draft-ietf-mpls-tp-gach-gal-02.txt   draft-ietf-mpls-tp-gach-gal-03.txt 
MPLS Working Group M. Bocci, Ed. MPLS Working Group M. Bocci, Ed.
Internet-Draft M. Vigoureux, Ed. Internet-Draft M. Vigoureux, Ed.
Updates: 3032, 4385, 5085 Alcatel-Lucent Updates: 3032, 4385, 5085 Alcatel-Lucent
(if approved) G. Swallow (if approved) G. Swallow
Intended status: Standards Track D. Ward Intended status: Standards Track D. Ward
Expires: August 27, 2009 S. Bryant Expires: October 11, 2009 S. Bryant
Cisco Cisco
R. Aggarwal R. Aggarwal
Juniper Networks Juniper Networks
February 23, 2009 April 9, 2009
MPLS Generic Associated Channel header MPLS Generic Associated Channel
draft-ietf-mpls-tp-gach-gal-02 draft-ietf-mpls-tp-gach-gal-03
Status of this Memo Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted to IETF in full conformance with the
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Drafts. Drafts.
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This Internet-Draft will expire on August 27, 2009. This Internet-Draft will expire on October 11, 2009.
Copyright Notice Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the Copyright (c) 2009 IETF Trust and the persons identified as the
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to this document.
Abstract Abstract
This document generalises the applicability of the pseudowire (PW) This document generalizes the applicability of the pseudowire (PW)
Associated Channel Header (ACH), enabling the realization of a Associated Channel Header (ACH), enabling the realization of a
control channel associated to MPLS Label Switched Paths (LSPs) and control channel associated to MPLS Label Switched Paths (LSPs) and
MPLS Sections in addition to MPLS pseudowires. In order to identify MPLS Sections in addition to MPLS pseudowires. In order to identify
the presence of this Associated Channel Header in the label stack, the presence of this Associated Channel Header in the label stack,
this document also assigns one of the reserved MPLS label values to this document also assigns one of the reserved MPLS label values to
the Generic Associated channel Label (GAL), to be used as a label the Generic Associated Channel Label (GAL), to be used as a label
based exception mechanism. based exception mechanism.
Requirements Language Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1]. document are to be interpreted as described in RFC 2119 [1].
Table of Contents Table of Contents
skipping to change at page 3, line 19 skipping to change at page 3, line 19
1.2. Objectives . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2. Objectives . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 1.4. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
2. Generic Associated Channel Header . . . . . . . . . . . . . . 6 2. Generic Associated Channel Header . . . . . . . . . . . . . . 6
2.1. Definition . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1. Definition . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Allocation of Channel Types . . . . . . . . . . . . . . . 7 2.2. Allocation of Channel Types . . . . . . . . . . . . . . . 7
3. ACH TLVs . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. ACH TLVs . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. ACH TLV Payload Structure . . . . . . . . . . . . . . . . 8 3.1. ACH TLV Payload Structure . . . . . . . . . . . . . . . . 8
3.2. ACH TLV Header . . . . . . . . . . . . . . . . . . . . . . 8 3.2. ACH TLV Header . . . . . . . . . . . . . . . . . . . . . . 8
3.3. ACH TLV Object . . . . . . . . . . . . . . . . . . . . . . 9 3.3. ACH TLV Object . . . . . . . . . . . . . . . . . . . . . . 9
4. Generalised Exception Mechanism . . . . . . . . . . . . . . . 9 4. Generalized Exception Mechanism . . . . . . . . . . . . . . . 9
4.1. Relationship with Existing MPLS OAM Alert Mechanisms . . . 10 4.1. Relationship with Existing MPLS OAM Alert Mechanisms . . . 10
4.2. GAL Applicability and Usage . . . . . . . . . . . . . . . 10 4.2. GAL Applicability and Usage . . . . . . . . . . . . . . . 10
4.2.1. GAL Processing . . . . . . . . . . . . . . . . . . . . 10 4.2.1. GAL Processing . . . . . . . . . . . . . . . . . . . . 10
4.3. Relationship wth RFC 3429 . . . . . . . . . . . . . . . . 13 4.3. Relationship with RFC 3429 . . . . . . . . . . . . . . . . 13
5. Compatability . . . . . . . . . . . . . . . . . . . . . . . . 13 5. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 14
6. Congestion Considerations . . . . . . . . . . . . . . . . . . 14 6. Congestion Considerations . . . . . . . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14 7. Security Considerations . . . . . . . . . . . . . . . . . . . 15
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.1. Normative References . . . . . . . . . . . . . . . . . . . 16 10.1. Normative References . . . . . . . . . . . . . . . . . . . 16
10.2. Informative References . . . . . . . . . . . . . . . . . . 17 10.2. Informative References . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction 1. Introduction
There is a need for Operations, Administration and Maintenance (OAM) There is a need for Operations, Administration and Maintenance (OAM)
mechanisms that can be used for fault detection, diagnostics, mechanisms that can be used for fault detection, diagnostics,
maintenance and other functions on a PW and an LSP. These functions maintenance and other functions on a pseudowire (PW) and a Label
can be used between any two Label Edge Routers (LERs) / Label Switched Path (LSP). These functions can be used between any two
Switching Router (LSRs) or Terminating Provider Edge routers (T-PEs) Label Edge Routers (LERs) / Label Switching Router (LSRs) or
/ Switching Provider Edge routers (S-PEs) along the path of an LSP or Terminating Provider Edge routers (T-PEs) / Switching Provider Edge
PW respectively [15]. Some of these functions can be supported using routers (S-PEs) along the path of an LSP or PW respectively [14].
