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

[Alexander Vainshtein <[e-mail]>]

Stewart,
Lots of thanks for a very nice re-write of the draft that, from my POV, resolves all outstanding technical issues raised so far and moved discussion of operational issues ( consolidation of VCCV Types, migration strategy etc.)  out of scope of a clear-cut technical specification.

I have added a couple of minor comments inline below that hopefully could be useful. Please feel free to use (or not to use) them as you see fit.

Regards,
       Sasha
Email: [e-mail]
Mobile: [phone]

From: Pals [mailto:[e-mail]] On Behalf Of Stewart Bryant
Sent: Wednesday, January 14, 2015 5:37 PM
To: [e-mail]; [e-mail]
Subject: [Pals] Candidate draft-ietf-pals-vccv-for-gal-01

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
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   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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   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[[Sasha]] not applicable to?   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.
[[Sasha]] Maybe you could add that VCCV Type 3 remains mandatory for segment OAM of MS-PWs and that it is  combined with VCCV Type 1 for MS-PWs that use the CW – this is explicitly stated in RFC 6073.

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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.
[[Sasha]] Maybe you could add that PWs without the CW are already widely deployed, and this is one of the reasons why mandating all PWs use the CW is not realistic.


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.[[Sasha]] Is this not a MUST?

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.[[Sasha]] is it not MUST?


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 [[Sasha]] pre-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[[Sasha]]? Migration strategy? Something seems to be missing here.   will be the
   subject of future work by the PALS working group.
[[Sasha]] I am not sure that discussion of the PALS WG long-term strategy in a  standards track document is appropriate. The rationale for introducing VCCV Type 4 is quite clear since it resolves specific issues with VCCV Type 2 and VCCV Type 3.
Maybe it is worth mentioning that, just as VCCV Type 1, VCCV Type 4 can be combined with VCCV Type 3 for segment OAM of MS-PWs.


   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]<mailto:[e-mail]>


   Luca Martini
   Cisco Systems

   Email: [e-mail]<mailto:[e-mail]>


   Stewart Bryant
   Cisco Systems

   Email: [e-mail]<mailto:[e-mail]>



















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