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IETF RFC 4124
Protocol Extensions for Support of Diffserv-aware MPLS Traffic Engineering
Last modified on Monday, June 27th, 2005
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Network Working Group F. Le Faucheur, Ed.
Request for Comments: 4124 Cisco Systems, Inc.
Category: Standards Track June 2005
Protocol Extensions for Support of
Diffserv-aware MPLS Traffic Engineering
 Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright © The Internet Society (2005).
Abstract
This document specifies the protocol extensions for support of
Diffserv-aware MPLS Traffic Engineering (DS-TE). This includes
generalization of the semantics of a number of Interior Gateway
Protocol (IGP) extensions already defined for existing MPLS Traffic
Engineering in RFC 3630, RFC 3784, and additional IGP extensions
beyond those. This also includes extensions to RSVP-TE signaling
beyond those already specified in RFC 3209 for existing MPLS Traffic
Engineering. These extensions address the requirements for DS-TE
spelled out in RFC 3564.
Table of Contents
1. Introduction ....................................................3
1.1. Specification of Requirements ..............................3
2. Contributing Authors ............................................4
3. Definitions .....................................................5
4. Configurable Parameters .........................................5
4.1. Link Parameters ............................................5
4.1.1. Bandwidth Constraints (BCs) .........................5
4.1.2. Overbooking .........................................6
4.2. LSR Parameters .............................................7
4.2.1. TE-Class Mapping ....................................7
4.3. LSP Parameters .............................................8
4.3.1. Class-Type ..........................................8
4.3.2. Setup and Holding Preemption Priorities .............8
4.3.3. Class-Type/Preemption Relationship ..................8
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RFC 4124 Protocols for Diffserv-aware TE June 2005
4.4. Examples of Parameters Configuration .......................9
4.4.1. Example 1 ...........................................9
4.4.2. Example 2 ...........................................9
4.4.3. Example 3 ..........................................10
4.4.4. Example 4 ..........................................11
4.4.5. Example 5 ..........................................11
5. IGP Extensions for DS-TE .......................................12
5.1. Bandwidth Constraints .....................................12
5.2. Unreserved Bandwidth ......................................14
6. RSVP-TE Extensions for DS-TE ...................................15
6.1. DS-TE-Related RSVP Messages Format ........................15
6.1.1. Path Message Format ................................16
6.2. CLASSTYPE Object ..........................................16
6.2.1. CLASSTYPE object ...................................16
6.3. Handling CLASSTYPE Object .................................17
6.4. Non-support of the CLASSTYPE Object .......................20
6.5. Error Codes for Diffserv-aware TE .........................20
7. DS-TE Support with MPLS Extensions .............................21
7.1. DS-TE Support and References to Preemption Priority .......22
7.2. DS-TE Support and References to Maximum Reservable
Bandwidth .................................................22
8. Constraint-Based Routing .......................................22
9. Diffserv Scheduling ............................................23
10. Existing TE as a Particular Case of DS-TE .....................23
11. Computing "Unreserved TE-Class [i]" and Admission
Control Rules .................................................23
11.1. Computing "Unreserved TE-Class [i]" .....................23
11.2. Admission Control Rules .................................24
12. Security Considerations .......................................24
13. IANA Considerations ...........................................25
13.1. A New Name Space for Bandwidth Constraints Model
Identifiers .............................................25
13.2. A New Name Space for Error Values under the
"Diffserv-aware TE ......................................25
13.3. Assignments Made in This Document .......................26
13.3.1. Bandwidth Constraints sub-TLV for
OSPF Version 2 ..................................26
13.3.2. Bandwidth Constraints sub-TLV for ISIS ..........26
13.3.3. CLASSTYPE Object for RSVP .......................26
13.3.4. "Diffserv-aware TE Error" Error Code ............27
13.3.5. Error Values for "Diffserv-aware TE Error" ......27
14. Acknowledgements ..............................................28
Appendix A: Prediction for Multiple Path Computation ..............29
Appendix B: Solution Evaluation ...................................29
Appendix C: Interoperability with non DS-TE capable LSRs ..........31
Normative References ..............................................34
Informative References ............................................35
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1. Introduction
[DSTE-REQ] presents the Service Provider requirements for support of
Differentiated-Service (Diffserv)-aware MPLS Traffic Engineering
(DS-TE). This includes the fundamental requirement to be able to
enforce different bandwidth constraints for different classes of
traffic.
This document specifies the IGP and RSVP-TE signaling extensions
(beyond those already specified for existing MPLS Traffic Engineering
[OSPF-TE][ISIS-TE][RSVP-TE]) for support of the DS-TE requirements
spelled out in [DSTE-REQ] including environments relying on
distributed Constraint-Based Routing (e.g., path computation
involving head-end Label Switching Routers).
[DSTE-REQ] provides a definition and examples of Bandwidth
Constraints models. The present document does not specify nor assume
a particular Bandwidth Constraints model. Specific Bandwidth
Constraints models are outside the scope of this document. Although
the extensions for DS-TE specified in this document may not be
sufficient to support all the conceivable Bandwidth Constraints
models, they do support the Russian Dolls Model specified in
[DSTE-RDM], the Maximum Allocation Model specified in [DSTE-MAM], and
the Maximum Allocation with Reservation Model specified in
[DSTE-MAR].
There may be differences between the quality of service expressed and
obtained with Diffserv without DS-TE and with DS-TE. Because DS-TE
uses Constraint-Based Routing, and because of the type of admission
control capabilities it adds to Diffserv, DS-TE has capabilities for
traffic that Diffserv does not: Diffserv does not indicate
preemption, by intent, whereas DS-TE describes multiple levels of
preemption for its Class-Types. Also, Diffserv does not support any
means of explicitly controlling overbooking, while DS-TE allows this.
When considering a complete quality of service environment, with
Diffserv routers and DS-TE, it is important to consider these
differences carefully.
1.1. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC 2119].
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2. Contributing Authors
This document was the collective work of several authors. The text
and content were contributed by the editor and the co-authors listed
below. (The contact information for the editor appears in the
Editor's Address section.)
Jim Boyle Kireeti Kompella
Protocol Driven Networks, Inc. Juniper Networks, Inc.
1381 Kildaire Farm Road #288 1194 N. Mathilda Ave.
Cary, NC 27511, USA Sunnyvale, CA 94099
Phone: (919) 852-5160 EMail: kireeti@juniper.net
EMail: jboyle@pdnets.com
William Townsend Thomas D. Nadeau
Tenor Networks Cisco Systems, Inc.
100 Nagog Park 250 Apollo Drive
Acton, MA 01720 Chelmsford, MA 01824
Phone: +1-978-264-4900 Phone: +1-978-244-3051
EMail: btownsend@tenornetworks.com EMail: tnadeau@cisco.com
Darek Skalecki
Nortel Networks
3500 Carling Ave,
Nepean K2H 8E9
Phone: +1-613-765-2252
EMail: dareks@nortelnetworks.com
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3. Definitions
For readability, a number of definitions from [DSTE-REQ] are repeated
here:
Traffic Trunk: an aggregation of traffic flows of the same class
(i.e., treated equivalently from the DS-TE
perspective), which is placed inside a Label
Switched Path (LSP).
Class-Type (CT): the set of Traffic Trunks crossing a link that is
governed by a specific set of bandwidth constraints.
CT is used for the purposes of link bandwidth
allocation, constraint-based routing and admission
control. A given Traffic Trunk belongs to the same
CT on all links.
TE-Class: A pair of:
i. a Class-Type
ii. a preemption priority allowed for that Class-
Type. This means that an LSP transporting a Traffic
Trunk from that Class-Type can use that preemption
priority as the setup priority, the holding
priority, or both.
Definitions for a number of MPLS terms are not repeated here. They
can be found in [MPLS-ARCH].