existing tools such as Virtual Circuit Connectivity Verification Some of these functions can be supported using existing tools such as
(VCCV) [2], Bidirectional Forwarding Detection for MPLS LSPs (BFD- Virtual Circuit Connectivity Verification (VCCV) [2], Bidirectional
MPLS)[3], LSP-Ping [4], or BFD-VCCV [5]. However, a requirement has Forwarding Detection for MPLS LSPs (BFD-MPLS) [3], LSP-Ping [4], or
been indicated to augment this set of maintenance functions, in BFD-VCCV [5]. However, a requirement has been indicated to augment
particular when MPLS networks are used for packet transport services this set of maintenance functions, in particular when MPLS networks
and transport network operations [16]. Examples of these functions are used for packet transport services and transport network
include performance monitoring, automatic protection switching, and operations [15]. Examples of these functions include performance
support for management and signaling communication channels. These monitoring, automatic protection switching, and support for
tools MUST be applicable to, and function in essentially the same management and signaling communication channels. These tools MUST be
manner (from an operational point of view) on MPLS PWs, MPLS LSPs and applicable to, and function in essentially the same manner (from an
MPLS Sections. They MUST also operate in-band on the PW or LSP such operational point of view) on MPLS PWs, MPLS LSPs and MPLS Sections.
that they do not depend on Packet Switched Network (PSN) routing or They MUST also operate in-band on the PW or LSP such that they do not
on user data traffic, and MUST also not depend on dynamic control depend on Packet Switched Network (PSN) routing or on user traffic,
plane functions. and MUST also NOT depend on dynamic control plane functions.
VCCV can use an Associated Channel Header (ACH) to provide a PW- VCCV [2] can use an Associated Channel Header (ACH) to provide a PW-
associated control channel between a PW's end points, over which OAM associated control channel between a PW's end points, over which OAM
and other control messages can be exchanged. This document and other control messages can be exchanged. This document
generalises the use of the ACH to enable the same associated control generalizes the applicability of the ACH to enable the same
channel mechanism to be used for Sections, LSPs and PWs. The associated control channel mechanism to be used for Sections, LSPs
associated control channel thus generalized is known as the Generic and PWs. The associated control channel thus generalized is known as
Associated Channel (G-ACh). The ACH, specified in RFC 4385 [6], may the Generic Associated Channel (G-ACh). The ACH, specified in RFC
be used with additional code points to support additional MPLS 4385 [6], may be used with additional code points to support
maintenance functions on the G-ACh. additional MPLS maintenance functions on the G-ACh.
Generalizing the associated control channel mechanism to LSPs and Generalizing the applicability of the ACH to LSPs and Sections also
Sections also requires a method to identify that a packet contains an requires a method to identify that a packet contains an ACH followed
ACH followed by a non-service payload. Therefore, this document also by a non-service payload. Therefore, this document also defines a
defines a label based exception mechanism that serves to inform an label based exception mechanism that serves to inform an LSR (or LER)
LSR (or LER) that a packet it receives on an LSP or Section belongs that a packet it receives on an LSP or Section belongs to an
to an associated control channel for that LSP or Section. associated control channel. The label used for that purpose is one
of the MPLS reserved labels and is referred to as the GAL (G-ACh
Label). The GAL mechanism is defined to work together with the ACH
for LSPs and MPLS Sections.
RFC 4379 [4] and BFD-MPLS [3] define alert mechanisms that enable an RFC 4379 [4] and BFD-MPLS [3] define alert mechanisms that enable an
MPLS LSR to identify and process MPLS OAM packets when these are MPLS LSR to identify and process MPLS OAM packets when these are
encapsulated in an IP header. These alert mechanisms are based on encapsulated in an IP header. These alert mechanisms are based, for
MPLS or PW label Time to Live (TTL) expiration and/or on the use of example, on Time To Live (TTL) expiration and/or on the use of an IP
an IP destination address in the range 127/8. These mechanisms are destination address in the range of 127/8 or 0:0:0:0:0:FFFF:
127.0.0.0/104, respectively for IPv4 and IPv6. These mechanisms are
the default mechanisms for identifying MPLS OAM packets when the default mechanisms for identifying MPLS OAM packets when
encapsulated in an IP header. However it may not always be possible encapsulated in an IP header. However it may not always be possible
to use these mechanisms in some MPLS applications, e.g. MPLS to use these mechanisms in some MPLS applications e.g., MPLS
Transport Profile (MPLS-TP) [15], particularly when IP based Transport Profile (MPLS-TP) [14], particularly when IP based
demultiplexing cannot be used. This document defines a mechanism demultiplexing cannot be used. This document defines a mechanism
that is RECOMMENDED for identifying and encapsulating MPLS OAM and that is RECOMMENDED for identifying and encapsulating MPLS OAM and
other maintenance messages when IP based mechanisms such as those in other maintenance messages when IP based mechanisms such as those
[4] and [3] are not available. This mechanism MAY be used in used in [4] and [3] are not available. Yet, this mechanism MAY be
addition to IP-based mechanisms. used in addition to IP-based mechanisms.
The GAL mechanism is defined to work together with the ACH for LSPs
and MPLS Sections.
Note that, in this document, maintenance functions and packets should Note that, in this document, maintenance functions and packets should
be understood in the broad sense. That is, a set of maintenance and be understood in the broad sense. That is, a set of maintenance and
management mechanisms that include OAM, Automatic Protection management mechanisms that include OAM, Automatic Protection
Switching (APS), Signalling Communication Channel (SCC) and Switching (APS), Signaling Communication Channel (SCC) and Management
Management Communication Channel (MCC) messages. Communication Channel (MCC) messages.
Also note that the GAL and ACH are applicable to MPLS in general. Also note that the GAL and ACH are applicable to MPLS in general.
Their applicability to specific applications of MPLS is outside the Their applicability to specific applications of MPLS is outside the
scope of this document. scope of this document.
