Explicit RPF Vector
draft-ietf-pim-explicit-rpf-vector-02

Versions: 02

PIM WG                                                   J. Asghar
Internet-Draft                                        IJ. Wijnands
Intended status: Informational                     S. Krishnaswamy
Expires: January 1, 2013                                  A. Karan
                                                     Cisco Systems
                                                           V. Arya
                                                     Directv, Inc.

                                                     July 12, 2013

                                                                                                         
                                                                                                         
                     Explicit RPF Vector
            draft-ietf-pim-explicit-rpf-vector-02

Abstract

   This document defines a new Reverse Path Forwarding (RPF) Vector 
   TLV to build multicast trees via an explicit path sent in the PIM 
   join. 

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on January 12, 2013.
   
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  Specification of Requirements . . . . . . . . . . . . . . . . . 3
   3.  Solution Requirements  . . . . . . . . . . . . . . . . . . . .  3
   4.  Use of the Explicit RPF Vector  . . . . . . . . . . . . . . . . 4
   5.  Explicit RPF Vector Attribute . . . . . . . . . . . . . . . . . 4
   6.  Mixed Vector Processing . . . . . . . . . . . . . . . . . . . . 4
   7.  Conflicting RPF Vectors . . . . . . . . . . . . . . . . . . . . 4
   8.  PIM Asserts  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   9.  Join Suppression. . . . . . . . . . . . . . . . . . . . . . . . 5
   10.  Vector Handling By Unsupported PIM Router . . . . . . . . . .  5
   11.  Explicit RPF Vector Attribute TLV Format   . . . . . . . . . . 5
   12.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 6
   13.  Security Considerations . . . . . . . . . . . . . . . . . . .  6
   14.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 6
   15.  Normative References   . . . . . . . . . . . . . . . . . . . . 6

1.  Introduction

   For some applications, it might be useful to have a way to specify
   the explicit path along which the PIM join is propagated.   

   This document defines a new TLV in the PIM Join Attribute message 
   [RFC5384] for specifying the explicit path.

   The procedures in [RFC5496] define how a RPF vector can be used 
   to influence the path selection in the absence of a route to the 
   source. However, the same procedures can be used to override a 
   route to the source when it exists. It is possible to include 
   multiple RPF vectors in the list where each router along the 
   path will perform a unicast route lookup on the first vector in 
   the attribute list. Once the router owning the address of the RPF 
   vector is reached, following the procedures in [RFC5496], the RPF
   vector will be removed from the attribute list. This will result 
   in a 'loosely' routed path based on the unicast reachability of 
   the RPF vector(s). We call this 'loosely' because we still depend 
   on unicast routing reachability to the RPF Vector.

   In some scenarios we don't want to rely on the unicast reachability 
   to the RPF vector address and we want to build a path strictly 
   based on the RPF vectors. In that case the RPF vectors represent 
   a list of directly connected PIM neighbors along the path. For 
   these vectors we MUST NOT do a unicast route lookup. We call 
   these 'explicit' RPF vector addresses. If a router receiving an 
   Explicit RPF Vector does not have a PIM neighbor matching the 
   Explicit RPF Vector address it MUST NOT fall back to loosely 
   routing the join. Instead, it may process the packet and store 
   the RPF Vector list so that the Explicit RPF Vector join may be 
   sent out as soon as the neighbor comes up. Since the behavior of 
   the Explicit RPF Vector differs from the loose RPF vector as 
   defined [RFC5496], we're defining a new attribute called the 
   Explicit RPF Vector.

2.  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].

   
3.  Solution Requirements

   Some broadcast video transport networks use a multicast PIM 
   Live-Live resiliency model for video delivery based on PIM SSM 
   or PIM ASM. Live-Live implies using 2 active spatially diverse 
   multicast trees to transport video flows from root to leaf 
   multicast routers. The leaf multicast router receives 2 copies 
   from the PIM multicast core and will replicate 1 copy towards 
   the receivers [draft-mofrr-karan].

   One of the requirements of the PIM Live-Live resiliency model 
   is to ensure path-diversity of the 2 active PIM trees in the 
   core such that they do not intersect to avoid a single point 
   of failure. IGP routed RPF paths of 2 PIM trees could be routed 
   over the same transit router and create a single point of failure. 
   It might be useful to have a way to specify the explicit path 
   along which the PIM join is propagated.
   
   How the Explicit RPF Vector list is determined is outside the 
   scope of this document. It may either be manually configured by
   the network operator or procedures may be implemented on the 
   egress router to dynamically calculate the vector list based on 
   a link state database protocol, like OSPF or IS-IS.

   Due to the fact that the leaf router receives two copies of the
   multicast stream via two diverse paths, there is no need for PIM
   to repair the broken path immediately. It is up to the egress 
   router to either wait for the broken path to be repaired or build 
   a new explicit path using a new RPF vector list. Which method is
   applied depends very much on how the vector list was determined 
   initially. Double failures are not considered and are outside the 
   scope of this document.

