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IETF RFC 6510
Last modified on Monday, February 20th, 2012
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Internet Engineering Task Force (IETF) L. Berger
Request for Comments: 6510 LabN
Updates: 4875, 5420 G. Swallow
Category: Standards Track Cisco
ISSN: 2070-1721 February 2012
Resource Reservation Protocol (RSVP) Message Formats for
Label Switched Path (LSP) Attributes Objects
 Abstract
Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs)
established using the Resource Reservation Protocol Traffic
Engineering (RSVP-TE) extensions may be signaled with a set of LSP-
specific attributes. These attributes may be carried in both Path
and Resv messages. This document specifies how LSP attributes are to
be carried in RSVP Path and Resv messages using the Routing Backus-
Naur Form and clarifies related Resv message formats. This document
updates RFC 4875 and RFC 5420.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/RFC 6510.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
Berger & Swallow Standards Track PAGE 1 
RFC 6510 RSVP Message Formats for LSP Attributes February 2012
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................2
1.1. Conventions Used in This Document ..........................3
2. Path Messages ...................................................3
2.1. Path Message Format ........................................3
3. Resv Messages ...................................................4
3.1. Resv Message Format -- Per LSP Operational Status ..........5
3.2. Resv Message Format -- Per S2L Operational Status ..........6
3.2.1. Compatibility .......................................6
4. Security Considerations .........................................6
5. Acknowledgments .................................................7
6. References ......................................................7
6.1. Normative References .......................................7
6.2. Informative References .....................................7
1. Introduction
Signaling in support of Multiprotocol Label Switching (MPLS) and
Generalized MPLS (GMPLS) point-to-point Label Switched Paths (LSPs)
is defined in [RFC 3209] and [RFC 3473]. [RFC 4875] defines signaling
support for point-to-multipoint (P2MP) Traffic Engineering (TE) LSPs.
Two LSP Attributes objects are defined in [RFC 5420]. These objects
may be used to provide additional information related to how an LSP
should be set up when carried in a Path message and, when carried in
a Resv message, how an LSP has been established. The definition of
the objects includes a narrative description of related message
formats (see Section 9 of [RFC 5420]). This definition does not
provide the related Routing Backus-Naur Form (BNF) [RFC 5511] that is
typically used to define how messages are to be constructed using
RSVP objects. The current message format description has led to the
open question of how the LSP Attributes objects are to be processed
in Resv messages of P2MP LSPs (which are defined in [RFC 4875]).
This document provides the BNF for Path and Resv messages carrying
the LSP Attributes object. The definition clarifies how the objects
are to be carried for all LSP types. Both Path and Resv message BNF
is provided for completeness.
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RFC 6510 RSVP Message Formats for LSP Attributes February 2012
This document presents the related RSVP message formats as modified
by [RFC 5420]. This document modifies formats defined in [RFC 3209],
[RFC 3473], and [RFC 4875]. See [RFC 5511] for the syntax used by RSVP.
Unmodified formats are not listed. An example of a case where the
modified formats are applicable is described in [RFC 6511].
1.1. Conventions Used in This Document
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].
2. Path Messages
This section updates [RFC 4875]. Path message formatting is
unmodified from the narrative description provided in Section 9 of
[RFC 5420]:
The LSP_ATTRIBUTES object and the LSP_REQUIRED_ATTRIBUTES object
MAY be carried in a Path message....
The order of objects in RSVP-TE messages is recommended, but
implementations must be capable of receiving the objects in any
meaningful order.
On a Path message, the LSP_ATTRIBUTES object and
LSP_REQUIRED_ATTRIBUTES objects are RECOMMENDED to be placed
immediately after the SESSION_ATTRIBUTE object if it is present,
or otherwise immediately after the LABEL_REQUEST object.
If both the LSP_ATTRIBUTES object and the LSP_REQUIRED_ATTRIBUTES
object are present, the LSP_REQUIRED_ATTRIBUTES object is
RECOMMENDED to be placed first.
LSRs MUST be prepared to receive these objects in any order in any
position within a Path message. Subsequent instances of these
objects within a Path message SHOULD be ignored and MUST be
forwarded unchanged.
2.1. Path Message Format
This section presents the Path message format as modified by
[RFC 5420]. Unmodified formats are not listed.