1.1. Contributing Authors 1.1. Contributing Authors
The editors gratefully acknowledge the contributions of Sami Boutros, The editors gratefully acknowledge the contributions of Sami Boutros,
Italo Busi, Marc Lasserre, Lieven Levrau and Siva Sivabalan Italo Busi, Marc Lasserre, Lieven Levrau and Siva Sivabalan
1.2. Objectives 1.2. Objectives
This document defines a mechanism that provides a solution to the This document defines a mechanism that provides a solution to the
extended maintenance needs of emerging applications for MPLS. It extended maintenance needs of emerging applications for MPLS. It
creates a generic control channel mechanism that may be applied to creates a generic control channel mechanism that may be applied to
MPLS LSPs and Sections, while maintaining compatibility with the PW MPLS LSPs and Sections, while maintaining compatibility with the PW
associated channel. It also normalises the use of the ACH for PWs in associated channel. It also normalizes the use of the ACH for PWs in
a transport context, and defines a label based exception mechanism to a transport context, and defines a label based exception mechanism to
alert LERs/LSRs of the presence of an ACH after the bottom of the alert LERs/LSRs of the presence of an ACH after the bottom of the
stack. stack.
1.3. Scope 1.3. Scope
This document defines the encapsulation header for LSP, MPLS Section This document defines the encapsulation header for Sections, LSPs,
and PW associated channel messages. and PWs associated control channel messages.
It does not define how associated control channel capabilities are It does not define how associated control channel capabilities are
signaled or negotiated between LERs/LSRs or PEs, or the operation of signaled or negotiated between LERs/LSRs or PEs, or the operation of
various OAM functions. various OAM functions.
This document does not deprecate existing MPLS and PW OAM mechanisms. This document does not deprecate existing MPLS and PW OAM mechanisms.
1.4. Terminology 1.4. Terminology
ACH: Associated Channel Header ACH: Associated Channel Header
G-ACh: Generic Associated Channel G-ACh: Generic Associated Channel
GAL: G-ACh Label GAL: G-ACh Label
Maintenance packet: Any packet containing a message belonging to a G-ACh packet: Any packet containing a message belonging to a protocol
maintenance protocol that is carried on a PW, LSP or MPLS Section that is carried on a PW, LSP or MPLS Section associated control
associated control channel. Examples of such maintenance protocols channel. Examples include maintenance protocols such as OAM
include OAM functions, signaling communications or management functions, signaling communications or management communications.
communications.
The terms 'Section' and 'Concatenated Segment' are defined in [17]. The terms 'Section' and 'Concatenated Segment' are defined in [16].
2. Generic Associated Channel Header 2. Generic Associated Channel Header
VCCV [2] defines three MPLS Control Channel (CC) Types that may be VCCV [2] defines three Control Channel (CC) Types that may be used to
used to exchange OAM messages through a PW: CC Type 1 uses an ACH and exchange OAM messages through a PW: CC Type 1 uses an ACH and is
is referred to as "In-band VCCV"; CC Type 2 uses the MPLS Router referred to as "In-band VCCV"; CC Type 2 uses the MPLS Router Alert
Alert Label to indicate VCCV packets and is referred to as "Out of Label to indicate VCCV packets and is referred to as "Out of Band
Band VCCV"; CC Type 3 uses the TTL to force the packet to be VCCV"; CC Type 3 uses the TTL to force the packet to be processed by
processed by the targeted router control plane and is referred to as the targeted router control plane and is referred to as "MPLS PW
"MPLS PW Label with TTL == 1". Label with TTL == 1".
2.1. Definition 2.1. Definition
The use of the CC Type 1, previously limited to PWs, is here extended The use of the ACH, previously limited to PWs, is here generalized to
to also apply to LSPs and to Sections. Note that for PWs, the PWE3 also apply to LSPs and to Sections. Note that for PWs, the PWE3
control word [6] MUST be present in the encapsulation of user packets control word [6] MUST be present in the encapsulation of user packets
when the ACH is used to realize the associated control channel. when the ACH is used to realize the associated control channel.
The CC Type 1 control channel header is depicted in figure below: The ACH used by CC Type 1 is depicted in figure below:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Reserved | Channel Type | |0 0 0 1|Version| Reserved | Channel Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Associated Channel Header Figure 1: Associated Channel Header
In the above figure, the first nibble is set to 0001b to indicate a In the above figure, the first nibble is set to 0001b to indicate a
control channel associated with a PW, an LSP or a Section. The control channel associated with a PW, an LSP or a Section. The
Version field is set to 0, as specified in RFC 4385 [6]. Bits 8 to Version field is set to 0, as specified in RFC 4385 [6]. Bits 8 to
14 of the G-ACH are reserved and MUST be set to 0 and ignored on 15 of the ACH are reserved and MUST be set to 0 and ignored on
reception. reception. Bits 16 to 31 are used to encode the possible Channel
Types.
Note that VCCV also includes mechanisms for negotiating the Control Note that VCCV [2] also includes mechanisms for negotiating the
Channel and Connectivity Verification (i.e. OAM functions) Types Control Channel and Connectivity Verification (i.e., OAM function)
between PEs. It is anticipated that similar mechanisms will be Types between PEs. It is anticipated that similar mechanisms will be
applied to LSPs. Such application will require further applied to LSPs. Such application will require further
specification. However, such specification is beyond the scope of specification. However, such specification is beyond the scope of
this document. this document.
2.2. Allocation of Channel Types 2.2. Allocation of Channel Types
The Channel Type field indicates the type of message carried on the The Channel Type field indicates the type of message carried on the
associated control channel e.g. IPv4 or IPv6 if IP demultiplexing is associated control channel e.g., IPv4 or IPv6 if IP demultiplexing is
used for messages sent on the associated control channel, or OAM or used for messages sent on the associated control channel, or OAM or
other maintenance function if IP demultiplexing is not used. For other maintenance function if IP demultiplexing is not used. For
associated control channel packets where IP is not used as the associated control channel packets where IP is not used as the
multiplexer, the Channel Type SHOULD indicate the specific multiplexer, the Channel Type indicates the specific protocol carried
maintenance protocol carried in the associated control channel. in the associated control channel.
Values for the Channel Type field currently used for VCCV are Values for the Channel Type field currently used for VCCV are
specified elsewhere, e.g. in RFC 4446 [7]and RFC 4385[6] . specified elsewhere e.g., in RFC 4446 [7] and RFC 4385 [6].