4. Configurable Parameters
This section only discusses the differences with the configurable
parameters supported for MPLS Traffic Engineering as per [TE-REQ],
[ISIS-TE], [OSPF-TE], and [RSVP-TE]. All other parameters are
unchanged.
4.1. Link Parameters
4.1.1. Bandwidth Constraints (BCs)
[DSTE-REQ] states that "Regardless of the Bandwidth Constraints
Model, the DS-TE solution MUST allow support for up to 8 BCs."
For DS-TE, the existing "Maximum Reservable link bandwidth" parameter
is retained, but its semantics is generalized and interpreted as the
aggregate bandwidth constraint across all Class-Types, so that,
independently of the Bandwidth Constraints Model in use:
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SUM (Reserved (CTc)) <= Max Reservable Bandwidth,
where the SUM is across all values of "c" in the range 0 <= c <= 7.
Additionally, on every link, a DS-TE implementation MUST provide for
configuration of up to 8 additional link parameters which are the
eight potential BCs, i.e., BC0, BC1, ... BC7. The LSR MUST interpret
these BCs in accordance with the supported Bandwidth Constraints
Model (i.e., what BC applies to what Class-Type, and how).
Where the Bandwidth Constraints Model imposes some relationship among
the values to be configured for these BCs, the LSR MUST enforce those
at configuration time. For example, when the Russian Dolls Bandwidth
Constraints Model ([DSTE-RDM]) is used, the LSR MUST ensure that BCi
is configured smaller than or equal to BCj, where i is greater than
j, and ensure that BC0 is equal to the Maximum Reservable Bandwidth.
As another example, when the Maximum Allocation Model ([DSTE-MAM]) is
used, the LSR MUST ensure that all BCi are configured smaller or
equal to the Maximum Reservable Bandwidth.
4.1.2. Overbooking
DS-TE enables a network administrator to apply different overbooking
(or underbooking) ratios for different CTs.
The principal methods to achieve this are the same as those
historically used in existing TE deployment:
(i) To take into account the overbooking/underbooking ratio
appropriate for the Ordered Aggregate (OA) or CT associated
with the considered LSP at the time of establishing the
bandwidth size of a given LSP. We refer to this method as the
"LSP Size Overbooking" method. AND/OR
(ii) To take into account the overbooking/underbooking ratio at the
time of configuring the Maximum Reservable Bandwidth/BCs and
use values that are larger (overbooking) or smaller
(underbooking) than those actually supported by the link. We
refer to this method as the "Link Size Overbooking" method.
The "LSP Size Overbooking" and "Link Size Overbooking" methods are
expected to be sufficient in many DS-TE environments and require no
additional configurable parameters. Other overbooking methods may
involve such additional configurable parameters, but are beyond the
scope of this document.
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4.2. LSR Parameters
4.2.1. TE-Class Mapping
In line with [DSTE-REQ], the preemption attributes defined in
[TE-REQ] are retained with DS-TE and applicable within, and across,
all CTs. The preemption attributes of setup priority and holding
priority retain existing semantics, and in particular these semantics
are not affected by the LSP CT. This means that if LSP1 contends
with LSP2 for resources, LSP1 may preempt LSP2 if LSP1 has a higher
setup preemption priority (i.e., lower numerical priority value) than
LSP2 holding preemption priority, regardless of LSP1 CT and LSP2 CT.
DS-TE LSRs MUST allow configuration of a TE-Class mapping whereby the
Class-Type and preemption level are configured for each of (up to) 8
TE-Classes.
This mapping is referred to as :
TE-Class[i] <--> < CTc , preemption p >
where 0 <= i <= 7, 0 <= c <= 7, 0 <= p <= 7
Two TE-Classes MUST NOT be identical (i.e., have both the same
Class-Type and the same preemption priority).
There are no other restrictions on how any of the 8 Class-Types can
be paired up with any of the 8 preemption priorities to form a TE-
Class. In particular, one given preemption priority can be paired up
with two (or more) different Class-Types to form two (or more) TE-
Classes. Similarly, one Class-Type can be paired up with two (or
more) different preemption priorities to form two (or more) TE-
Classes. Also, there is no mandatory ordering relationship between
the TE-Class index (i.e., "i" above) and the Class-Type (i.e., "c"
above) or the preemption priority (i.e., "p" above) of the TE-Class.
Where the network administrator uses less than 8 TE-Classes, the DS-
TE LSR MUST allow remaining ones to be configured as "Unused". Note
that configuring all the 8 TE-Classes as "Unused" effectively results
in disabling TE/DS-TE since no TE/DS-TE LSP can be established (nor
even configured, since as described in Section 4.3.3 below, the CT
and preemption priorities configured for an LSP MUST form one of the
configured TE-Classes).
To ensure coherent DS-TE operation, the network administrator MUST
configure exactly the same TE-Class mapping on all LSRs of the DS-TE
domain.
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When the TE-Class mapping needs to be modified in the DS-TE domain,
care ought to be exercised during the transient period of
reconfiguration during which some DS-TE LSRs may be configured with
the new TE-Class mapping while others are still configured with the
old TE-Class mapping. It is recommended that active tunnels do not
use any of the TE-Classes that are being modified during such a
transient reconfiguration period.
4.3. LSP Parameters
4.3.1. Class-Type
With DS-TE, LSRs MUST support, for every LSP, an additional
configurable parameter that indicates the Class-Type of the Traffic
Trunk transported by the LSP.
There is one and only one Class-Type configured per LSP.
The configured Class-Type indicates, in accordance with the supported
Bandwidth Constraints Model, the BCs that MUST be enforced for that
LSP.
4.3.2. Setup and Holding Preemption Priorities
As per existing TE, DS-TE LSRs MUST allow every DS-TE LSP to be
configured with a setup and holding priority, each with a value
between 0 and 7.
4.3.3. Class-Type/Preemption Relationship
With DS-TE, the preemption priority configured for the setup priority
of a given LSP and the Class-Type configured for that LSP MUST be
such that, together, they form one of the (up to) 8 TE-Classes
configured in the TE-Class mapping specified in Section 4.2.1 above.
The preemption priority configured for the holding priority of a
given LSP and the Class-Type configured for that LSP MUST also be
such that, together, they form one of the (up to) 8 TE-Classes
configured in the TE-Class mapping specified in Section 4.2.1 above.
The LSR MUST enforce these two rules at configuration time.
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4.4. Examples of Parameters Configuration
For illustration purposes, we now present a few examples of how these
configurable parameters may be used. All these examples assume that
different BCs need to be enforced for different sets of Traffic
Trunks (e.g., for Voice and for Data) so that two or more Class-Types
need to be used.
4.4.1. Example 1
The network administrator of a first network using two CTs (CT1 for
Voice and CT0 for Data) may elect to configure the following TE-Class
mapping to ensure that Voice LSPs are never driven away from their
shortest path because of Data LSPs:
TE-Class[0] <--> < CT1 , preemption 0 >
TE-Class[1] <--> < CT0 , preemption 1 >
TE-Class[i] <--> unused, for 2 <= i <= 7
Voice LSPs would then be configured with:
CT = CT1, setup priority = 0, holding priority = 0
Data LSPs would then be configured with:
CT = CT0, setup priority = 1, holding priority = 1
A new Voice LSP would then be able to preempt an existing Data LSP in
case they contend for resources. A Data LSP would never preempt a
Voice LSP. A Voice LSP would never preempt another Voice LSP. A
Data LSP would never preempt another Data LSP.
