





Internet Engineering Task Force                             Luca Martini
Internet Draft                                            George Swallow
Intended status: Standards Track                             Giles Heron
Expires: May 15, 2012                                              Cisco
                                                           Matthew Bocci
                                                          Alcatel-Lucent

                                                       November 15, 2011


                Pseudowire Status for Static Pseudowires


                draft-ietf-pwe3-static-pw-status-10.txt

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Drafts.

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   material or to cite them other than as "work in progress."

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   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on May 15, 2010

Abstract

   This document specifies a mechanism to signal Pseudowire (PW) status
   messages using an PW associated channel (ACh). Such a mechanism is
   suitable for use where no PW dynamic control plane exits, known as
   static PWs, or where a Terminating Provider Edge (T-PE) needs to send
   a PW status message directly to a far end T-PE. The mechanism allows
   PW OAM message mapping and PW redundancy to operate on static PWs.
   This document also updates rfc5885 in the case when Bi-directional
   Forwarding Detection (BFD) is used to convey PW status signaling



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   information.



Table of Contents

    1        Specification of Requirements  ........................   2
    2        Introduction  .........................................   3
    3        Terminology  ..........................................   3
    4        Applicability  ........................................   3
    5        Pseudowire Status Operation  ..........................   4
    5.1      PW OAM Message  .......................................   4
    5.2      Sending a PW Status Message  ..........................   5
    5.3      PW OAM status message transmit and receive  ...........   6
    5.3.1    Acknowledgment of PW status  ..........................   7
    5.4      MPLS Label Stack  .....................................   7
    5.4.1    Label stack for a message destined to the next PE  ....   7
    5.4.2    Label stack for a message destined to the egress PE  ..   8
    5.5      S-PE bypass mode  .....................................   8
    5.5.1    S-PE bypass mode LDP flag bit  ........................   9
    6        S-PE operation  .......................................  10
    6.1      Static PW to another Static PW  .......................  10
    6.2      Dynamic PW to Static PW or vice versa  ................  10
    7        Security Considerations  ..............................  11
    8        IANA Considerations  ..................................  11
    9        References  ...........................................  12
    9.1      Normative References  .................................  12
    9.2      Informative References  ...............................  12
   10        Authors' Addresses  ...................................  13





1. Specification of Requirements

   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].












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2. Introduction

   The default control plane for Pseudowire (PW) technology, as defined
   in [RFC4447], is based on Label Distribution Protocol (LDP). However
   that document also describes a static provisioning mode without a
   control plane.  When a static PW is used, there is no method to
   transmit the status of the PW, or attachment circuit (AC) between the
   two Provider Edge (PE) devices at each end of the PW. This document
   defines a method to transport the PW status codes defined in
   [RFC4447], sec 5.4.2, and elsewhere [REDUNDANCY] in-band with the PW
   data using a generic associated channel [RFC5586].


3. Terminology

   FEC: Forwarding Equivalence Class

   LDP: Label Distribution Protocol

   LSP: Label Switching Path

   MS-PW: Multi-Segment Pseudowire

   PE: Provider Edge

   PW: Pseudowire

   SS-PW: Single-Segment Pseudowire

   S-PE: Switching Provider Edge Node of MS-PW

   T-PE: Terminating Provider Edge Node of MS-PW


4. Applicability

   As described in [RFC4447] and [RFC6310], a PE that establishes an
   MPLS PW using means other than LDP, e.g., by static configuration,
   MUST support some alternative method of status reporting. The
   procedures described in this document are for use when PWs are
   statically configured and a LDP control plane is not available.

   As defined in [RFC4447], a PE that establishes a PW using LDP MUST
   use the PW status TLV mechanism for AC and PW status and defect
   notification on that PW. In order to avoid duplicate notifications
   and potentially conflicting notifications, such PEs MUST NOT use the
   mechanisms described in this document for those PWs, except that the
   'S-PE' bypass mode described in Section 5.5 MAY be used when both T-



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   PE at each end of the PW use LDP to establish the PW.

