Network Working Group                                     Dino Farinacci
INTERNET DRAFT                                          Procket Networks
                                                           Yakov Rekhter
                                                             David Meyer
                                                           Cisco Systems
                                                          Peter Lothberg
                                                                  Sprint
                                                             Hank Kilmer
                                                             Jeremy Hall
                                                                   UUnet
Category                                                 Standards Track
                                                         January, 2000


               Multicast Source Discovery Protocol (MSDP)
                     <draft-ietf-msdp-spec-02.txt>



1. Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC 2026.

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

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.













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2. Abstract

   The Multicast Source Discovery Protocol, MSDP, describes a mechanism
   to connect multiple PIM-SM domains together. Each PIM-SM domain uses
   its own independent RP(s) and does not have to depend on RPs in other
   domains.


3. Copyright Notice

   Copyright (C) The Internet Society (20000).  All Rights Reserved.


4.  Introduction

   The Multicast Source Discovery Protocol, MSDP, describes a mechanism
   to connect multiple PIM-SM domains together. Each PIM-SM domain uses
   its own independent RP(s) and does not have to depend on RPs in other
   domains. Advantages of this approach include:

   o No Third-party resource dependencies on RP

     PIM-SM domains can rely on their own RPs only.

   o Receiver only Domains

     Domains with only receivers get data without globally
     advertising group membership.

   o Global Source State

     Global source state is not required, since a router need not
     cache Source  Active (SA) messages (see below). MSDP is a
     periodic protocol.

   The keywords MUST, MUST NOT, MAY, OPTIONAL, REQUIRED, RECOMMENDED,
   SHALL, SHALL NOT, SHOULD, SHOULD NOT are to be interpreted as defined
   in RFC 2119 [RFC2119].













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5. Overview

   An RP (or other MSDP SA originator) in a PIM-SM [RFC2362] domain will
   have a MSDP peering relationship with a MSDP speaker in another
   domain. The peering relationship will be made up of a TCP connection
   in which control information exchanged. Each domain will have one or
   more connections to this virtual topology.

   The purpose of this topology is to have domains discover multicast
   sources from other domains. If the multicast sources are of interest
   to a domain which has receivers, the normal source-tree building
   mechanism in PIM-SM will be used to deliver multicast data over an
   inter-domain distribution tree.

   We envision this virtual topology will essentially be congruent to
   the existing BGP topology used in the unicast-based Internet today.
   That is, the TCP connections between MSDP speakers can be realized by
   the underlying BGP routing system.


6. Procedure

   A source in a PIM-SM domain originates traffic to a multicast group.
   The PIM DR which is directly connected to the source sends the data
   encapsulated in a PIM Register message to the RP in the domain.

   The RP will construct a "Source-Active" (SA) message and send it to
   its MSDP peers. The SA message contains the following fields:

    o Source address of the data source.
    o Group address the data source sends to.
    o IP address of the RP.

   Each MSDP peer receives and forwards the message away from the RP
   address in a "peer-RPF flooding" fashion. The notion of peer-RPF
   flooding is with respect to forwarding SA messages. The BGP routing
   table is examined to determine which peer is the NEXT_HOP towards the
   originating RP of the SA message.  Such a peer is called an "RPF
   peer". See section 10 below for the details of peer-RPF forwarding.

   If the MSDP peer receives the SA from a non-RPF peer towards the
   originating RP, it will drop the message. Otherwise, it forwards the
   message to all its MSDP peers.

   The flooding can be further constrained to children of the peer by
   interrogating BGP reachability information. That is, if a BGP peer
   advertises a route (back to you) and you are the next to last AS in
   the AS_PATH, the peer is using you as the NEXT_HOP. This is known in



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   other circles as Split-Horizon with Poison Reverse. An implementation
   SHOULD NOT forward SA messages (which were originated from the RP
   address covered by a route) to peers which have not Poison Reversed
   that route.