4.4.2. Example 2
The network administrator of another network may elect to configure
the following TE-Class mapping in order to optimize global network
resource utilization by favoring placement of large LSPs closer to
their shortest path:
TE-Class[0] <--> < CT1 , preemption 0 >
TE-Class[1] <--> < CT0 , preemption 1 >
TE-Class[2] <--> < CT1 , preemption 2 >
TE-Class[3] <--> < CT0 , preemption 3 >
TE-Class[i] <--> unused, for 4 <= i <= 7
Large-size Voice LSPs could be configured with:
CT = CT1, setup priority = 0, holding priority = 0
Large-size Data LSPs could be configured with:
CT = CT0, setup priority = 1, holding priority = 1
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Small-size Voice LSPs could be configured with:
CT = CT1, setup priority = 2, holding priority = 2
Small-size Data LSPs could be configured with:
CT = CT0, setup priority = 3, holding priority = 3
A new large-size Voice LSP would then be able to preempt a small-size
Voice LSP or any Data LSP in case they contend for resources. A new
large-size Data LSP would then be able to preempt a small-size Data
LSP or a small-size Voice LSP in case they contend for resources, but
it would not be able to preempt a large-size Voice LSP.
4.4.3. Example 3
The network administrator of another network may elect to configure
the following TE-Class mapping in order to ensure that Voice LSPs are
never driven away from their shortest path because of Data LSPs.
This also achieves some optimization of global network resource
utilization by favoring placement of large LSPs closer to their
shortest path:
TE-Class[0] <--> < CT1 , preemption 0 >
TE-Class[1] <--> < CT1 , preemption 1 >
TE-Class[2] <--> < CT0 , preemption 2 >
TE-Class[3] <--> < CT0 , preemption 3 >
TE-Class[i] <--> unused, for 4 <= i <= 7
Large-size Voice LSPs could be configured with:
CT = CT1, setup priority = 0, holding priority = 0.
Small-size Voice LSPs could be configured with:
CT = CT1, setup priority = 1, holding priority = 1.
Large-size Data LSPs could be configured with:
CT = CT0, setup priority = 2, holding priority = 2.
Small-size Data LSPs could be configured with:
CT=CT0, setup priority = 3, holding priority = 3.
A Voice LSP could preempt a Data LSP if they contend for resources.
A Data LSP would never preempt a Voice LSP. A large-size Voice LSP
could preempt a small-size Voice LSP if they contend for resources.
A large-size Data LSP could preempt a small-size Data LSP if they
contend for resources.
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4.4.4. Example 4
The network administrator of another network may elect to configure
the following TE-Class mapping in order to ensure that no preemption
occurs in the DS-TE domain:
TE-Class[0] <--> < CT1 , preemption 0 >
TE-Class[1] <--> < CT0 , preemption 0 >
TE-Class[i] <--> unused, for 2 <= i <= 7
Voice LSPs would then be configured with:
CT = CT1, setup priority =0, holding priority = 0
Data LSPs would then be configured with:
CT = CT0, setup priority = 0, holding priority = 0
No LSP would then be able to preempt any other LSP.
4.4.5. Example 5
The network administrator of another network may elect to configure
the following TE-Class mapping in view of increased network stability
through a more limited use of preemption:
TE-Class[0] <--> < CT1 , preemption 0 >
TE-Class[1] <--> < CT1 , preemption 1 >
TE-Class[2] <--> < CT0 , preemption 1 >
TE-Class[3] <--> < CT0 , preemption 2 >
TE-Class[i] <--> unused, for 4 <= i <= 7
Large-size Voice LSPs could be configured with: CT = CT1, setup
priority = 0, holding priority = 0.
Small-size Voice LSPs could be configured with: CT = CT1, setup
priority = 1, holding priority = 0.
Large-size Data LSPs could be configured with: CT = CT0, setup
priority = 2, holding priority = 1.
Small-size Data LSPs could be configured with: CT = CT0, setup
priority = 2, holding priority = 2.
A new large-size Voice LSP would be able to preempt a Data LSP in
case they contend for resources, but it would not be able to preempt
any Voice LSP even a small-size Voice LSP.
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A new small-size Voice LSP would be able to preempt a small-size Data
LSP in case they contend for resources, but it would not be able to
preempt a large-size Data LSP or any Voice LSP.
A Data LSP would not be able to preempt any other LSP.
5. IGP Extensions for DS-TE
This section only discusses the differences with the IGP
advertisement supported for (aggregate) MPLS Traffic Engineering as
per [OSPF-TE] and [ISIS-TE]. The rest of the IGP advertisement is
unchanged.
5.1. Bandwidth Constraints
As detailed above in Section 4.1.1, up to 8 BCs (BCb, 0 <= b <= 7)
are configurable on any given link.
With DS-TE, the existing "Maximum Reservable Bandwidth" sub-TLV
([OSPF-TE], [ISIS-TE]) is retained with a generalized semantics so
that it MUST now be interpreted as the aggregate bandwidth constraint
across all Class-Types; i.e., SUM (Reserved (CTc)) <= Max Reservable
Bandwidth, independently of the Bandwidth Constraints Model.
This document also defines the following new optional sub-TLV to
advertise the eight potential BCs (BC0 to BC7):
"Bandwidth Constraints" sub-TLV:
- Bandwidth Constraints Model Id (1 octet)
- Reserved (3 octets)
- Bandwidth Constraints (N x 4 octets)
Where:
- With OSPF, the sub-TLV is a sub-TLV of the "Link TLV" and its
sub-TLV type is 17.
- With ISIS, the sub-TLV is a sub-TLV of the "extended IS
reachability TLV" and its sub-TLV type is 22.
- Bandwidth Constraints Model Id: a 1-octet identifier for the
Bandwidth Constraints Model currently in use by the LSR
initiating the IGP advertisement. See the IANA Considerations
section for assignment of values in this name space.
- Reserved: a 3-octet field. This field should be set to zero
by the LSR generating the sub-TLV and should be ignored by the
LSR receiving the sub-TLV.
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- Bandwidth Constraints: contains BC0, BC1,... BC(N-1). Each BC
is encoded on 32 bits in IEEE floating point format. The
units are bytes (not bits!) per second. Where the configured
TE-Class mapping and the Bandwidth Constraints model in use
are such that BCh+1, BCh+2, ...and BC7 are not relevant to any
of the Class-Types associated with a configured TE-Class, it
is RECOMMENDED that only the Bandwidth Constraints from BC0 to
BCh be advertised, in order to minimize the impact on IGP
scalability.
All relevant generic TLV encoding rules (including TLV format,
padding and alignment, as well as IEEE floating point format
encoding) defined in [OSPF-TE] and [ISIS-TE] are applicable to this
new sub-TLV.
The "Bandwidth Constraints" sub-TLV format is illustrated below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BC Model Id | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BC0 value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// . . . //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BCh value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A DS-TE LSR MAY optionally advertise BCs.
A DS-TE LSR, which does advertise BCs, MUST use the new "Bandwidth
Constraints" sub-TLV (in addition to the existing Maximum Reservable
Bandwidth sub-TLV) to do so. For example, in the case where a
service provider deploys DS-TE with TE-Classes associated with CT0
and CT1 only, and where the Bandwidth Constraints Model is such that
only BC0 and BC1 are relevant to CT0 and CT1, a DS-TE LSR which does
advertise BCs would include in the IGP advertisement the Maximum
Reservable Bandwidth sub-TLV, as well as the "Bandwidth Constraints"
sub-TLV. The former should contain the aggregate bandwidth
constraint across all CTs, and the latter should contain BC0 and BC1.