Additional Channel Type values and the associated maintenance Additional Channel Type values and the associated maintenance
functionality will be defined in other documents. Each document functionality will be defined in other documents. Each document,
specifying a protocol solution relying on the ACH MUST also specify specifying a protocol solution relying on the ACH, MUST also specify
the applicable Channel Type field value. the applicable Channel Type field value.
Note that these values are allocated from the PW Associated Channel Note that these values are allocated from the PW Associated Channel
Type registry, but this document modifies the existing policy to Type registry [7], but this document modifies the existing policy to
accommodate a level of experimentation. See Section 8 for further accommodate a level of experimentation. See Section 8 for further
details. details.
3. ACH TLVs 3. ACH TLVs
In some applications of the "In-band VCCV" associated control channel In some applications of the generalized associated control channel it
it is necessary to include one or more ACH TLVs to provide additional is necessary to include one or more ACH TLVs to provide additional
context information to the maintenance packet. One use of these ACH context information to the G-ACh packet. One use of these ACH TLVs
TLVs might be to identify the source and/or intended destination of might be to identify the source and/or intended destination of the
the associated control channel maintenance message. However, the use associated channel message. However, the use of this construct is
of this construct is not limited to providing addressing information not limited to providing addressing information nor is the
nor is the applicability restricted to transport network applicability restricted to transport network applications.
applications.
If the maintenance message MAY be preceded by one or more ACH TLVs, If the G-ACh message MAY be preceded by one or more ACH TLVs, then
then this MUST be explicitly specified in the definition of an ACH this MUST be explicitly specified in the definition of an ACH Channel
Channel Type. If the ACH Channel Type definition does state that one Type. If the ACH Channel Type definition does state that one or more
or more ACH TLVs MAY precede the maintenance message, an ACH TLV ACH TLVs MAY precede the G-ACh message, an ACH TLV Header MUST follow
Header MUST follow the ACH. If no ACH TLVs are required in a the ACH. If no ACH TLVs are required in a specific associated
specific associated control channel packet, but the Channel Type channel packet, but the Channel Type nevertheless defines that ACH
nevertheless defines that ACH TLVs MAY be used, an ACH TLV Header TLVs MAY be used, an ACH TLV Header MUST be present but with a length
MUST be present but with a length field set to zero to indicate that field set to zero to indicate that no ACH TLV follow this header.
no ACH TLV follow this header.
If a channel type specification does not explicitly specify that ACH If an ACH Channel Type specification does not explicitly specify that
TLVs MAY be used, then an ACH TLV Header MUST NOT be used. ACH TLVs MAY be used, then the ACH TLV Header MUST NOT be used.
3.1. ACH TLV Payload Structure 3.1. ACH TLV Payload Structure
This section defines and describes the structure of an ACH payload This section defines and describes the structure of an ACH payload
when an ACH TLV Header is present. The structure of ACH TLVs that when an ACH TLV Header is present. The structure of ACH TLVs that
MAY follow an ACH TLV Header is defined and described in the MAY follow an ACH TLV Header is defined and described in the
following sections. following sections.
The following figure (Figure 2) shows the structure of a G-ACh packet The following figure (Figure 2) shows the structure of a G-ACh packet
payload. payload.
skipping to change at page 8, line 32 skipping to change at page 8, line 30
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACH | | ACH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACH TLV Header | | ACH TLV Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ~ | ~
~ zero or more ACH TLVs ~ ~ zero or more ACH TLVs ~
~ | ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ~ | ~
~ Maintenance Message ~ ~ G-ACh Message ~
~ | ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: ACH TLV Payload Structure Figure 2: ACH TLV Payload Structure
3.2. ACH TLV Header 3.2. ACH TLV Header
The ACH TLV Header defines the length of the set of ACH TLVs that The ACH TLV Header defines the length of the set of ACH TLVs that
follow. follow.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Reserved | | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: ACH TLV Header Figure 3: ACH TLV Header
The length field specifies the length in octets of the complete set The Length field specifies the length in octets of the complete set
of TLVs including TLVs that follow the ACH TLV header. A length of of TLVs including sub-TLVs that follow the ACH TLV header. A length
zero indicates that no ACH TLV follow this header. of zero indicates that no ACH TLV follow this header. Note that no
padding is required for the set of ACH TLVs.
The reserved field is for future use and MUST be set to zero on The Reserved field is for future use and MUST be set to zero on
transmission and ignored on reception. transmission and ignored on reception.
3.3. ACH TLV Object 3.3. ACH TLV Object
An ACH TLV consists of a 16-bit Type field, followed by a 16-bit An ACH TLV consists of a 16-bit Type field, followed by a 16-bit
Length field which specifies the number of octets of the Value field Length field which specifies the number of octets of the Value field
which follows the Length field. This 32-bit word is followed by zero which follows the Length field. This 32-bit word is followed by zero
or more octets of Value information. The format and semantics of the or more octets of Value information. The format and semantics of the
value information are defined by the TLV Type as recorded in the TLV Value information are defined by the TLV Type as recorded in the TLV
Type registry. See Section 8 for further details. Note that the Type registry. See Section 8 for further details. Note that the
Value field of ACH TLVs MAY contain sub-TLV objects. Value field of ACH TLVs MAY contain sub-TLVs. Note that no padding
is required for individual TLVs or sub-TLVs.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV Type | Length | | TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ~ | ~
~ Value ~ ~ Value ~
~ | ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: ACH TLV Format Figure 4: ACH TLV Format
4. Generalised Exception Mechanism 4. Generalized Exception Mechanism
Generalizing the associated channel mechanism to LSPs and Sections Generalizing the associated control channel mechanism to LSPs and
also requires a method to identify that a packet contains an ACH Sections also requires a method to identify that a packet contains an
followed by a non-service payload. This document specifies that a ACH followed by a non-service payload. This document specifies that
label is used for that purpose and calls this special label the G-ACh a label is used for that purpose and calls this special label the
Label (GAL). One of the reserved label values defined in RFC 3032 G-ACh Label (GAL). One of the reserved label values defined in RFC
[8] is assigned for this purpose. The value of the label is to be 3032 [8] is assigned for this purpose. The value of the label is to
allocated by IANA; this document suggests the value 13. be allocated by IANA; this document suggests the value 13.