   When an MSDP peer which is also an RP for its own domain receives a
   new SA message, it determines if it has any group members interested
   in the group which the SA message describes. That is, the RP checks
   for a (*,G) entry with a non-empty outgoing interface list; this
   implies that the domain is interested in the group. In this case, the
   RP triggers a (S,G) join event towards the data source as if a
   Join/Prune message was received addressed to the RP itself (See
   [RFC2362] Section 3.2.2). This sets up a branch of the source-tree to
   this domain. Subsequent data packets arrive at the RP which are
   forwarded down the shared-tree inside the domain. If leaf routers
   choose to join the source-tree they have the option to do so
   according to existing PIM-SM conventions.  Finally, if an RP in a
   domain receives a PIM Join message for a new group G, and it is
   caching SAs, then the RP should trigger a (S,G) join event for each
   SA for that group in its cache.

   This procedure has been affectionately named flood-and-join because
   if any RP is not interested in the group, they can ignore the SA
   message. Otherwise, they join a distribution tree.


7. Controlling State

   While RPs which receive SA messages are not required to keep MSDP
   (S,G) state, an RP SHOULD cache SA messages by default. The advantage
   of caching is that newly formed MSDP peers can get MSDP (S,G) state
   sooner and therefore reduce join latency for new joiners. In
   addition, caching greatly aids in diagnosis and debugging of various
   problems.


7.1. Timers

   The main timers for MSDP are: SA-Advertisement-Timer, SA-Hold-Down-
   Timer, SA Cache entry timers, and KeepAlive timer.











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7.1.1. SA-Advertisement-Timer

   RPs which originate SA messages do it periodically as long as there
   is data being sent by the source. There is one SA-Advertisement-Timer
   covering the sources that an RP may advertise. [SA-Advertisement-
   Timer] MUST be 60 seconds. An RP will not send more than one SA
   message for a given (S,G) within an SA Advertisement interval.
   Originating periodic SA messages is important so that new receivers
   who join after a source has been active can get data quickly via the
   receiver's own RP when it is not caching SA state.


7.1.1.1. SA-Advertisement-Timer Processing

   When an RP is processing a PIM register message, it encapsulates the
   data (if any) in an SA message and sends the SA message it to each of
   its peers. The RP starts the SA Advertisement-Timer for the (S,G) at
   this time. When the timer expires, and there is (S,G) state for a
   source within the RP's domain, an (S,G)-SA message is sent to each
   peer and the timer is reset to [SA-Advertisement-Timer] seconds. If
   no (S,G) state exists, the timer is deleted.

   The following table summarizes (S,G)-SA-Advertisement-Timer
   processing:


   Set to                   | When                         | Applies to
   [SA-Advertisement-Timer] | created off Register packet  | (S,G)

   Reset to                 | When                         | Applies to
   [SA-Advertisement-Timer] | Timer expires and (S,G)      | (S,G)
                            | state exists and was         |
                            | created by a register        |

   Deleted                  | When                         | Applies to
   [SA-Advertisement-Timer] | Timer expires and (S,G)      | (S,G)
                            | state has expired            |


   Note that a caching implementation may also wish to check the SA-
   Cache on this timer event.










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7.1.2. SA Cache Timeout (SA-State-Timer)

   Each entry in an SA Cache has an associated SA-State-Timer.  A
   (S,G)-SA-State-Timer is is started when an (S,G)-SA message is
   initially received by a caching MSDP speaker. The timer is reset to
   [SA-State-Timer] if another (S,G)-SA message is received before the
   (S,G)-SA-State-Timer expires. [SA-State-Timer] MUST NOT be less than
   90 seconds.  The following table summarizes SA-State-Timer
   processing:


   Set to              | When                         | Applies to
   [SA-State-Timer]    | creating (S,G)-SA cache      | (S,G)-SA Cache Entry
                       | entry (on receipt of a       |
                       | (S,G)-SA message)            |

   Reset to            | When                         | Applies to
   [SA-State-Timer]    | On receipt of (S,G)-SA       | (S,G)-SA Cache Entry
                       | message                      |

