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Versions: (draft-farinacci-pim-port) 00 01 02 03 04 05 06 07 08 09 RFC 6559

Network Working Group                                       D. Farinacci
Internet-Draft                                              IJ. Wijnands
Intended status: Experimental                                  S. Venaas
Expires: April 28, 2011                                    cisco Systems
                                                            M. Napierala
                                                               AT&T Labs
                                                        October 25, 2010


                 A Reliable Transport Mechanism for PIM
                       draft-ietf-pim-port-04.txt

Abstract

   This draft describes how a reliable transport mechanism can be used
   by the PIM protocol to optimize CPU and bandwidth resource
   utilization by eliminating periodic Join/Prune message transmission.
   This draft proposes a modular extension to PIM to use either the TCP
   or SCTP transport protocol.

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
   and may be updated, replaced, or obsoleted by other documents at any
   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 April 28, 2011.

Copyright Notice

   Copyright (c) 2010 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Requirements Notation  . . . . . . . . . . . . . . . . . .  5
     1.2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . . .  6
   3.  New PIM Hello Options  . . . . . . . . . . . . . . . . . . . .  8
     3.1.  PIM over the TCP Transport Protocol  . . . . . . . . . . .  8
     3.2.  PIM over the SCTP Transport Protocol . . . . . . . . . . .  9
   4.  Establishing Transport Connections . . . . . . . . . . . . . . 11
     4.1.  TCP Connection Maintenance . . . . . . . . . . . . . . . . 12
     4.2.  Moving from PORT to Datagram Mode  . . . . . . . . . . . . 13
     4.3.  On-demand versus Pre-configured Connections  . . . . . . . 14
     4.4.  Possible Hello Suppression Considerations  . . . . . . . . 14
     4.5.  Avoiding a Pair of Connections between Neighbors . . . . . 15
   5.  Common Header Definition . . . . . . . . . . . . . . . . . . . 16
   6.  Explicit Tracking  . . . . . . . . . . . . . . . . . . . . . . 20
   7.  Multiple Instances and Address-Family Support  . . . . . . . . 21
   8.  Miscellany . . . . . . . . . . . . . . . . . . . . . . . . . . 22
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 24
   11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 25
   12. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 26
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 27
     13.2. Informative References . . . . . . . . . . . . . . . . . . 27
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28



















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1.  Introduction

   The goals of this specification are:

   o  To create a simple incremental mechanism to provide reliable PIM
      message delivery in PIM version 2 for use with PIM Sparse-Mode
      [RFC4601] (including Source-Specific Multicast) and Bidirectional
      PIM [RFC5015].

   o  The reliable transport mechanism will be used for Join-Prune
      message transmission only.

   o  When a router supports this specification, it need not use the
      reliable transport mechanism with every neighbor.  That is,
      negotiation on a per neighbor basis will occur.

   The explicit non-goals of this specification are:

   o  Changes to the PIM message formats as defined in [RFC4601].

   o  Provide support for automatic switching between Datagram mode and
      Transport mode.  Two routers that are PIM neighbors on a link will
      always use Transport mode if and only if both have Transport mode
      enabled.

   This document will specify how periodic Join/Prune message
   transmission can be eliminated by using TCP [RFC0793] or SCTP
   [RFC4960] as the reliable transport mechanism for Join/Prune
   messages.

   This specification enables greater scalability in terms of control
   traffic overhead.  However, for routers connected to multi-access
   links that comes at the price of increased control plane state
   overhead and the control plane overhead required to maintain this
   state.

   In many existing and emerging networks, particularly wireless and
   mobile satellite systems, link degradation due to weather,
   interference, and other impairments can result in temporary spikes in
   the packet loss.  In these environments, periodic PIM joining can
   cause join latency when messages are lost causing a retransmission
   only 60 seconds later.  By applying a reliable transport, a lost join
   is retransmitted rapidly.  Furthermore, when the last user leaves a
   multicast group, any lost prune is similarly repaired and the
   multicast stream is quickly removed from the wireless/satellite link.
   Without a reliable transport, the multicast transmission could
   otherwise continue until it timed out, roughly 3 minutes later.  As
   network resources are at a premium in many of these environments,



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   rapid termination of the multicast stream is critical to maintaining
   efficient use of bandwidth.

















































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1.1.  Requirements Notation

   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].

