[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 RFC 3618

INTERNET-DRAFT                          Bill Fenner (Editor)
draft-ietf-msdp-spec-20.txt             David Meyer (Editor)
Category                                        Experimental
Expires: November 2003                              May 2003


               Multicast Source Discovery Protocol (MSDP)
                     <draft-ietf-msdp-spec-20.txt>



Status of this Document

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   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.


   This document is a product of an individual.  Comments are solicited
   and should be addressed to the author(s).

Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.












Fenner and Meyer                                                [Page 1]

INTERNET-DRAFT           Expires: November 2003                 May 2003


                                Abstract


   The Multicast Source Discovery Protocol, MSDP, describes a mechanism
   to connect multiple IP Version 4 Protocol Independent Multicast
   Sparse-Mode (PIM-SM) [RFC2362] domains together. Each PIM-SM domain
   uses its own independent Rendezvous Point (RP) and does not have to
   depend on RPs in other domains. This document reflects existing MSDP
   implementations.










































Fenner and Meyer                                                [Page 2]

INTERNET-DRAFT           Expires: November 2003                 May 2003


                           Table of Contents


   1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . .   5
   2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3. Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4. Caching. . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   5. Timers . . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
    5.1. SA-Advertisement-Timer. . . . . . . . . . . . . . . . . . .   7
    5.2. SA-Advertisement-Timer Processing . . . . . . . . . . . . .   8
    5.3. SA Cache Timeout (SA-State Timer) . . . . . . . . . . . . .   8
    5.4. Peer Hold Timer . . . . . . . . . . . . . . . . . . . . . .   8
    5.5. KeepAlive Timer . . . . . . . . . . . . . . . . . . . . . .   9
    5.6. ConnectRetry Timer. . . . . . . . . . . . . . . . . . . . .   9
   6. Intermediate MSDP Peers. . . . . . . . . . . . . . . . . . . .   9
   7. SA Filtering and Policy. . . . . . . . . . . . . . . . . . . .  10
   8. Encapsulated Data Packets. . . . . . . . . . . . . . . . . . .  10
   9. Other Scenarios. . . . . . . . . . . . . . . . . . . . . . . .  10
   10. MSDP Peer-RPF Forwarding. . . . . . . . . . . . . . . . . . .  11
    10.1. Definitions. . . . . . . . . . . . . . . . . . . . . . . .  11
     10.1.1. Multicast RPF Routing Information Base. . . . . . . . .  11
     10.1.2. Peer-RPF Route. . . . . . . . . . . . . . . . . . . . .  11
     10.1.3. Peer-RPF Forwarding Rules . . . . . . . . . . . . . . .  11
    10.2. MSDP mesh-group semantics. . . . . . . . . . . . . . . . .  13
   11. MSDP Connection State Machine . . . . . . . . . . . . . . . .  14
    11.1. Events . . . . . . . . . . . . . . . . . . . . . . . . . .  15
    11.2. Actions. . . . . . . . . . . . . . . . . . . . . . . . . .  16
    11.3. Peer-specific Events . . . . . . . . . . . . . . . . . . .  16
    11.4. Peer-independent Events. . . . . . . . . . . . . . . . . .  17
   12. Packet Formats. . . . . . . . . . . . . . . . . . . . . . . .  17
    12.1. MSDP TLV format. . . . . . . . . . . . . . . . . . . . . .  17
    12.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . .  18
     12.2.1. IPv4 Source-Active TLV. . . . . . . . . . . . . . . . .  18
     12.2.2. KeepAlive TLV . . . . . . . . . . . . . . . . . . . . .  20
   13. MSDP Error Handling . . . . . . . . . . . . . . . . . . . . .  20
   14. SA Data Encapsulation . . . . . . . . . . . . . . . . . . . .  21
   15. Applicability Statement . . . . . . . . . . . . . . . . . . .  21
    15.1. Between PIM Domains. . . . . . . . . . . . . . . . . . . .  21
    15.2. Between Anycast-RPs. . . . . . . . . . . . . . . . . . . .  21
   16. Intellectual Property . . . . . . . . . . . . . . . . . . . .  21
   17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  22
   18. Security Considerations . . . . . . . . . . . . . . . . . . .  23
   19. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  23
    19.1. IANA Allocated TLV Range . . . . . . . . . . . . . . . . .  23
    19.2. Experimental TLV Range . . . . . . . . . . . . . . . . . .  23
   20. References. . . . . . . . . . . . . . . . . . . . . . . . . .  24
    20.1. Normative References . . . . . . . . . . . . . . . . . . .  24
    20.2. Informative References . . . . . . . . . . . . . . . . . .  24