A DS-TE LSR receiving the "Bandwidth Constraints" sub-TLV with a
Bandwidth Constraints Model Id that does not match the Bandwidth
Constraints Model it currently uses SHOULD generate a warning to the
operator/management system, reporting the inconsistency between
Bandwidth Constraints Models used on different links. Also, in that
case, if the DS-TE LSR does not support the Bandwidth Constraints
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Model designated by the Bandwidth Constraints Model Id, or if the
DS-TE LSR does not support operations with multiple simultaneous
Bandwidth Constraints Models, the DS-TE LSR MAY discard the
corresponding TLV. If the DS-TE LSR does support the Bandwidth
Constraints Model designated by the Bandwidth Constraints Model Id,
and if the DS-TE LSR does support operations with multiple
simultaneous Bandwidth Constraints Models, the DS-TE LSR MAY accept
the corresponding TLV and allow operations with different Bandwidth
Constraints Models used in different parts of the DS-TE domain.
5.2. Unreserved Bandwidth
With DS-TE, the existing "Unreserved Bandwidth" sub-TLV is retained
as the only vehicle to advertise dynamic bandwidth information
necessary for Constraint-Based Routing on head-ends, except that it
is used with a generalized semantics. The Unreserved Bandwidth sub-
TLV still carries eight bandwidth values, but they now correspond to
the unreserved bandwidth for each of the TE-Classes (instead of for
each preemption priority, as per existing TE).
More precisely, a DS-TE LSR MUST support the Unreserved Bandwidth
sub-TLV with a definition that is generalized into the following:
The Unreserved Bandwidth sub-TLV specifies the amount of bandwidth
not yet reserved for each of the eight TE-Classes, in IEEE floating
point format arranged in increasing order of TE-Class index.
Unreserved bandwidth for TE-Class [0] occurs at the start of the
sub-TLV, and unreserved bandwidth for TE-Class [7] at the end of the
sub-TLV. The unreserved bandwidth value for TE-Class [i] ( 0 <= i <=
7) is referred to as "Unreserved TE-Class [i]". It indicates the
bandwidth that is available, for reservation, to an LSP that:
- transports a Traffic Trunk from the Class-Type of TE-Class[i], and
- has a setup priority corresponding to the preemption priority of
TE-Class[i].
The units are bytes per second.
Because the bandwidth values are now ordered by TE-class index and
thus can relate to different CTs with different BCs and to any
arbitrary preemption priority, a DS-TE LSR MUST NOT assume any
ordered relationship among these bandwidth values.
With existing TE, because all preemption priorities reflect the same
(and only) BCs and bandwidth values are advertised in preemption
priority order, the following relationship is always true, and is
often assumed by TE implementations:
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If i < j, then "Unreserved Bw [i]" >= "Unreserved Bw [j]"
With DS-TE, no relationship is to be assumed such that:
If i < j, then any of the following relationships may be true:
"Unreserved TE-Class [i]" = "Unreserved TE-Class [j]"
OR
"Unreserved TE-Class [i]" > "Unreserved TE-Class [j]"
OR
"Unreserved TE-Class [i]" < "Unreserved TE-Class [j]".
Rules for computing "Unreserved TE-Class [i]" are specified in
Section 11.
If TE-Class[i] is unused, the value advertised by the IGP in
"Unreserved TE-Class [i]" MUST be set to zero by the LSR generating
the IGP advertisement, and MUST be ignored by the LSR receiving the
IGP advertisement.
6. RSVP-TE Extensions for DS-TE
In this section, we describe extensions to RSVP-TE for support of
Diffserv-aware MPLS Traffic Engineering. These extensions are in
addition to the extensions to RSVP defined in [RSVP-TE] for support
of (aggregate) MPLS Traffic Engineering and to the extensions to RSVP
defined in [DIFF-MPLS] for support of Diffserv over MPLS.
6.1. DS-TE-Related RSVP Messages Format
One new RSVP object is defined in this document: the CLASSTYPE
object. Detailed description of this object is provided below. This
new object is applicable to Path messages. This specification only
defines the use of the CLASSTYPE object in Path messages used to
establish LSP Tunnels in accordance with [RSVP-TE] and thus
containing a session object with a CT equal to LSP_TUNNEL_IPv4 and
containing a LABEL_REQUEST object.
Restrictions defined in [RSVP-TE] for support of establishment of LSP
Tunnels via RSVP-TE are also applicable to the establishment of LSP
Tunnels supporting DS-TE. For instance, only unicast LSPs are
supported, and multicast LSPs are for further study.
This new CLASSTYPE object is optional with respect to RSVP so that
general RSVP implementations not concerned with MPLS LSP setup do not
have to support this object.
An LSR supporting DS-TE MUST support the CLASSTYPE object.
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6.1.1. Path Message Format
The format of the Path message is as follows:
<Path Message> ::= <Common Header> [ <INTEGRITY> ]
<SESSION> <RSVP_HOP>
<TIME_VALUES>
[ <EXPLICIT_ROUTE> ]
<LABEL_REQUEST>
[ <SESSION_ATTRIBUTE> ]
[ <DIFFSERV> ]
[ <CLASSTYPE> ]
[ <POLICY_DATA> ... ]
[ <sender descriptor> ]
<sender descriptor> ::= <SENDER_TEMPLATE> [ <SENDER_TSPEC> ]
[ <ADSPEC> ]
[ <RECORD_ROUTE> ]
6.2. CLASSTYPE Object
The CLASSTYPE object Class Name is CLASSTYPE. Its Class Number is
66. Currently, there is only one defined C-Type which is C-Type 1.
The CLASSTYPE object format is shown below.
6.2.1. CLASSTYPE object
Class Number = 66
Class-Type = 1
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | CT |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved: 29 bits
This field is reserved. It MUST be set to zero on transmission
and MUST be ignored on receipt.
CT: 3 bits
Indicates the Class-Type. Values currently allowed are
1, 2, ... , 7. Value of 0 is Reserved.
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6.3. Handling CLASSTYPE Object
To establish an LSP tunnel with RSVP, the sender LSR creates a Path
message with a session type of LSP_Tunnel_IPv4 and with a
LABEL_REQUEST object as per [RSVP-TE]. The sender LSR may also
include the DIFFSERV object as per [DIFF-MPLS].
If the LSP is associated with Class-Type 0, the sender LSR MUST NOT
include the CLASSTYPE object in the Path message. This allows
backward compatibility with non-DSTE-configured or non-DSTE-capable
LSRs as discussed below in Section 10 and Appendix C.
If the LSP is associated with Class-Type N (1 <= N <=7), the sender
LSR MUST include the CLASSTYPE object in the Path message with the
Class-Type (CT) field set to N.
If a Path message contains multiple CLASSTYPE objects, only the first
one is meaningful; subsequent CLASSTYPE object(s) MUST be ignored and
MUST NOT be forwarded.
Each LSR along the path MUST record the CLASSTYPE object, when it is
present, in its path state block.
If the CLASSTYPE object is not present in the Path message, the LSR
MUST associate the Class-Type 0 to the LSP.
The destination LSR responding to the Path message by sending a Resv
message MUST NOT include a CLASSTYPE object in the Resv message
(whether or not the Path message contained a CLASSTYPE object).
During establishment of an LSP corresponding to the Class-Type N, the
LSR MUST perform admission control over the bandwidth available for
that particular Class-Type.
An LSR that recognizes the CLASSTYPE object and that receives a Path
message that:
- contains the CLASSTYPE object, but
- does not contain a LABEL_REQUEST object or does not have a
session type of LSP_Tunnel_IPv4,
MUST send a PathErr towards the sender with the error code
"Diffserv-aware TE Error" and an error value of "Unexpected CLASSTYPE
object". These codes are defined in Section 6.5.
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An LSR receiving a Path message with the CLASSTYPE object that:
- recognizes the CLASSTYPE object, but
- does not support the particular Class-Type,
MUST send a PathErr towards the sender with the error code
"Diffserv-aware TE Error" and an error value of "Unsupported Class-
Type". These codes are defined in Section 6.5.
