAX: (703) 724-2005
Tom.worster@nokia.com Liwen.wu@and.alcatel.com
Jamoussi, et. al. draft-ietf-mpls-cr-ldp-03.txt 28 Internet Draft Constraint-Based LSP Setup using LDP August, 1999
Appendix A: CR-LSP Establishment Examples
A.1 Strict Explicit Route Example
This appendix provides an example for the setup of a strictly routed
CR-LSP. In this example, a specific node represents each abstract
node.
The sample network used here is a four node network with two edge
LSRs and two core LSRs as follows:
abc
LSR1------LSR2------LSR3------LSR4
LSR1 generates a Label Request Message as described in Section 3.1
of this draft and sends it to LSR2. This message includes the CR-
TLV.
A vector of three ER-Hop TLVs <a, b, c> composes the ER-TLV.
The ER-Hop TLVs used in this example are of type 0x0801 (IPv4
prefix) with a prefix length of 32. Hence, each ER-Hop TLV
identifies a specific node as opposed to a group of nodes.
At LSR2, the following processing of the ER-TLV per Section 4.8.1 of
this draft takes place:
1) The node LSR2 is part of the abstract node described by the
first hop <a>. Therefore, the first step passes the test.
Go to step 2.
2) There is a second ER-Hop, <b>. Go to step 3.
3) LSR2 is not part of the abstract node described by the
second ER-Hop <b>. Go to Step 4.
4) LSR2 determines that it is topologically adjacent to the
abstract node described by the second ER-Hop <b>. LSR2
selects a next hop (LSR3) which is the abstract node. LSR2
deletes the first ER-Hop <a> from the ER-TLV, which now
becomes <b, c>. Processing continues with Section 4.8.2.
At LSR2, the following processing of Section 4.8.2 takes place:
Executing algorithm 4.8.1 did not result in the removal of the ER-
TLV.
Also, LSR2 is not a member of the abstract node described by the
first ER-Hop <b>.
Finally, the first ER-Hop <b> is a strict hop.
Therefore, processing section 4.8.2 does not result in the insertion
of new ER-Hops. The selection of the next hop has been already done
is step 4 of Section 4.8.1 and the processing of the ER-TLV is
Jamoussi, et. al. draft-ietf-mpls-cr-ldp-03.txt 29 Internet Draft Constraint-Based LSP Setup using LDP August, 1999
completed at LSR2. In this case, the Label Request Message including
the ER-TLV <b, c> is progressed by LSR2 to LSR3.
At LSR3, a similar processing to the ER-TLV takes place except that
the incoming ER-TLV = <b, c> and the outgoing ER-TLV is <c>.
At LSR4, the following processing of section 4.8.1 takes place:
1) The node LSR4 is part of the abstract node described by the
first hop <c>. Therefore, the first step passes the test. Go
to step 2.
2) There is no second ER-Hop, this indicates the end of the CR-
LSP. The ER-TLV is removed from the Label Request Message.
Processing continues with Section 4.8.2.
At LSR4, the following processing of Section 4.8.2 takes place:
Executing algorithm 4.8.1 resulted in the removal of the ER-TLV.
LSR4 does not add a new ER-TLV.
Therefore, processing section 4.8.2 does not result in the insertion
of new ER-Hops. This indicates the end of the CR-LSP and the
processing of the ER-TLV is completed at LSR4.
At LSR4, processing of Section 3.2 is invoked. The first condition
is satisfied (LSR4 is the egress end of the CR-LSP and upstream
mapping has been requested). Therefore, a Label Mapping Message is
generated by LSR4 and sent to LSR3.
At LSR3, the processing of Section 3.2 is invoked. The second
condition is satisfied (LSR3 received a mapping from its downstream
next hop LSR4 for a CR-LSP for which an upstream request is still
pending). Therefore, a Label Mapping Message is generated by LSR3
and sent to LSR2.
At LSR2, a similar processing to LSR 3 takes place and a Label
Mapping Message is sent back to LSR1, which completes the end-to-end
CR-LSP setup.
A.2 Node Groups and Specific Nodes Example
A request at ingress LSR to setup a CR-LSP might originate from a
management system or an application, the details are implementation
specific.