Fenner and Meyer                                                [Page 3]

INTERNET-DRAFT           Expires: November 2003                 May 2003


   21. Editor's Addresses. . . . . . . . . . . . . . . . . . . . . .  25
   22. Full Copyright Statement. . . . . . . . . . . . . . . . . . .  25

















































Fenner and Meyer                                                [Page 4]

INTERNET-DRAFT           Expires: November 2003                 May 2003


1.  Introduction


   The Multicast Source Discovery Protocol, MSDP, describes a mechanism
   to connect multiple PIM Sparse-Mode (PIM-SM) [RFC2362] 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 a domain's 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.


   Note that MSDP may be used with protocols other than PIM-SM, but such
   usage is not specified in this memo.



2.  Overview


   MSDP-speaking routers in a PIM-SM domain have a MSDP peering
   relationship with MSDP peers in another domain. The peering
   relationship is made up of a TCP connection in which control
   information is exchanged. Each domain has one or more connections to
   this virtual topology.

   The purpose of this topology is to allow domains to 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.



3.  Procedure


   When an RP in a PIM-SM domain first learns of a new sender, e.g. via
   PIM register messages, it constructs a "Source-Active" (SA) message
   and sends it to its MSDP peers. All RPs, which intend to originate or



Fenner and Meyer                                    Section 3.  [Page 5]

INTERNET-DRAFT           Expires: November 2003                 May 2003


   receive SA messages, must establish MSDP peering with other RPs,
   either directly or via an intermediate MSDP peer. 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.

   Note that an RP that isn't a DR on a shared network SHOULD NOT
   originate SA's for directly connected sources on that shared network;
   it should only originate in response to receiving Register messages
   from the DR.

   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 Multicast RPF
   Routing Information Base (MRIB) is examined to determine which peer
   towards the originating RP of the SA message is selected. Such a peer
   is called an "RPF peer". See section 13 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 (except the one from which it received
   the SA message).

   When an MSDP peer which is also an RP for its own domain receives a
   new SA message, it determines if there are any group members within
   the domain interested in any group described by an (Source, Group),
   or (S,G) entry within the SA message.  That is, the RP checks for a
   (*,G) entry with a non-empty outgoing interface list; this implies
   that some system in 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. This
   sets up a branch of the source-tree to this domain. Subsequent data
   packets arrive at the RP via this tree branch, and 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, the RP SHOULD trigger a (S,G) join event
   for each active (S,G) for that group in its SA 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.




Fenner and Meyer                                    Section 3.  [Page 6]

INTERNET-DRAFT           Expires: November 2003                 May 2003


4.  Caching


   A MSDP speaker MUST cache SA messages. Caching allows pacing of MSDP
   messages as well as reducing join latency for new receivers of a
   group G at an originating RP which has existing MSDP (S,G) state. In
   addition, caching greatly aids in diagnosis and debugging of various
   problems.

   An MSDP speaker must provide a mechanism to reduce the forwarding of
   new SA's. The SA-cache is used to reduce storms and performs this by
   not forwarding SA's unless they are in the cache or are new SA
   packets that the MSDP speaker will cache for the first time. The SA-
   cache also reduces storms by advertising from the cache at a period
   of no more than twice per SA-Advertisement-Timer interval and not
   less than 1 time per SA Advertisement period.




5.  Timers


   The main timers for MSDP are: SA-Advertisement-Timer, SA Cache Entry
   timer, Peer Hold Timer, KeepAlive timer, and ConnectRetry timer. Each
   is considered below.



5.1.  SA-Advertisement-Timer


   RPs which originate SA messages do so 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-
   Period] MUST be 60 seconds. An RP MUST not send more than one
   periodic SA message for a given (S,G) within an SA Advertisement
   interval. Originating periodic SA messages is required to keep
   announcements alive in caches. Finally, an originating RP SHOULD
   trigger the transmission of an SA message as soon as it receives data
   from an internal source for the first time. This initial SA message
   may be in addition to the periodic sa-message forwarded in that first
   60 seconds for that (S,G).