1.2.  Definitions

   PORT:   Stands for PIM Over Reliable Transport.  Which is the short
      form for describing the mechanism in this specification where PIM
      can use the TCP or SCTP transport protocol.

   Periodic Join/Prune message:   A Join/Prune message sent periodically
      to refresh state.

   Incremental Join/Prune message:   A Join/Prune message sent as a
      result of state creation or deletion events.  Also known as a
      triggered message.

   Native Join/Prune message:   A Join/Prune message which is carried
      with an IP protocol type of PIM.

   PORT Join/Prune message:   A Join/Prune message using TCP or SCTP for
      transport.

   Datagram Mode:   The current procedures PIM uses by encapsulating
      Join/Prune messages in IP packets sent either triggered or
      periodically.

   PORT Mode:   Procedures used by PIM defined in this specification for
      sending Join/Prune messages over the TCP or SCTP transport layer.




















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2.  Protocol Overview

   PIM Over Reliable Transport (PORT) is a simple extension to PIMv2 for
   refresh reduction of PIM Join/Prune messages.  It involves sending
   incremental rather than periodic Join/Prune messages over a TCP/SCTP
   connection between PIM neighbors.

   PORT only applies to PIM Sparse-Mode [RFC4601] and Bidirectional PIM
   [RFC5015] Join/Prune messages.

   This document does not restrict PORT to any specific link types.
   However, the use of PORT on e.g. multi-access LANs with many PIM
   neighbors should be carefully evaluated.  This due to the fact that
   there may be a full mesh of PORT connections, and that explicit
   tracking of all PIM PORT routers is required.

   PORT can be incrementally used on a link between PORT capable
   neighbors.  Routers which are not PORT capable can continue to use
   PIM in Datagram Mode.  PORT capability is detected using new PORT
   Capable PIM Hello Options.

   Once PORT is enabled on an interface and a PIM neighbor also
   announces that it is PORT enabled, only PORT Join/Prune messages will
   be used.  That is, only PORT Join/Prune messages are accepted from,
   and sent to, that particular neighbor.  Native Join/Prune messages
   may still be used for other neighbors.

   PORT Join/Prune messages are sent using a TCP/SCTP connection.  When
   two PIM neighbors are PORT enabled, both for TCP or both for SCTP,
   they will immediately, or on-demand, establish a connection.  If the
   connection goes down, they will again immediately, or on-demand, try
   to reestablish the connection.  No Join/Prune messages (neither
   Native nor PORT) are sent while there is no connection.

   When PORT is used, only incremental Join/Prune messages are sent from
   downstream routers to upstream routers.  As such, downstream routers
   do not generate periodic Join/Prune messages for state for which the
   RPF neighbor is PORT-capable.

   For Joins and Prunes, which are received over a TCP/SCTP connection,
   the upstream router does not start or maintain timers on the outgoing
   interface entry.  Instead, it keeps track of which downstream routers
   have expressed interest.  An interface is deleted from the outgoing
   interface list only when all downstream routers on the interface, no
   longer wish to receive traffic.

   There is no change proposed for the PIM Join/Prune packet format.
   However, for Join/Prune messages sent over TCP/SCTP connections, no



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   IP Header is included.  The message begins with the PIM common
   header, followed by the Join/Prune message.  See section Section 5
   for details on the common header.
















































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3.  New PIM Hello Options

3.1.  PIM over the TCP Transport Protocol

   Option Type: PIM-over-TCP Capable


        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 = 27           |         Length = X + 8        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    TCP Connection ID AFI      |          Reserved     |  Exp  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       TCP Connection ID                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Interface ID                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Allocated Hello Type values can be found in [HELLO-OPT].

   When a router is configured to use PIM over TCP on a given interface,
   it MUST include the PIM-over-TCP Capable hello option in its Hello
   messages for that interface.  If a router is explicitly disabled from
   using PIM over TCP it MUST NOT include the PIM-over-TCP Capable hello
   option in its Hello messages.  When the router cannot setup a TCP
   connection, it will refrain from including this option.

   Implementations may provide a configuration option to enable or
   disable PORT functionality.  We recommend that this capability be
   disabled by default.

