Francois Le Faucheur, Editor
Cisco Systems, Inc.
IETF Internet Draft
Expires: March, 2004
Document: draft-ietf-tewg-diff-te-proto-06.txt January, 2004
Protocol extensions for support of
Differentiated-Service-aware MPLS Traffic Engineering
Status of this Memo
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all provisions of Section 10 of RFC2026. Internet-Drafts are
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document specifies the protocol extensions for support of
Differentiated-Service-aware MPLS Traffic Engineering (DS-TE). This
includes generalization of the semantic of a number of IGP extensions
already defined for existing MPLS Traffic Engineering in RFC3630 and
RFC-TBD as well as additional IGP extensions beyond those. This also
includes extensions to RSVP-TE signaling beyond those already
specified in RFC3209 for existing MPLS Traffic Engineering. These
extensions address the Requirements for DS-TE spelt out in RFC3564.
<RFC-Editor-note> To be removed by the RFC editor at the time of
publication:
Please replace ôTBDö above by the actual RFC number when
an RFC number is allocated to [ISIS-TE]
Le Faucheur, et. al 1
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</RFC-Editor-note>
Table of Contents
<RFC-Editor-note> To be removed by the RFC editor at the time of
publication:
Could you please insert the Table of Content (or otherwise
remove this section)?
</RFC-Editor-note>
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 [RFC2119].
1. Introduction
[DSTE-REQ] presents the Service Providers requirements for support of
Differentiated-Service (Diff-Serv)-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
spelt out in [DSTE-REQ] including environments relying on distributed
Constraint Based Routing (e.g. path computation involving Head-end
LSRs).
[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 model are outside the scope of this document. While 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 ôRussian Dollsö Model specified in [DSTE-RDM], the
ôMaximum Allocationö Model specified in [DSTE-MAM] and the ôMaximum
Allocation with Reservationö Model specified in [DSTE-MAR].
2. Contributing Authors
This document was the collective work of several. The text and
content of this document was contributed by the editor and the co-
authors listed below. (The contact information for the editor appears
in Section 18, and is not repeated below.)
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Protocols for Diff-Serv-aware TE January 2004
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: Email: tnadeau@cisco.com
btownsend@tenornetworks.com
Darek Skalecki
Nortel Networks
3500 Carling Ave,
Nepean K2H 8E9
Phone: +1-613-765-2252
Email: dareks@nortelnetworks.com
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. which are to be treated equivalently from the DS-TE
perspective] which are placed inside a Label Switched Path.
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
set-up priority, as the holding priority or both.
Definitions for a number of MPLS terms are not repeated here. Those
can be found in [MPLS-ARCH].
4. Configurable Parameters
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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 ôRegardless of the Bandwidth Constraints
Model, the DS-TE solution MUST allow support for up to 8 BCs.ö
For DS-TE, the existing ôMaximum Reservable link bandwidthö parameter
is retained but its semantic is generalized and interpreted as the
aggregate bandwidth constraints across all Class-Types, so that,
independently of the Bandwidth Constraints Model in use:
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 Bandwidth Constraints i.e. BC0, BC1 , ... BC7. The
LSR MUST interpret these Bandwidth Constraints in accordance with the
supported Bandwidth Constraints Model (i.e. what bandwidth constraint
applies to what Class-Type and how).
Where the Bandwidth Constraints Model imposes some relationship among
the values to be configured for these Bandwidth Constraints, the LSR
MUST enforce those at configuration time. For example, when the
ôRussian Dollö Bandwidth Constraints Model ([DSTE-RDM]) is used, the
LSR must ensure that BCi is configured smaller 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 historically
used in existing TE deployment, which are :
(i) To take into account the overbooking/underbooking ratio
appropriate for the OA/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 ôLSP Size Overbooking
methodö. AND/OR
(ii) To take into account the overbooking/underbooking ratio at
the time of configuring the Maximum Reservable
Bandwidth/Bandwidth Constraints and use values which are
larger(overbooking) or smaller(underbooking) than actually
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supported by the link. We refer to this method as the ôLink
Size Overbooking methodö.
The ôLSP Size Overbookingö method and the ôLink Size Overbookingö
method 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.