An LSR receiving a Path message with the CLASSTYPE object that:
- recognizes the CLASSTYPE object, but
- determines that the Class-Type value is not valid (i.e.,
Class-Type value 0),
MUST send a PathErr towards the sender with the error code
"Diffserv-aware TE Error" and an error value of "Invalid Class-Type
value". These codes are defined in Section 6.5.
An LSR receiving a Path message with the CLASSTYPE object, which:
- recognizes the CLASSTYPE object and
- supports the particular Class-Type, but
- determines that the tuple formed by (i) this Class-Type and
(ii) the setup priority signaled in the same Path message, is
not one of the eight TE-Classes configured in the TE-class
mapping,
MUST send a PathErr towards the sender with the error code
"Diffserv-aware TE Error" and an error value of "CT and setup
priority do not form a configured TE-Class". These codes are defined
in Section 6.5.
An LSR receiving a Path message with the CLASSTYPE object that:
- recognizes the CLASSTYPE object and
- supports the particular Class-Type, but
- determines that the tuple formed by (i) this Class-Type and
(ii) the holding priority signaled in the same Path message,
is not one of the eight TE-Classes configured in the TE-class
mapping,
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MUST send a PathErr towards the sender with the error code
"Diffserv-aware TE Error" and an error value of "CT and holding
priority do not form a configured TE-Class". These codes are defined
in Section 6.5.
An LSR receiving a Path message with the CLASSTYPE object that:
- recognizes the CLASSTYPE object and
- supports the particular Class-Type, but
- determines that the tuple formed by (i) this Class-Type and
(ii) the setup priority signaled in the same Path message, is
not one of the eight TE-Classes configured in the TE-class
mapping, AND
- determines that the tuple formed by (i) this Class-Type and
(ii) the holding priority signaled in the same Path message,
is not one of the eight TE-Classes configured in the TE-class
mapping
MUST send a PathErr towards the sender with the error code
"Diffserv-aware TE Error" and an error value of "CT and setup
priority do not form a configured TE-Class AND CT and holding
priority do not form a configured TE-Class". These codes are defined
in Section 6.5.
An LSR receiving a Path message with the CLASSTYPE object and with
the DIFFSERV object for an L-LSP that:
- recognizes the CLASSTYPE object,
- has local knowledge of the relationship between Class-Types
and Per Hop Behavior (PHB) Scheduling Class, e.g., via
configuration, and
- determines, based on this local knowledge, that the PHB
Scheduling Class (PSC) signaled in the DIFFSERV object is
inconsistent with the Class-Type signaled in the CLASSTYPE
object,
MUST send a PathErr towards the sender with the error code
"Diffserv-aware TE Error" and an error value of "Inconsistency
between signaled PSC and signaled CT". These codes are defined below
in Section 6.5.
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An LSR receiving a Path message with the CLASSTYPE object and with
the DIFFSERV object for an E-LSP that:
- recognizes the CLASSTYPE object,
- has local knowledge of the relationship between Class-Types
and PHBs (e.g., via configuration)
- determines, based on this local knowledge, that the PHBs
signaled in the MAP entries of the DIFFSERV object are
inconsistent with the Class-Type signaled in the CLASSTYPE
object,
MUST send a PathErr towards the sender with the error code
"Diffserv-aware TE Error" and an error value of "Inconsistency
between signaled PHBs and signaled CT". These codes are defined in
Section 6.5.
An LSR MUST handle situations in which the LSP cannot be accepted for
reasons other than those already discussed in this section, in
accordance with [RSVP-TE] and [DIFF-MPLS] (e.g., a reservation is
rejected by admission control, and a label cannot be associated).
6.4. Non-support of the CLASSTYPE Object
An LSR that does not recognize the CLASSTYPE object Class-Num MUST
behave in accordance with the procedures specified in [RSVP] for an
unknown Class-Num whose format is 0bbbbbbb (i.e., it MUST send a
PathErr with the error code "Unknown object class" toward the
sender).
An LSR that recognizes the CLASSTYPE object Class-Num but that does
not recognize the CLASSTYPE object C-Type, MUST behave in accordance
with the procedures specified in [RSVP] for an unknown C-type (i.e.,
it MUST send a PathErr with the error code "Unknown object C-Type"
toward the sender).
Both of the above situations cause the path setup to fail. The
sender SHOULD notify the operator/management system that an LSP
cannot be established and might take action to retry reservation
establishment without the CLASSTYPE object.
6.5. Error Codes for Diffserv-aware TE
In the procedures described above, certain errors are reported as a
"Diffserv-aware TE Error". The value of the "Diffserv-aware TE
Error" error code is 28.
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The following table defines error values for the Diffserv-aware TE
Error:
Value Error
1 Unexpected CLASSTYPE object
2 Unsupported Class-Type
3 Invalid Class-Type value
4 Class-Type and setup priority do not form a configured
TE-Class
5 Class-Type and holding priority do not form a
configured TE-Class
6 Class-Type and setup priority do not form a configured
TE-Class AND Class-Type and holding priority do not form
a configured TE-Class
7 Inconsistency between signaled PSC and signaled
Class-Type
8 Inconsistency between signaled PHBs and signaled
Class-Type
See the IANA Considerations section for allocation of additional
values.
7. DS-TE Support with MPLS Extensions
There are a number of extensions to the initial base specification
for signaling [RSVP-TE] and IGP support for TE [OSPF-TE][ISIS-TE].
Those include enhancements for generalization ([GMPLS-SIG] and
[GMPLS-ROUTE]), as well as for additional functionality, such as LSP
hierarchy [HIERARCHY], link bundling [BUNDLE], and fast restoration
[REROUTE]. These specifications may reference how to encode
information associated with certain preemption priorities, how to
treat LSPs at different preemption priorities, or they may otherwise
specify encodings or behavior that have a different meaning for a
DS-TE router.
In order for an implementation to support both this specification for
Diffserv-aware TE and a given MPLS enhancement, such as those listed
above (but not limited to those), it MUST treat references to
"preemption priority" and to "Maximum Reservable Bandwidth" in a
generalized manner, i.e., the manner in which this specification uses
those terms.
Additionally, current and future MPLS enhancements may include more
precise specification for how they interact with Diffserv-aware TE.
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7.1. DS-TE Support and References to Preemption Priority
When a router supports both Diffserv-aware TE and one of the MPLS
protocol extensions such as those mentioned above, encoding of values
of preemption priority in signaling or encoding of information
associated with preemption priorities in IGP defined for the MPLS
extension, MUST be considered an encoding of the same information for
the corresponding TE-Class. For instance, if an MPLS enhancement
specifies advertisement in IGP of a parameter for routing information
at preemption priority N, in a DS-TE environment it MUST actually be
interpreted as specifying advertisement of the same routing
information but for TE-Class [N]. On receipt, DS-TE routers MUST
also interpret it as such.
When there is discussion on how to comparatively treat LSPs of
different preemption priority, a DS-TE LSR MUST treat the preemption
priorities in this context as those associated with the TE-Classes of
the LSPs in question.
7.2. DS-TE Support and References to Maximum Reservable Bandwidth
When a router supports both Diffserv-aware TE and MPLS protocol
extensions such as those mentioned above, advertisements of Maximum
Reservable Bandwidth MUST be done with the generalized interpretation
defined in Section 4.1.1 as the aggregate bandwidth constraint across
all Class-Types. It MAY also allow the optional advertisement of all
BCs.
8. Constraint-Based Routing
Let us consider the case where a path needs to be computed for an LSP
whose Class-Type is configured to CTc and whose setup preemption
priority is configured to p.
Then the pair of CTc and p will map to one of the TE-Classes defined
in the TE-Class mapping. Let us refer to this TE-Class as TE-
Class[i].
The Constraint-Based Routing algorithm of a DS-TE LSR is still only
required to perform path computation satisfying a single BC which is
to fit in "Unreserved TE-Class [i]" as advertised by the IGP for
every link. Thus, no changes to the existing TE Constraint-Based
Routing algorithm itself are required.