   In order to protect against duplicate notifications and potentially
   conflicting notifications, when the Pseudowire Status protocol for
   Static Pseudowires described in this document is used, the BFD-VCCV
   status signaling mechanisms described in [RFC5885] (CV Types 0x08 and
   0x20) MUST NOT be used. VCCV-BFD Connectivity Verification (CV) for
   fault detection (CV types 0x04 and 0x10) MAY still be used.


5. Pseudowire Status Operation

5.1. PW OAM Message

   The PW status TLV as defined in [RFC4447] sec 5.4.2 is transported in
   a PW OAM message using the PW associated channel (ACH).

    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 0 0 1|Version|   Reserved    | 0xZZ PW OAM Message           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Refresh Timer         |  TLV Length   |A|   Flags     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                              TLVs                             ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 1: ACH PW OAM Message Packet Header.


   The first 32 bits are the standard ACH header construct as defined in
   [RFC5586].

   The first nibble (0001b) indicates the ACH instead of PW data. The
   version and the reserved values are both set to 0 as specified in
   [RFC4385].

   The refresh timer is an unsigned integer and specifies refresh time
   in seconds with a range from 1 to 65535. The value 0 means that the
   refresh timer is set indefinitely, and the PW OAM message will never
   be refreshed, and will never timeout.

   The TLV length field indicates the length of all TLVs only.  This
   document defines the only the PW status TLV as defined in [RFC4447]
   sec 5.4.2 is transported in TLV field. In the future additional TLVs
   may be defined to be used in this field with code points allocated
   from the IANA registry called "LDP TLV Type Name Space".



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   The A flag bit is used to indicate an acknowledgment of the PW status
   TLV included. The rest of the flag bits are reserved and they MUST be
   set to 0 on transmit, and ignored upon receive. When the A bit is
   set, the refresh timer value is a requested timer value.

   The PW OAM Message code point value is 0xZZ.  [RFC Editor: 0xZZ to be
   assigned by IANA from the PW Associated Channel Type registry.]


5.2. Sending a PW Status Message

   The PW Status messages are sent in-band using the PW OAM message
   containing the PW Status TLV, for a particular PW, as defined in
   [RFC4447].  The PW Status TLV format almost as defined in [RFC4447],
   and is repeated here for the reader's convenience:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Res|     PW Status (0x096A)    |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Status Code                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             Figure 2: PW Status TLV Format.


   Unlike the case in [RFC4447], here the first 2 bits are reserved, and
   MUST be set to zero on transmit, and ignored on receive.

   The PW Status TLV is prepended with an PW OAM message header and sent
   on the ACH of the PW to which the status update applies.

   To clear a particular status indication, the PE needs to send a new
   PW OAM message containing a PW Status TLV with the corresponding bit
   cleared as defined in [RFC4447].

   The procedures described in [RFC6073] that apply to an S-PE and PW
   using an LDP control plane also apply when sending PW status using
   the PW OAM channel. The OPTIONAL procedures using the SP-PE TLV
   described in [RFC6073] can also be applied when sending PW status
   using the PW OAM channel.

   The detailed message transmit, and receive procedures are specified
   in the next section. PW OAM Status Messages MUST NOT be used as a
   connectivity verification method.






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5.3. PW OAM status message transmit and receive

   Unlike the PW status procedures defined in [RFC4447] with this method
   there is no TCP/IP session, or session management. Therefore unlike
   the TCP/IP case, where each message is sent only once, the PW OAM
   message containing the PW status TLV needs to be transmitted
   repeatedly to ensure reliable message delivery. If a malformed TLV,
   or an unknown TLV is received in an PW OAM status message, the TLV
   MUST be ignored, and the PE SHOULD report the event to the operator.

   A PW OAM message containing a PW status TLV with a new status bit set
   or reset, will be transmitted immediately by the PE. Unless the
   message is acknowledged within a second, the PW OAM message will then
   be repeated twice more at an initial interval of one second.
   Subsequently the PW OAM message will be transmitted with an interval
   specified by the refresh timer value in the packet. Note that this
   value MAY be updated in the new PW OAM message packet, in which case
   the new refresh timer value becomes the new packet transmit interval.

   The suggested default value for the refresh timer is 30 seconds. This
   default is adeguate for typical deployments, and PEs are designed to
   take into account processing these messages at the required rate.

