[Pals] Candidate draft-ietf-pals-vccv-for-gal-01

[Stewart Bryant <[e-mail]>]

Working Group/Co-authors

Following discussion on the list I have edited draft-ietf-pals-vccv-for-gal
to just define the GAL VCCV CC Type 4. As suggested the plan will then be
to write a new draft describing the migration strategy to type 1 and 4 only.
There is some text in here on migration and I am torn between taking it out
and leaving it in to explain why we are introducing the new CC type.

Because of the extensive changes I thought it best to post this candidate
to the list to make sure we are all on the same page. If this is going in
the right direction I will upload it as a draft replacing
draft-ietf-pals-vccv-for-gal-00.

I took Sasha's proposal of making FAT and GAL mutually exclusive which
in my view usefully simplified that aspect of the design.

I did quite a lot of work on the Capability Advertisment section which
will need to be checked very carefully, in particular the handling of the
error processing.

I would appreciate a quick review to see whether this is what the WG was
expecting, and then I can upload it ready for a detailed review if it
is on the right lines.

- Stewart



PWE3                                                           T. Nadeau
Internet-Draft lucidvision
Intended status: Standards Track                              L. Martini
Expires: July 18, 2015                                         S. Bryant
                                                            Cisco Systems
                                                         January 14, 2015


           Candidate for Using GAL as a VCCV Channel Indicator
                     draft-ietf-pals-vccv-for-gal-01

Abstract

    This document specifies a new Virtual Circuit Connectivity
    Verification (VCCV) (RFC5085) control channel type for use with
    pseudowires (PW) carried over an MPLS network.  This new channel type
    uses the Generic Associated Channel Label (GAL) (RFC5586) to
    distinguish VCCV packets from packets carrying user data.

Status of This Memo

    This Internet-Draft is submitted in full conformance with the
    provisions of BCP 78 and BCP 79.

    Internet-Drafts are working documents of the Internet Engineering
    Task Force (IETF).  Note that other groups may also distribute
    working documents as Internet-Drafts.  The list of current Internet-
    Drafts is at http://datatracker.ietf.org/drafts/current/.

    Internet-Drafts are draft documents valid for a maximum of six months
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    time.  It is inappropriate to use Internet-Drafts as reference
    material or to cite them other than as "work in progress."

    This Internet-Draft will expire on July 18, 2015.

Copyright Notice

    Copyright (c) 2015 IETF Trust and the persons identified as the
    document authors.  All rights reserved.

    This document is subject to BCP 78 and the IETF Trust's Legal
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    (http://trustee.ietf.org/license-info) in effect on the date of
    publication of this document.  Please review these documents
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    include Simplified BSD License text as described in Section 4.e of



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    the Trust Legal Provisions and are provided without warranty as
    described in the Simplified BSD License.

Table of Contents

    1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
    2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
    3.  GAL VCCV Control Channel Type . . . . . . . . . . . . . . . .   3
    4.  FAT PWs . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
    5.  VCCV Capability Advertisement . . . . . . . . . . . . . . . .   4
    6.  Manageability Considerations  . . . . . . . . . . . . . . . .   5
    7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
    8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
      8.1.  MPLS VCCV Control Channel (CC) Type 4 . . . . . . . . . .   5
      8.2.  LDP Status Code . . . . . . . . . . . . . . . . . . . . .   6
    9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
    10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
      10.1.  Normative References . . . . . . . . . . . . . . . . . .   6
      10.2.  Informative References . . . . . . . . . . . . . . . . .   7
    Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

    This document specifies a new Virtual Circuit Connectivity
    Verification (VCCV) [RFC5085] control channel (CC) type for use with
    pseudowires (PW) carried over an MPLS network that do not use the PW
    Control Word (CW) [RFC4385].  This new VCCV CC type uses the Generic
    Associated Channel Label (GAL) [RFC5586] to distinguish VCCV packets
    from packets carrying user data.  This new VCCV CC type introduces
    compatibility with the method of MPLS Label Switched Path (LSP)
    Operations, Administration, and Maintenance (OAM) identification,
    particularly in MPLS-TP networks [RFC5921].