The Constraint-Based Routing algorithm MAY also take into account,
when used, the optional additional information advertised in IGP such
as the BCs and the Maximum Reservable Bandwidth. For example, the
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BCs MIGHT be used as tie-breaker criteria in situations where
multiple paths, otherwise equally attractive, are possible.
9. Diffserv Scheduling
The Class-Type signaled at LSP establishment MAY optionally be used
by DS-TE LSRs to dynamically adjust the resources allocated to the
Class-Type by the Diffserv scheduler. In addition, the Diffserv
information (i.e., the PSC) signaled by the TE-LSP signaling
protocols as specified in [DIFF-MPLS], if used, MAY optionally be
used by DS-TE LSRs to dynamically adjust the resources allocated by
the Diffserv scheduler to a PSC/OA within a CT.
10. Existing TE as a Particular Case of DS-TE
We observe that existing TE can be viewed as a particular case of
DS-TE where:
(i) a single Class-Type is used,
(ii) all 8 preemption priorities are allowed for that Class-Type,
and
(iii) the following TE-Class mapping is used:
TE-Class[i] <--> < CT0 , preemption i >
Where 0 <= i <= 7.
In that case, DS-TE behaves as existing TE.
As with existing TE, the IGP advertises:
- Unreserved Bandwidth for each of the 8 preemption priorities.
As with existing TE, the IGP may advertise:
- Maximum Reservable Bandwidth containing a BC applying across
all LSPs .
Because all LSPs transport traffic from CT0, RSVP-TE signaling is
done without explicit signaling of the Class-Type (which is only used
for Class-Types other than CT0, as explained in Section 6) as with
existing TE.
11. Computing "Unreserved TE-Class [i]" and Admission Control Rules
11.1. Computing "Unreserved TE-Class [i]"
We first observe that, for existing TE, details on admission control
algorithms for TE LSPs, and consequently details on formulas for
computing the unreserved bandwidth, are outside the scope of the
current IETF work. This is left for vendor differentiation. Note
that this does not compromise interoperability across various
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implementations because the TE schemes rely on LSRs to advertise
their local view of the world in terms of Unreserved Bw to other
LSRs. This way, regardless of the actual local admission control
algorithm used on one given LSR, Constraint-Based Routing on other
LSRs can rely on advertised information to determine whether an
additional LSP will be accepted or rejected by the given LSR. The
only requirement is that an LSR advertises unreserved bandwidth
values that are consistent with its specific local admission control
algorithm and take into account the holding preemption priority of
established LSPs.
In the context of DS-TE, again, details on admission control
algorithms are left for vendor differentiation, and formulas for
computing the unreserved bandwidth for TE-Class[i] are outside the
scope of this specification. However, DS-TE places the additional
requirement on the LSR that the unreserved bandwidth values
advertised MUST reflect all the BCs relevant to the CT associated
with TE-Class[i] in accordance with the Bandwidth Constraints Model.
Thus, formulas for computing "Unreserved TE-Class [i]" depend on the
Bandwidth Constraints Model in use and MUST reflect how BCs apply to
CTs. Example formulas for computing "Unreserved TE-Class [i]" Model
are provided for the Russian Dolls Model and Maximum Allocation Model
respectively in [DSTE-RDM] and [DSTE-MAM].
As with existing TE, DS-TE LSRs MUST consider the holding preemption
priority of established LSPs (as opposed to their setup preemption
priority) for the purpose of computing the unreserved bandwidth for
TE-Class [i].
11.2. Admission Control Rules
A DS-TE LSR MUST support the following admission control rule:
Regardless of how the admission control algorithm actually computes
the unreserved bandwidth for TE-Class[i] for one of its local links,
an LSP of bandwidth B, of setup preemption priority p and of Class-
Type CTc is admissible on that link if, and only if,:
B <= Unreserved Bandwidth for TE-Class[i]
where TE-Class [i] maps to < CTc , p > in the TE-Class mapping
configured on the LSR.
12. Security Considerations
This document does not introduce additional security threats beyond
those described for Diffserv ([DIFF-ARCH]) and MPLS Traffic
Engineering ([TE-REQ], [RSVP-TE], [OSPF-TE], [ISIS-TE]) and the same
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security measures and procedures described in these documents apply
here. For example, the approach for defense against theft- and
denial-of-service attacks discussed in [DIFF-ARCH], which consists of
the combination of traffic conditioning at DS boundary nodes along
with security and integrity of the network infrastructure within a
Diffserv domain, may be followed when DS-TE is in use. Also, as
stated in [TE-REQ], it is specifically important that manipulation of
administratively configurable parameters (such as those related to
DS-TE LSPs) be executed in a secure manner by authorized entities.
13. IANA Considerations
This document creates two new name spaces that are to be managed by
IANA. Also, a number of assignments from existing name spaces have
been made by IANA in this document. They are discussed below.
13.1. A New Name Space for Bandwidth Constraints Model Identifiers
This document defines in Section 5.1 a "Bandwidth Constraints Model
Id" field (name space) within the "Bandwidth Constraints" sub-TLV,
both for OSPF and ISIS. The new name space has been created by the
IANA and they will maintain this new name space. The field for this
namespace is 1 octet, and IANA guidelines for assignments for this
field are as follows:
o values in the range 0-239 are to be assigned according to the
"Specification Required" policy defined in [IANA-CONS].
o values in the range 240-255 are reserved for "Private Use" as
defined in [IANA-CONS].
13.2. A New Name Space for Error Values under the "Diffserv-aware TE
Error"
An Error Code is an 8-bit quantity defined in [RSVP] that appears in
an ERROR_SPEC object to define an error condition broadly. With each
Error Code there may be a 16-bit Error Value (which depends on the
Error Code) that further specifies the cause of the error.
This document defines in Section 6.5 a new RSVP error code, the
"Diffserv-aware TE Error" (see Section 13.3.4). The Error Values for
the "Diffserv-aware TE Error" constitute a new name space to be
managed by IANA.
This document defines, in Section 6.5, values 1 through 7 in that
name space (see Section 13.3.5).
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Future allocations of values in this name space are to be assigned by
IANA using the "Specification Required" policy defined in
[IANA-CONS].
13.3. Assignments Made in This Document
13.3.1. Bandwidth Constraints sub-TLV for OSPF Version 2
[OSPF-TE] creates a name space for the sub-TLV types within the "Link
TLV" of the Traffic Engineering Link State Advertisement (LSA) and
rules for management of this name space by IANA.
This document defines in Section 5.1 a new sub-TLV, the "Bandwidth
Constraints" sub-TLV, for the OSPF "Link" TLV. In accordance with
the IANA considerations provided in [OSPF-TE], a sub-TLV type in the
range 10 to 32767 was requested, and the value 17 has been assigned
by IANA for the "Bandwidth Constraints" sub-TLV.
13.3.2. Bandwidth Constraints sub-TLV for ISIS
[ISIS-TE] creates a name space for the sub-TLV types within the ISIS
"Extended IS Reachability" TLV and rules for management of this name
space by IANA.
This document defines in Section 5.1 a new sub-TLV, the "Bandwidth
Constraints" sub-TLV, for the ISIS "Extended IS Reachability" TLV.
In accordance with the IANA considerations provided in [ISIS-TE], a
sub-TLV type was requested, and the value 22 has been assigned by
IANA for the "Bandwidth Constraints" sub-TLV.
13.3.3. CLASSTYPE Object for RSVP
[RSVP] defines the Class Number name space for RSVP object, which is
managed by IANA. Currently allocated Class Numbers are listed at
http://www.iana.org/assignments/rsvp-parameters.