   When a PW OAM message containing a status TLV is received, a timer is
   started according to the refresh rate specified in the packet. If
   another non zero PW status message is not received within 3.5 times
   the specified timer value, the status condition will timeout in 3.5
   times the last refresh timer value received, and the default status
   of zero is assumed on the PW.  It is also a good practice to
   introduce some jitter in the delay between refresh transmissions, as
   long as the maximum jitter delay is within the prescribed maximum
   refresh time of 3.5 times the specified timer value for 3 consecutive
   refresh packets.

   To clear a particular status fault the PE need only send an updated
   message with the corresponding bit cleared. If the PW status code is
   zero, the PW OAM message will be sent like any other PW OAM status
   message using the procedures described above, however it MUST be
   acknowledged with a packet with a timer value of zero. This will
   cause the PE sending the PW status notification message with PW
   status code equal to zero to stop sending, and to continue normal
   operation.









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5.3.1. Acknowledgment of PW status

   The PE receiving a PW OAM message containing a PW status message can
   acknowledge the PW status message by simply building an almost
   identical reply packet with the A bit set, and transmitting it on the
   PW ACH back to the source of the PW status message. The timer value
   set in the reply packet SHOULD then be used by the PE as the new
   transmit interval. If the transmitting PE does not want to use the
   new timer value (for local policy reasons, or because it simply
   cannot support it) it MUST refresh the PW OAM message with the timer
   value it desires. The receiving PE will then set its timeout timer
   according to the timer value that is in the packet received,
   regardless of what timer value it sent. The receiving PE MUST NOT
   retry to set the timer value more then once per timer value.

   The suggested default value for the refresh timer value in the
   acknowledgment packet is 600 seconds.

   If the sender PE receives an acknowledgment message that does not
   match the current active PW status message being sent, it simply
   ignores the acknowledgment packet.

   If a PE that has a non zero status code for a particular PW, detects
   by any means that the peer PE has become unreachable, it will follow
   the standard procedures [RFC4447] and consider that PW as having an
   additional status bit set. This would normally trigger sending
   updates again, and canceling the acknowledgment refresh timer state.


5.4. MPLS Label Stack

   With one exception, all PW OAM status messages are are sent to the
   adjacent PE across the PSN tunnel. In many cases the transmitting PE
   has no way to determine whether the adjacent PE is a S-PE, or a T-PE.
   This is a necessary behavior to preserve backward compatibility with
   PEs that do not understand MS-PWs. In the procedures described in
   this document there are two possible destinations for the PW OAM
   status messages: the adjacent PE, or the T-PE. Sending a PW status
   message directly to the T-PE is a enhanced method that is only
   applicable using PW OAM status messages sent in the PW ACH.


5.4.1. Label stack for a message destined to the next PE

   A PE that needs to forward a PW OAM status message to the adjacent PE
   across the PSN tunnel, MUST set the PW label TTL field to 1.
   Furthermore if the control word is not in use on the particular PW,
   the PE MUST also place the GAL reserved label [RFC5586], below the PW



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   label also with the TTL field set to 1.


5.4.2. Label stack for a message destined to the egress PE

   This is also known as "S-PE bypass mode" see below. A T-PE that
   requires sending a PW OAM status message directly to the
   corresponding T-PE at the other end of the PW MUST set the TTL of the
   PW label to a value that is sufficient to reach the corresponding T-
   PE. This value will be greater then one, but will be set according to
   the local policy on the transmitting T-PE. Furthermore if the control
   word is not in use on the particular PW, the PE MUST also place the
   GAL reserved label [RFC5586], below the PW label with the TTL field
   set to 1.



5.5. S-PE bypass mode

   S-PE bypass mode enables a T-PE that uses LDP as the pw setup and
   control protocol, to bypass all S-PEs that might be present along the
   MS-PW and to send a message directly to the remote T-PE. This is used
   for very fast message transmission in-band with the PW PDUs. This
   mode is OPTIONAL, and MUST be supported by both T-PEs to be enabled.
   This mode MUST NOT be used if the first PW segment connected to each
   T-PE is not using LDP.

