RFC 7074

Revised Definition of the GMPLS Switching Capability and Type Fields

📅 published November 2013, from ietf

RFC 7074: Revised Definition of the GMPLS Switching Capability and Type Fields 🎀

okay bestie, RFC 7074 is a Standards Track doc from the IETF, published November 2013 ✨. The authors are L. Berger from LabN and J. Meuric from Orange 💅. It's ISSN 2070-1721, and it updates RFCs 3471, 4202, 4203, and 5307 🔥. Basically it's the one that cleans up how GMPLS uses its Switching Capability and Switching Type fields 🧚

Abstract 💜

okay so GMPLS controls a bunch of different switching technologies, and it also handles hierarchical switching inside one technology 🦋. GMPLS routing and signaling both use the same values to say what kind of switching technology you're dealing with. In routing protocols those values live in the Switching Capability field, and in signaling protocols they live in the Switching Type field 🌸. The values are the main signal for which technology and which hierarchy level is being controlled, but they haven't been defined or used consistently across the technologies GMPLS supports 😭. This doc fixes that by narrowing down what the two fields mean and how they get used 💖. It updates every document that uses the GMPLS Switching Capability and Switching Type fields, and it calls out RFCs 3471, 4202, 4203, and 5307 by name ✨.

Status of This Memo 🌈

This is an Internet Standards Track document 💅.

It's a product of the Internet Engineering Task Force (IETF) and reflects the consensus of the IETF community 🫶. It got public review and was approved for publication by the Internet Engineering Steering Group (IESG) 👑. If you want more info on Internet Standards, check out Section 2 of RFC 5741 🍓.

For the current status, any errata, and how to send feedback, go to http://www.rfc-editor.org/info/rfc7074 🧚

Copyright Notice 🌸

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) as they stand on the date this document was published 📜. Please actually read them, because they spell out your rights and restrictions for this doc 🙈. Code Components pulled out of this document must include Simplified BSD License text, as described in Section 4.e of the Trust Legal Provisions, and they come with no warranty, as the Simplified BSD License describes 🔥.

1. Introduction ✨

okay so GMPLS (Generalized Multiprotocol Label Switching) gives you control over multiple switching technologies 🦋. It also does hierarchical switching within a single technology 💅. The original GMPLS Architecture, per [RFC3945], covered five types of switching capability, and [RFC6002] added one more 🌈. The switching types defined in those docs are:

Packet Switch Capable (PSC)
Layer-2 Switch Capable (L2SC)
Time-Division Multiplex Capable (TDM)
Lambda Switch Capable (LSC)
Fiber-Switch Capable (FSC)
Data Channel Switching Capable (DCSC)

The original types got routing support in [RFC4202], [RFC4203], and [RFC5307], where they show up in the Switching Capability (Switching Cap) field 💖. Generally, hierarchy inside a type gets handled in a type-specific way, and each type gets one Switching Capability field value 🎀. PSC is the exception, since it got four values for four hierarchy levels: PSC-1, PSC-2, PSC-3, and PSC-4 🍓. Signaling uses the same values, defined in [RFC3471], and they're carried in the Switching Type field ✨. Following the IANA registry, we call the values used in the routing Switching Capability field and the signaling Switching Type field Switching Types 👑.

Here's the tea: a Switching Type doesn't tell you the specific data-plane technology, so you have to work that out from context 🔍. For example, L2SC was defined to cover Ethernet and ATM, and TDM was defined to cover both SONET/SDH [RFC4606] and G.709 [RFC4328] 🫶. The basic assumption was that different technologies of the same type would never run in the same control domain, meaning the same signaling and routing domains 🙈.

The old approach to assigning Switching Types caused problems from two angles 😭. First, some switching technologies have different levels of switching inside the same technology. For example, there are several types of Ethernet switching that can happen in a provider network 💅. Second, the Switching Capability field value tells Interior Gateway Protocols (IGPs) what format the Switching Capability-specific information (SCSI) field uses. Mapping a type to a SCSI format implicitly just isn't practical for implementations that support multiple switching technologies 💀. Those issues led to two new Ethernet types, from [RFC6004] and [RFC6060]:

Ethernet Virtual Private Line (EVPL)
802_1 PBB-TE (Provider Backbone Bridge Traffic Engineering)

There's also one more value envisioned by [GMPLS-G709] to support G.709v3, which exists to disambiguate the format of the SCSI field 🧚.