    VCCV currently specifies three CC types.  VCCV CC Type 1 uses the PW
    Control Word (CW) to distinguish VCCV packets from packets carrying
    user data.  VCCV CC Types 2 and 3 require IP encapsulation for OAM
    packets they carry.  This was not an issue when [RFC5085] was
    designed, but is in conflict with the design goals of MPLS-TP
    [RFC5921] which does not otherwise require the availability of IP.
    VCCV CC Type 2 is not supported by multi-segment PWs (MS-PWs)
    [RFC6073].  A MS-PW operating without the CW therefore has to use
    VCCV CC Type 3 which identifies VCCV packets on the basis of TTL
    expiry.  Whilst less of an issue with a single segment PW (SS-PW), on
    an MS-PW this need to be accurately set to cause TTL expiry at the
    egress Terminating Provider Edge (T-PE) [RFC6073].  In the event of a
    error in the setting of the PW LSE TTL this can result in VCCV
    packets leaking into the attachment circuit which may disrupt the
    operation of the PW, or the user service, and is a security risk.



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    The new VCCV CC type defined in this specification addresses these
    problems for PWs that do not use the CW.

    For reasons of network efficiency and due to hardware constraints it
    is not possible to address these issue by mandating that all PWs use
    the PW CW, hence the introduction of this new VCCV CC type.

2.  Requirements Language

    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
    "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
    "OPTIONAL" in this document are to be interpreted as described in
    [RFC2119].

3.  GAL VCCV Control Channel Type

    When the PW CW is not used, the GAL VCCV Control Channel (CC) type
    defined in this section MAY be used.  This is referred to as VCCV CC
    Type4 throughout the rest of this of this document.  VCCV Type 4 uses
    the encapsulation shown in Figure 1.

    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

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                            PW LSE |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           GAL LSE |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0 0 0 1|Version|   Reserved    |        Channel Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | |
    ~                        VCCV Message Body ~
    | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                  Figure 1

    The VCCV message body is preceded by a Generic Associated Channel
    Header as defined in [RFC5586], in which the Channel Type identifies
    the type and format of the OAM message carried in the VCCV message
    body.

    The GAL LSE MUST contain the GAL reserved label as defined in
    [RFC5586].





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    The PW LSE is constructed according to the existing procedures that
    apply to the type of pseudowire that is in use.

    Note that the inclusion of a GAL following the PW LSE over a label
    switched path subject to Equal-Cost Multi-path (ECMP) load balancing
    can cause the OAM packet to take a different path through the network
    from the corresponding PW data packets.  If that is not acceptable,
    then an alternative VCCV type must be used.

4.  FAT PWs

    [RFC6391] specifies that when the flow-aware transport (FAT) of
    pseudowires over an MPLS packet switched network has been signalled
    or configured, the Flow LSE MUST be present.  It further specifies
    that "the flow label MUST NOT be an MPLS reserved label (values in
    the range 0..15) [RFC3032]", and that "If a flow LSE is present, it
    MUST be checked to determine whether it carries a reserved label.  If
    it is a reserved label, the packet is processed according to the
    rules associated with that reserved label; otherwise, the LSE is
    discarded."

    This document specifies that if the flow-aware transport of
    pseudowires over an MPLS packet switched network has been signalled
    or configured then the presence of VCCV message is indicated by the
    use of a GAL in place of the flow LSE.

    This is consistent with [RFC6391], and the packet structure is
    identical to that shown in Figure 1.

    Note that the use of a GAL in place of the flow label over a label
    switched path subject to ECMP can cause the OAM packet to take a
    different path through the network from the corresponding PW data
    packets.  If that is not acceptable, then an alternative VCCV type
    must be used.

5.  VCCV Capability Advertisement

    The VCCV capability advertisement MUST match the c-bit setting that
    is advertised in the PW FEC element [RFC4447].  If the c-bit is set,
    indicating the use of the PW CW, then VCCV CC Type 4 MUST NOT be
    advertised.  If the c-bit is not set, indicating that the PW CW is
    not in use, then an equipment supporting this specification MUST
    advertise VCCV CC Type 4.  Advertisement of VCCV CC Types 1 and 4 are
    therefore mutually exclusive.

    A PE supporting VCCV CC Type 4 MAY advertise other VCCV CC types as
    defined in [RFC5085] .