The ingress LSR uses information provided by the management system
or the application and possibly also information from the routing
database to calculate the explicit route and to create the Label
Request Message.
The Label request message carries together with other necessary
information an ER-TLV defining the explicitly routed path. In our
example the list of hops in the ER-Hop TLV is supposed to contain an
Jamoussi, et. al. draft-ietf-mpls-cr-ldp-03.txt 30 Internet Draft Constraint-Based LSP Setup using LDP August, 1999
abstract node representing a group of nodes, an abstract node
representing a specific node, another abstract node representing a
group of nodes, and an abstract node representing a specific egress
point.
In--{Group 1}--{Specific A}--{Group 2}--{Specific Out: B}
The ER-TLV contains four ER-Hop TLVs:
1. An ER-Hop TLV that specifies a group of LSR valid for the
first abstract node representing a group of nodes (Group 1).
2. An ER-Hop TLV that indicates the specific node (Node A).
3. An ER-Hop TLV that specifies a group of LSRs valid for the
second abstract node representing a group of nodes (Group
2).
4. An ER-Hop TLV that indicates the specific egress point for
the CR-LSP (Node B).
All the ER-Hop TLVs are strictly routed nodes.
The setup procedure for this CR-LSP works as follows:
1. The ingress node sends the Label Request Message to a node
that is a member the group of nodes indicated in the first
ER-Hop TLV, following normal routing for the specific node
(A).
2. The node that receives the message identifies itself as part
of the group indicated in the first ER-Hop TLV, and that it
is not the specific node (A) in the second. Further it
realizes that the specific node (A) is not one of its next
hops.
3. It keeps the ER-Hop TLVs intact and sends a Label Request
Message to another node that is part of the group indicated
in the first ER-Hop TLV (Group 1), following normal routing
for the specific node (A).
4. The node that receives the message identifies itself as part
of the group indicated in the first ER-Hop TLV, and that it
is not the specific node (A) in the second ER-Hop TLV.
Further it realizes that the specific node (A) is one of its
next hops.
5. It removes the first ER-Hop TLVs and sends a Label Request
Message to the specific node (A).
6. The specific node (A) recognizes itself in the first ER-Hop
TLV. Removes the specific ER-Hop TLV.
Jamoussi, et. al. draft-ietf-mpls-cr-ldp-03.txt 31 Internet Draft Constraint-Based LSP Setup using LDP August, 1999
7. It sends a Label Request Message to a node that is a member
of the group (Group 2) indicated in the ER-Hop TLV.
8. The node that receives the message identifies itself as part
of the group indicated in the first ER-Hop TLV, further it
realizes that the specific egress node (B) is one of its
next hops.
9. It sends a Label Request Message to the specific egress node
(B).
10.The specific egress node (B) recognizes itself as the egress
for the CR-LSP, it returns a Label Mapping Message, that
will traverse the same path as the Label Request Message in
the opposite direction.
Jamoussi, et. al. draft-ietf-mpls-cr-ldp-03.txt 32 Internet Draft Constraint-Based LSP Setup using LDP August, 1999
Appendix B. QoS Service Examples
B.1 Service Examples
Construction of an end-to-end service is the result of the rules
enforced at the edge and the treatment that packets receive at the
network nodes. The rules define the traffic conditioning actions
that are implemented at the edge and they include policing with
pass, mark, and drop capabilities. The edge rules are expected tobe
defined by the mutual agreements between the service providers and
their customers and they will constitute an essential part of the
SLA. Therefore edge rules are not included in the signaling
protocol.
Packet treatment at a network node is usually referred to as the
local behavior. Local behavior could be specified in many ways. One
example for local behavior specification is the service frequency
introduced in section 4.3.2.1, together with the resource
reservation rules implemented at the nodes.
Edge rules and local behaviors can be viewed as the main building
blocks for the end-to-end service construction. The following table
illustrates the applicability of the building block approach for
constructing different services including those defined for ATM.