Fenner and Meyer                                  Section 5.1.  [Page 7]

INTERNET-DRAFT           Expires: November 2003                 May 2003


5.2.  SA-Advertisement-Timer Processing


   An RP MUST spread the generation of periodic SA messages (i.e.
   messages advertising the active sources for which it is the RP) over
   its reporting interval (i.e. SA-Advertisement-Period). An RP starts
   the SA-Advertisement-Timer when the MSDP process is configured. When
   the timer expires, an RP resets the timer to [SA-Advertisement-
   Period] seconds, and begins the advertisement of its active sources.
   Active sources are advertised in the following manner: An RP packs
   its active sources into an SA message until the largest MSDP packet
   that can be sent is built or there are no more sources, and then
   sends the message. This process is repeated periodically within the
   SA-Advertisement-Period in such a way that all of the RP's sources
   are advertised. Note that since MSDP is a periodic protocol, an
   implementation SHOULD send all cached SA messages when a connection
   is established. Finally, the timer is deleted when the MSDP process
   is de-configured.



5.3.  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 started when an (S,G)-SA message is initially
   received by an MSDP peer. The timer is reset to [SG-State-Period] if
   another (S,G)-SA message is received before the (S,G)-SA-State Timer
   expires. [SG-State-Period] MUST NOT be less than [SA-Advertisement-
   Period] + [SA-Hold-Down-Period].



5.4.  Peer Hold Timer


   The Hold Timer is initialized to [HoldTime-Period] when the peer's
   transport connection is established, and is reset to [HoldTime-
   Period]  when any MSDP message is received.  Finally, the timer is
   deleted when the peer's transport connection is closed. [HoldTime-
   Period] MUST be at least three seconds. The recommended value for
   [HoldTime-Period] is 75 seconds.









Fenner and Meyer                                  Section 5.4.  [Page 8]

INTERNET-DRAFT           Expires: November 2003                 May 2003


5.5.  KeepAlive Timer


   Once an MSDP transport connection is established, each side of the
   connection sends a KeepAlive message and sets a KeepAlive timer. If
   the KeepAlive timer expires, the local system sends a KeepAlive
   message and restarts its KeepAlive timer.

   The KeepAlive timer is set to [KeepAlive-Period] when the peer comes
   up. The timer is reset to [KeepAlive-Period] each time an MSDP
   message is sent to the peer, and reset when the timer expires.

   Finally, the KeepAlive timer is deleted when the peer's transport
   connection is closed.

   [KeepAlive-Period] MUST be less than [HoldTime-Period], and MUST be
   at least one second. The recommended value for [KeepAlive-Period] is
   60 seconds.




5.6.  ConnectRetry Timer


   The ConnectRetry timer is used by the MSDP peer with the lower IP
   address to transition from INACTIVE to CONNECTING states. There is
   one timer per peer, and the [ConnectRetry-Period] SHOULD be set to 30
   seconds.  The timer is initialized to [ConnectRetry-Period] when an
   MSDP speaker attempts to actively open a TCP connection to its peer
   (see section 15, event E2, action A2 ). When the timer expires, the
   peer retries the connection and the timer is reset to [ConnectRetry-
   Period]. It is deleted if either the connection transitions into
   ESTABLISHED state or the peer is de-configured.




6.  Intermediate MSDP Peers


   Intermediate MSDP speakers do not originate periodic SA messages on
   behalf of sources in other domains. In general, an RP MUST only
   originate an SA for a source which would register to it, and ONLY RPs
   may originate SA messages. Intermediate MSDP speakers MAY forward SA
   messages received from other domains.





Fenner and Meyer                                    Section 6.  [Page 9]

INTERNET-DRAFT           Expires: November 2003                 May 2003


7.  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. 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 may cause undesired lack of connectivity). In general, policy
   should be expressed using MBGP [RFC2283]. This will cause MSDP
   messages to 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.




8.  Encapsulated Data Packets


   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 packets 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 the same group ranges such as with Anycast RP's. As
   long as all RPs have a interconnected MSDP topology, each can learn
   about active sources as well as RPs in other domains.



Fenner and Meyer                                   Section 9.  [Page 10]

INTERNET-DRAFT           Expires: November 2003                 May 2003


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, which generally compares the
   packet's source address against the interface upon which the packet
   was received, the Peer-RPF check compares the RP address carried in
   the SA message against the MSDP peer from which the message was
   received.