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
Class Types. The preemption attributes of setup priority and holding
priority retain existing semantics, and in particular these semantics
are not affected by the LSP Class Type. This means that if LSP1
contends with LSP2 for resources, LSP1 may preempt LSP2 if LSP1 has a
higher set-up 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. ôiö above) and the Class-Type (i.e. ôcö
above) or the preemption priority (i.e. ôpö 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 ôUnusedö. 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
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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.
When the TE-class mapping needs to be modified in the DS-TE domain,
care must 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 which 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 which 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 Bandwidth Constraints 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.
4.4. Examples of Parameters Configuration
Protocols for Diff-Serv-aware TE January 2004
For illustrative purposes, we now present a few examples of how these
configurable parameters may be used. All these examples assume that
different bandwidth constraints 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 Class Types
(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, set-up priority =0, holding priority=0
Data LSPs would then be configured with:
- CT=CT0, set-up 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, set-up priority =0, holding priority=0
Large size Data LSPs could be configured with:
- CT=CT0, set-up priority = 1, holding priority=1
Small size Voice LSPs could be configured with:
- CT=CT1, set-up priority = 2, holding priority=2
Small size Data LSPs could be configured with:
- CT=CT0, set-up priority = 3, holding priority=3.
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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 while
also achieving 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, set-up priority = 0, holding priority=0.
Small size Voice LSPs could be configured with:
- CT=CT1, set-up priority = 1, holding priority=1.
Large size Data LSPs could be configured with:
- CT=CT0, set-up priority = 2, holding priority=2.
Small size Data LSPs could be configured with:
- CT=CT0, set-up 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.
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:
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- CT=CT1, set-up priority =0, holding priority=0
Data LSPs would then be configured with:
- CT=CT0, set-up 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, set-up priority = 0, holding priority=0.
Small size Voice LSPs could be configured with:
- CT=CT1, set-up priority = 1, holding priority=0.
Large size Data LSPs could be configured with:
- CT=CT0, set-up priority = 2, holding priority=1.
Small size Data LSPs could be configured with:
- CT=CT0, set-up 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.
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
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As detailed above in section 4.1.1, up to 8 Bandwidth Constraints
( BCb, 0 <= b <= 7) are configurable on any given link.
With DS-TE, the existing ôMaximum Reservable Bandwidthö sub-TLV
([OSPF-TE], [ISIS-TE]) is retained with a generalized semantic 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 Bandwidth Constraints (BC0 to BC7):
ôBandwidth Constraintsö sub-TLV:
- Bandwidth Constraints Model Id (1 octet)
- Reserved (3 octets)
- Bandwidth Constraints (Nx4 octets)
Where:
- With OSPF, the sub-TLV is a sub-TLV of the ôLink TLVö and its
sub-TLV type is TBD
- With ISIS, the sub-TLV is a sub-TLV of the ôextended IS
reachability TLVö and its sub-TLV type is TBD ().
<IANA-note> To be removed by the RFC editor at the time of
publication:
When the sub-TLV numbers are allocated by IANA for OSPF and
ISIS, replace ôTBDö in the two bullet points above by the respective
assigned value. See IANA Considerations section for allocation
request.
</IANA-note>
- Bandwidth Constraints Model Id: 1 octet identifier for the
Bandwidth Constraints Model currently in use by the LSR
initiating the IGP advertisement. See the IANA Considerations
section below 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.
- Bandwidth Constraints: contains BC0, BC1,... BC(N-1).
Each Bandwidth Constraint 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,
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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 ôBandwidth Constraintsö 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 Bandwidth Constraints.
A DS-TE LSR which does advertise Bandwidth Constraints MUST use the
new ôBandwidth Constraintsö sub-TLV (in addition to the existing
Maximum Reservable Bandwidth sub-TLV) to do so. For example,
considering 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 Bandwidth Constraints would
include in the IGP advertisement the Maximum Reservable Bandwidth
sub-TLV as well as the ôBandwidth Constraintsö sub-TLV, where the
former should contain the aggregate bandwidth constraint across all
CTs and the latter would contain BC0 and BC1.
A DS-TE LSR receiving the ôBandwidth Constraintsö sub-TLV with a
Bandwidth Constraints Model Id which 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
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
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With DS-TE, the existing ôUnreserved Bandwidthö 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 semantic. The Unreserved Bandwidth sub-TLV
still carries eight bandwidth values but they now correspond to the
unreserved bandwidth for each of the TE-Class (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 which 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, with
unreserved bandwidth for TE-Class [0] occurring 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 ôUnreserved TE-Class [i]ö. It indicates the
bandwidth that is available, for reservation, to an LSP which :
- 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.