   Length:   In bytes for the value part of the Type/Length/Value
      encoding.  Where X is 4 bytes if AFI of value 1 (IPv4) is used and
      16 bytes when AFI of value 2 (IPv6) is used [AFI].

   TCP Connection ID AFI:   The AFI value to describe the address-family
      of the address of the TCP Connection ID field.  When this field is
      0, a mechanism outside the scope of this spec is used to obtain
      the addresses used to establish the TCP connection.

   Reserved:   Set to zero on transmission and ignored on receipt.

   Exp:   For experimental use [RFC3692].






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   TCP Connection ID:   An IPv4 or IPv6 address used to establish the
      TCP connection.  This field is omitted (length 0) for the
      Connection ID AFI 0.

   Interface ID:   An Interface ID is used to associate the connection a
      Join/Prune message is received over with an interface which is
      added or removed from an oif-list.  When unnumbered interfaces are
      used or when a single Transport connection is used for sending and
      receiving Join/Prune messages over multiple interfaces, the
      Interface ID is used convey the interface from Join/Prune message
      sender to Join/Prune message receiver.  When a PIM router sets a
      locally generated value for the Interface ID in the Hello TLV, it
      must send the same Interface ID value in all Join/Prune messages
      it is sending to the PIM neighbor.

3.2.  PIM over the SCTP Transport Protocol

   Option Type: PIM-over-SCTP Capable


        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 = 28           |         Length = X + 8        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   SCTP Connection ID AFI      |          Reserved     |  Exp  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                      SCTP Connection ID                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Interface ID                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Allocated Hello Type values can be found in [HELLO-OPT].

   When a router is configured to use PIM over SCTP on a given
   interface, it MUST include the PIM-over-SCTP Capable hello option in
   its Hello messages for that interface.  If a router is explicitly
   disabled from using PIM over SCTP it MUST NOT include the PIM-over-
   SCTP Capable hello option in its Hello messages.  When the router
   cannot setup a SCTP connection, it will refrain from including this
   option.

   Implementations may provide a configuration option to enable or
   disable PORT functionality.  We recommend that this capability be
   disabled by default.





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   Length:   In bytes for the value part of the Type/Length/Value
      encoding.  Where X is 4 bytes if AFI of value 1 (IPv4) is used and
      16 bytes when AFI of value 2 (IPv6) is used [AFI].

   SCTP Connection ID AFI:   The AFI value to describe the address-
      family of the address of the SCTP Connection ID field.  When this
      field is 0, a mechanism outside the scope of this spec is used to
      obtain the addresses used to establish the SCTP connection.

   Reserved:   Set to zero on transmission and ignored on receipt.

   Exp:   For experimental use [RFC3692].

   SCTP Connection ID:   An IPv4 or IPv6 address used to establish the
      SCTP connection.  This field is omitted (length 0) for the
      Connection ID AFI 0.

   Interface ID:   An Interface ID is used to associate the connection a
      Join/Prune message is received over with an interface which is
      added or removed from an oif-list.  When unnumbered interfaces are
      used or when a single Transport connection is used for sending and
      receiving Join/Prune messages over multiple interfaces, the
      Interface ID is used convey the interface from Join/Prune message
      sender to Join/Prune message receiver.  When a PIM router sets a
      locally generated value for the Interface ID in the Hello TLV, it
      must send the same Interface ID value in all Join/Prune messages
      it is sending to the PIM neighbor.
























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4.  Establishing Transport Connections

   While a router interface is PORT enabled, a PIM-over-TCP or a PIM-
   over-SCTP option is included in the PIM Hello messages sent on that
   interface.  When a router on a PORT-enabled interface receives a
   Hello message containing a PIM-over-TCP/PIM-over-SCTP Option from a
   new neighbor, or an existing neighbor that did not previously include
   the option, it switches to PORT mode for that particular neighbor.

   When a router switches to PORT mode for a neighbor, it stops sending
   and accepting Native Join/Prune messages for that neighbor.  Any
   state from previous Native Join/Prune messages is left to expire as
   normal.  It will also attempt to establish a Transport connection
   (TCP or SCTP) with the neighbor.  If both the router and its neighbor
   have announced both PIM-over-TCP and PIM-over-SCTP options, SCTP MUST
   be used.