10.1.  Definitions


   The following definitions are used in the description of the Peer-RPF
   Forwarding Rules:




10.1.1.  Multicast RPF Routing Information Base


   The Multicast RPF Routing Information Base (MRIB) is the multicast
   topology table. It is typically derived from the unicast routing
   table or from other routing protocols such as multi-protocol BGP
   [RFC2283].



10.1.2.  Peer-RPF Route


   The Peer-RPF route is the route that the MRIB chooses for a given
   address. The Peer-RPF route for a SA's originating RP is used to
   select the peer from which the SA is accepted.



10.1.3.  Peer-RPF Forwarding Rules



   An SA message originated by R and received by X from N is accepted if
   N is the peer-RPF neighbor for X, and is discarded otherwise.




Fenner and Meyer                              Section 10.1.3.  [Page 11]

INTERNET-DRAFT           Expires: November 2003                 May 2003


                MPP(R,N)                 MP(N,X)
        R ---------....-------> N ------------------> X
                SA(S,G,R)                SA(S,G,R)


   MP(N,X) is an MSDP peering between N and X.  MPP(R,N) is an MSDP
   peering path (zero or more MSDP peers) between R and N, e.g. MPP(R,N)
   = MP(R, A) + MP(A, B) + MP(B, N). SA(S,G,R) is an SA message for
   source S on group G originated by an RP R.

   The peer-RPF neighbor N is chosen deterministically, using the first
   of the following rules that matches. In particular, N is the RPF
   neighbor of X with respect to R if






































Fenner and Meyer                              Section 10.1.3.  [Page 12]

INTERNET-DRAFT           Expires: November 2003                 May 2003


    (i).    N == R (X has an MSDP peering with R).

    (ii).   N is the eBGP NEXT_HOP of the Peer-RPF route for R.

    (iii).  The Peer-RPF route for R is learned through a
            distance-vector or path-vector routing protocol
            (e.g. BGP, RIP, DVMRP) and N is the neighbor that
            advertised the Peer-RPF route for R (e.g. N is the iBGP
            advertiser of the route for R), or N is the IGP next hop
            for R if the route for R is learned via a link-state
            protocol (e.g. OSPF [RFC2178] or IS-IS [RFC1142]).

    (iv).   N resides in the closest AS in the best path towards
            R. If multiple MSDP peers reside in the closest AS, the
            peer with the highest IP address is the rpf-peer.

    (v).    N is configured as the static RPF-peer for R.


   MSDP peers, which are NOT in state ESTABLISHED (i.e., down peers),
   are not eligible for peer RPF consideration.




10.2.  MSDP mesh-group semantics


   An MSDP mesh-group is a operational mechanism for reducing SA
   flooding, typically in an intra-domain setting. In particular, when
   some subset of a domain's MSDP speakers are fully meshed, they can be
   configured into a mesh-group.

   Note that mesh-groups assume that a member doesn't have to forward an
   SA to other members of the mesh-group because the originator will
   forward to all members. To be able for the originator to forward to
   all members (and to have each member also be a potential originator),
   the mesh-group must be a full mesh of MSDP peering among all members.

   The semantics of the mesh-group are as follows:


    (i).    If a member R of a mesh-group M receives a SA message
            from an MSDP peer that is also a member of mesh-group M,
            R accepts the SA message and forwards it to all of its
            peers that are not part of mesh-group M. R MUST NOT
            forward the SA message to other members of mesh-group M.




Fenner and Meyer                                Section 10.2.  [Page 13]

INTERNET-DRAFT           Expires: November 2003                 May 2003


    (ii).   If a member R of a mesh-group M receives an SA message
            from an MSDP peer that is not a member of mesh-group M,
            and the SA message passes the peer-RPF check, then R
            forwards the SA message to all members of mesh-group M
            and to any other msdp peers.




11.  MSDP Connection State Machine


   MSDP uses TCP as its transport protocol. In a peering relationship,
   one MSDP peer listens for new TCP connections on the well-known port
   639. The other side makes an active connect to this port. The peer
   with the higher IP address will 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 the startup time depends
   completely upon the active side and its connect retry timer; the
   passive side cannot cause the connection to be established.