Since the bandwidth values are now ordered by TE-class index and thus
can relate to different CTs with different bandwidth constraints and
can relate to any arbitrary preemption priority, a DS-TE LSR MUST NOT
assume any ordered relationship among these bandwidth values.
With existing TE, since all preemption priorities reflect the same
(and only) bandwidth constraints and since bandwidth values are
advertised in preemption priority order, the following relationship
is always true, and is often assumed by TE implementations:
If i < j , then ôUnreserved Bw [i]ö >= ôUnreserved Bw [j]ö
With DS-TE, no relationship is to be assumed so that:
If i < j , then any of the following relationship may be true
ôUnreserved TE-Class [i]ö = ôUnreserved TE-Class [j]ö
OR
ôUnreserved TE-Class [i]ö > ôUnreserved TE-Class [j]ö
OR
ôUnreserved TE-Class [i]ö < ôUnreserved TE-Class [j]ö.
Rules for computing ôUnreserved TE-Class [i]ö are specified in
section 11.
If TE-Class[i] is unused, the value advertised by the IGP in
ôUnreserved TE-Class [i]ö MUST be set to zero by the LSR generating
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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
Diff-Serv-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 Diff-Serv 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 C-Type 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 set up do
not have to support this object.
An LSR supporting DS-TE MUST support the CLASSTYPE Object.
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> ]
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6.2. CLASSTYPE Object
The CLASSTYPE object Class Name is CLASSTYPE. Its Class Number is
TBD. Currently, there is only one defined C_Type which is C_Type 1.
The CLASSTYPE object format is shown below.
<IANA-note> To be removed by the RFC editor at the time of
publication:
When the RSVP Class-Num is assigned by IANA replace ôTBDö
above by the assigned value. See IANA Considerations section
for allocation request.
</IANA-note>
6.2.1. CLASSTYPE object
Class Number = TBD
Class Type = 1
<IANA-note> To be removed by the RFC editor at the time of
publication:
When the RSVP Class Number is assigned by IANA replace ôTBDö
above by the assigned value. See IANA Considerations section
for allocation request.
</IANA-note>
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.
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
Le Faucheur et. al 14
Protocols for Diff-Serv-aware TE January 2004
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
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 the Path message contained a CLASSTYPE object or not).
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 which:
- contains the CLASSTYPE object, but
- which does not contain a LABEL_REQUEST object or which does
not have a session type of LSP_Tunnel_IPv4,
MUST send a PathErr towards the sender with the error code æDiff-
Serv-aware TE ErrorÆ and an error value of æUnexpected CLASSTYPE
objectÆ. Those are defined below in section 6.5.
An LSR receiving a Path message with the CLASSTYPE object, which:
- recognizes the CLASSTYPE object, but
- does not support the particular Class-Type,
MUST send a PathErr towards the sender with the error code æDiff-
Serv-aware TE ErrorÆ and an error value of æUnsupported Class-TypeÆ.
Those are defined below in section 6.5.
An LSR receiving a Path message with the CLASSTYPE object, which:
- 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 æDiff-
Serv-aware TE ErrorÆ and an error value of æInvalid Class-Type
valueÆ. Those are defined below in section 6.5.
An LSR receiving a Path message with the CLASSTYPE object, which:
-
- supports the particular Class-Type, but
Le Faucheur et. al 15
Protocols for Diff-Serv-aware TE January 2004
- determines that the tuple formed by (i) this Class-Type and
(ii) the set-up 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 æDiff-
Serv-aware TE ErrorÆ and an error value of æCT and setup priority do
not form a configured TE-ClassÆ. Those are defined below in section
6.5.
An LSR receiving a Path message with the CLASSTYPE object, which:
- recognizes the CLASSTYPE object,
- 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,
MUST send a PathErr towards the sender with the error code æDiff-
Serv-aware TE ErrorÆ and an error value of æCT and holding priority
do not form a configured TE-ClassÆ. Those are defined below in
section 6.5.
An LSR receiving a Path message with the CLASSTYPE object and with
the DIFFSERV object for an L-LSP, which:
- recognizes the CLASSTYPE object,
- has local knowledge of the relationship between Class-Types
and PSC (e.g. via configuration)
- based on this local knowledge, determines that the 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 æDiff-
Serv-aware TE ErrorÆ and an error value of æInconsistency between
signaled PSC and signaled CTÆ. Those are defined below in section
6.5.