<Path Message> ::= <Common Header> [ <INTEGRITY> ]
[ [<MESSAGE_ID_ACK> | <MESSAGE_ID_NACK>] ...]
[ <MESSAGE_ID> ]
<SESSION> <RSVP_HOP>
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RFC 6510 RSVP Message Formats for LSP Attributes February 2012
<TIME_VALUES>
[ <EXPLICIT_ROUTE> ]
<LABEL_REQUEST>
[ <PROTECTION> ]
[ <LABEL_SET> ... ]
[ <SESSION_ATTRIBUTE> ]
[ <LSP_REQUIRED_ATTRIBUTES> ... ]
[ <LSP_ATTRIBUTES> ... ]
[ <NOTIFY_REQUEST> ]
[ <ADMIN_STATUS> ]
[ <POLICY_DATA> ... ]
<sender descriptor>
[<S2L sub-LSP descriptor list>]
Note that PathErr and PathTear messages are not impacted by the
introduction of the LSP Attributes objects.
3. Resv Messages
This section updates [RFC 4875] and [RFC 5420]. Section 9 of [RFC 5420]
contains the following text regarding Resv messages:
The LSP_ATTRIBUTES object MAY be carried in a Resv message.
The order of objects in RSVP-TE messages is recommended, but
implementations must be capable of receiving the objects in any
meaningful order.
...
On a Resv message, the LSP_ATTRIBUTES object is placed in the flow
descriptor and is associated with the FILTER_SPEC object that
precedes it. It is RECOMMENDED that the LSP_ATTRIBUTES object be
placed immediately after the LABEL object.
LSRs MUST be prepared to receive this object in any order in any
position within a Resv message, subject to the previous note.
Only one instance of the LSP_ATTRIBUTES object is meaningful
within the context of a FILTER_SPEC object. Subsequent instances
of the object SHOULD be ignored and MUST be forwarded unchanged.
This means that LSP attributes may be present per sender (LSP) and
allows for the LSP Attributes object to be modified using make-
before-break (see [RFC 3209]). This definition is sufficient for
point-to-point ([RFC 3209] and [RFC 3473]) LSPs and the special case
where all point-to-multipoint source-to-leaf (S2L) sub-LSPs
([RFC 4875]) report the same operational status (as used in
[RFC 5420]). However, this definition does not allow for different
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RFC 6510 RSVP Message Formats for LSP Attributes February 2012
egress Label Switching Routers (LSRs) to report different operational
statuses. In order to allow such reporting, this document adds the
following definition:
An LSR that wishes to report the operational status of a (point-
to-multipoint) S2L sub-LSP may include the LSP Attributes object
in a Resv message or update the object that is already carried in
a Resv message. LSP Attributes objects representing S2L sub-LSP
status MUST follow a S2L_SUB_LSP object. Only the first instance
of the LSP Attributes object is meaningful within the context of a
S2L_SUB_LSP object. Subsequent instances of the object SHOULD be
ignored and MUST be forwarded unchanged.
When an LSP Attributes object is present before the first
S2L_SUB_LSP object, the LSP Attributes object represents the
operational status of all S2L sub-LSPs identified in the message.
Subsequent instances of the object (e.g., in the filter spec or
the S2L sub-LSP flow descriptor) SHOULD be ignored and MUST be
forwarded unchanged. When a branch node is combining Resv state
from multiple receivers into a single Resv message and an LSP
Attributes object is present before the first S2L_SUB_LSP object
in a received Resv message, the received LSP Attributes object
SHOULD be moved to follow the first received S2L_SUB_LSP object
and then SHOULD be duplicated for, and placed after, each
subsequent S2L_SUB_LSP object.
3.1. Resv Message Format -- Per LSP Operational Status
This section presents the Resv message format for LSPs as modified by
[RFC 5420] and can be used to report operational status per LSP.
Unmodified formats are not listed. The following is based on
[RFC 4875].