   Deleted             | When                         | Applies to
   (S,G) SA Cache      | Timer expires                | (S,G)-SA Cache Entry
    entry              |                              |



7.1.3. SA-Hold-Down-Timer

   A caching MSDP speaker SHOULD NOT forward an SA message it has
   received in the last SA-Hold-Down interval. [SA-Hold-Down-Timer]
   SHOULD be set to 30 seconds. The following table summarizes SA-Hold-
   Down-Timer processing:

   Set to                    | When                         | Applies to
   [SA-Hold-Down-Timer]      | Upon receipt of              | (S,G)-SA Cache Entry
                             | (S,G)-SA message             |

   Reset to                  | When                         | Applies to
   [SA-Hold-Down-Timer]      | When forwarding (S,G)-SA     | (S,G)-SA Cache Entry
                             | message                      |

   Deleted                   | When                         | Applies to
   (S,G)-SA-Hold-Down-Timer] | (S,G)-SA entry is            | (S,G)-SA Cache Entry
                                deleted







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7.1.4. KeepAlive Timer

   Set to               | When                         | Applies to
   [KeepAliver-Timer]   | passive-connect peer comes   | each peer
                        | up                           |

   Reset to             | When                         | Applies to
   [KeepAliver-Timer]   | Receipt of data from peer    | each peer

   Deleted              | When                         | Applies to
   KeepAliver-Timer     | Timer expires                | each peer
                        | or passive-connect peer      |
                        | closes connection            |



7.2. Intermediate MSDP Speakers

   Intermediate RPs do not originate periodic SA messages on behalf of
   sources in other domains. In general, an RP MUST only originate an SA
   for its own sources.


7.3. SA Filtering and Policy

   As the number of (S,G) pairs increases in the Internet, an RP may
   want to filter which sources it describes in SA messages. Also,
   filtering may be used as a matter of policy which at the same time
   can reduce state. Only the RP co-located in the same domain as the
   source can restrict SA messages. Note, however, that MSDP peers in
   transit domains should not filter SA messages or the flood-and-join
   model can not guarantee that sources will be known throughout the
   Internet (i.e., SA filtering by transit domains can cause undesired
   lack of connectivity). In general, policy should be expressed using
   MBGP [RFC2283]. This will cause MSDP messages will flow in the
   desired direction and peer-RPF fail otherwise. An exception occurs at
   an administrative scope [RFC2365] boundary. In particular, a SA
   message for a (S,G) MUST NOT be sent to peers which are on the other
   side of an administrative scope boundary for G.


7.4. SA Requests

   If an MSDP peer decides to cache SA state, it MAY accept SA-Requests
   from other MSDP peers. When an MSDP peer receives an SA-Request for a
   group range, it will respond to the peer with a set of SA entries, in
   an SA-Response message, for all active sources sending to the group
   range requested in the SA-Request message. The peer that sends the



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   request will not flood the responding SA-Response message to other
   peers. See section 12 for discussion of error handling relating to SA
   requests and responses.


8. Encapsulated Data Packets

   For bursty sources, the RP may encapsulate multicast data from the
   source. An interested RP may decapsulate the packet, which SHOULD be
   forwarded as if a PIM register encapsulated packet was received. That
   is, if packets are already arriving over the interface toward the
   source, then the packet is dropped. Otherwise, if the outgoing
   interface list is non-null, the packet is forwarded appropriately.
   Note that when doing data encapsulation, an implementation MUST bound
   the time during which the source which are encapsulated.

   This allows for small bursts to be received before the multicast tree
   is built back toward the source's domain. For example, an
   implementation SHOULD encapsulate at least the first packet to
   provide service to bursty sources.


9. Other Scenarios

   MSDP is not limited to deployment across different routing domains.
   It can be used within a routing domain when it is desired to deploy
   multiple RPs for different group ranges. As long as all RPs have a
   interconnected MSDP topology, each can learn about active sources as
   well as RPs in other domains. Another example is the Anycast RP
   mechanism [ANYCASTRP].


