LDP 'Typed Wildcard' Forwarding Equivalence Class (FEC) for PWid and Generalized PWid FEC Elements
draft-ietf-pwe3-pw-typed-wc-fec-03

PWE3 Working Group                                          Kamran Raza 
Internet Draft                                             Sami Boutros 
Intended Status: Standards Track                       Carlos Pignataro
Expiration Date: August 5, 2012                              
                                                          Cisco Systems 
 
 
                                                       February 6, 2012 
                                      
 
                                      
         LDP Typed Wildcard FEC for PWid and Generalized PWid  
                            FEC Elements  
                                      
               draft-ietf-pwe3-pw-typed-wc-fec-03.txt 

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Abstract 

   The "Typed Wildcard Forwarding Equivalence Class (FEC) Element" 
   defines an extension to the Label Distribution Protocol (LDP) that 
   can be used when it is desired to request or withdraw or release all 
   label bindings for a given FEC Element type.  However, a typed 
   wildcard FEC element must be individually defined for each FEC 
   element type.  This specification defines the typed wildcard FEC 
   elements for the PWid (0x80) and Generalized PWid (0x81) FEC element 
   types. 

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 [RFC2119]. 

Table of Contents 

   1. Introduction .................................................. 3 
   2. Typed Wildcard for PW FEC Elements ............................ 3 
   3. Applicability Statement ....................................... 4 
   4. Operation ..................................................... 5 
     4.1. PW Consistency Check ...................................... 5 
     4.2. PW Graceful Shutdown ...................................... 5 
     4.3. Wildcard PW Status ........................................ 6 
     4.4. Typed Wildcard MAC Withdrawal in VPLS ..................... 6 
   5. Security Considerations ....................................... 7 
   6. IANA Considerations ........................................... 7 
   7. Acknowledgments ............................................... 7 
   8. References .................................................... 7 
     8.1. Normative References ...................................... 7 
     8.2. Informative References .................................... 8 
   Authors' Addresses ............................................... 8 
    
 
 
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1. Introduction 

   An extension [RFC5918] to the Label Distribution Protocol (LDP) 
   [RFC5036] defines the general notion of a "Typed Wildcard Forwarding 
   Equivalence Class (FEC) Element".  This can be used when it is 
   desired to request all label bindings for a given type of FEC 
   Element, or to release or withdraw all label bindings for a given 
   type of FEC element.  However, a typed wildcard FEC element must be 
   individually defined for each type of FEC element. 

   [RFC4447] defines the "PWid FEC Element" and "Generalized PWid FEC 
   Element", but does not specify the Typed Wildcard format for these 
   elements. This document specifies the format of the Typed Wildcard 
   FEC Element for the "PWid FEC Element" and "Generalized PWid FEC 
   Element". The procedures for Typed Wildcard processing for PWid and  
   Generalized PWid FEC Elements are same as described in [RFC5918] for 
   any typed wildcard FEC Element type. 

2. Typed Wildcard for PW FEC Elements 

   The format of the Typed Wildcard FEC Element for PWid and 
   Generalized PWid is specified as: 

    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 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |Typed Wcard=0x5| Type=PW FEC   |   Len = 2     |R|   PW type   | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |    . . .      | 
   +-+-+-+-+-+-+-+-+ 
    
     Figure 1: Format of Typed Wildcard FEC Element for PW FEC Element 
                                   Types 
    
   Where:  

      Typed Wcard (one octet): Typed Wildcard FEC element type (0x05) 
           as specified in [RFC5918]     

      [FEC Element] Type (one octet): PW FEC Element type: 

        PWid: (type 0x80 [RFC4447]) 
        Generalized PWid: (type 0x81 [RFC4447]) 
         

 
 
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      Len [FEC Type Info] (one octet):  Two. (i.e. there is additional 
           FEC info to scope the Typed Wildcard) 

      R bit (Reserved bit): Must be set to ZERO on transmit and ignored 
           on receipt. 

      PW type (15-bits): PW type as specified in [RFC4447]. This field 
           is used to scope the wildcard FEC operation to limit to all 
           PWs of a given type. This MUST be set to "Wildcard" type 
           (0x7FFF), as defined in [IANA-PWE3], when referring PWs of 
           all types (see Section 4 for its usage).  

  [RFC4447] defines "PW Grouping ID TLV" that can be used for wildcard 
  withdrawal or status messages related to Generalized PWid FECs. When 
  Typed Wildcard FEC for Generalized PWid FEC element is in use, "PW 
  Grouping ID TLV" MUST NOT be present in the same message. If found 
  present, the receiving LSR MUST ignore this TLV silently, and process 
  the rest of the message. 
 