<FF flow descriptor list> ::= <FF flow descriptor>
[ <FF flow descriptor list> ]
<FF flow descriptor> ::= [ <FLOWSPEC> ] <FILTER_SPEC> <LABEL>
[ <LSP_ATTRIBUTES> ... ]
[ <RECORD_ROUTE> ]
[ <S2L sub-LSP flow descriptor list> ]
<SE flow descriptor> ::= <FLOWSPEC> <SE filter spec list>
<SE filter spec list> ::= <SE filter spec>
[ <SE filter spec list> ]
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RFC 6510 RSVP Message Formats for LSP Attributes February 2012
<SE filter spec> ::= <FILTER_SPEC> <LABEL>
[ <LSP_ATTRIBUTES> ... ]
[ <RECORD_ROUTE> ]
[ <S2L sub-LSP flow descriptor list> ]
3.2. Resv Message Format -- Per S2L Operational Status
This section presents the Resv message format for LSPs as modified by
this document and [RFC 5420], and can be used to report operational
status per S2L sub-LSP. Unmodified formats are not listed. The
following is based on [RFC 4875].
<FF flow descriptor> ::= [ <FLOWSPEC> ] <FILTER_SPEC> <LABEL>
[ <RECORD_ROUTE> ]
[ <S2L sub-LSP flow descriptor list> ]
<SE filter spec> ::= <FILTER_SPEC> <LABEL> [ <RECORD_ROUTE> ]
[ <S2L sub-LSP flow descriptor list> ]
<S2L sub-LSP flow descriptor list> ::=
<S2L sub-LSP flow descriptor>
[ <S2L sub-LSP flow descriptor list> ]
<S2L sub-LSP flow descriptor> ::= <S2L_SUB_LSP>
[ <LSP_ATTRIBUTES> ... ]
[ <P2MP_SECONDARY_RECORD_ROUTE> ]
3.2.1. Compatibility
A node that supports [RFC 4875] and [RFC 5420], but not this document,
will interpret the first LSP Attributes object present in a received
message, which is formatted as described in this document, as
representing LSP operational status rather than S2L sub-LSP status.
It is unclear if this is a significant issue as the LSP Attributes
object is currently considered to be an unsuitable mechanism for
reporting operational status of P2MP LSPs, for example, see Section
2.1 of [RFC 6511]. The intent of this document is to correct this
limitation; it is expected that networks that wish to make use of
such operational reporting will deploy this extension.
4. Security Considerations
This document clarifies usage of objects defined in [RFC 5420]. No
new information is conveyed; therefore, no additional security
considerations are included here. For a general discussion on MPLS-
and GMPLS-related security issues, see the MPLS/GMPLS security
framework [RFC 5920].
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RFC 6510 RSVP Message Formats for LSP Attributes February 2012
5. Acknowledgments
The authors would like to acknowledge the contributions of Adrian
Farrel.
6. References
6.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 3209] 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.
[RFC 3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
January 2003.
[RFC 4875] Aggarwal, R., Ed., Papadimitriou, D., Ed., and S.
Yasukawa, Ed., "Extensions to Resource Reservation
Protocol - Traffic Engineering (RSVP-TE) for Point-to-
Multipoint TE Label Switched Paths (LSPs)", RFC 4875, May
2007.
[RFC 5420] Farrel, A., Ed., Papadimitriou, D., Vasseur, JP., and A.
Ayyangarps, "Encoding of Attributes for MPLS LSP
Establishment Using Resource Reservation Protocol Traffic
Engineering (RSVP-TE)", RFC 5420, February 2009.
[RFC 5511] Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
Used to Form Encoding Rules in Various Routing Protocol
Specifications", RFC 5511, April 2009.
6.2. Informative References
[RFC 5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, July 2010.
[RFC 6511] Ali, Z., Swallow, G., and R. Aggarwal, "Non-Penultimate
Hop Popping Behavior and Out-of-Band Mapping for RSVP-TE
Label Switched Paths", RFC 6511, February 2012.
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RFC 6510 RSVP Message Formats for LSP Attributes February 2012
Authors' Addresses
Lou Berger
LabN Consulting, L.L.C.
Phone: +1-301-468-9228
EMail: lberger@labn.net
George Swallow
Cisco Systems, Inc.
EMail: swallow@cisco.com
Berger & Swallow Standards Track PAGE 8
RFC TOTAL SIZE: 16650 bytes
PUBLICATION DATE: Monday, February 20th, 2012
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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