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    If the remote PE supports VCCV CC Type 4, and the PW CW is not in
    use, then the following capability advertisement precedence rules
    supersede those defined in Section 7 of [RFC5085] :

    1.  Type 4: GAL VCCV Control Channel.

    2.  Type 2: MPLS Router Alert Label.

    3.  Type 3: MPLS PW Label with TTL == 1.

    If the remote PE finds that VCCV CC Types 1 and 4 are both
    advertised, or that c-bit is set and VCCV CC Type 4 is advertised,
    then it should report the error to the operator through the
    management interface in use, and send a Label Release Message with a
    status code "VCCV Type Error".

6.  Manageability Considerations

    Whilst the introduction of this additional VCCV CC type increases the
    number of VCCV CC types that the operator needs to manage, it
    addresses the issues with VCCV CC Types 2 and 3 described in
    Section 1, and is a necessary per-requisite of the long term strategy
    of the PALS working group to consolidate the VCCV channel types down
    to only VCCV CC Types 1 and 4.  This consolidation and will be the
    subject of future work by the PALS working group.

    In the event of a misconfiguration of this VCCV CC type, the PW is
    taken out of service and the operator advised as described in
    Section 5.

    Attention is drawn to the possible absence of fate sharing between PW
    data packets and VCCV CC Type 4 packets described in Section 3 and
    Section 4.

7.  Security Considerations

    This document does not by itself raise any new security
    considerations beyond those described in [RFC5085].  It addresses the
    possibility of packet leaking that can occur with VCCV CC Type 3.

8.  IANA Considerations

8.1.  MPLS VCCV Control Channel (CC) Type 4

    IANA is requested to assign a new bit from the MPLS VCCV Control
    Channel (CC) Types registry in the PWE3-parameters name space in
    order to identify VCCV type 4.  It is recommended that Bit 3 be
    assigned to this purpose which would have a value of 0x08.



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    MPLS VCCV Control Channel (CC) Types

          Bit (Value)    Description   Reference
          ============   ===========   ==================
          Bit X (0x0Y)   Type 4        This Specification

8.2.  LDP Status Code

    IANA is requested to assign a new Status Code from the Label
    Distribution Protocol (LDP) Parameters name space:

    Status Code Name Space

          Range/Value  E  Description      Reference
          ===========  =  ===============  =========
          0x000000xx   0  VCCV Type Error  This Specification


9.  Acknowledgments

    The authors wish to thank Alexander (Sasha) Vainshtein for his review
    comments and for his proposal to make the GAL and Flow labels
    mutually exclusive.  This proposal let to a significant
    simplification of this design.

10.  References

10.1.  Normative References

    [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

    [RFC4385]  Bryant, S., Swallow, G., Martini, L., and D. McPherson,
               "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
               Use over an MPLS PSN", RFC 4385, February 2006.

    [RFC4447]  Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G.
               Heron, "Pseudowire Setup and Maintenance Using the Label
               Distribution Protocol (LDP)", RFC 4447, April 2006.

    [RFC5085]  Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
               Connectivity Verification (VCCV): A Control Channel for
               Pseudowires", RFC 5085, December 2007.

    [RFC5586]  Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic
               Associated Channel", RFC 5586, June 2009.





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    [RFC6073]  Martini, L., Metz, C., Nadeau, T., Bocci, M., and M.
               Aissaoui, "Segmented Pseudowire", RFC 6073, January 2011.

    [RFC6391]  Bryant, S., Filsfils, C., Drafz, U., Kompella, V., Regan,
               J., and S. Amante, "Flow-Aware Transport of Pseudowires
               over an MPLS Packet Switched Network", RFC 6391, November
               2011.

10.2.  Informative References

    [RFC5921]  Bocci, M., Bryant, S., Frost, D., Levrau, L., and L.
               Berger, "A Framework for MPLS in Transport Networks", RFC
               5921, July 2010.

Authors' Addresses

    Thomas D. Nadeau
    lucidvision

    Email: [e-mail]


    Luca Martini
    Cisco Systems

    Email: [e-mail]


    Stewart Bryant
    Cisco Systems

    Email: [e-mail]



















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