10. MSDP Peer-RPF Forwarding

   The MSDP Peer-RPF Forwarding rules are used for forwarding SA
   messages throughout an MSDP enabled internet. Unlike the RPF check
   used when forwarding data packets, the Peer-RPF check is against the
   RP address carried in the SA message.


10.1. Peer-RPF Forwarding Rules

   An SA message originated by an MSDP originator R and received by a
   MSDP router from MSDP peer N is accepted if N is the appropriate RPF
   neighbor for originator R, and discarded otherwise.

   The RPF neighbor is chosen using the first of the following rules
   that matches:



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   (i).   R is the RPF neighbor if we have an MSDP peering with R.

   (ii).  The external MBGP neighbor towards which we are
          poison-reversing the MBGP route towards R is the RPF neighbor
          if we have an MSDP peering with it.

   (iii). If we have any MSDP peerings with neighbors in the first
          AS along the AS_PATH (the AS from which we learned this
          route), but no external MBGP peerings with them,
          pick one via a deterministic rule.

   (vi).  The internal MBGP advertiser of the router towards R is
          the RPF neighbor if we have an MSDP peering with it.

   (v).   If none of the above match, and we have an MSDP
          default-peer configured, the MSDP default-peer is
          the RPF neighbor.



10.2. MSDP default-peer semantics

   A MSDP default-peer is much like a default route. It is intended to
   be used in those cases where a stub network isn't running BGP or
   MBGP. A MSDP speaker configured with a default-peer accepts all SA
   messages from the default-peer. Note that a router running BGP or
   MBGP SHOULD NOT allow configuration of default peers, since this
   allows the possibility for SA looping to occur.


11. MSDP Connection Establishment

   MSDP messages will be encapsulated in a TCP connection using well-
   known port 639. One side of the MSDP peering relationship will listen
   on the well-known port and the other side will do an active connect
   on the well-known port. The side with the higher peer IP address will
   do the listen. This connection establishment algorithm avoids call
   collision. Therefore, there is no need for a call collision
   procedure. It should be noted, however, that the disadvantage of this
   approach is that it may result in longer startup times at the passive
   end.

   An MSDP speaker starts in the INACTIVE state. MSDP speakers establish
   peering sessions according to the following state machine:







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                De-configured or
                  disabled
              +-------------------------------------------+
              |                                           |
              |                                           |
          Enable                                          |
        +-----|--------->+----------+                     |
        |     |       +->| INACTIVE |----------------+    |
        |     |       |  +----------+                |    |
   Deconf'ed  |       |   |  /|\ /|\                 | Higher Address
       or     |       |   |   |   |                  |    |
    disabled  |       |   |   |   |                 \|/   |
        |     |       |   |   |   |               +-------------+
        |     |       |   |   |   +---------------|  CONNECTING |
        |     |       |   |   |     Timeout or    +-------------+
        |     |       |   |   |     Local Address Change      |
       \|/   \|/      |   |   |                               |
     +----------+     |   |   |                               |
     | DISABLED |     |   |   +---------------------+         | TCP Established
     +----------+     |   |                         |         |
     /|\ /|\          |   |   Connection Timeout,   |         |
      |   |           |   |   Local Address change, |         |
      |   |           |   |   Authorization Failure |         |
      |   |           |   |                         |         |
      |   |           |   |                         |        \|/
      |   |           |   |                       +-------------+
      |   | Local     |   |                       | ESTABLISHED |
      |   | Address   |   |   Lower Address       +-------------+
      |   | Change    |  \|/                          /|\    |
      |   |           |  +--------+                    |     |
      |   |           +--| LISTEN |--------------------+     |
      |   |              +--------+     TCP Accept           |
      |   |               |                                  |
      |   |               |                                  |
      |   +---------------+                                  |
      |    De-configured or                                  |
      |      disabled                                        |
      |                                                      |
      +------------------------------------------------------+
          De-configured or
           disabled










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12. Packet Formats

   MSDP messages will be encoded in TLV format. If an implementation
   receives a TLV that has length that is longer than expected, the TLV
   SHOULD be accepted. Any additional data SHOULD be ignored.