Look, a common way to represent hierarchy levels within a switching technology totally fits GMPLS's design goals 🌈. But having multiple PSC Switching Types hasn't really been useful either. Notably, there are no known uses of PSC-2, PSC-3, and PSC-4 🙈.

This document fixes the inconsistent definitions and uses of Switching Types by shrinking the scope of the related fields and narrowing how they're used 🦋. Specifically, it deprecates using Switching Types to identify hierarchy levels inside a switching technology, and limits them to identifying the SCSI field format for each switching technology 💖.

This document updates all documents that use the GMPLS Switching Capability and Switching Type fields, in particular RFCs 3471, 4202, 4203, and 5307 ✨.

1.1. Current Switching Type Definition 🌸

The Switching Type values get carried in both routing and signaling protocols 💜. The values are listed in IANA's "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Parameters" registry, which currently lives at http://www.iana.org/assignments/gmpls-sig-parameters/ 📜.

For routing, there's a common information element that carries Switching Type values for both OSPF and IS-IS, defined in [RFC4202] 🔥. Per [RFC4202], Switching Type values are carried in a Switching Capability (Switching Cap) field inside an Interface Switching Capability Descriptor 💅. This info is formatted the same way in OSPF, as defined by [RFC4203], and in IS-IS, as defined by [RFC5307] 🍓:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Switching Cap |   Encoding    |           Reserved            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Switching Capability-specific information              |
   |                  (variable)                                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   ...

   The content of the Switching Capability-specific information field
   depends on the value of the Switching Capability field.

Signaling works similarly. The Switching Type field is defined as part of a common format for GMPLS signaling protocols in [RFC3471], and it's used by [RFC3473] 🦋:

    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 Enc. Type |Switching Type |             G-PID             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Switching Type: 8 bits. Indicates the type of switching that should be performed on a particular link. This field is needed for links that advertise more than one type of switching capability. This field should map to one of the values advertised for the corresponding link in the routing Switching Capability Descriptor ...

1.2. 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 [RFC2119] 🧚

2. Revised Switching Type Definition 🔥

This document changes the definition of Switching Type 💖. The definitions are a bit different for routing and signaling, so they're covered in the sections below 🫶.

2.1. Routing -- Switching Cap Field 🦋

For routing [RFC4202] [RFC4203] [RFC5307], the following definition should be used for the Switching Cap field 💅:

The Switching Cap field indicates the type of switching being advertised via GMPLS Switching Type values. A different Switching Type value SHOULD be used for each data-plane technology, even when those technologies share the same type of multiplexing or switching. For example, Time Division Multiplexing (TDM) technologies that have different multiplexing structures, such as Synchronous Digital Hierarchy (SDH) [G.707] and Optical Transport Network (OTN) [G.709], should use two different Switching Types. As the format of the Switching Capability-specific information field is dependent on the value of this field, a different Switching Type value MUST be used to differentiate between different Switching Capability-specific information field formats. This definition does not modify the format of the Interface Switching Capability Descriptor.

Note that from a practical standpoint, this means that any time a new switching technology might use a different Switching Capability-specific information field format, a new Switching Type SHOULD be used 🌈.

2.2. Signaling -- Switching Type Field 💜

For signaling [RFC3471], which is used by [RFC3473], the following definition should be used for the Switching Type field 🙈:

Indicates the type of switching that should be performed on a particular link via GMPLS Switching Type values. This field maps to one of the values advertised for the corresponding link in the routing Switching Capability Descriptor, see [RFC4203] and [RFC5307].

Note that from a practical standpoint, there is no change in the definition of this field 🎀.

2.3. Assigned Switching Types 🍓

This document deprecates the following Switching Types ⭐:

   Value                 Name
     2       Packet-Switch Capable-2 (PSC-2)
     3       Packet-Switch Capable-3 (PSC-3)
     4       Packet-Switch Capable-4 (PSC-4)

These values SHOULD be treated as unsupported types and, in the case of signaling, processed according to Section 2.1.1 of [RFC3473]. 🚫

3. Compatibility ✨

okay so bestie, the big deal here is that this document basically deprecates PSC-2, 3, and 4 💅 🫶 For anyone already running code, that's the main impact. And here's the tea: at the time of publication, there are no known deployments (or even implementations) using those values, so there are no compatibility issues for current routing and signaling implementations 🌸 no drama at all, iconic 👑

4. Security Considerations 🔒

okay so this document only touches the values carried in a single field in signaling and routing protocols 🧚 no new protocol formats or mechanisms are defined, so there are no particular security implications raised by this document 💖 not me being chill about it 😭

if you want the full picture on MPLS and GMPLS security issues in general, go check the MPLS/GMPLS security framework [RFC5920] 🦋 it's the main character of that topic, periodt 💜