The GAL provides an alert based exception mechanism to: The GAL provides an alert based exception mechanism to:
o differentiate specific packets (e.g. maintenance messages) from o differentiate specific packets (i.e., G-ACh packets) from others,
others, such as normal user-plane ones, such as user-plane ones,
o indicate that the ACH appears immediately after the bottom of the o indicate that the ACH appears immediately after the bottom of the
label stack. label stack.
The GAL MUST only be used where both of these purposes apply. The GAL MUST only be used where both these purposes apply.
4.1. Relationship with Existing MPLS OAM Alert Mechanisms 4.1. Relationship with Existing MPLS OAM Alert Mechanisms
RFC 4379 [4] and BFD-MPLS [3] have defined alert mechanisms that RFC 4379 [4] and BFD-MPLS [3] define alert mechanisms that enable an
enable a MPLS LSR to identify and process MPLS OAM packets when the MPLS LSR to identify and process MPLS OAM packets when these are
OAM packets are encapsulated in an IP header. These alert mechanisms encapsulated in an IP header. These alert mechanisms are based, for
are based on TTL expiration and/or use an IP destination address in example, on Time To Live (TTL) expiration and/or on the use of an IP
the range 127/8. destination address in the range of 127/8 or 0:0:0:0:0:FFFF:
127.0.0.0/104, respectively for IPv4 and IPv6.
These alert mechanisms SHOULD be used in non MPLS-TP environments, These mechanisms are the default mechanisms for identifying MPLS OAM
although the mechanism defined in this document MAY also be used. packets when encapsulated in an IP header although the mechanism
defined in this document MAY also be used.
4.2. GAL Applicability and Usage 4.2. GAL Applicability and Usage
The GAL MUST only be used with LSPs, concatenated segments of LSPs, The GAL MUST only be used with LSPs, Concatenated Segments of LSPs,
and with Sections. and with Sections.
In MPLS-TP, the GAL MUST always be at the bottom of the label stack In MPLS-TP, the GAL MUST always be at the bottom of the label stack
(i.e. S bit set to 1). However, in other MPLS environments, this (i.e., S bit set to 1). However, in other MPLS environments, for
document places no restrictions on where the GAL may appear within example those using entropy labels [17], this document places no
the label stack. restrictions on where the GAL may appear within the label stack.
Where the GAL is at the bottom of the label stack (i.e. S bit set to
1) then it MUST always be followed by an ACH.
The GAL MUST NOT appear in the label stack when transporting normal The GAL MUST NOT appear in the label stack when transporting normal
user-plane packets. Furthermore, when present, the GAL MUST only user-plane packets. Furthermore, when present, the GAL MUST only
appear once in the label stack. appear once in the label stack.
4.2.1. GAL Processing 4.2.1. GAL Processing
The Traffic Class (TC) field (formerly known as the EXP field) of the The Traffic Class (TC) field (formerly known as the EXP field) of the
label stack entry containing the GAL follows the definition and Label Stack Entry (LSE) containing the GAL follows the definition and
processing rules specified and referenced in [9]. processing rules specified and referenced in [9].
The Time-To-Live (TTL) field of the label stack entry that contains The Time-To-Live (TTL) field of the LSE that contains the GAL follows
the GAL follows the definition and processing rules specified in the definition and processing rules specified in [10].
[10].
4.2.1.1. MPLS Label Switched Paths and Segments 4.2.1.1. MPLS Label Switched Paths and Segments
The following figure (Figure 5) depicts two LERs (A and D) and two The following figure (Figure 5) depicts two LERs (A and D) and two
LSRs (B and C) for a given LSP which is established from A to D and LSRs (B and C) for a given LSP which is established from A to D and
switched in B and C. switched in B and C.
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
| A |-------------| B |-------------| C |-------------| D | | A |-------------| B |-------------| C |-------------| D |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
Figure 5: MPLS-TP maintenance over a LSP Figure 5: Maintenance over a LSP
In this example, a G-ACh exists on an LSP that extends between LERs A In this example, a G-ACh exists on the LSP that extends between LERs
and D, via LSRs B and C. Only these nodes may insert, extract or A and D, via LSRs B and C. Only A and D may initiate the generation
process packets on this G-ACh. of G-ACh packets. A, B, C and D may also originate and process G-ACh
packets.
The following figure (Figure 6) depicts the format of a MPLS-TP The following figure (Figure 6) depicts the format of a MPLS-TP G-ACh
maintenance message when used for an LSP. packet when used for an LSP.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP Label | TC |S| TTL | | LSP Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GAL | TC |S| TTL | | GAL | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACH | | ACH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACH TLV Header (if present) | | ACH TLV Header (if present) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ~ | ~
~ Zero or more ACH TLVs ~ ~ Zero or more ACH TLVs ~
~ (if present) | ~ (if present) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ~ | ~
~ Maintenance Message ~ ~ G-ACh Message ~
~ | ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: MPLS-TP maintenance message format for a LSP Figure 6: G-ACh packet format for a LSP
Note that it is possible that the LSP may be tunnelled in another LSP Note that it is possible that the LSP may be tunneled in another LSP
(e.g. if a MPLS Tunnel exists between B and C), and as such other (e.g., if a MPLS Tunnel exists between B and C), and as such other
labels may be present in the label stack. LSEs may be present in the label stack.