   When the router is using TCP it will compare the TCP Connection ID it
   announced in the PIM-over-TCP Capable Option with the TCP Connection
   ID in the Hello received from the neighbor.  The router with the
   lower Connection ID will do an active Transport open to the neighbor
   Connection ID.  The router with the higher Connection ID will do a
   passive Transport open.  An implementation may open connections only
   on-demand, in that case it may be that the neighbor with the higher
   Connection ID does the active open, see Section 4.3.  Note that the
   source address of the active open must be the announced Connection
   ID.

   When the router is using SCTP, the IP address comparison need not be
   done since the SCTP protocol can handle call collision.

   If PORT is used both for IPv4 and IPv6, both IPv4 and IPv6 PIM Hello
   messages are sent, both containing PORT Hello options.  If two
   neighbors announce the same transport (TCP or SCTP) and the same
   Connection ID in the IPv4 and IPv6 Hello messages, then only one
   connection is established and is shared.  Otherwise, two connections
   are established and are used separately.

   The PIM router that performs the active open initiates the connection
   with a locally generated source transport port number and a well-
   known destination transport port number.  The PIM router that
   performs the passive open listens on the well-known local transport
   port number and does not qualify the remote transport port number.
   See Section 5 for well-known port number assignment for PORT.

   When a Transport connection is established (or reestablished), the
   two routers MUST both send a full set of Join/Prune messages for
   state for which the other router is the upstream neighbor.  This is



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   needed to ensure that the upstream neighbor has the correct state.
   When moving from Datagram mode, or when the connection has gone down,
   the router cannot be sure that all the previous Join/Prune state was
   received by the neighbor.  Any state received while in Datagram mode
   that is not refreshed, will be left to expire.

   When a Transport connection goes down, Join/Prune state that was sent
   over the Transport connection is still retained.  The neighbor should
   not be considered down until the neighbor timer has expired.  This
   allows routers to do a control-plane switchover without disrupting
   the network.  If a Transport connection is reestablished before the
   neighbor timer expires, the previous state is intact and any new
   Join/Prune messages sent cause state to be created or removed
   (depending on if it was a Join or Prune).  If the neighbor timer does
   expire, only the upstream router, that has oif-list state, to the
   expired downstream neighbor will need to clear state.  A downstream
   router, when an upstream neighboring router has expired, will simply
   update the RPF for the corresponding state to a new neighbor where it
   would trigger Join/Prune messages like it would in [RFC4601].  It is
   required of a PIM router to clear its neighbor table for a neighbor
   who has timed out due to neighbor holdtime expiration.

   Note that, a Join sent over a Transport connection will only be seen
   by the upstream router, and thus will not cause routers on the link
   that do not use PIM PORT with the upstream router to possibly delay
   the refresh of Join state for the same state.  Similarly, a Prune
   sent over a Transport connection will only be seen by the upstream
   router, and will thus never cause routers on the link on the link
   that do not use PIM PORT with the upstream router, to send a Join to
   override this Prune.

   Note also, that a datagram PIM Join/Prune message for a said (S,G) or
   (*,G) sent by some router on a link will not cause routers on the
   same link that use a Transport connection with the upstream router
   for that state, to suppress the refresh of that state to the usptream
   router (because they don't need to periodically refresh this state)
   or to send a Join to override a Prune (as the upstream router will
   only stop forwarding the traffic when all joined routers that use a
   Transport connection have explicitly sent a Prune for this state, as
   explained in Section 6).

4.1.  TCP Connection Maintenance

   TCP is designed to keep connections up indefinitely during a period
   of network disconnection.  If a PIM-over-TCP router fails, the TCP
   connection may stay up until the neighbor actually reboots, and even
   then it may continue to stay up until you actually try to send the
   neighbor some information.  This is particularly relevant to PIM,



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   since the flow of Join/Prune messages might be in only one direction,
   and the downstream neighbor might never get any indication via TCP
   that the other end of the connection is not really there.

   Implementations SHOULD support the use of TCP Keep-Alives, see
   [RFC1122] section 4.2.3.6.  We recommend the use of Keep-Alives to be
   optional, allowing network administrators to use it as needed.  Note
   that Keep-Alives can be used by a peer, independently of whether the
   other peer supports it.  With the use of Keep-Alives one can detect
   that a connection is not working without sending any TCP data.