5. IANA Considerations 🎀

okay this section is where the registry changes live 📋 IANA has deprecated some values and redefined the related values in the "IANA-GMPLS-TC-MIB" definitions 💅 specifically, the Switching Types portion of the "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Parameters" registry been revised to read:

   Switching Types

      Registration Procedures

   Standards Action

      Reference
              [RFC3471][RFC4328][This Document]

       Value                  Name                  Reference
         0    Unassigned
         1    Packet-Switch Capable-1 (PSC-1)       [RFC3471]
         2    Deprecated                            [This Document]
         3    Deprecated                            [This Document]
         4    Deprecated                            [This Document]
       5-29   Unassigned
        30    Ethernet Virtual Private Line (EVPL)  [RFC6004]
       31-39  Unassigned
        40    802_1 PBB-TE                          [RFC6060]
       41-50  Unassigned
        51    Layer-2 Switch Capable (L2SC)         [RFC3471]
       52-99  Unassigned
       100    Time-Division-Multiplex Capable (TDM) [RFC3471]
      101-124 Unassigned
       125    Data Channel Switching Capable (DCSC) [RFC6002]
      126-149 Unassigned
       150    Lambda-Switch Capable (LSC)           [RFC3471]
      151-199 Unassigned
       200    Fiber-Switch Capable (FSC)            [RFC3471]
      201-255 Unassigned

a parallel change happened in IANA-GMPLS-TC-MIB too 🌈 under IANAGmplsSwitchingTypeTC, a reference to this document has been added as item 3, and the related values got updated like this:

       psc2(2),      -- Deprecated [This Document]
       psc3(3),      -- Deprecated [This Document]
       psc4(4),      -- Deprecated [This Document]

6. Acknowledgments 🫶

we thank John Drake for highlighting the inconsistent definitions tied to the Switching Capability and Type fields 💖 Daniele Ceccarelli and Adrian Farrel gave valuable feedback on this document ✨ literally the real MVPs 👑

7. References 📚

7.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3471] Berger, L., Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description", RFC 3471, January 2003.
[RFC4202] Kompella, K., Ed., and Y. Rekhter, Ed., "Routing Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4202, October 2005.
[RFC4203] Kompella, K., Ed., and Y. Rekhter, Ed., "OSPF Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4203, October 2005.
[RFC5307] Kompella, K., Ed., and Y. Rekhter, Ed., "IS-IS Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 5307, October 2008.

7.2. Informative References

[G.707] ITU-T Recommendation G.707/Y.1322 (2007), "Network node interface for the synchronous digital hierarchy (SDH)".
[G.709] ITU-T Recommendation G.709/Y.1331 (2009), "Interfaces for the Optical Transport Network (OTN)".
[GMPLS-G709] Zhang, F., Li, D., Li, H., Belotti, S., and D. Ceccarelli, "Framework for GMPLS and PCE Control of G.709 Optical Transport Networks", Work in Progress, September 2013.
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.
[RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Architecture", RFC 3945, October 2004.
[RFC4328] Papadimitriou, D., Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Extensions for G.709 Optical Transport Networks Control", RFC 4328, January 2006.
[RFC4606] Mannie, E. and D. Papadimitriou, "Generalized Multi-Protocol Label Switching (GMPLS) Extensions for Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) Control", RFC 4606, August 2006.
[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS Networks", RFC 5920, July 2010.
[RFC6002] Berger, L. and D. Fedyk, "Generalized MPLS (GMPLS) Data Channel Switching Capable (DCSC) and Channel Set Label Extensions", RFC 6002, October 2010.
[RFC6004] Berger, L. and D. Fedyk, "Generalized MPLS (GMPLS) Support for Metro Ethernet Forum and G.8011 Ethernet Service Switching", RFC 6004, October 2010.
[RFC6060] Fedyk, D., Shah, H., Bitar, N., and A. Takacs, "Generalized Multiprotocol Label Switching (GMPLS) Control of Ethernet Provider Backbone Traffic Engineering (PBB-TE)", RFC 6060, March 2011.

8. Authors' Addresses 🌸

Lou Berger LabN Consulting, L.L.C. Phone: +1 301 468 9228

EMail: lberger@labn.net

Julien Meuric Orange Research & Development 2, Avenue Pierre Marzin 22307 Lannion Cedex -- France

Phone: +33 2 96 05 28 28 EMail: julien.meuric@orange.com

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