An LSR receiving a Path message with the CLASSTYPE object and with
the DIFFSERV object for an E-LSP, which:
- recognizes the CLASSTYPE object,
- has local knowledge of the relationship between Class-Types
and PHBs (e.g. via configuration)
- based on this local knowledge, determines 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 æDiff-
Serv-aware TE ErrorÆ and an error value of æInconsistency between
signaled PHBs and signaled CTÆ. Those are defined below in section
An LSR MUST handle the situations where the LSP can not be accepted
for other reasons than those already discussed in this section, in
accordance with [RSVP-TE] and [DIFF-MPLS] (e.g. a reservation is
rejected by admission control, a label can not be associated).
Le Faucheur et. al 16
Protocols for Diff-Serv-aware TE January 2004
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 æUnknown object classÆ toward the
sender).
An LSR that recognizes the CLASSTYPE object Class-Num but 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 æUnknown object C-TypeÆ
toward the sender).
In both situations, this causes the path set-up to fail. The sender
SHOULD notify the operator/management-system that an LSP cannot be
established and possibly might take action to retry reservation
establishment without the CLASSTYPE object.
6.5. Error Codes For Diff-Serv-aware TE
In the procedures described above, certain errors must be reported as
a æDiff-Serv-aware TE ErrorÆ. The value of the æDiff-Serv-aware TE
ErrorÆ error code is (TBD)().
<IANA-note> To be removed by the RFC editor at the time of
publication:
When the ôDiff-Serv-aware TE Errorö Error Code is assigned by
IANA, replace ôTBDö above by the assigned value.
See IANA Considerations section for allocation request.
</IANA-note>
The following defines error values for the Diff-Serv-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 Inconsistency between signaled PSC and signaled
Class-Type
7 Inconsistency between signaled PHBs and signaled
Class-Type
See the IANA Considerations section for allocation of additional
Values.
Le Faucheur et. al 17
Protocols for Diff-Serv-aware TE January 2004
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]
[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 otherwise specify
encodings or behavior that have a different meaning for an DS-TE
router.
In order for an implementation to support both this specification for
Diff-Serv-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 ôMaximum Reservable Bandwidthö in a
generalized manner, such as it is used in this specification.
Additionally, current and future MPLS enhancements may include more
precise specification for how they interact with Diff-Serv-aware TE.
7.1. DS-TE support and references to preemption priority
When a router supports both Diff-Serv-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 to be 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 interpret it as such as well.
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 the preemption priorities 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 Diff-Serv-aware TE and MPLS protocol
extensions such as those mentioned above, advertisements of Maximum
Reservable Bandwidth MUST be done with the generalized interpretation
defined above in section 4.1.1 as the aggregate bandwidth constraint
across all Class-Types and MAY also allow the optional advertisement
of all Bandwidth Constraints.
Le Faucheur et. al 18
Protocols for Diff-Serv-aware TE January 2004
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 set-up 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 bandwidth
constraint which is to fit in ôUnreserved TE-Class [i]ö as advertised
by the IGP for every link. Thus, no changes are required to the
existing TE Constraint Based Routing algorithm itself.
The Constraint Based Routing algorithm MAY also take into account,
when used, the optional additional information advertised in IGP such
as the Bandwidth Constraints and the Maximum Reservable Bandwidth. As
an example, the Bandwidth Constraints MIGHT be used as a tie-breaker
criteria in situations where multiple paths, otherwise equally
attractive, are possible.
9. Diff-Serv 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 Diff-Serv scheduler. In addition, the Diff-Serv
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 to a PSC/OA within
a Class Type by the Diff-Serv scheduler.
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
Le Faucheur et. al 19
Protocols for Diff-Serv-aware TE January 2004
As with existing TE, the IGP may advertise:
- Maximum Reservable Bandwidth containing a bandwidth
constraint applying across all LSPs
Since all LSPs transport traffic from CT0, RSVP-TE signaling is done
without explicit signaling of the Class-Type (which is only used for
other Class-Types than CT0 as explained in section 6) as with
existing TE.