To send a maintenance message on the LSP associated control channel, To send a maintenance message on the LSP associated control channel,
the LER (A) generates a maintenance message, to which it MAY the LER (A) generates a G-ACh message, to which it MAY prepend an ACH
prepended an ACH TLV header and appropriate ACH TLVs, and with a ACH TLV Header and appropriate ACH TLVs, adds an ACH to which it, pushes
to which it pushes a GAL and finally the LSP label. a GAL LSE and finally the LSP Label LSE.
o The TTL field of the GAL MUST be set to at least 1. The exact o The TTL field of the GAL LSE MUST be set to at least 1. The exact
value of the TTL is application specific. value of the TTL is application specific. See Section 4.2.1 for
definition and processing rules.
o The S bit of the GAL MUST be set according to its position in the o The S bit of the GAL MUST be set according to its position in the
label stack. label stack (see Section 4.2).
o The setting of the TC field is application specific. o The setting of the TC field of the GAL is application specific.
See Section 4.2.1 for definition and processing rules.
The maintenance message, the ACH or the GAL SHOULD NOT be modified The G-ACh message, the ACH or the GAL SHOULD NOT be modified towards
towards the targeted destination. Upon reception of the labelled the targeted destination. Upon reception of the labeled packet, the
packet, the targeted destination, after having checked both the LSP targeted destination, after having checked both the LSP Label and GAL
label and GAL fields, SHOULD pass the whole maintenance message to LSEs fields, SHOULD pass the whole packet to the appropriate
the appropriate processing entity. processing entity.
4.2.1.2. MPLS Section 4.2.1.2. MPLS Section
The following figure (Figure 7) depicts an example of a MPLS Section. The following figure (Figure 7) depicts an example of an MPLS
Section.
+---+ +---+ +---+ +---+
| A |-------------| Z | | A |-------------| Z |
+---+ +---+ +---+ +---+
Figure 7: Maintenance over an MPLS Section Figure 7: Maintenance over an MPLS Section
With regard to the MPLS Section, a G-ACh exists between A and Z. Only With regard to the MPLS Section, a G-ACh exists between A and Z. Only
A and Z can insert, extract or process packets on this G-ACh. A and Z can insert, extract or process packets on this G-ACh.
The following figure (Figure 8) depicts the format of a maintenance The following figure (Figure 8) depicts the format of a G-ACh packet
message when used for a MPLS Section. The GAL MAY provide the when used for an MPLS Section. The GAL MAY provide the exception
exception mechanism for a control channel in its own right without mechanism for a control channel in its own right without being
being associated with a specific LSP, thus providing maintenance associated with a specific LSP, thus providing maintenance related
related communications across a specific link interconnecting two communications across a specific link interconnecting two LSRs. In
LSRs. In this case, the GAL is the only label in the stack. this case, the GAL is the only label in the stack.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GAL | TC |S| TTL | | GAL | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACH | | ACH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACH TLV Header (if present) | | ACH TLV Header (if present) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ~ | ~
~ Zero or more ACH TLVs ~ ~ Zero or more ACH TLVs ~
~ (if present) | ~ (if present) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ~ | ~
~ Maintenance Message ~ ~ G-ACh message ~
~ | ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Maintenance message format for a MPLS Section Figure 8: G-ACh packet format for an MPLS Section
To send a maintenance message on a control channel associated to the To send a G-ACh message on a control channel associated to the
Section, the head-end LSR (A) of the Section generates a maintenance Section, the head-end LSR (A) of the Section generates a G-ACh
message, to which it MAY prepend an ACH TLV Header and appropriate message, to which it MAY prepend an ACH TLV Header and appropriate
ACH TLVs, and with a ACH to which it pushes a GAL. ACH TLVs, adds an ACH to which it pushes a GAL LSE.
o The TTL field of the GAL MUST be set to at least 1. The exact o The TTL field of the GAL MUST be set to at least 1. The exact
value of the TTL is application specific. value of the TTL is application specific. See Section 4.2.1 for
definition and processing rules.
o The S bit of the GAL MUST be set according to its position in the o The S bit of the GAL MUST be set according to its position in the
label stack. For MPLS Sections, the S bit MUST be set to 1. label stack. (see Section 4.2).
o The setting of the TC field is application specific. o The setting of the TC field of the GAL is application specific.
See Section 4.2.1 for definition and processing rules.
The maintenance message, the ACH and the GAL SHOULD NOT be modified The G-ACh message, the ACH and the GAL SHOULD NOT be modified towards
towards the tail-end LSR (Z). Upon reception of the labelled packet, the tail-end LSR (Z). Upon reception of the G-ACh packet, the tail-
the tail-end LSR (Z), after having checked the GAL fields, SHOULD end LSR (Z), after having checked the GAL LSE fields, SHOULD pass the
pass the whole packet to the appropriate processing entity. whole packet to the appropriate processing entity.
4.3. Relationship wth RFC 3429 4.3. Relationship with RFC 3429
RFC 3429 [18] describes the assignment of one of the reserved label RFC 3429 [18] describes the assignment of one of the reserved label
values, defined in RFC 3032 [8], to the 'OAM Alert Label' that is values, defined in RFC 3032 [8], to the 'OAM Alert Label' that is
used by user-plane MPLS OAM functions for the identification of MPLS used by user-plane MPLS OAM functions for the identification of MPLS
OAM packets. The value of 14 is used for that purpose. OAM packets. The value of 14 is used for that purpose.
Both this document and RFC 3429 [18] therefore describe the Both this document and RFC 3429 [18] therefore describe the
assignment of reserved label values for similar purposes. The assignment of reserved label values for similar purposes. The
rationale for the assignment of a new reserved label can be rationale for the assignment of a new reserved label can be
summarized as follows: summarized as follows:
o Unlike the mechanisms described and referenced in RFC 3429 [18], o Unlike the mechanisms described and referenced in RFC 3429 [18],
MPLS-TP maintenance messages will not reside immediately after the G-ACh messages will not reside immediately after the GAL but
GAL but instead behind the ACH, which itself resides after the instead behind the ACH, which itself resides after the bottom of
bottom of the label stack. This ensures that OAM, using the the label stack.
