MPLS Working Group M. Vigoureux (Editor) Internet Draft Alcatel-Lucent Intended status: Standard Track Expires: December 2008 G. Swallow (Editor) Cisco Systems, Inc. R. Aggarwal (Editor) Juniper Networks June 26, 2008 Assignment of the Generic Associated Channel Header Label (GAL) draft-vigoureux-mpls-tp-gal-00 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress". The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on December 26, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Vigoureux et al. Expires December 26, 2008 [Page 1] Internet-Draft Generic Associated Channel Header Label June 2008 Abstract This document describes the assignment of one of the reserved label values, defined in RFC 3032 [3], to the 'Generic-ACH Label (GAL)', that is used as generic exception mechanism, for example by MPLS Transport Profile (MPLS-TP) for Operations and Management (OAM) functions. 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 [1]. Table of Contents 1. Introduction...................................................2 2. Generic Exception Mechanism....................................3 3. Relationship with RFC 3429.....................................3 4. Relationship with Existing MPLS OAM Alert Mechanisms...........4 5. Applicability and Usages.......................................4 5.1. GAL Processing............................................5 5.1.1. Section..............................................5 5.1.2. Label Switched Paths.................................6 5.1.3. LSP Tandem Connection Monitoring Entity..............7 5.2. Considerations on Penultimate Hop Popping.................7 5.3. Compatibility.............................................8 6. Security Considerations........................................8 7. IANA Considerations............................................8 8. Acknowledgments................................................8 9. References.....................................................8 9.1. Normative References......................................8 9.2. Informative References....................................9 Authors' Addresses................................................9 Contributing Authors' Addresses..................................10 Intellectual Property Statement..................................10 Disclaimer of Validity...........................................11 1. Introduction This document describes the assignment of one of the reserved label values, defined in RFC 3032 [3], to the 'Generic-ACH Label (GAL)', that is used as generic exception mechanism, for example by MPLS Transport Profile (MPLS-TP) for Operations and Management (OAM) functions. Vigoureux et al. Expires December 26, 2008 [Page 2] Internet-Draft Generic Associated Channel Header Label June 2008 2. Generic Exception Mechanism MPLS-TP requires [12] a mechanism to differentiate specific packets (e.g. OAM) from others, such as normal user-plane ones. This document proposes that a label be used and calls this special label the 'Generic-ACH Label (GAL)'. One of the reserved label values defined in RFC 3032 [3] is assigned to the 'Generic-ACH Label (GAL)'. The value of the label is to be allocated by IANA; this document suggests the value 13. The 'Generic-ACH Label (GAL)' is a generic exception mechanism used firstly to differentiate specific packets (e.g. OAM) from others, such as normal user-plane ones, and secondly, to indicate that the Generic Associated Channel Header (GE-ACH) [10] appears immediately after the bottom of the label stack. The 'Generic-ACH Label (GAL)' MUST only be used if those two purposes are fulfilled simultaneously. Note that, in this document, MPLS-TP OAM (functions, packets) should be understood in the broad sense, that is, as a set of mechanisms including Automatic Protection Switching (APS), Signalling Control Channel (SCC) and Management Control Channel (MCC). Further, while transport applications are expected to be the first to use the 'Generic-ACH Label (GAL)', the use of this label is by no means restricted to MPLS-TP. 3. Relationship with RFC 3429 RFC 3429 [11] describes the assignment of one of the reserved label values, defined in RFC 3032 [3], to the 'OAM Alert Label' that is used by user-plane MPLS OAM functions for the identification of MPLS OAM packets. The value of 14 is used for that purpose. This document and RFC 3429 [11], thus describe the assignment of reserved label values for similar purposes. The rationales for the assignment of a new reserved label can be summarized as follows: Vigoureux et al. Expires December 26, 2008 [Page 3] Internet-Draft Generic Associated Channel Header Label June 2008 o Unlike the mechanisms described and referenced in RFC 3429 [11], MPLS-TP OAM packets will not reside immediately after the 'Generic-ACH Label (GAL)' but behind the Generic Associated Channel Header (GE-ACH) [10] which, itself, resides immediately after the bottom of the label stack when the 'Generic-ACH Label (GAL)' appears in this label stack. This will ensure that MPLS-TP OAM complies with RFC 4928 [7]. o The set of OAM functions potentially operated in the context of MPLS-TP is wider than the set of OAM functions referenced in RFC 3429 [11]. o It has been reported that there are existing implementations and running deployments using the 'OAM Alert Label' as described in RFC 3429 [11]. It is therefore not possible to modify the 'OAM Alert Label' allocation, purpose or usage. Nevertheless, it is RECOMMENDED by this document that no further OAM extensions based on 'OAM Alert Label' (Label 14) usage be specified or developed. 