11. Computing ôUnreserved TE-Class [i]ö and Admission Control Rules
11.1. Computing ôUnreserved TE-Class [i]ö
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
implementations since 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 which 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 of the Bandwidth Constraints relevant to
the CT associated with TE-Class[i] in accordance with the Bandwidth
Constraints Model. Thus, formulas for computing ôUnreserved TE-Class
[i]ö depend on the Bandwidth Constraints Model in use and MUST
reflect how bandwidth constraints apply to CTs. Example formulas for
computing ôUnreserved TE-Class [i]ö 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 set-up 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:
Le Faucheur et. al 20
Protocols for Diff-Serv-aware TE January 2004
Regardless of how the admission control algorithm actually computes
the unreserved bandwidth for TE-Class[i] for one of its local link,
an LSP of bandwidth B, of set-up 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 Diff-Serv ([DIFF-ARCH]) and MPLS Traffic
Engineering ([TE-REQ], [RSVP-TE], [OSPF-TE], [ISIS-TE]) and the same
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
Diff-Serv 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. Acknowledgments
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.
14. IANA Considerations
This document creates two new name spaces which are to be managed by
IANA. Also, a number of assignments from existing name spaces have
been made by IANA in this document. Those are discussed below.
14.1. 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. IANA is requested to create and maintain this
new name space. The field for this namespace is 1 octet, and IANA
guidelines for assignments for this field are as follows:
Le Faucheur et. al 21
Protocols for Diff-Serv-aware TE January 2004
o values in the range 0-127 are to be assigned according to
the "Specification Required" policy defined in [IANA-CONS].
o values in the range 128-239 are not to be assigned at this
time. Before any assignments can be made in this range, there MUST be
a Standards Track RFC that specifies IANA Considerations that cover
assignment within that range.
o values in the range 240-255 are for experimental use; these
will not be registered with IANA, and MUST NOT be mentioned by RFCs.
14.2. A new name space for Error Values under the ôDiff-Serv-aware TE
Errorö
An Error Code is an 8-bit quantity defined in [RSVP] that appears in
an ERROR_SPEC object to broadly define an error condition. 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
"Diff-Serv-aware TE Error" (see section 14.3.4). The Error Values for
the "Diff-Serv-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 14.3.5).
Future allocations of values in this name space are to be assigned by
IANA using the ôSpecification Requiredö policy defined in [IANA-
CONS].
14.3. Assignments made in this Document
14.3.1. Bandwidth Constraints sub-TLV for OSPF version 2
[OSPF-TE] creates a name space for the sub-TLV types within the ôLink
TLVö of the Traffic Engineering 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 TBD has been assigned
by IANA for the "Bandwidth Constraints" sub-TLV.
<IANA-note> To be removed by the RFC editor at the time of
publication:
When the sub-TLV Type is assigned by IANA replace ôTBDö above
by the assigned value.
</IANA-note>
14.3.2. Bandwidth Constraints sub-TLV for ISIS
Le Faucheur et. al 22
Protocols for Diff-Serv-aware TE January 2004
[ISIS-TE] creates a name space for the sub-TLV types within the ISIS
ôExtended IS Reachabilityö 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 ôExtended IS Reachability" TLV. In
accordance with the IANA considerations provided in [ISIS-TE], a sub-
TLV type was requested and the value TBD has been assigned by IANA
for the "Bandwidth Constraints" sub-TLV.
<IANA-note> To be removed by the RFC editor at the time of
publication:
When the sub-TLV Type is assigned by IANA replace ôTBDö above
by the assigned value.
</IANA-note>
14.3.3. 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
ôhttp://www.iana.org/assignments/rsvp-parameters"
This document defines in section 6.2.1 a new RSVP object, the
CLASSTYPE object. IANA was requested to assign a Class Number for
this RSVP object from the range defined in section 3.10 of [RSVP] for
those objects which, 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 TBD to the CLASSTYPE object. C_Type 1 is
defined in this document for the CLASSTYPE object.
<IANA-note> To be removed by the RFC editor at the time of
publication:
When the RSVP Class-Num is assigned by IANA replace ôTBDö
above by the assigned value.
</IANA-note>
14.3.4. ôDiff-Serv-aware TE Errorö 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 ôhttp://www.iana.org/assignments/rsvp-parameters"
This document defines in section 6.5 a new RSVP Error Code, the
"Diff-Serv-aware TE Error". In accordance with the IANA
considerations provided in [RSVP], Error Code TBD was assigned by
IANA to the ôDiff-Serv-aware TE Errorö.