   Most applications using TCP want to detect when a neighbor is no
   longer there, so that the associated application state can be
   released.  Also, one wants to clean up the TCP state, and not keep
   half-open connections around indefinitely.  This is accomplished by
   using PIM Hellos and by not introducing an application-specific or
   new PIM keep-alive message.  Therefore, when a GENID changes from a
   received PIM Hello message, and a TCP connection is established or
   attempting to be established, the local side will tear down the
   connection and attempt to reopen a new one for the new instance of
   the neighbor coming up.  However, if the connection is shared by
   multiple interfaces and the GENID changes only for one of them, then
   there was not a full reboot and the connection is likely to still
   work.  In that case, the router should just resend all Join/Prune
   state for that particular neighbor.  This is similar to how state is
   refreshed when GENID changes for PIM in datagram mode.

   There may be situations where a router ignores some joins or prunes.
   E.g. due to wrong RP information or receiving joins on an RPF
   interface.  A router may try to cache such messages and apply them
   later if only a temporary error.  It may however also ignore the
   message, and later change its GENID for that interface to make the
   neighbor resend all state, including any that may have been
   previously ignored.  It is possible that one receives Join/Prune
   messages for an interface/link that is down.  As long as the neighbor
   has not expired, we recommend processing those messages as usual.  If
   they are ignored, then the router should change the GENID for that
   interface when it comes back up, in order to get a full update.

4.2.  Moving from PORT to Datagram Mode

   There may be situations where an administrator decides to stop using
   PORT.  If PORT is disabled on a router interface, we start expiry
   timers with the respective neighbor holdtimes as the initial values.
   Similarly if we receive a Hello message without a PORT Capable option
   from a neighbor, we start expiry timers for all Join/Prune state we
   have for that particular neighbor.  The Transport connection should
   be shut down as soon as there are no more PIM neighborships using it.



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   That is, for the connection we have associated local and remote
   Connection IDs.  When there is no PIM neighbor with that particular
   remote connection ID on any interface where we announce the local
   connection ID, the connection should be shut down.

4.3.  On-demand versus Pre-configured Connections

   Transport connections could be established when they are needed or
   when a router interface to other PIM neighbors has come up.  The
   advantage of on-demand Transport connection establishment is the
   reduction of router resources.  Especially in the case where there is
   no need for n^2 connections on a network interface.  The disadvantage
   is additional delay and queueing when a Join/Prune message needs to
   be sent and a Transport connection is not established yet.

   If a router interface has become operational and PIM neighbors are
   learned from Hello messages, at that time, Transport connections may
   be established.  The advantage is that a connection is ready to
   transport data by the time a Join/Prune message needs to be sent.
   The disadvantage is there can be more connections established than
   needed.  This can occur when there is a small set of RPF neighbors
   for the active distribution trees compared to the total number of
   neighbors.  Even when Transport connections are pre-established
   before they are needed, a connection can go down and an
   implementation will have to deal with an on-demand situation.

   Note that for TCP, it is the router with the lower Connection ID that
   decides whether to open a connection immediately, or on-demand.  The
   router with the higher Connection ID should only initiate a
   connection on-demand.  That is, if it needs to send a Join/Prune
   message and there is no currently established connection.

   Therefore, this specification recommends but does not mandate the use
   of on-demand Transport connection establishment.

4.4.  Possible Hello Suppression Considerations

   This specification indicates that a Transport connection cannot be
   established until a Hello message is received.  One reason for this
   is to determine if the PIM neighbor supports this specification and
   the other is to determine the remote address to use to establish the
   Transport connection.

   There are cases where it is desirable to suppress entirely the
   transmission of Hello messages.  In this case, it is outside the
   scope of this document on how to determine if the PIM neighbor
   supports this specification as well as an out-of-band (outside of the
   PIM protocol) method to determine the remote address to establish the



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   Transport connection.

4.5.  Avoiding a Pair of Connections between Neighbors

   To ensure there are not two connections between a pair of PIM
   neighbors, the following set of rules must be followed.  Let A and B
   be two PIM neighbors where A's Connection ID is numerically smaller
   than B's Connection ID, and each is known to the other as having a
   potential PIM adjacency relationship.