4. Relationship with Existing MPLS OAM Alert Mechanisms RFC 4379 [6] and BFD for MPLS LSPs [8] have defined alert mechanisms that enable a MPLS LSR to identify and process MPLS OAM packets when the OAM packets are encapsulated in an IP header. These alert mechanisms are based on TTL expiration and/or use an IP destination address in the range 127/8. These alert mechanisms SHOULD preferably be used in non MPLS-TP environments. The mechanism defined in this document MAY also be used. 5. Applicability and Usages The 'Generic-ACH Label (GAL)' MUST only be used with Label Switched Paths (LSPs), with their associated Tandem Connection Monitoring Entities (see [12] for definitions of TCMEs) and with MPLS Sections. A MPLS Section is a network segment between two LSRs that are immediately adjacent at the MPLS layer. The 'Generic-ACH Label (GAL)' applies to both P2P and P2MP LSPs, unless otherwise stated. In MPLS-TP, the 'Generic-ACH Label (GAL)' MUST always be at the bottom of the label stack (i.e. S bit set to 1). However, in other MPLS environments, this document places no restrictions on where the 'Generic-ACH Label (GAL)' may appear within the label stack. Vigoureux et al. Expires December 26, 2008 [Page 4] Internet-Draft Generic Associated Channel Header Label June 2008 The 'Generic-ACH Label (GAL)' MUST NOT be used with Pseudowires (PWs) neither with their associated Tandem Connection Monitoring Entities. The 'Generic-ACH Label (GAL)' MUST NOT appear in the label stack when transporting normal user-plane packets. Furthermore, the 'Generic-ACH Label (GAL)' MUST only appear once in the label stack. 5.1. GAL Processing The Class of Service (CoS) field (former EXP field) of the 'Generic- ACH Label (GAL)' follows the definition and processing rules specified and referenced in [9]. The Time To Live (TTL) field of the 'Generic-ACH Label (GAL)' follows the definition and processing rules specified in [4]. For detailed information on the Generic-ACH (GE-ACH) mentioned in the following sub-sections, please see [10]. 5.1.1. Section The following figure (Figure 1) depicts two MPLS LSRs immediately adjacent at the MPLS layer. +---+ +---+ | A |-------------| Z | +---+ +---+ Figure 1 : MPLS-TP OAM over a MPLS Section With regards to the MPLS Section, both LERs are Maintenance End Points (see [12] for definitions of MEPs). The following figure (Figure 2) depicts the format of a labelled MPLS-TP OAM packet when used for MPLS Section OAM. Vigoureux et al. Expires December 26, 2008 [Page 5] Internet-Draft Generic Associated Channel Header Label June 2008 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | GAL | CoS |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Generic-ACH | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . . MPLS-TP OAM packet . . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2 : Labelled MPLS-TP OAM packet for MPLS Section OAM To perform MPLS-TP OAM functions on the MPLS Section, the head-end LSR (A) of the MPLS Section generates a MPLS-TP OAM packet with a GE- ACH to which it prepends a 'Generic-ACH Label (GAL)'. o The TTL field of the 'Generic-ACH Label (GAL)' SHOULD be set to 1. o The S bit of the 'Generic-ACH Label (GAL)' MUST be set to 1. The MPLS-TP OAM packet, the GE-ACH or the 'Generic-ACH Label (GAL)' SHOULD NOT be modified towards the tail-end LSR (Z). Upon reception of the labelled packet, the tail-end LSR (Z), after having checked the 'Generic-ACH Label (GAL)' fields, SHOULD pass the whole packet to the appropriate processing entity. 5.1.2. Label Switched Paths The following figure (Figure 3) depicts four LSRs. A LSP is established from A to D and switched in B and C. +---+ +---+ +---+ +---+ | A |-------------| B |-------------| C |-------------| D | +---+ +---+ +---+ +---+ Figure 3 : MPLS-TP OAM over a LSP With regards to the considered LSP, LERs A and D are MEPs. Furthermore, LSRs B and C could be Maintenance Intermediate Points (see [12] for definitions of MEPs and MIPs). The following figure (Figure 4) depicts the format of a labelled MPLS-TP OAM packet when used for LSP OAM. Vigoureux et al. Expires December 26, 2008 [Page 6] Internet-Draft Generic Associated Channel Header Label June 2008 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LSP Label | CoS |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | GAL | CoS |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Generic-ACH | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . . MPLS-TP OAM packet . . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4 : Labelled MPLS-TP OAM packet for LSP OAM Note that, in the general case, the considered LSP MAY be tunnelled (e.g. in a MPLS Tunnel existing between B and C), and as such, other labels MAY be present above in the label stack. To perform MPLS-TP OAM functions on the LSP, the head-end LSR (A) of the LSP generates a MPLS-TP OAM packet with a GE-ACH to which it prepends a 'Generic-ACH Label (GAL)' to which it prepends the label of the LSP. o The TTL field of the 'Generic-ACH Label (GAL)' SHOULD be set to 1. o The S bit of the 'Generic-ACH Label (GAL)' SHOULD be set to 1, in MPLS-TP. The MPLS-TP OAM packet, the GE-ACH or the 'Generic-ACH Label (GAL)' SHOULD NOT be modified towards the targeted destination. Upon reception of the labelled packet, the targeted destination, after having checked both the LSP label and 'Generic-ACH Label (GAL)' fields, SHOULD pass the whole packet to the appropriate processing entity. 5.1.3. LSP Tandem Connection Monitoring Entity To be covered in a next version of this document. 5.2. Considerations on Penultimate Hop Popping OAM operations require context awareness. The label, immediately above the 'Generic-ACH Label (GAL)' in the label stack, provides this context. Additionally, a requirement of MPLS-TP OAM is that user- plane and OAM packets share the same fate [12]. As such, when Vigoureux et al. Expires December 26, 2008 [Page 7] Internet-Draft Generic Associated Channel Header Label June 2008 operating MPLS-TP OAM, Penultimate Hop Popping (PHP) SHOULD be disabled by default for the label immediately above the 'Generic-ACH Label (GAL)' in the label stack, otherwise neither all MPLS-TP OAM requirements [12] nor all MPLS-TP OAM functions can be satisfied. In case PHP is enabled, the context, normally provided by the label immediately above the 'Generic-ACH Label (GAL)' in the label stack, SHALL be provided by other means. Moreover, PHP MUST NOT be applied to the 'Generic-ACH Label (GAL)' itself. 5.3. Compatibility LERs and LSRs not capable of processing the 'Generic-ACH Label (GAL)' SHOULD silently discard the packet. 6. Security Considerations This document does not raise any security issue that is not already present in either the MPLS architecture [2], the PWE3 architecture . [5] or the MPLS-TP framework [ref]. Security considerations, for the GE-ACH, can be found in [10]. 7. IANA Considerations This document requests that IANA allocates a Label value, to the 'Generic-ACH Label (GAL)', from the pool of reserved labels, and suggests this value to be 13. 8. Acknowledgments The authors would like to thank all members of the teams (the Joint Working Team, the MPLS Interoperability Design Team in IETF and the T-MPLS Ad Hoc Group in ITU-T) involved in the definition and specification of MPLS Transport Profile. 9. References 9.1. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997 [2] Rosen, E., Viswanathan, A., Callon, R., "Multiprotocol Label Switching Architecture", RFC 3031, January 2001 Vigoureux et al. Expires December 26, 2008 [Page 8] Internet-Draft Generic Associated Channel Header Label June 2008 [3] Rosen, E., et al., "MPLS Label Stack Encoding", RFC 3032, January 2001 [4] Agarwal, P., Akyol, B., "Time To Live (TTL) Processing in Multi-Protocol Label Switching (MPLS) Networks", RFC 3443, January 2003 [5] Bryant, S., Pate, P., "Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture", RFC 3985, March 2005 [6] Kompella, K., Swallow, G., "Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures", RFC 4379, February 2006 [7] Swallow, G., Bryant, S., Andersson, L., "Avoiding Equal Cost Multipath Treatment in MPLS Networks", BCP 128, RFC 4928, June 2007 [8] Aggarwal, R., Kompella, K., Swallow, G., Nadeau, T., "BFD For MPLS LSPs", draft-ietf-bfd-mpls-07, June 2008 [9] Andersson, L., ""EXP field" renamed to "CoS Field"", draft- ietf-mpls-cosfield-def-02, June 2008 [10] Bocci, M., Ward, D., "MPLS Generic Associated Channel", draft- bocci-pwe3-ge-ach-00, June 2008 9.2. Informative References [11] Ohta, H., "Assignment of the 'OAM Alert Label' for Multiprotocol Label Switching Architecture (MPLS) Operation and Maintenance (OAM) Functions", RFC 3429, November 2002 [12] Vigoureux, M., Betts, M., Ward, D., "Requirements for OAM in MPLS Transport Networks", draft-vigoureux-mpls-tp-oam- requirements-00, July 2008 Authors' Addresses Martin Vigoureux (Editor) Alcatel-Lucent Email: martin.vigoureux@alcatel-lucent.com Vigoureux et al. Expires December 26, 2008 [Page 9] Internet-Draft Generic Associated Channel Header Label June 2008 George Swallow (Editor) Cisco Systems, Inc. Email: swallow@cisco.com Rahul Aggarwal (Editor) Juniper Networks Email: rahul@juniper.net Contributing Authors' Addresses David Ward Cisco Systems, Inc. Email: dward@cisco.com Matthew Bocci Alcatel-Lucent Email: matthew.bocci@alcatel-lucent.co.uk Italo Busi Alcatel-Lucent Email: italo.busi@alcatel-lucent.it Marc Lasserre Alcatel-Lucent Email: mlasserre@alcatel-lucent.com Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights 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; nor does it represent that it has made any independent effort to identify any such rights. Information Vigoureux et al. Expires December 26, 2008 [Page 10] Internet-Draft Generic Associated Channel Header Label June 2008 on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Vigoureux et al. Expires December 26, 2008 [Page 11]