4.  Use of the PIM Explicit RPF Vector
 
   Figure 1 provides an example multicast join path 
   R4->R3->R6->R5->R2->R1, where the multicast join is explicitly 
   routed to the source hop-by-hop using the Explicit RPF Vector 
   list. 

   [S]---(R1)--(R2)---(R3)--(R4)---[R]
          <---   |      |  ---
             |   |      |  |
             | (R5)---(R6) |
             - (S,G) Join -

                Figure 1

5.  Explicit RPF Vector Attribute 

   This draft uses PIM join attribute type 4 for specifying an Explicit 
   RPF Vector. 

6.  Mixed Vector Processing 
 
   Explicit RPF Vector attribute does not impact or restrict the 
   functionality of other RPF vector attributes in a PIM join. It is 
   possible to mix vectors of different types, such that some part of 
   the tree is explicit and other parts are loosely routed. RPF vectors
   are processed in the order in which they are specified. That is, the
   first RPF vector attribute is looked at and processed, it can be 
   either loose or explicit.

7.  Conflicting RPF Vectors 
 
   It is possible that a PIM router has multiple downstream neighbors.
   If for the same multicast route there is an inconsistency between the 
   Explicit RPF Vector lists provided by the downstream PIM neighbor, 
   the procedures as documented in section 3.3.3 [RFC5384] apply.
   
   
8.  PIM Asserts

   Section 3.3.3 of [RFC5496] specifies the procedures for how to deal 
   with PIM asserts when RPF vectors are used. The same procedures apply 
   to the Explicit RPF Vector. There is minor behavioral difference, 
   the routing protocol's Metric that is included in the PIM Assert 
   should be taken from the first Explicit vector in the list. However, 
   the first Explicit vector should always be directly connected, so 
   the Metric may likely be zero. The Metric will therefore not be a tie 
   breaker in the PIM Assert selection procedure.

9.  Join Suppression 
 
   Section 3.3.4 of [RFC5496] specifies the procedures how to apply join 
   suppression when an RPF Vector attribute is included in the PIM join. 
   The same procedure applies to the Explicit RPF Vector attribute. The 
   procedure MUST match against all the Explicit RPF Vectors in the PIM 
   join before a PIM join can be suppressed.

  
10.  Unsupported Explicit Vector Handling

   Routers that don't support the Explicit Vector attribute MUST NOT 
   forward the vector to their upstream PIM neighbor and if required 
   send a PIM join with these attributes removed. Such router will not 
   be able to remove the Explicit Vector attribute from the list, 
   causing a PIM control plane routing loop with the upstream PIM 
   neighbor. For that reason the F bit MUST be set to 0. See section 
   3.3.2 of [RFC5384]. 

11.  Explicit RPF Vector Attribute TLV Format

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |F|E| Type      | Length        |        Value
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-.......

   F bit
   -----
   The F bit MUST be set to 0. Otherwise there could be loops.
   
   E bit
   -----
   End of Attributes. If this bit is set then this is the last TLV 
   specified in the list.

   Type
   ----
   The Vector Attribute type is 4.

   Length
   ------
   Length depending on the Address Family of the Encoded-Unicast 
   address.

   Value
   -----
   Encoded-Unicast address. This could be a valid primary or secondary 
   address.

12.  IANA Considerations

   A new attribute type from the "PIM Join Attribute Types" registry
   needs to be assigned by IANA for the RPF Vector attribute. The 
   proposed value is 4.

13.  Security Considerations

   This document describes Explicit RPF Vector Attribute only which by 
   itself does not modify the security of PIM join packet or PIM-SM 
   operation and shares the security considerations described in 
   [RFC4601].

14.  Acknowledgments

   The authors would like to thank Vatsa Kumar and Nagendra Kumar for 
   the comments on the document.

15.  Normative References

   [RFC5496]  Wijnands, IJ., Boers, A., Rosen, E., "The Reverse Path
              Forwarding (RPF) Vector TLV", RFC 5496, March 2009. 

   [RFC5384]  Boers, A., Wijnands, IJ., Rosen, E., "The Protocol
              Independent Multicast (PIM) Join Attribute Format", 
              RFC 5384, Nov 2008.
   
   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4601]  Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
              "Protocol Independent Multicast - Sparse Mode (PIM-SM):
              Protocol Specification (Revised)", RFC 4601, August
              2006.

Authors' Addresses

   Javed Asghar
   Cisco Systems, Inc.
   725, Alder Drive
   Milpitas, CA 95035 
  
   Email: jasghar@cisco.com

   IJsbrand Wijnands
   Cisco Systems, Inc.
   De kleetlaan 6a
   Diegem  1831
   Belgium

   EMail: ice@cisco.com

   Sowmya Krishnaswamy
   Cisco Systems, Inc.
   3750 Cisco Way
   San Jose, CA 95134 

   EMail: sowkrish@cisco.com

   Apoorva Karan
   Cisco Systems, Inc.
   3750 Cisco Way
   San Jose, CA 95134 

   EMail: apoorva@cisco.com

   Vishal Arya
   DIRECTV Inc.
   2230 E Imperial Hwy
   El Segundo, CA  90245

   Email: varya@directv.com