Service PDR PBS CDR CBS EBS Service Conditioning
Examples Frequency Action
DS S S =PDR =PBS 0 Frequent drop>PDR
TS S S S S 0 Unspecified drop>PDR,PBS
mark>CDR,CBS
BE inf inf inf inf 0 Unspecified -
FRS S S CIR ~B_C ~B_E Unspecified drop>PDR,PBS
mark>CDR,CBS,EBS
ATM-CBR PCR CDVT =PCR =CDVT 0 VeryFrequent drop>PCR
ATM-VBR.3(rt) PCR CDVT SCR MBS 0 Frequent drop>PCR
mark>SCR,MBS
ATM-VBR.3(nrt) PCR CDVT SCR MBS 0 Unspecified drop>PCR
mark>SCR,MBS
ATM-UBR PCR CDVT - - 0 Unspecified drop>PCR
ATM-GFR.1 PCR CDVT MCR MBS 0 Unspecified drop>PCR
ATM-GFR.2 PCR CDVT MCR MBS 0 Unspecified drop>PCR
mark>MCR,MFS
Jamoussi, et. al. draft-ietf-mpls-cr-ldp-03.txt 33 Internet Draft Constraint-Based LSP Setup using LDP August, 1999
int-serv-CL p m r b 0 Frequent drop>p
drop>r,b
S= User specified
In the above table, the DS refers to a delay sensitive service where
the network commits to deliver with high probability user datagrams
at a rate of PDR with minimum delay and delay requirements.
Datagrams in excess of PDR will be discarded.
The TS refers to a generic throughput sensitive service where the
network commits to deliver with high probability user datagrams at a
rate of at least CDR. The user may transmit at a rate higher than
CDR but datagrams in excess of CDR would have a lower probability of
being delivered.
The BE is the best effort service and it implies that there are no
expected service guarantees from the network.
B.2 Establishing CR-LSP Supporting Real-Time Applications
In this scenario the customer needs to establish an LSP for
supporting real-time applications such as voice and video. The
Delay-sensitive (DS) service is requested in this case.
The first step is the specification of the traffic parameters in the
signaling message. The two parameters of interest to the DS service
are the PDR and the PBS and the user based on his requirements
specifies their values. Since all the traffic parameters are
included in the signaling message, appropriate values must be
assigned to all of them. For DS service, the CDR and the CBS values
are set equal to the PDR and the PBS respectively. An indication of
whether the parameter values are subject to negotiation is flagged.
The transport characteristics of the DS service require Frequent
frequency to be requested to reflect the real-time delay
requirements of the service.
In addition to the transport characteristics, both the network
provider and the customer need to agree on the actions enforced at
the edge. The specification of those actions is expected to be a
part of the service level agreement (SLA) negotiation and is not
included in the signaling protocol. For DS service, the edge action
is to drop packets that exceed the PDR and the PBS specifications.
The signaling message will be sent in the direction of the ER path
and the LSP is established following the normal LDP procedures. Each
LSR applies its admission control rules. If sufficient resources are
not available and the parameter values are subject to negotiation,
then the LSR could negotiate down the PDR, the PBS, or both.
Jamoussi, et. al. draft-ietf-mpls-cr-ldp-03.txt 34 Internet Draft Constraint-Based LSP Setup using LDP August, 1999
The new parameter values are echoed back in the Label Mapping
Message. LSRs might need to re-adjust their resource reservations
based on the new traffic parameter values.
B.3 Establishing CR-LSP Supporting Delay Insensitive Applications
In this example we assume that a throughput sensitive (TS) service
is requested. For resource allocation the user assigns values for
PDR, PBS, CDR, and CBS. The negotiation flag is set if the traffic
parameters are subject to negotiation.
Since the service is delay insensitive by definition, the
Unspecified frequency is signaled to indicate that the service
frequency is not an issue.
Similar to the previous example, the edge actions are not subject
for signaling and are specified in the service level agreement
between the user and the network provider.
For TS service, the edge rules might include marking to indicate
high discard precedence values for all packets that exceed CDR and
the CBS. The edge rules will also include dropping of packets that
conform to neither PDR nor PBS.
Each LSR of the LSP is expected to run its admission control rules
and negotiate traffic parameters down if sufficient resources do not
exist. The new parameter values are echoed back in the Label Mapping
Message. LSRs might need to re-adjust their resources based on the
new traffic parameter values.