12.1. MSDP TLV format:

   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       |           Length              |  Value ....   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type (8 bits)
    Describes the format of the Value field.

   Length (16 bits)
    Length of Type, Length, and Value fields in octets. The
    minimum length required is 3 octets.

   Value (variable length)
    Format is based on the Type value. See below. The length of
    the value field is Length field minus 3.


12.2. Defined TLVs

   The following TLV Types are defined:


   Code                                  Type
   ===========================================================
    1                  IPv4 Source-Active
    2                  IPv4 Source-Active Request
    3                  IPv4 Source-Active Response
    4                  KeepAlive
    5                  Notification

   Each TLV is described below.


12.2.1. IPv4 Source-Active TLV

   The maximum size SA message that can be sent is 1400 octets. If an
   MSDP peer needs to originate a message with information greater than
   1400 octets, it sends successive 1400-octet messages. The 1400 octet
   size does not include the TCP, IP, layer-2 headers.



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   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       1       |           x + y               |  Entry Count  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          RP Address                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Reserved            |  Sprefix Len  | \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  \
   |                         Group Address                         |   ) z
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  /
   |                         Source Address                        | /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type
    IPv4 Source-Active TLV is type 1.

   Length x
    Is the length of the control information in the message. x is
    8 octets (for the first two 32-bit quantities) plus 12 times
    Entry Count octets.

   Length y
    If 0, then there is no data encapsulated. Otherwise an IPv4
    packet follows and y is the length of the total length field
    of the IPv4 header encapsulated. If there are multiple SA TLVs
    in a message, and data is also included, y must be 0 in all SA
    TLVs except the last one. And the last SA TLV must reflect the
    source and destination addresses in the IP header of the
    encapsulated data.

   Entry Count
    Is the count of z entries (note above) which follow the RP
    address field. This is so multiple (S,G)s from the same domain
    can be encoded efficiently for the same RP address.

   RP Address
    The address of the RP in the domain the source has become
    active in.

   Reserved
    The Reserved field MUST be transmitted as zeros and ignored
    by a receiver.

   Sprefix Len
    The route prefix length associated with source address.

   Group Address
    The group address the active source has sent data to.



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   Source Address
    The IP address of the active source.

   Multiple SA TLVs MAY appear in the same message and can be batched
   for efficiency at the expense of data latency. This would typically
   occur on intermediate forwarding of SA messages.


12.2.2. IPv4 Source-Active Request TLV

   The Source-Active Request is used to request SA-state from a caching
   MSDP peer. If an RP in a domain receives a PIM Join message for a
   group, creates (*,G) state and wants to know all active sources for
   group G, and it has been configured to peer with an SA-state caching
   peer, it may send an SA-Request message for the group.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       2       |             8                 |  Reserved     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Group Address                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type
    IPv4 Source-Active Request TLV is type 2.

   Reserved
    The Reserved field MUST be transmitted as zeros and ignored
    by a receiver.

   Group Address
    The group address the MSDP peer is requesting.


12.2.3. IPv4 Source-Active Response TLV

   The Source-Active Response is sent in response to a Source-Active
   Request message. The Source-Active Response message has the same
   format as a Source-Active message but does not allow encapsulation of
   multicast data.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       3       |             x                 |     ....      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type
    IPv4 Source-Active Response TLV is type 3.



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   Length x
    Is the length of the control information in the message. x is 8
    octets (for the first two 32-bit quantities) plus 12 times Entry
    Count octets.