This document defines in Section 6.2.1 a new RSVP object, the
CLASSTYPE object. IANA has assigned a Class Number for this RSVP
object from the range defined in Section 3.10 of [RSVP] for objects
that, if not understood, cause the entire RSVP message to be rejected
with an error code of "Unknown Object Class". Such objects are
identified by a zero in the most significant bit of the class number
(i.e., Class-Num = 0bbbbbbb).
IANA assigned Class-Number 66 to the CLASSTYPE object. C_Type 1 is
defined in this document for the CLASSTYPE object.
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13.3.4. "Diffserv-aware TE Error" Error Code
[RSVP] defines the Error Code name space and rules for management of
this name space by IANA. Currently allocated Error Codes are listed
at http://www.iana.org/assignments/rsvp-parameters.
This document defines in Section 6.5 a new RSVP Error Code, the
"Diffserv-aware TE Error". In accordance with the IANA
considerations provided in [RSVP], Error Code 28 was assigned by IANA
to the "Diffserv-aware TE Error".
13.3.5. Error Values for "Diffserv-aware TE Error"
An Error Code is an 8-bit quantity defined in [RSVP] that appears in
an ERROR_SPEC object to define an error condition broadly. With each
Error Code there may be a 16-bit Error Value (which depends on the
Error Code) that further specifies the cause of the error.
This document defines in Section 6.5 a new RSVP error code, the
"Diffserv-aware TE Error" (see Section 13.3.4). The Error Values for
the "Diffserv-aware TE Error" constitute a new name space to be
managed by IANA.
This document defines, in Section 6.5, the following Error Values for
the "Diffserv-aware TE Error":
Value Error
1 Unexpected CLASSTYPE object
2 Unsupported Class-Type
3 Invalid Class-Type value
4 Class-Type and setup priority do not form a configured
TE-Class
5 Class-Type and holding priority do not form a configured
TE-Class
6 Class-Type and setup priority do not form a configured
TE-Class AND Class-Type and holding priority do not
form a configured TE-Class
7 Inconsistency between signaled PSC and signaled
Class-Type
8 Inconsistency between signaled PHBs and signaled
Class-Type
See Section 13.2 for allocation of other values in that name space.
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14. Acknowledgements
We thank Martin Tatham, Angela Chiu, and Pete Hicks for their earlier
contribution in this work. We also thank Sanjaya Choudhury for his
thorough review and suggestions.
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Appendix A: Prediction for Multiple Path Computation
There are situations where a head-end needs to compute paths for
multiple LSPs over a short period of time. There are potential
advantages for the head-end in trying to predict the impact of the
n-th LSP on the unreserved bandwidth when computing the path for the
(n+1)-th LSP, before receiving updated IGP information. For example,
better load-distribution of the multiple LSPs would be performed
across multiple paths. Also, when the (n+1)-th LSP would no longer
fit on a link after establishment of the n-th LSP, the head-end would
avoid Connection Admission Control (CAC) rejection. Although there
are a number of conceivable scenarios where worse situations might
result, doing such predictions is more likely to improve situations.
As a matter of fact, a number of network administrators have elected
to use such predictions when deploying existing TE.
Such predictions are local matters, are optional, and are outside the
scope of this specification.
Where such predictions are not used, the optional BC sub-TLV and the
optional Maximum Reservable Bandwidth sub-TLV need not be advertised
in IGP for the purpose of path computation, since the information
contained in the Unreserved Bw sub-TLV is all that is required by
Head-Ends to perform Constraint-Based Routing.
Where such predictions are used on head-ends, the optional BCs sub-
TLV and the optional Maximum Reservable Bandwidth sub-TLV MAY be
advertised in IGP. This is in order for the head-ends to predict as
accurately as possible how an LSP affects unreserved bandwidth values
for subsequent LSPs.
Remembering that actual admission control algorithms are left for
vendor differentiation, we observe that predictions can only be
performed effectively when the head-end LSR predictions are based on
the same (or a very close) admission control algorithm as that used
by other LSRs.
Appendix B: Solution Evaluation
B.1. Satisfying Detailed Requirements
This DS-TE Solution addresses all the scenarios presented in
[DSTE-REQ].
It also satisfies all the detailed requirements presented in
[DSTE-REQ].
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The objective set out in the last paragraph of Section 4.7 of
[DSTE-REQ], "Overbooking", is only partially addressed by this DS-TE
solution. Through support of the "LSP size Overbooking" and "Link
Size Overbooking" methods, this DS-TE solution effectively allows CTs
to have different overbooking ratios and simultaneously allows
overbooking to be tweaked differently (collectively across all CTs)
on different links. But, in a general sense, it does not allow the
effective overbooking ratio of every CT to be tweaked differently in
different parts of the network independently of other CTs, while
maintaining accurate bandwidth accounting of how different CTs
mutually affect each other through shared BCs (such as the Maximum
Reservable Bandwidth).
B.2. Flexibility
This DS-TE solution supports 8 CTs. It is entirely flexible as to
how Traffic Trunks are grouped together into a CT.
B.3. Extendibility
A maximum of 8 CTs is considered more than comfortable by the authors
of this document. A maximum of 8 TE-Classes is considered sufficient
by the authors of this document. However, this solution could be
extended to support more CTs or more TE-Classes if deemed necessary
in the future; this would necessitate additional IGP extensions
beyond those specified in this document.
Although the prime objective of this solution is support of
Diffserv-aware Traffic Engineering, its mechanisms are not tightly
coupled with Diffserv. This makes the solution amenable, or more
easily extendable, for support of potential other future Traffic
Engineering applications.
B.4. Scalability
This DS-TE solution is expected to have a very small scalability
impact compared to that of existing TE.
From an IGP viewpoint, the amount of mandatory information to be
advertised is identical to that of existing TE. One additional sub-
TLV has been specified, but its use is optional, and it only contains
a limited amount of static information (at most 8 BCs).
We expect no noticeable impact on LSP Path computation because, as
with existing TE, this solution only requires Constrained Shortest
Path First (CSPF) to consider a single unreserved bandwidth value for
any given LSP.
Le Faucheur Standards Track PAGE 30
RFC 4124 Protocols for Diffserv-aware TE June 2005
From a signaling viewpoint, we expect no significant impact due to
this solution because it only requires processing of one additional
item of information (the Class-Type) and does not significantly
increase the likelihood of CAC rejection. Note that DS-TE has some
inherent impact on LSP signaling in that it assumes that different
classes of traffic are split over different LSPs so that more LSPs
need to be signaled. However, this is due to the DS-TE concept
itself and not to the actual DS-TE solution discussed here.
B.5. Backward Compatibility/Migration
This solution is expected to allow smooth migration from existing TE
to DS-TE. This is because existing TE can be supported as a
particular configuration of DS-TE. This means that an "upgraded" LSR
with a DS-TE implementation can directly interwork with an "old" LSR
supporting existing TE only.
This solution is expected to allow smooth migration when the number
of CTs actually deployed is increased, as it only requires
configuration changes. However, these changes need to be performed
in a coordinated manner across the DS-TE domain.
Appendix C: Interoperability with Non-DS-TE Capable LSRs
This DSTE solution allows operations in a hybrid network where some
LSRs are DS-TE capable and some are not, as may occur during
migration phases. This appendix discusses the constraints and
operations in such hybrid networks.
We refer to the set of DS-TE-capable LSRs as the DS-TE domain. We
refer to the set of non-DS-TE-capable (but TE-capable) LSRs as the
TE-domain.
Hybrid operations require that the TE-Class mapping in the DS-TE
domain be configured so that:
- a TE-Class exists for CT0 for every preemption priority
actually used in the TE domain, and
- the index in the TE-class mapping for each of these TE-
Classes is equal to the preemption priority.