Jamoussi, et. al. draft-ietf-mpls-cr-ldp-03.txt 35 Internet Draft Constraint-Based LSP Setup using LDP August, 1999
Appendix C. LSP Modification Using CR-LDP
After a CR-LSP is set up, its bandwidth reservation may need to be
changed by the network operator, due to the new requirements for the
traffic carried on that CR-LSP. This contribution presents an
approach to modify the bandwidth and possibly other parameters of an
established CR-LSP using CR-LDP without service interruption. The
LSP modification feature can be supported by CR-LDP with a minor
extension of an _action indicator flag_. This feature has
application in dynamic network resources management where traffic of
different priorities and service classes is involved.
Conventions used in this Appendix:
L: LSP (Label Switched Path)
Lid: LSPID (LSP Identifier)
T: Traffic Parameters
R: LSR (Label Switching Router)
FTN: FEC To NHLFE
FEC: Forwarding Equivalence Class
NHLFE: Next Hop Label Forwarding Entity
TLV: Type Length Value
C.1 Introduction
Consider an LSP L1 that has been established with its set of traffic
parameters T0. A certain amount of bandwidth is reserved along the
path of L1. Consider then that some changes are required on L1. For
example, the bandwidth of L1 needs to be increased to accommodate
the increased traffic on L1. Or the SLA associated with L1 needs to
be modified because a different service class is desired. The
network operator, in these cases, would like to modify the
characteristics of L1, for example, to change its traffic parameter
set from T0 to T1, without releasing the LSP L1 to interrupt the
service. In some other cases, network operators may want to reroute
a CR-LSP to a different path for either improved performance or
better network resource utilization. In all these cases, LSP
modification is required. In section C.2 below, a method to modify
an active LSP using CR-LDP is presented. The concept of LSPID in CR-
LDP is used to achieve the LSP modification, without releasing the
LSP and interrupting the service and, without double booking the
bandwidth. Only a minimum extension on CR-LDP, an action indication
flag of _modify_ is needed in order to explicitly specify the
behavior, and allow the existing LSPID to support other networking
capabilities in the future. Section 4.5 specifies the action
indication flag of _modify_ for CR-LDP. An example is described to
demonstrate an application of the presented method in dynamically
managing network bandwidth requirements without interrupting
service.
Jamoussi, et. al. draft-ietf-mpls-cr-ldp-03.txt 36 Internet Draft Constraint-Based LSP Setup using LDP August, 1999
C.2 Basic Procedure
LSP modification can only be allowed when the LSP is already set up
and active. That is, modification is not defined nor allowed during
the LSP establishment or label release/withdraw phases. Only
modification requested by the ingress LSR of the LSP is considered
in this draft for CR-LSP. Ingress LSR cannot modify an LSP before a
previous modification procedure is completed.
Assume that CR-LSP L1 is set up with LSPID L-id1, which is unique in
the MPLS network. The ingress LSR R1 of L1 has in its FTN (FEC To
NHLFE) table FEC1 -> Label A mapping where A is the outgoing label
for LSP L1. To modify the characteristics of L1, R1 sends a Label
Request Message. In the messages, the TLVs will have the new
requested values, and the LSPID TLV is included which indicates the
value of L-id1. The Traffic Parameters TLV, the ER-TLV, the Resource
Class (color) TLV and the Preemption TLV can have values different
from those in the original Label Request Message, which has been
used to set up L1 earlier. Thus, L1 can be changed in its bandwidth
request (traffic parameter TLV), its traffic service class (traffic
parameter TLV), the route it traverses (ER TLV) and its setup and
holding (Preemption TLV) priorities. The ingress LSR R1 now still
has the entry in FTN as FEC1 -> Label A. R1 is waiting to establish
another entry for FEC1.
When an LSR Ri along the path of L1 receives the Label Request
message, its behavior is the same as that of receiving any Label
request message. The only extension is that Ri examines the LSPID
carried in the Label Request Message, L-id1 and identifies if it
already has L-id1. If Ri does not have L-id1, Ri behaves the same as
receiving a new Label Request message. If Ri already has L-id1, Ri
takes the newly received Traffic Parameter TLV and computes the new
bandwidth required and derives the new service class. Compared with
the already reserved bandwidth for L-id1, Ri now reserves only the
difference of the bandwidth requirements. This prevents Ri from
doing bandwidth double booking. If a new service class is requested,
Ri also prepares to receive the traffic on L1 in, perhaps a
different type of queue, just the same as handling it for a Label
Request Message. Ri assigns a new label for the Label Request
Message.