Le Faucheur et. al 23
Protocols for Diff-Serv-aware TE January 2004
<IANA-note> To be removed by the RFC editor at the time of
publication:
When the RSVP Class-Num is assigned by IANA replace ôTBDö
above by the assigned value.
</IANA-note>
14.3.5. Error Values for ôDiff-Serv-aware TE Errorö
An Error Code is an 8-bit quantity defined in [RSVP] that appears in
an ERROR_SPEC object to broadly define an error condition. 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
"Diff-Serv-aware TE Error" (see section 14.3.4). The Error Values for
the "Diff-Serv-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 ôDiff-Serv-aware TE Errorö:
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 Inconsistency between signaled PSC and signaled
Class-Type
7 Inconsistency between signaled PHBs and signaled
Class-Type
See section 14.2 for allocation of other values in that name space.
15. Intellectual Property Considerations
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in RFC 2028. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
Le Faucheur et. al 24
Protocols for Diff-Serv-aware TE January 2004
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
16. Normative References
[DSTE-REQ] Le Faucheur et al, Requirements for support of Diff-Serv-
aware MPLS Traffic Engineering, RFC3564, .
[MPLS-ARCH] Rosen et al., ôMultiprotocol Label Switching
Architectureö, RFC3031.
[DIFF-ARCH] Blake et al., ôAn Architecture for Differentiated
Servicesö, RFC2475.
[TE-REQ] Awduche et al., ôRequirements for Traffic Engineering Over
MPLSö, RFC2702.
[OSPF-TE] Katz et al., ôTraffic Engineering (TE) Extensions to OSPF
Version 2ö, RFC3630.
[ISIS-TE] Smit, Li, IS-IS extensions for Traffic Engineering, draft-
ietf-isis-traffic-05.txt, work in progress.
[RSVP-TE] Awduche et al, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209.
[RSVP] Braden et al, "Resource ReSerVation Protocol (RSVP) - Version
1 Functional Specification", RFC 2205.
[DIFF-MPLS] Le Faucheur et al, "MPLS Support of Diff-Serv", RFC3270.
[RFC2119] S. Bradner, Key words for use in RFCs to Indicate
Requirement Levels, RFC2119.
[IANA-CONS], T. Narten et al, ôGuidelines for Writing an IANA
Considerations Section in RFCsö, RFC2434.
17. Informative References
[DSTE-RDM] Le Faucheur et al., ôRussian Dolls Bandwidth Constraints
Model for DS-TEö, draft-ietf-tewg-diff-te-russian-04.txt, work in
progress.
Le Faucheur et. al 25
Protocols for Diff-Serv-aware TE January 2004
[DSTE-MAM] Le Faucheur, Lai, ôMaximum Allocation Bandwidth
Constraints Model for DS-TEö, draft-ietf-tewg-diff-te-mam-02.txt,
work in progress .
[DSTE-MAR] Ash, ôMax Allocation with Reservation Bandwidth
Constraints Model for MPLS/DiffServ TE & Performance Comparisonsö,
draft-ietf-tewg-diff-te-mar-03.txt, work in progress .
[GMPLS-SIG] Berger et. al., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description", RFC3471
[GMPLS-ROUTE] Kompella et. al., "Routing Extensions in Support of
Generalized MPLS", draft-ietf-ccamp-gmpls-routing-09.txt, work in
progress.
[BUNDLE] Kompella, Rekhter, Berger, "Link Bundling in MPLS Traffic
Engineering", draft-ietf-mpls-bundle-04.txt, work in progress.
[HIERARCHY] Kompella, Rekhter, "LSP Hierarchy with Generalized MPLS
TE", draft-ietf-mpls-lsp-hierarchy-08.txt, work in progress.
[REROUTE] Pan et. al., "Fast Reroute Extensions to RSVP-TE for LSP
Tunnels", draft-ietf-mpls-rsvp-lsp-fastreroute-03.txt, work in
progress.
18. EditorÆs 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
19. Full Copyright Statement
Copyright (C) The Internet Society (2004). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
Le Faucheur et. al 26
Protocols for Diff-Serv-aware TE January 2004
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Appendix A û 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. One example
would be to perform better load-distribution of the multiple LSPs
across multiple paths. Another example would be to avoid CAC
rejection when the (n+1)-th LSP would no longer fit on a link after
establishment of the n-th LSP. While there are also a number of
conceivable scenarios where doing such predictions might result in a
worse situation, it is more likely to improve the situation. 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 Bandwidth
Constraint 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 Bandwidth
Constraints 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 used by
other LSRs.