3. Applicability Statement 

   The Typed wildcard FEC Elements defined in this document for the 
   PWid and Generalized PWid FEC Elements provide a finer degree of 
   granularity when compared to the wildcard FEC mechanics defined in 
   [RFC5036]. 

   The PWid FEC Element as defined in [RFC4447] contains a Group ID 
   field. This field is defined as an arbitrary 32-bit value that 
   represents a group of PWs, and is used to create groups in the PW 
   space, including potentially a single group of all PWs for a given 
   FEC Element type. This grouping enables an LSR to send "wildcard" 
   label withdrawals and/or status notification messages corresponding 
   to a PW group upon physical port failures. Similarly, [RFC4447] 
   defines the "PW Grouping ID TLV" used in the same fashion for the 
   Generalized PWid FEC Element.  

  The PW Typed Wildcard FEC elements defined in this document help us 
  achieve the similar functionality as "Group ID" field or "PW Grouping 
  ID TLV" for label withdrawal and status notification messages; 
  Additionally, the Typed Wildcard procedures [RFC5918] also provide 
  more generalized and comprehensive solution by allowing: 
   
   
  1. Typed-Wildcard Label Request messages 

 
 
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  2. Label TLV in label messages to further constraint the wildcard to 
      all FECs of the specified FEC type [and its specific filter] that 
      are also bound to the specified label.  
    

   This document allows the use of Typed Wildcard PW FEC Element in any 
   LDP message that specifies a FEC TLV as mandatory or optional 
   parameter of the message. In addition to LDP label messages, this 
   also applies to Notification messages (containing PW Status) and 
   Address Withdraw (for MAC address withdrawal [RFC4762]) in the 
   context of LDP PW signaling. When a Typed Wildcard PW FEC element is 
   used in a Address Withdraw message for VPLS MAC address withdrawal, 
   the MAC List TLV MUST contain an empty list. 

4. Operation 

   The use of Typed Wildcard FEC elements for PW can be useful under 
   several scenarios. This section describes some use cases to 
   illustrate their usage. The following use cases consider two LSR 
   nodes, A and B, with LDP session between them to exchange L2VPN PW 
   bindings. 

4.1. PW Consistency Check 

   A user may request a control plane consistency check at LSR A for 
   the Generalized PWid FEC bindings that it had learnt from LSR B over 
   LDP session.  To perform this consistency check, LSR A marks all its 
   learnt Generalized PWid FEC bindings from LSR B as stale, and then 
   sends a Label Request message towards LSR B for Typed Wildcard FEC 
   element for Generalized PWid FEC element type with PW type set to 
   "Wildcard" (0x7FFF). Upon receipt of such request, LSR B replays its 
   database related to Generalized PWid FEC element using one or more 
   Label Mapping messages. As a PW binding is received at LSR A, the 
   associated binding state is marked as refreshed (no stale).  When 
   replay completes for Generalized PWid FEC type, LSR B marks end of 
   its replay by sending End-of-LIB notification [RFC5919] 
   corresponding to Generalized PWid FEC element type. Upon receipt of 
   this notification at LSR A, any remaining stale PW binding of 
   Generalized PWid FEC type learnt from the peer LSR B, is cleaned up 
   and removed from the database. This completes consistency check with 
   LSR B at LSR A for Generalized PWid FEC type. 

4.2. PW Graceful Shutdown 

   It may be desirable to perform shutdown/removal of existing PW 
   bindings advertised towards a peer in a graceful manner - i.e. all 
 
 
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   advertised PW bindings to be removed from a peer without session 
   flap.  For example, to request a graceful delete of the PWid FEC and 
   Generalized PWid FEC bindings at LSR A learnt from LSR B, LSR A 
   would send a Label Withdraw message towards LSR B with Typed 
   Wildcard FEC elements pertaining to PWid FEC element (with PW type 
   set to 0x7FFF) and Generalized PWid FEC element (with PW type set to 
   0x7FFF). Upon receipt of such message, LSR B will delete all PWid 
   and Generalized PWid bindings learnt from LSR A. Afterwards, LSR B 
   would send Label Release messages corresponding to received Label 
   Withdraw messages with Typed FEC element.  

4.3. Wildcard PW Status 

  The Typed Wildcard FEC Elements for PW FECs can be very useful when 
  used to convey PW status amongst LSRs. The PE devices can send "PW 
  Status TLV" in an LDP Notification message to indicate PW status 
  (i.e., a Pseudowire Status Code denoting for example a particular 
  fault) to their remote peers [RFC4447]. In case of a global failure 
  affecting all PWs, an LSR typically sends one PW Status LDP 
  Notification message per PW. This per PW Status message has 
  scalability implications in a large-scale network with large number 
  of PWs.  
   