G-ACh, complies with RFC 4928 [11].
o The set of maintenance functions potentially operated in the o The set of maintenance functions potentially operated in the
context of the G-ACh is wider than the set of OAM functions context of the G-ACh is wider than the set of OAM functions
referenced in RFC 3429 [18]. referenced in RFC 3429 [18].
o It has been reported that there are existing implementations and o It has been reported that there are existing implementations and
running deployments using the 'OAM Alert Label' as described in running deployments using the 'OAM Alert Label' as described in
RFC 3429 [18]. It is therefore not possible to modify the 'OAM RFC 3429 [18]. It is therefore not possible to modify the 'OAM
Alert Label' allocation, purpose or usage. Nevertheless, it is Alert Label' allocation, purpose or usage. Nevertheless, it is
RECOMMENDED by this document that no further OAM extensions based RECOMMENDED that no further OAM extensions based on 'OAM Alert
on 'OAM Alert Label' (Label 14) usage be specified or developed. Label' (Label 14) usage be specified or developed.
5. Compatability 5. Compatibility
Procedures for handling a packet received with an invalid incoming Procedures for handling a packet received with an invalid incoming
label are specified in RFC 3031[12]. label are specified in RFC 3031[11].
An LER, LSR or PE MUST discard received associated channel packets on An LER, LSR or PE MUST discard received associated channel packets on
which all of the MPLS or PW labels have been popped if any one of the which all of the MPLS or PW labels have been popped if any one of the
following conditions is true: following conditions is true:
o It is not capable of processing packets on the Channel Type o It is not capable of processing packets on the Channel Type
indicated by the ACH of the received packet. indicated by the ACH of the received packet.
o It has not, through means outside the scope of this document, o It has not, through means outside the scope of this document,
indicated to the sending LSR, LER or PE that it will process indicated to the sending LSR, LER or PE that it will process
associated channel packets on the Channel Type indicated by the associated channel packets on the Channel Type indicated by the
ACH of the received packet. ACH of the received packet.
o The packet is received on an Experimental Channel Type that is
locally disabled.
o If the ACH was indicated by the presence of a GAL, and the first o If the ACH was indicated by the presence of a GAL, and the first
nibble of the ACH of the received packet is not 0b0001. nibble of the ACH of the received packet is not 0b0001.
o The ACH version is not recognised. o The ACH version is not recognized.
In addition, it MAY increment an error counter and MAY also In addition, it MAY increment an error counter and MAY also issue a
optionally issue a system and/or SNMP notification. system and/or SNMP notification.
6. Congestion Considerations 6. Congestion Considerations
The congestion considerations detailed in RFC 5085 [2] apply. The congestion considerations detailed in RFC 5085 [2] apply.
7. Security Considerations 7. Security Considerations
The security considerations for the associated control channel are The security considerations for the associated control channel are
described in RFC 4385[6]. Further security considerations MUST be described in RFC 4385[6]. Further security considerations MUST be
described in the relevant associated channel type specification. described in the relevant associated channel type specification.
RFC 5085 [2] provides data plane related security considerations. RFC 5085 [2] provides data plane related security considerations.
These also apply to a G-ACh, whether the alert mechanism uses a GAL These also apply to a G-ACh, whether the alert mechanism uses a GAL
or only an ACH. or only an ACH.
8. IANA Considerations 8. IANA Considerations
This document requests that IANA allocates a label value, to the GAL, This document requests that IANA allocates a label value, to the GAL,
from the pool of reserved labels, and suggests this value to be 13. from the pool of reserved labels in the "Multiprotocol Label
Switching Architecture (MPLS) Label Values" registry, and suggests
this value to be 13.
Channel Types for the Associated Channel Header are allocated from Channel Types for the Associated Channel Header are allocated from
the IANA PW Associated Channel Type registry [7]. The PW Associated the IANA "PW Associated Channel Type" registry [7]. The PW
Channel Type registry is currently allocated based on the IETF Associated Channel Type registry is currently allocated based on the
consensus process, described in [13]. This allocation process was IETF consensus process, described in [12]. This allocation process
chosen based on the consensus reached in the PWE3 working group that was chosen based on the consensus reached in the PWE3 working group
pseudowire associated channel mechanisms should be reviewed by the that pseudowire associated channel mechanisms should be reviewed by
IETF and only those that are consistent with the PWE3 architecture the IETF and only those that are consistent with the PWE3
and requirements should be allocated a code point. architecture and requirements should be allocated a code point.
However, a requirement has emerged (see [16]) to allow for However, a requirement has emerged (see [15]) to allow for
optimizations or extensions to OAM and other control protocols optimizations or extensions to OAM and other control protocols
running in an associated channel to be experimented without resorting running in an associated channel to be experimented without resorting
to the IETF standards process, by supporting experimental code to the IETF standards process, by supporting experimental code
points. This would prevent code points used for such functions from points. This would prevent code points used for such functions from
being used from the range allocated through the IETF standards and being used from the range allocated through the IETF standards and
thus protects an installed base of equipment from potential thus protects an installed base of equipment from potential
inadvertent overloading of code points. In order to support this inadvertent overloading of code points. In order to support this
requirement, this document requests that the code point allocation requirement, this document requests that the code point allocation
scheme for the PW Associated Channel Type be changed as follows: scheme for the PW Associated Channel Type be changed as follows:
0 - 32751 : IETF Consensus 0 - 32751 : IETF Consensus
32752 - 32767 : Experimental 32760 - 32767 : Experimental
Code points in the experimental range MUST be used according to the Code points in the experimental range MUST be used according to the
guidelines of RFC 3692 [14]. Experimental OAM functions MUST be guidelines of RFC 3692 [13]. Functions using experimental G-ACh code
disabled by default. The Channel Type value used for a given points MUST be disabled by default. The Channel Type value used for
experimental OAM function MUST be configurable, and care MUST be a given experimental OAM function MUST be configurable, and care MUST
taken to ensure that different OAM functions that are not inter- be taken to ensure that different OAM functions that are not inter-
operable are configured to use different Channel Type values. operable are configured to use different Channel Type values.