   At node A:

   o  If there is already an established TCP connection to B, on the
      PIM-over-TCP port, then A MUST NOT attempt to establish a new
      connection to B. Rather it uses the established connection to send
      Join/Prune messages to B. (This is independent of which node
      initiated the connection.)

   o  If A has initiated a connection to B, but the connection is still
      in the process of being established, then A MUST refuse any
      connection on the PIM-over-TCP port from B.

   o  At any time when A does not have a connection to B which is either
      established or in the process of being established, A MUST accept
      connections from B.

   At node B:

   o  If there is already an established TCP connection to A, on the
      PIM-over-TCP port, then B MUST NOT attempt to establish a new
      connection to A. Rather it uses the established connection to send
      Join/Prune messages to A. (This is independent of which node
      initiated the connection.)

   o  If B has initiated a connection to A, but the connection is still
      in the process of being established, then if A initiates a
      connection too, B MUST accept the connection initiated by A and
      must release the connection which it (B) initiated.













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5.  Common Header Definition

   It may be desirable for scaling purposes to allow Join/Prune messages
   from different PIM protocol instances to be sent over the same
   Transport connection.  Also, it may be desirable to have a set of
   Join/Prune messages for one address-family sent over a Transport
   connection that is established over a different address-family
   network layer.

   To be able to do this we need a common header that is inserted and
   parsed for each PIM Join/Prune message that is sent on a Transport
   connection.  This common header will provide both record boundary and
   demux points when sending over a stream protocol like Transport.

   Each Join/Prune message will have in front of it the following common
   header in Type/Length/Value format.  And multiple different TLV types
   can be sent over the same Transport connection.

   To make sure PIM Join/Prune messages are delivered as soon as the TCP
   transport layer receives the Join/Prune buffer, the TCP Push flag
   will be set in all outgoing Join/Prune messages sent over a TCP
   transport connection.

   PIM messages will be sent using destination TCP port number 8471.
   When using SCTP as the reliable transport, destination port number
   8471 will be used.  See Section 10 for IANA considerations.

   Join/Prune messages are error checked.  This includes a bad PIM
   checksum, illegal type fields, illegal addresses or a truncated
   message.  If any parsing errors occur in a Join/Prune message, it is
   skipped, and we proceed processing any following TLVs.

   The TLV type field is 16 bits.  The range 61440 - 65535 is for
   experimental use [RFC3692].

   The current list of defined TLVs are:















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   IPv4 Join/Prune Message

        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 = 1             |        Length = X + 16        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        Reserved               |  Exp  |I-Type |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Interface ID                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Instance ID . . .                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     . . . Instance ID                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                   PIMv2 Join/Prune Message                    |
       |                               .                               |
       |                               .                               |
       |                               .                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The IPv4 Join/Prune common header is used when a Join/Prune message
   is sent that has all IPv4 encoded addresses in the PIM payload.

   Length:   In bytes for the value part of the Type/Length/Value
      encoding.  Where X is the number of bytes that make up the PIMv2
      Join/Prune message.

   Reserved:   Set to zero on transmission and ignored on receipt.

   Exp:   For experimental use [RFC3692].

   I-Type:   Defines the encoding and semantics of the Instance ID
      field.  Instance Type 0 means Instance ID is not used.  Other
      values are not defined in this specification.  A message with an
      unknown Instance Type MUST be ignored.

   Interface ID:   This is the Interface ID from the Hello TLV, defined
      in this specification, the PIM router is sending to the PIM
      neighbor.  It indicates to the PIM neighbor what interface to
      associate the Join/Prune with.

   Instance ID:   This document only defines this for Instance Type 0.
      For type 0 the field should be set to zero on transmission and
      ignored on receipt.  This field is always 64 bits.






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   PIMv2 Join/Prune Message:   PIMv2 Join/Prune message and payload with
      no IP header in front of it.  As you can see from the packet
      format diagram, multiple Join/Prune messages can go into one TCP/
      SCTP stream from the same or different Interface and Instance IDs.

   IPv6 Join/Prune Message

        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 = 2             |        Length = X + 16        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        Reserved               |  Exp  |I-Type |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Interface ID                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Instance ID . . .                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     . . . Instance ID                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                   PIMv2 Join/Prune Message                    |
       |                               .                               |
       |                               .                               |
       |                               .                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The IPv6 Join/Prune common header is used when a Join/Prune message
   is sent that has all IPv6 encoded addresses in the PIM payload.