12.2.4. KeepAlive TLV

   A KeepAlive TLV is sent to an MSDP peer if and only if there were no
   MSDP messages sent to the peer after a period of time. This message
   is necessary for the active connect side of the MSDP connection. The
   passive connect side of the connection knows that the connection will
   be reestablished when a TCP SYN packet is sent from the active
   connect side. However, the active connect side will not know when the
   passive connect side goes down. Therefore, the KeepAlive timeout will
   be used to reset the TCP connection.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       4       |             4                 |    Reserved   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The length of the message is 4 octets which encompasses the 1-octet
   Type field and the 2-octet Length field, plus the Reserved field. The
   Reserved field MUST be transmitted as zeros and ignored by a
   receiver.



12.2.5. Notification TLV

   A Notification message is sent when an error condition is detected,
   and has the following form:


   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       5       |          x + 5                |O| Error Code  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Error subcode |          ...                                  |
   +-+-+-+-+-+-+-+-+                                               |
   |                         Data                                  |
   |                          ...                                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type
    The Notification TLV is type 7.




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   Length
    Length is a two octet field with value x + 5, where x is
    the length of the notification data field.

   O-bit
    Open-bit. If reset, the connection will be closed [MASC].

   Error code
    This 7-bit unsigned integer indicates the type of Notification.
    The following Error Codes have been defined:

    Error Code       Symbolic Name                  Reference

        1          Message Header Error             Section 12.3

        2          Finite State Machine Error       Section 12.4

        3          Notification Message Error       Section 12.5

        4          SA-Request Error                 Section 12.6

        5          SA-Response Error                Section 12.7

        6          SA-Message Error                 Section 12.8

   Error subcode:
    This one-octet unsigned integer provides more specific information
    about the reported error.  Each Error Code may have one or more Error
    Subcodes associated with it.  If no appropriate Error Subcode is
    defined, then a zero (Unspecific) value is used for the Error Subcode
    field, and the O-bit must be reset (i.e. the connection will be
    closed).  The used notation in the error description below is: MC =
    Must Close connection = O-bit reset; CC = Can Close connection =
    O-bit might be reset [MASC].

   Message Header Error subcodes:

            0 - Unspecific                        (MC)
            1 - Bad Message Length                (MC)
            2 - Bad Message Type                  (MC)

   Finite State Machine Error subcodes:

            0 - Unspecific                        (MC)
            1 - Unexpected Message Type FSM Error (MC)

   Notification subcodes (the O-bit is always reset):




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            0 - Unspecific                        (CC)

   SA-Request Error subcodes:

            0 - Not caching                       (MC)
            0 - Invalid Group Address prefix      (CC)

   SA-Reponse Error subcodes:

            0 - Didn't send Request               (MC)

   SA-Message Error subcodes

            0 - Invalid Entry Count               (CC)
            1 - Invalid RP Address                (CC)
            2 - Invalid Group Address             (CC)
            3 - Invalid Source Address            (CC)
            4 - Invalid Sprefix Length            (CC)
            5 - Looping SA (Self is RP)           (CC)
            6 - Unknown Encapsulation             (MC)



12.3.  Message Header Error Handling

   All errors detected while processing the Message Header are indicated
   by sending the Notification message with Error Code Message Header
   Error. The Error Subcode describes the specific nature of the error.
   The Data field contains the erroneous Message (including the message
   header).

   If the Length field of the message header is less than 4 or greater
   than 1400, or the length of a Keepalive message is not equal to 4,
   then the Error Subcode is set to Bad Message Length.

   If the Type field of the message header is not recognized, then the
   Error Subcode is set to Bad Message Type.


12.4. Finite State Machine Error Handling

   Any error detected by the MSDP Finite State Machine (e.g., receipt of
   an unexpected event) is indicated by sending the Notification message
   with Error Code Finite State Machine Error.







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12.5. Notification Message Error Handling

   If a node sends a Notification message, and there is an error in that
   message, and the O-bit of that message is not reset, a Notification
   with O-bit reset, Error Code of Notification Error, and subcode
   Unspecific must be sent.  In addition, the Data field must include
   the Notification message that triggered the error.  However, if the
   erroneous Notification message had the O-bit reset, then any error,
   such as an unrecognized Error Code or Error Subcode, should be
   noticed, logged locally, and brought to the attention of the
   administrator of the remote node.