  Using Typed Wildcard FEC Element for given type of PW FEC Element, 
  the LSR will need to send only one PW Status Notification message 
  with Typed Wildcard PW FEC specified to notify about the common 
  status applicable to all PWs as scoped by the PW Typed Wildcard FEC. 
   
4.4. Typed Wildcard MAC Withdrawal in VPLS 

  [RFC4762] defines a pseudowire based solution to implement Virtual 
  Private LAN Service (VPLS). Section 6.2 of RFC-4762 describes MAC 
  Withdrawal procedures and extensions in an VPLS environment. These 
  procedures use LDP Address Withdraw message containing FEC TLV (with 
  PW FEC element corresponding to the VPLS instance) and MAC List TLV 
  (to specify addresses to be withdrawn). RFC-4762 procedures also 
  allow MAC addresses withdrawal wildcarding for a given VPLS instance. 
   
  Using RFC-4762 procedures, a PE LSR can withdraw all MAC addresses 
  for a given VPLS instance by sending an Address Withdraw message with 
  VPLS instance corresponding PW FEC element in a FEC TLV, and MAC List 
  TLV with an empty list of addresses. If there are more than one VPLS 
  instance on a given PE LSR node, separate Address Withdraw messages 
 
 
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  will need to be sent by PE LSR if it wishes to withdraw MAC addresses 
  for all or subset of VPLS instances upon some global failure or 
  configuration. This per PW (VPLS instance) MAC Withdraw messages may 
  have some scalability implications in large-scale network. 
   
  As stated in section 3, this document allows use of Typed Wildcard PW 
  FEC in Address Withdraw messages corresponding to VPLS MAC 
  Withdrawal. The usage of PW Typed Wildcard FEC enhances the scope of 
  MAC withdrawal beyond just a single VPLS instance, and allows a PE 
  node to wildcard withdraw all MAC addresses for: 
   
     o  all VPLS instances; or 
     o  all VPLS instances corresponding to a given PW type. 

5. Security Considerations 

  No new security considerations beyond that apply to the base LDP 
  specification [RFC5036], [RFC4447], [RFC4762], and [RFC5920] apply to 
  the use of the PW Typed Wildcard FEC Element types described in this 
  document. 
   
6. IANA Considerations 

  None. 
    
7. Acknowledgments 

  The authors would like to thank Eric Rosen, Reshad Rahman, Siva 
  Sivabalan, and Zafar Ali for their review and valuable comments. We 
  also acknowledge Daniel Cohn for suggesting the use of Typed Wildcard 
  PW FEC for VPLS MAC withdrawal. 
   
  This document was prepared using 2-Word-v2.0 template.dot. 
   
8. References 

8.1. Normative References 

  [RFC5036] L. Andersson, I. Minei, and B. Thomas, "LDP Specification", 
            RFC 5036, September 2007. 
   
 
 
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  [RFC5918] R. Asati, I. Minei, and B. Thomas, "LDP Typed Wildcard 
            Forwarding Equivalence Class", RFC 5918, August 2010. 
   
  [RFC5919] R. Asati, P. Mohapatra, E. Chen, and B. Thomas, "Signaling 
            LDP Label Advertisement Completion", RFC 5919, August 2009. 
   
  [RFC4447] L. Martini, E. Rosen, El-Aawar, T. Smith, and G. Heron,  
            "Pseudowire Setup and Maintenance using the Label 
            Distribution Protocol", RFC 4447, April 2006. 
   
  [RFC4762] M. Lasserre, and V. Kompella,  "Virtual Private LAN Service 
            (VPLS) Using Label Distribution Protocol (LDP) Signaling", 
            RFC 4762, January 2007. 
   
  [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate 
            Requirement Levels", BCP 14, RFC2119, March 1997. 
 
8.2.  Informative References 

  [RFC5920] L. Fang (Editor), et al., "Security Framework for MPLS and 
            GMPLS Networks", RFC 5920, July 2010. 

  [IANA-PWE3] Internet Assigned Numbers Authority, "Pseudo Wires Name 
              Spaces (PWE3)", http://www.iana.org/assignments/pwe3-
              parameters, May 2011. 
 
 
Authors' Addresses 

  Kamran Raza 
  Cisco Systems, Inc., 
  2000 Innovation Drive, 
  Ottawa, ON K2K-3E8, Canada. 
  Email: skraza@cisco.com 
 
  Sami Boutros 
  Cisco Systems, Inc., 
  3750 Cisco Way, 
  San Jose, CA 95134, USA. 
  Email: sboutros@cisco.com 
  
 
 
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  Carlos Pignataro 
  Cisco Systems, Inc., 
  7200 Kit Creek Road,  
  Research Triangle Park, NC 27709-4987, USA. 
  Email: cpignata@cisco.com 

 
 
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