   Length:   In bytes for the value part of the Type/Length/Value
      encoding.  Where X is the number of bytes that make up the PIMv2
      Join/Prune message.

   Reserved:   Set to zero on transmission and ignored on receipt.

   Exp:   For experimental use [RFC3692].

   I-Type:   Defines the encoding and semantics of the Instance ID
      field.  Instance Type 0 means Instance ID is not used.  Other
      values are not defined in this specification.

   Interface ID:   This is the Interface ID from the Hello TLV, defined
      in this specification, the PIM router is sending to the PIM
      neighbor.  It indicates to the PIM neighbor what interface to
      associate the Join/Prune with.






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   Instance ID:   This document only defines this for Instance Type 0.
      For type 0 the field should be set to zero on transmission and
      ignored on receipt.

   PIMv2 Join/Prune Message:   PIMv2 Join/Prune message and payload with
      no IP header in front of it.  As you can see from the packet
      format diagram, multiple Join/Prune messages can go into one TCP/
      SCTP stream from the same or different Interface and Instance IDs.











































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6.  Explicit Tracking

   When explicit tracking is used, a router keeps track of join state
   for individual downstream neighbors on a given interface.  This is
   done for all PORT joins and prunes.  It may also be done for native
   join/prune messages, if all neighbors on the LAN have set the T bit
   of the LAN Prune Delay option.  In the discussion below we will talk
   about ET (explicit tracking) neighbors, and non-ET neighbors.  The
   set of ET neighbors always includes the PORT neighbors.  The set of
   non-ET neighbors consists of all the non-PORT neighbors unless all
   neighbors have set the LAN Prune Delay T bit.  Then the ET neighbors
   set contains all neighbors.

   For some link-types, e.g. point-to-point, tracking neighbors is no
   different than tracking interfaces.  It may also be possible for an
   implementation to treat different downstream neighbors as being on
   different logical interfaces, even if they are on the same physical
   link.  Exactly how this is implemented and for which link types, is
   left to the implementer.

   For (*,G) and (S,G) state, the router starts forwarding traffic on an
   interface when a Join is received from a neighbor on such an
   interface.  When a non-ET neighbor sends a Prune, there is generally
   a small delay to see if another non-ET neighbor sends a Join to
   override the Prune.  If there is no override, one should note that no
   non-ETP neighbor is interested.  If no ET neighbors are interested,
   the interface can be removed from the oif-list.  When a ET neighbor
   sends a Prune, one removes the join state for that neighbor.  If no
   other ET or non-ET neighbors are interested, the interface can be
   removed from the oif-list.  When a PORT neighbor sends a prune, there
   can be no Prune Override, since the Prune is not visible to other
   neighbors.

   For (S,G,R) state, the router needs to track Prune state on the
   shared tree.  It needs to know which ET neighbors have sent prunes,
   and whether any non-ET neighbors have sent prunes.  Normally one
   would forward a packet from a source S to a group G out on an
   interface if a (*,G)-join is received, but no (S,G,R)-prune.  With ET
   one needs to do this check per ET neighbor.  That is, the packet
   should be forwarded unless all ET neighbors that have sent
   (*,G)-joins have also sent (S,G,R)-prunes, and if a non-ET neighbor
   has sent a (*,G)-join, whether there also is non-ET (S,G,R)-prune
   state.








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7.  Multiple Instances and Address-Family Support

   Multiple instances of the PIM protocol may be used to support e.g.
   multiple address families.  Multiple instances can cause a multiplier
   effect on the number of router resources consumed.  To be able to
   have an option to use router resources more efficiently, muxing Join/
   Prune messages over fewer Transport connections can be performed.

   There are two ways this can be accomplished, one using a common
   header format over a TCP connection and the other using multiple
   streams over a single SCTP connection.

   Using the Common Header format described previously in this
   specification, using different TLVs, both IPv4 and IPv6 based Join/
   Prune messages can be encoded within a Transport connection.
   Likewise, within a TLV, multiple occurrences of Join/Prune messages
   can occur and are tagged with an instance-ID so multiple Join/Prune
   messages for different instances can use a single Transport
   connection.

   When using SCTP multi-streaming, the common header is still used to
   convey instance information but an SCTP association is used, on a
   per-instance basis, to send data concurrently for multiple instances.
   When data is sent concurrently, head of line blocking, which can
   occur when using TCP, is avoided.


