12.6. SA-Request Error Handling

   The SA-Request Error code is used to signal the receipt of a SA
   request at a non-caching MSDP speaker, or at a caching MSDP speaker
   when an invalid group address requested.

   When a non-caching MSDP speaker receives an SA-Request, it returns
   the following notification and closes the connection:

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       7       |           16                  |O|     4       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    0x0        |             Reserved                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Group Address                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Source Address                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   If a caching MSDP speaker receives a request for an invalid group, it
   returns the following notification and closes the connection:

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       7       |           12                  |O|     4       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    0x1        |             Reserved                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Invalid Group Address                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+







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12.7. SA-Response Error Handling

   The SA-Response Error code is used to signal the receipt of a SA
   Response at MSDP speaker which did not issue a SA-Request to the
   peer. It has the following form:

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       7       |              8                |O|     5       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    0x0        |             Reserved                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



12.8. SA-Message Error Handling

   The SA-Message Error code is used to signal the receipt of an SA
   message that contains invalid data.


12.8.1. Invalid Entry Count

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       7       |           12                  |O|     6       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    0x0        |             Reserved                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Invalid Entry Count                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


12.8.2. Invalid RP Address

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       7       |           12                  |O|     6       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    0x1        |             Reserved                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Invalid RP Address                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+








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12.8.3. Invalid Group Address

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       7       |           12                  |O|     6       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    0x2        |             Reserved                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Invalid Group Address                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


12.8.4. Invalid Source Address

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       7       |           12                  |O|     6       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    0x3        |             Reserved                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Invalid Source Address                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


12.9.  Invalid Sprefix Length

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       7       |           12                  |O|     6       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    0x4        |             Reserved                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Invalid Sprefix Length                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


12.10.  Looping SAs (Self is RP in received SA)

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       7       |            8                  |O|     6       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    0x5        |             Reserved                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+







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12.11. Unknown Encapsulation

   This notification is sent on receipt of SA data that is encapsulated
   in an unknown encapsulation type. See section 12.12 for known
   encapsulations.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       7       |            8                  |O|     6       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    0x6        |             Reserved                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



12.12.  SA Data Encapsulation

   This section describes UDP and GRE encapsulation of SA data.
   Encapsulation type is a configuration option.


12.12.1. UDP Data Encapsulation

   MSDP SA-data MAY be encapsulated in UDP. In this case, the UDP
   psuedo-header has the following form:

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Source Port        |         Destination Port        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Length             |             Checksum            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Origin RP Address                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Source Port
     Port to be used by the remote end, and is known via
     configuration.

   Destination Port
    The Destination Port is set to the remote endpoint's Source port,
    and is known via configuration.

   Length
    Length is the length in octets of this user datagram
    including  this header and the data. The minimum value
    of the length is twelve.




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   Checksum
    The checksum is computed according to RFC 768 [RFC768].

   Originating RP Address
    The Originating RP Address is the address of the RP sending
    the encapsulated data.













































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12.12.2. GRE Encapsulation

   MSDP SA-data MAY be encapsulated in GRE using protocol type [MSDP-
   GRE-ProtocolType].

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Delivery Headers .....                                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |C|       Reserved0       | Ver |     [MSDP-GRE-ProtocolType]   |\
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ GRE Header
   |      Checksum (optional)      |          Reserved1            |/
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Originating RP IPv4 Address                  |\
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Payload
   |                    (S,G) Data Packet ....                      /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