   Note that this method MUST NOT be used to send messages which are
   permitted to originate at an S-PE, since otherwise race conditions
   could occur between messages sent via the control plane by S-PEs, and
   messages sent via the data plane by T-PEs.

   Status codes, except for those listed below, MUST NOT be sent using
   the S-PE bypass procedure:

   0x00000002 - Local Attachment Circuit (ingress) Receive Fault
   0x00000004 - Local Attachment Circuit (egress) Transmit Fault
   0x00000020 - PW forwarding standby
   0x00000040 - Request switchover to this PW

   Note that since "clear all failures" may be sent by an S-PE it MUST
   NOT be sent using the S-PE bypass mode.

   When S-PE bypass mode is enabled, all PW Status TLVs received using
   this method have priority over PW Status TLVs sent via control
   protocols such as LDP [RFC4447]. However the same PW Status TLVs MUST
   also be sent in LDP to keep the S-PEs state updated.




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5.5.1. S-PE bypass mode LDP flag bit

   When a PW Segment along an MS-PW is using the LDP control protocol
   wishes to request the use of the S-PE bypass status message mode, it
   sets the B bit in the generic protocol flags interface parameters
   sub-TLV as shown in Figure 3. This flag can only be set by a T-PE
   using LDP as the PW configuration and management protocol. If the S-
   PE bypass mode LDP flag bit in the generic protocol flags interface
   parameter does not mach in the FEC advertisement for directions of a
   specific PW, that PW MUST NOT be enabled.

   The interface parameter is defined as follows:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Type=0X16  |   Length=4    |R R R R R R R R R R R R R R R B|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   Figure 3. PW Generic Protocol Flags sub-TLV.


     - TLV Type.

       Type 0x16 - PW Generic Protocol Flags.  Note: Value 0x16
       suggested for assignment pending IANA allocation.

     - Length

       TLV length always 4 octets.

     - Flags

       Bit B, in position 31 above, is set to request the S-PE bypass
       mode. Bits R are to be allocated by IANA as described in the IANA
       section.  If they are not allocated they are to be considered as
       reserved for future use and MUST be zero on transmission, and
       ignored on reception of this TLV.

   If the T-PE receives an LDP label mapping message containing a
   generic protocol flags interface parameter TLV with the bit "B" set,
   then the T-PE receiving the label mapping message MAY send S-PE
   bypass status messages in the G-ACH. If Bit "B" of said TLV, is not
   set, or the TLV is not present, then the T-PE receiving the label
   mapping message MUST NOT send S-PE bypass status messages in the G-
   ACH.






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6. S-PE operation

   The S-PE will operate according to the procedures defined in
   [RFC6073].  The following additional procedures apply to the case
   where a static PW segment is switched to a dynamic PW segment that
   uses LDP, and the case a static PW segment is switched to another
   static PW segment.


6.1. Static PW to another Static PW

   The procedures that are described in [RFC6073] section 10 also apply
   to the case of a static PW switched to another static PW. The LDP
   header is simply replaced by the PW OAM header, otherwise the packet
   format will be identical. The information that is necessary to form a
   SP-PE TLV MUST be configured in the S-PE, or no SP-PE TLV will be
   sent.  The Document [RFC6073] defines a IANA registry named
   "Pseudowire Switching Point PE TLV Type". In order to support the
   static PW configuration and addressing scheme, a new code point is
   requested as follows:

   Type  Length   Description
   0x07      24   Static PW/MPLS-TP PW segment ID of last
                  PW segment traversed


   The format of this TLV is that of the "Static Pseudowire Sub-TLV"
   defined in [ON DEMAND].


6.2. Dynamic PW to Static PW or vice versa

   The procedures that are described in [RFC6073] section 10 also apply
   to this situation. However if the PW label of the LDP controlled PW
   segment is withdrawn, by the adjacent PE, the S-PE will set the PW
   status code "0x00000001 - Pseudowire Not Forwarding" to the adjacent
   PW on the static PW segment.

   The S-PE will only withdraw its label for the dynamic, LDP
   controlled, PW segment if the S-PE is un-provisioned.