The PW Associated Channel Type registry needs to be updated to The PW Associated Channel Type registry needs to be updated to
include a column indicating whether the ACH is followed by a ACH TLV include a column indicating whether the ACH is followed by a ACH TLV
header (Yes/No). There are two ACH Channel Type code-points header (Yes/No). There are two ACH Channel Type code-points
currently assigned and in both cases no ACH TLV header is used. Thus currently assigned and in both cases no ACH TLV header is used. Thus
the new format of the PW Channel Type registry is: the new format of the PW Channel Type registry is:
Registry: Registry:
Value Description TLV Follows Reference Value Description TLV Follows Reference
----- ---------------------------- ----------- --------- ----- ---------------------------- ----------- ---------
0x21 ACH carries an IPv4 packet No [RFC4385] 0x21 ACH carries an IPv4 packet No [RFC4385]
0x57 ACH carries an IPv6 packet No [RFC4385] 0x57 ACH carries an IPv6 packet No [RFC4385]
Figure 9: PW Channel Type registry Figure 9: PW Channel Type registry
IANA is requested create a new registry called the Associated Channel IANA is requested create a new registry called the Associated Channel
TLV Registry. The allocation policy for this registry is IETF Header TLV Registry. The allocation policy for this registry is IETF
consensus. This registry MUST record the following information. consensus. This registry MUST record the following information.
There are no initial entries. There are no initial entries.
Name Type Length Description Reference Name Type Length Description Reference
(octets) (octets)
Figure 10: PW ACH TLV registry Figure 10: ACH TLV registry
9. Acknowledgements 9. Acknowledgments
The authors would like to thank all members of the teams (the Joint The authors would like to thank all members of the teams (the Joint
Working Team, the MPLS Interoperability Design Team in IETF and the Working Team, the MPLS Interoperability Design Team in IETF and the
MPLS-TP Ad-Hoc Team in ITU-T) involved in the definition and MPLS-TP Ad-Hoc Team in ITU-T) involved in the definition and
specification of MPLS Transport Profile. specification of MPLS Transport Profile.
10. References 10. References
10.1. Normative References 10.1. Normative References
skipping to change at page 16, line 46 skipping to change at page 17, line 29
"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use
over an MPLS PSN", RFC 4385, February 2006. over an MPLS PSN", RFC 4385, February 2006.
[7] Martini, L., "IANA Allocations for Pseudowire Edge to Edge [7] Martini, L., "IANA Allocations for Pseudowire Edge to Edge
Emulation (PWE3)", BCP 116, RFC 4446, April 2006. Emulation (PWE3)", BCP 116, RFC 4446, April 2006.
[8] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, [8] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci,
D., Li, T., and A. Conta, "MPLS Label Stack Encoding", D., Li, T., and A. Conta, "MPLS Label Stack Encoding",
RFC 3032, January 2001. RFC 3032, January 2001.
[9] Andersson, L. and R. Asati, "Multi-Protocol Label Switching [9] Andersson, L. and R. Asati, "Multiprotocol Label Switching
(MPLS) label stack entry: "EXP" field renamed to "Traffic (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
Class" field", draft-ietf-mpls-cosfield-def-08 (work in Class" Field", RFC 5462, February 2009.
progress), December 2008.
[10] Agarwal, P. and B. Akyol, "Time To Live (TTL) Processing in [10] Agarwal, P. and B. Akyol, "Time To Live (TTL) Processing in
Multi-Protocol Label Switching (MPLS) Networks", RFC 3443, Multi-Protocol Label Switching (MPLS) Networks", RFC 3443,
January 2003. January 2003.
[11] Swallow, G., Bryant, S., and L. Andersson, "Avoiding Equal Cost [11] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label
Multipath Treatment in MPLS Networks", BCP 128, RFC 4928,
June 2007.
[12] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label
Switching Architecture", RFC 3031, January 2001. Switching Architecture", RFC 3031, January 2001.
[13] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA [12] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
[14] Narten, T., "Assigning Experimental and Testing Numbers [13] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692, January 2004. Considered Useful", BCP 82, RFC 3692, January 2004.
10.2. Informative References 10.2. Informative References
[15] Bocci, M., Bryant, S., and L. Levrau, "A Framework for MPLS in [14] Bocci, M., Bryant, S., and L. Levrau, "A Framework for MPLS in
Transport Networks", draft-ietf-mpls-tp-framework-00 (work in Transport Networks", draft-ietf-mpls-tp-framework-00 (work in
progress), November 2008. progress), November 2008.
[16] Vigoureux, M., Ward, D., and M. Betts, "Requirements for OAM in [15] Vigoureux, M., Ward, D., and M. Betts, "Requirements for OAM in
MPLS Transport Networks", MPLS Transport Networks",
draft-ietf-mpls-tp-oam-requirements-00 (work in progress), draft-ietf-mpls-tp-oam-requirements-01 (work in progress),
December 2008. March 2009.
[17] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and [16] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and
S. Ueno, "MPLS-TP Requirements", S. Ueno, "MPLS-TP Requirements",
draft-ietf-mpls-tp-requirements-04 (work in progress), draft-ietf-mpls-tp-requirements-06 (work in progress),
February 2009. April 2009.
[17] Kompella, K. and S. Amante, "The Use of Entropy Labels in MPLS
Forwarding", draft-kompella-mpls-entropy-label-00 (work in
progress), July 2008.
[18] Ohta, H., "Assignment of the 'OAM Alert Label' for [18] Ohta, H., "Assignment of the 'OAM Alert Label' for
Multiprotocol Label Switching Architecture (MPLS) Operation and Multiprotocol Label Switching Architecture (MPLS) Operation and
Maintenance (OAM) Functions", RFC 3429, November 2002. Maintenance (OAM) Functions", RFC 3429, November 2002.
Authors' Addresses Authors' Addresses
Matthew Bocci (editor) Matthew Bocci (editor)
Alcatel-Lucent Alcatel-Lucent
Voyager Place, Shoppenhangers Road Voyager Place, Shoppenhangers Road
 End of changes. 96 change blocks. 
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