12.12.2.1. GRE Encapsulation and PMTU Discovery [RFC1191]

   Existing implementations of GRE, when using IPv4 as the Delivery
   Header, do not implement Path MTU discovery and do not set the Don't
   Fragment bit in the Delivery Header.  This can cause large packets to
   become fragmented within the tunnel and reassembled at the tunnel
   exit (independent of whether the payload packet is using PMTU).  If a
   tunnel entry point were to use Path MTU discovery, however, that
   tunnel entry point would also need to relay ICMP unreachable error
   messages (in particular the "fragmentation needed and DF set" code)
   back to the originator of the packet, which is not required by the
   GRE specification [GRE]. Failure to properly relay Path MTU
   information to an originator can result in the following behavior:
   the originator sets the don't fragment bit, the packet gets dropped
   within the tunnel, but since the originator doesn't receive proper
   feedback, it retransmits with the same PMTU, causing subsequently
   transmitted packets to be dropped.















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13. Security Considerations

   An MSDP implementation MAY use IPsec [RFC1825] or keyed MD5 [RFC1828]
   to secure control messages. When encapsulating SA data in GRE,
   security should be relatively similar to security in a normal IPv4
   network, as routing using GRE follows the same routing that IPv4 uses
   natively. Route filtering will remain unchanged. However packet
   filtering at a firewall requires either that a firewall look inside
   the GRE packet or that the filtering is done on the GRE tunnel
   endpoints. In those environments in which this is considered to be a
   security issue it may be desirable to terminate the tunnel at the
   firewall.


14. Acknowledgments

   The authors would like to thank Dave Thaler, Bill Nickless, John
   Meylor, Liming Wei, Manoj Leelanivas, Mark Turner, John Zwiebel, and
   Cristina Radulescu-Banu for their design feedback and comments. Bill
   Fenner also made many contributions, including clarification of the
   Peer-RPF rules.






























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15. Author's Address:

   Dino Farinacci
   Procket Networks
   3850 No. First St., Ste. C
   San Jose, CA 95134
   Email: dino@procket.com

   Yakov Rehkter
   Cisco Systems, Inc.
   170 Tasman Drive
   San Jose, CA, 95134
   Email: yakov@cisco.com

   Peter Lothberg
   Sprint
   VARESA0104
   12502 Sunrise Valley Drive
   Reston VA, 20196
   Email: roll@sprint.net

   Hank Kilmer
   Email: hank@rem.com

   Jeremy Hall
   UUnet Technologies
   3060 Williams Drive
   Fairfax, VA 22031
   Email: jhall@uu.net

   David Meyer
   Cisco Systems, Inc.
   170 Tasman Drive
   San Jose, CA, 95134
   Email: dmm@cisco.com
















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16. REFERENCES


   [ANYCASTRP] Meyer, et. al, "Anycast RP mechanism using PIM and
               MSDP", draft-ietf-mboned-anycast-rp-04.txt, November,
               1999. Work in Progress.

   [GRE]       Farinacci, D., et al., "Generic Routing Encapsulation
               (GRE)", draft-meyer-gre-update-02.txt, January,
               2000. Work in Progress.

   [MASC]      Estrin, D., et al., "The Multicast Address-Set Claim
               (MASC) Protocol", draft-ietf-malloc-masc-04.txt,
               October, 1999. Work in Progress.

   [RFC768]    Postel, J. "User Datagram Protocol", RFC 768, August,
               1980.

   [RFC1191]   Mogul, J., and S. Deering, "Path MTU Discovery",
               RFC 1191, November 1990.

   [RFC1825]   Atkinson, R., "Security Architecture for the Internet
               Protocol", RFC 1825, August, 1995.

   [RFC1828]   P. Metzger and W. Simpson, "IP Authentication using
               Keyed MD5", RFC 1828, August, 1995.

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

   [RFC2283]   Bates, T., Chandra, R., Katz, D., and Y. Rekhter.,
               "Multiprotocol Extensions for BGP-4", RFC 2283,
               February 1998.

   [RFC2362]   Estrin D., et al., "Protocol Independent Multicast -
               Sparse Mode (PIM-SM): Protocol Specification", RFC
               2362, June 1998.

   [RFC2365]   Meyer, D. "Administratively Scoped IP Multicast", RFC
               2365, July, 1998.











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