Le Faucheur et. al 27
Protocols for Diff-Serv-aware TE January 2004
Appendix B - Solution Evaluation
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].
The objective set out in the last paragraph of section ô4.7
overbookingö of [DSTE-REQ] is only partially addressed by this DS-TE
solution. Through support of the ôLSP Size Overbookingö and ôLink
Size Overbookingö 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 Bandwidth Constraints (such
as the Maximum Reservable Bandwidth).
2. Flexibility
This DS-TE solution supports 8 CTs. It is entirely flexible as to how
Traffic Trunks are grouped together into a CT.
3. Extendibility
A maximum of 8 CTs is considered by the authors of this document as
more than comfortable. A maximum of 8 TE-classes is considered by the
authors of this document as sufficient. 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 Diff-
Serv-aware Traffic Engineering, its mechanisms are not tightly
coupled with Diff-Serv. This makes the solution amenable, or more
easily extendable, for support of potential other future Traffic
Engineering applications.
4. Scalability
This DS-TE solution is expected to have a very small scalability
impact compared to existing TE.
From an IGP viewpoint, the amount of mandatory information to be
advertised is identical to existing TE. One additional sub-TLV has
been specified, but its use is optional and it only contains a
Le Faucheur et. al 28
Protocols for Diff-Serv-aware TE January 2004
limited amount of static information (at most 8 Bandwidth
Constraints).
We expect no noticeable impact on LSP Path computation since, as with
existing TE, this solution only requires CSPF to consider a single
unreserved bandwidth value for any given LSP.
From a signaling viewpoint we expect no significant impact due to
this solution since it only requires processing of one additional
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 the sense that it assumes that different classes
of traffic are split over different LSPs so that more LSPs need to be
signaled; but this is due to the DS-TE concept itself and not to the
actual DS-TE solution discussed here.
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 ôupgradedö LSR
with a DS-TE implementation can directly interwork with an ôoldö LSR
supporting existing TE only.
This solution is expected to allow smooth migration when increasing
the number of CTs actually deployed since it only requires
configuration changes. however, these changes must be performed in a
coordinated manner across the DS-TE domain.
Appendix C û Interoperability with non DS-TE capable LSRs
This DSTE solution allows operations in a hybrid network where some
LSRs are DS-TE capable while some LSRs are not DS-TE capable, which
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 requires that the TE-class mapping in the DS-TE
domain is configured so that:
- a TE-class exist for CT0 for every preemption priority
actually used in the TE domain
- the index in the TE-class mapping for each of these TE-
classes is equal to the preemption priority.
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
Le Faucheur et. al 29
Protocols for Diff-Serv-aware TE January 2004
====================================
2 CT0 2
3 CT0 3
Another way to look at this is to say that, the whole TE-class
mapping does not have to be consistent with the TE domain, but the
subset of this TE-Class mapping applicable to CT0 must effectively be
consistent with the TE domain.
Hybrid operations also requires that:
- non DS-TE capable LSRs be configured to advertise the Maximum
Reservable Bandwidth
- DS-TE capable LSRs be configured to advertise Bandwidth
Constraints (using the Max Reservable Bandwidth sub-TLV as
well as the Bandwidth Constraints sub-TLV, as specified in
section 5.1 above).
This allows DS-TE capable LSRs to unambiguously identify non DS-TE
capable LSRs.
Finally hybrid operations require that non DS-TE capable LSRs be able
to accept Unreserved Bw sub-TLVs containing non decreasing bandwidth
values (ie with Unreserved [p] < Unreserved [q] with p <q).
In such hybrid networks :
- CT0 LSPs can be established by both DS-TE capable LSRs and
non-DSTE capable LSRs
- CT0 LSPs can transit via (or terminate at) both DS-TE capable
LSRs and non-DSTE 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
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
LetÆs assume again that preemption 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
3 CT0 3
Le Faucheur et. al 30
Protocols for Diff-Serv-aware TE January 2004
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.
LSR0 will advertise in IGP for Link01:
- 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
- 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.
LSR1 will advertise in IGP for Link01:
- 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 relates to other preemption priorities
for CT0, but will actually never use those since we assume
that only preemption 2 and 3 are used in the TE domain.
Le Faucheur et. al 31
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