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8.  Miscellany

   No changes expected in processing of other PIM messages like PIM
   Asserts, Grafts, Graft-Acks, Registers, and Register-Stops.  This
   goes for BSR and Auto-RP type messages as well.

   This extension is applicable only to PIM-SM, PIM-SSM and Bidir-PIM.
   It does not take requirements for PIM-DM into consideration.











































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9.  Security Considerations

   Transport connections can be authenticated using HMACs MD5 and SHA-1
   similar to use in BGP [RFC4271] and MSDP [RFC3618].

   When using SCTP as the transport protocol, [RFC4895] can be used, on
   a per SCTP association basis to authenticate PIM data.












































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10.  IANA Considerations

   This specification makes use of a TCP port number and a SCTP port
   number for the use of PIM-Over-Reliable-Transport that has been
   allocated by IANA.  It also makes use of IANA PIM Hello Options
   allocations that should be made permanent.  In addition, a registry
   for PORT message types is requested.  The registry should cover the
   range 0 - 61439.  An RFC is required for assignments in that range.
   This document defines two PORT message types.  Type 1, IPv4 Join/
   Prune Message; and Type 2, IPv6 Join/Prune Message.  The type range
   61440 - 65535 is for experimental use [RFC3692].








































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11.  Contributors

   In addition to the persons listed as authors, significant
   contributions were provided by Apoorva Karan and Arjen Boers.















































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12.  Acknowledgments

   The authors would like to give a special thank you and appreciation
   to Nidhi Bhaskar for her initial design and early prototype of this
   idea.

   Appreciation goes to Randall Stewart for his authoritative review and
   recommendation for using SCTP.

   Thanks also goes to the following for their ideas and commentary
   review of this specification, Mike McBride, Toerless Eckert, Yiqun
   Cai, Albert Tian, Suresh Boddapati, Nataraj Batchu, Daniel Voce, John
   Zwiebel, Yakov Rekhter, Lenny Giuliano, Gorry Fairhurst, Sameer
   Gulrajani, Thomas Morin and Dimitri Papadimitriou.

   A special thank you goes to Eric Rosen for his very detailed review
   and commentary.  Many of his comments are reflected as text in this
   specification.

































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13.  References

13.1.  Normative References

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, September 1981.

   [RFC1122]  Braden, R., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122, October 1989.

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

   [RFC3618]  Fenner, B. and D. Meyer, "Multicast Source Discovery
              Protocol (MSDP)", RFC 3618, October 2003.

   [RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
              Protocol 4 (BGP-4)", RFC 4271, January 2006.

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

   [RFC4895]  Tuexen, M., Stewart, R., Lei, P., and E. Rescorla,
              "Authenticated Chunks for the Stream Control Transmission
              Protocol (SCTP)", RFC 4895, August 2007.

   [RFC4960]  Stewart, R., "Stream Control Transmission Protocol",
              RFC 4960, September 2007.

   [RFC5015]  Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
              "Bidirectional Protocol Independent Multicast (BIDIR-
              PIM)", RFC 5015, October 2007.

13.2.  Informative References

   [AFI]      IANA, "Address Family Indicators (AFIs)", ADDRESS FAMILY
              NUMBERS http://www.iana.org/numbers.html, February 2007.

   [HELLO-OPT]
              IANA, "PIM Hello Options", PIM-HELLO-OPTIONS per
              RFC4601 http://www.iana.org/assignments/pim-hello-options,
              March 2007.

   [RFC3692]  Narten, T., "Assigning Experimental and Testing Numbers
              Considered Useful", BCP 82, RFC 3692, January 2004.





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Authors' Addresses

   Dino Farinacci
   cisco Systems
   Tasman Drive
   San Jose, CA  95134
   USA

   Email: dino@cisco.com


   IJsbrand Wijnands
   cisco Systems
   Tasman Drive
   San Jose, CA  95134
   USA

   Email: ice@cisco.com


   Stig Venaas
   cisco Systems
   Tasman Drive
   San Jose, CA  95134
   USA

   Email: stig@cisco.com


   Maria Napierala
   AT&T Labs
   200 Laurel Drive
   Middletown, New Jersey  07748>
   USA

   Email: mnapierala@att.com















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