Le Faucheur Standards Track PAGE 31
RFC 4124 Protocols for Diffserv-aware TE June 2005
For example, imagine the TE domain uses preemption 2 and 3. Then,
DS-TE can be deployed in the same network by including the following
TE-Classes in the TE-Class mapping:
i <---> CT preemption
====================================
2 CT0 2
3 CT0 3
Another way to look at this is to say that although the whole TE-
class mapping does not have to be consistent with the TE domain, the
subset of this TE-Class mapping applicable to CT0 effectively has to
be consistent with the TE domain.
Hybrid operations also require that:
- non-DS-TE-capable LSRs be configured to advertise the Maximum
Reservable Bandwidth, and
- DS-TE-capable LSRs be configured to advertise BCs (using the
Max Reservable Bandwidth sub-TLV as well as the BCs sub-TLV,
as specified in Section 5.1).
This allows DS-TE-capable LSRs to identify non-DS-TE-capable LSRs
unambiguously.
Finally, hybrid operations require that non-DS-TE-capable LSRs be
able to accept Unreserved Bw sub-TLVs containing non decreasing
bandwidth values (i.e., with Unreserved [p] < Unreserved [q] with p <
q).
In such hybrid networks, the following apply:
- CT0 LSPs can be established by both DS-TE-capable LSRs and
non-DS-TE-capable LSRs.
- CT0 LSPs can transit via (or terminate at) both DS-TE-capable
LSRs and non-DS-TE-capable LSRs.
- LSPs from other CTs can only be established by DS-TE-capable
LSRs.
- LSPs from other CTs can only transit via (or terminate at)
DS-TE-capable LSRs.
Le Faucheur Standards Track PAGE 32
RFC 4124 Protocols for Diffserv-aware TE June 2005
Let us consider the following example to illustrate operations:
LSR0--------LSR1----------LSR2
Link01 Link12
where:
LSR0 is a non-DS-TE-capable LSR
LSR1 and LSR2 are DS-TE-capable LSRs
Let's assume again that preemptions 2 and 3 are used in the TE-domain
and that the following TE-Class mapping is configured on LSR1 and
LSR2:
i <---> CT preemption
====================================
0 CT1 0
1 CT1 1
2 CT0 2
3 CT0 3
rest unused
LSR0 is configured with a Max Reservable Bandwidth = m01 for Link01.
LSR1 is configured with a BC0 = x0, a BC1 = x1 (possibly = 0), and a
Max Reservable Bandwidth = m10 (possibly = m01) for Link01.
In IGP for Link01, LSR0 will advertise:
- Max Reservable Bw sub-TLV = <m01>
- Unreserved Bw sub-TLV = <CT0/0, CT0/1, CT0/2, CT0/3, CT0/4,
CT0/5, CT0/6, CT0/7>
On receipt of such advertisement, LSR1 will:
- understand that LSR0 is not DS-TE-capable because it
advertised a Max Reservable Bw sub-TLV and no Bandwidth
Constraints sub-TLV, and
- conclude that only CT0 LSPs can transit via LSR0 and that
only the values CT0/2 and CT0/3 are meaningful in the
Unreserved Bw sub-TLV. LSR1 may effectively behave as if the
six other values contained in the Unreserved Bw sub-TLV were
set to zero.
Le Faucheur Standards Track PAGE 33
RFC 4124 Protocols for Diffserv-aware TE June 2005
In IGP for Link01, LSR1 will advertise:
- Max Reservable Bw sub-TLV = <m10>
- Bandwidth Constraints sub-TLV = <BC Model ID, x0, x1>
- Unreserved Bw sub-TLV =
<CT1/0, CT1/1, CT0/2, CT0/3, 0, 0, 0, 0>
On receipt of such advertisement, LSR0 will:
- ignore the Bandwidth Constraints sub-TLV (unrecognized)
- correctly process CT0/2 and CT0/3 in the Unreserved Bw sub-
TLV and use these values for CTO LSP establishment
- incorrectly believe that the other values contained in the
Unreserved Bw sub-TLV relate to other preemption priorities
for CT0; but it will actually never use those since we assume
that only preemptions 2 and 3 are used in the TE domain.
Normative References
[DSTE-REQ] Le Faucheur, F. and W. Lai, "Requirements for Support
of Differentiated Services-aware MPLS Traffic
Engineering", RFC 3564, July 2003.
[MPLS-ARCH] Rosen, E., Viswanathan, A. and R. Callon,
"Multiprotocol Label Switching Architecture", RFC 3031,
January 2001.
[TE-REQ] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M. and
J. McManus, "Requirements for Traffic Engineering Over
MPLS", RFC 2702, September 1999.
[OSPF-TE] Katz, D., Kompella, K. and D. Yeung, "Traffic
Engineering (TE) Extensions to OSPF Version 2", RFC
3630, September 2003.
[ISIS-TE] Smit, H. and T. Li, "Intermediate System to
Intermediate System (IS-IS) Extensions for Traffic
Engineering (TE)", RFC 3784, June 2004.
[RSVP-TE] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan,
V. and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
Le Faucheur Standards Track PAGE 34
RFC 4124 Protocols for Diffserv-aware TE June 2005
[RSVP] Braden, R., Zhang, L., Berson, S., Herzog, S. and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version
1 Functional Specification", RFC 2205, September 1997.
[DIFF-MPLS] Le Faucheur, F., Wu, L., Davie, B., Davari, S.,
Vaananen, P., Krishnan, R., Cheval, P. and J. Heinanen,
"Multi-Protocol Label Switching (MPLS) Support of
Differentiated Services", RFC 3270, May 2002.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[IANA-CONS] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26, RFC
2434, October 1998.
Informative References
[DIFF-ARCH] Blake, S., Black, D., Carlson, M., Davies, E., Wang,
Z., and W. Weiss, "An Architecture for Differentiated
Service", RFC 2475, December 1998.
[DSTE-RDM] Le Faucheur,F., Ed., "Russian Dolls Bandwidth
Constraints Model for Diffserv-aware MPLS Traffic
Engineering", RFC 4127, June 2005.
[DSTE-MAM] Le Faucheur, F. and W. Lai, "Maximum Allocation
Bandwidth Constraints Model for Diffserv-aware Traffice
Engineering", RFC 4125, June 2005.
[DSTE-MAR] Ash, J., "Max Allocation with Reservation Bandwidth
Constraints Model for DiffServ-aware MPLS Traffic
Engineering & Performance Comparisons", RFC 4126, June
2005.
[GMPLS-SIG] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Functional Description", RFC 3471,
January 2003.
[GMPLS-ROUTE] Kompella, et al., "Routing Extensions in Support of
Generalized MPLS", Work in Progress.
[BUNDLE] Kompella, Rekhter, Berger, "Link Bundling in MPLS
Traffic Engineering", Work in Progress.
[HIERARCHY] Kompella, Rekhter, "LSP Hierarchy with Generalized MPLS
TE", Work in Progress.
Le Faucheur Standards Track PAGE 35
RFC 4124 Protocols for Diffserv-aware TE June 2005
[REROUTE] Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
Extensions to RSVP-TE for LSP Tunnels", RFC 4090, May
2005.
Editor's Address
Francois Le Faucheur
Cisco Systems, Inc.
Village d'Entreprise Green Side - Batiment T3
400, Avenue de Roumanille
06410 Biot-Sophia Antipolis
France
Phone: +33 4 97 23 26 19
EMail: flefauch@cisco.com
Le Faucheur Standards Track PAGE 36
RFC 4124 Protocols for Diffserv-aware TE June 2005
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Le Faucheur Standards Track PAGE 37
Protocol Extensions for Support of Diffserv-aware MPLS Traffic Engineering
RFC TOTAL SIZE: 79265 bytes
PUBLICATION DATE: Monday, June 27th, 2005
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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