When the Label Mapping message is received, two sets of labels exist
for the same LSPID. Then the ingress LSR R1 will have two outgoing
labels, A and B, associated with the same FEC, where B is the new
outgoing label received for LSP L1. The ingress LSR R1 can now
activate the new entry in FTN, FEC1 - > Label B. This means that R1
swaps traffic on L1 to the new label _B_ (_new_ path) for L1. The
packets can now be sent with the new label B, with the new set of
traffic parameters if any, on a new path, that is, if a new path is
requested in the Label Request Message for the modification. All the
other LSRs along the path will start to receive the incoming packets
with the new label. For the incoming new label, the LSR has already
Jamoussi, et. al. draft-ietf-mpls-cr-ldp-03.txt 37 Internet Draft Constraint-Based LSP Setup using LDP August, 1999
established its mapping to the new outgoing label. Thus, the packets
will be sent out with the new outgoing label. The LSRs do not have
to implement new procedures to track the new and old
characteristics of the LSP.
The ingress LSR R1 then starts to release the original label A for
LSP L1. The Label Release Message is sent by R1 towards the down
stream LSRs. The Release message carries the LSPID of L-id1 and the
Label TLV to indicate which label is to be released. The Release
Message is propagated to the egress LSR to release the original
labels previously used for L1. Upon receiving the Label Release
Message, LSR R1 examines the LSPID, L-id1 and finds out that the L-
id1 has still another set of label (incoming/outgoing) under it.
Thus, the old label is released without releasing the resource in
use. That is, if the bandwidth has been decreased for L1, the delta
bandwidth is released. Otherwise, no bandwidth is released. This
modification procedure can not only be applied to modify the traffic
parameters and/or service class of an active LSP, but also to
reroute an existing LSP, and/or change its setup/holding priority if
desired. After the release procedure, the modification of the LSP is
completed.
The method described above follows the normal behavior of Label
Request / Mapping / Notification / Release /Withdraw procedure of a
CR-LDP operated LSR with a specific action taken on LSPID. If Label
Withdraw Message is used to withdraw a label associated with an
LSPID, the Label TLV should be included to specify which label to
withdraw. Since the LSPID can also be used for other feature
support, an action indication flag of _modify_ assigned to the LSPID
would explicitly explain the action/semantics that should be
associated with the messaging procedure. The details of this flag
are addressed in Section 4.5.
C.3 Priority Handling
When sending a Label Request Message for an active LSP L1 to request
changes, the setup priority used in the label Request Message can be
different from the one used in the previous Label Request Message,
effectively indicating the priority of this _modification_ request.
Network operators can use this feature to decide what priority is to
be assigned to a modification request, based on their
policies/algorithms and other traffic situations in the network. For
example, the priority for modification can be determined by the
priority of the customer/LSP. If a customer has exceeded the
reserved bandwidth of its VPN LSP tunnel by too much, the
modification request's priority may be given higher.
The Label Request message for the modification of an active LSP can
also be sent with a holding priority different from its previous
one. This effectively changes the holding priority of the LSP. Upon
receiving a Label Request Message that requests a new holding
priority, the LSR assigns the new holding priority to the bandwidth.
That is, the new holding priority is assigned to both the existing
Jamoussi, et. al. draft-ietf-mpls-cr-ldp-03.txt 38 Internet Draft Constraint-Based LSP Setup using LDP August, 1999
incoming / outgoing labels and the new labels to be established for
the LSPID in question. In this way self-bumping is prevented.
C.4 Modification Failure Case Handling
A modification attempt may fail due to insufficient resource or
other situations. A Notification message is sent back to the ingress
LSR R1 to indicate the failure of Label Request Message that
intended to modify the LSP. Retry may be attempted if desired by the
network operator.
If the LSP on the original path failed when a modification attempt
is in progress, the attempt should be aborted by using the Label
Abort Request message as specified in LDP draft.
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Jamoussi, et. al. draft-ietf-mpls-cr-ldp-03.txt 39
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