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7. Security Considerations

   The security measures described in [RFC4447], [RFC5085] and [RFC6073]
   are adequate for the proposed mechanism.


8. IANA Considerations

   IANA has to set up the registry of "PW Generic Protocol Flags". These
   are bit strings of length 16. Bit 0 is defined in this document. Bits
   1 through 15 are to be assigned by IANA using the "IETF consensus"
   policy defined in [RFC5226].

   Any requests for allocation from this registry require a description
   of up to 65 characters.

   Initial PW Generic Protocol Flags value allocations are as follows:

   Bit Mask     Description
   ====================================================================
   0x0001    -  S-PE bypass mode                              [RFCXXXX]


   This document uses a new Associated Channel Type. IANA already
   maintains a registry of name "Pseudowire Associated Channel Types". A
   value of 0x0022 is suggested for assignment with TLVs. The
   description is "PW OAM Message".

   This document uses a new Pseudowire Switching Point PE TLV Type. IANA
   already maintains a registry of name "Pseudowire Switching Point PE
   Sub-TLV Type". A value of 0x07 is suggested for assignment. The
   description is "Static PW/MPLS-TP PW segment ID of last PW segment
   traversed".

   This document uses a new interface parameter type. IANA already
   maintains a registry of name "Pseudowire Interface Parameters Sub-TLV
   type Registry". A value of 0x16 is suggested for assignment. The
   description is "PW Generic Protocol Flags".













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9. References

9.1. Normative References

   [RFC5226] T. Narten, H. Alvestrand, "Guidelines for Writing
        an IANA Considerations Section in RFCs", RFC 5226, May 2008

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

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

   [RFC4447] "Transport of Layer 2 Frames Over MPLS", Martini, L.,
        et al., rfc4447 April 2006.

   [RFC6073] Martini et.al. "Segmented Pseudowire",
        RFC 6073, January 2011.

   [RFC4385] " Pseudowire Emulation Edge-to-Edge (PWE3)
        Control Word for Use over an MPLS PSN", S. Bryant, et al.,
        RFC4385, February 2006.

   [ON DEMAND] Bahadur et.al. "MPLS on-demand Connectivity
        Verification, Route Tracing and Adjacency Verification",
        draft-ietf-mpls-tp-on-demand-cv-07.txt, IETF Work in Progress,
        September 2011

   [RFC6310] M. Aissaoui, P. Busschbach, L. Martini, M. Morrow,
        T. Nadeau, Y(J). Stein, "Pseudowire (PW) Operations,
        Administration, and Maintenance (OAM) Message Mapping",
        RFC6310, July 2011


9.2. Informative References

   [REDUNDANCY] Muley et.al. "Preferential Forwarding Status
         bit definition", draft-ietf-pwe3-redundancy-bit-05.txt,
        IETF Work in Progress, September 2011.

   [RFC5586] M. Bocci, Ed., M. Vigoureux, Ed., S. Bryant, Ed.,
        "MPLS Generic Associated Channel", rfc5586,  June 2009

   [RFC5885] T. Nadeau, Ed.,C. Pignataro, Ed., "Bidirectional
        Forwarding Detection (BFD) for the Pseudowire Virtual
        Circuit Connectivity Verification (VCCV)", RFC5885, June 2010.




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10. Authors' Addresses


   Luca Martini
   Cisco Systems, Inc.
   9155 East Nichols Avenue, Suite 400
   Englewood, CO, 80112
   e-mail: lmartini@cisco.com


   George Swallow
   Cisco Systems, Inc.
   300 Beaver Brook Road
   Boxborough, Massachusetts  01719
   United States
   e-mail: swallow@cisco.com


   Giles Heron
   Cisco Systems
   9-11 New Square
   Bedfont Lakes
   Feltham
   Middlesex
   TW14 8HA
   United Kingdom
   e-mail: giheron@cisco.com


   Matthew Bocci
   Alcatel-Lucent
   Grove House, Waltham Road Rd
   White Waltham, Berks, UK. SL6 3TN
   e-mail: matthew.bocci@alcatel-lucent.co.uk


Copyright Notice

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   document authors. All rights reserved.

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   to this document. Code Components extracted from this document must
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   Expiration Date: May 2012















































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