   An MSDP peer starts in the DISABLED state. MSDP peers establish
   peering sessions according to the following state machine:



























Fenner and Meyer                                  Section 11.  [Page 14]

INTERNET-DRAFT           Expires: November 2003                 May 2003


                     --------------->+----------+
                    /                | DISABLED |<----------
                   |          ------>+----------+           \
                   |         /            |E1->A1            |
                   |        |             |                  |
                   |        |             V                  |E7->A7
                   |        |        +----------+ E3->A3 +--------+
                   |        |        | INACTIVE |------->| LISTEN |
                   |        |        +----------+        +--------+
                   |        |     E2->A2|    ^               |E5->A5
                   |        |           |    |               |
                   |        |E7->A6     V    |E6             |
                   |         \      +------------+           |
                   |          ------| CONNECTING |           |
                   |                +------------+           |
          E7->A8   |                      |E4->A4            |
          E8->A8   |                      |                  |
          E9->A8   |                      V                  |
                   \               +-------------+          /
                     --------------| ESTABLISHED |<---------
                                   +-------------+
                                      |       ^
                                      |       |
                              E10->A9 \______/




11.1.  Events


    E1) Enable MSDP peering with P
    E2) Own IP address < P's IP address
    E3) Own IP address > P's IP address
    E4) TCP established (active side)
    E5) TCP established (passive side)
    E6) ConnectRetry timer expired
    E7) Disable MSDP peering with P (e.g. when one's own address is
        changed)
    E8) Hold Timer expired
    E9) MSDP TLV format error detected
    E10) Any other error detected









Fenner and Meyer                                Section 11.1.  [Page 15]

INTERNET-DRAFT           Expires: November 2003                 May 2003


11.2.  Actions



    A1) Allocate resources for peering with P Compare one's own and
        peer's IP addresses
    A2) TCP active OPEN Set ConnectRetry timer to
        [ConnectRetry-Period]
    A3) TCP passive OPEN (listen)
    A4) Delete ConnectRetry timer Send KeepAlive TLV
        Set KeepAlive timer to [KeepAlive-Period]
        Set Hold Timer to [HoldTime-Period]
    A5) Send KeepAlive TLV
        Set KeepAlive timer to [KeepAlive-Period]
        Set Hold Timer to [HoldTime-Period]
    A6) Abort TCP active OPEN attempt
        Release resources allocated for peering with P
    A7) Abort TCP passive OPEN attempt
        Release resources allocated for peering with P
    A8) Close the TCP connection
        Release resources allocated for peering with P
    A9) Drop the packet




11.3.  Peer-specific Events


   The following peer-specific events can occur in the ESTABLISHED
   state, they do not cause a state transition. Appropriate actions are
   listed for each event.


    *) KeepAlive timer expired:
       -> Send KeepAlive TLV
       -> Set KeepAlive timer to [KeepAlive-Period]
    *) KeepAlive TLV received:
       -> Set Hold Timer to [HoldTime-Period]
    *) Source-Active TLV received:
       -> Set Hold Timer to [HoldTime-Period]
       -> Run Peer-RPF Forwarding algorithm
       -> Set KeepAlive timer to [KeepAlive-Period] for those peers
          the Source-Active TLV is forwarded to
       -> Send information to PIM-SM
       -> Store information in cache





Fenner and Meyer                                Section 11.3.  [Page 16]

INTERNET-DRAFT           Expires: November 2003                 May 2003


11.4.  Peer-independent Events


   There are also a number of events that affect more than one peering
   session, but still require actions to be performed on a per-peer
   basis.

    *) SA-Advertisement-Timer expired:
       -> Start periodic transmission of Source-Active TLV(s)
        -> Set KeepAlive timer to [KeepAlive-Period] each time a
           Source-Active TLV is sent
    *) MSDP learns of a new active internal source (e.g. PIM-SM
       register received for a new source):
       -> Send Source-Active TLV
       -> Set KeepAlive timer to [KeepAlive-Period]
    *) SG-State-Timer expired (one timer per cache entry):
       -> Implementation specific, typically mark the cache entry
          for deletion




12.  Packet Formats


   MSDP messages are encoded in TLV format. If an implementation
   receives a TLV whose length exceeds the maximum TLV length specified
   below, the TLV SHOULD be accepted.  Any additional data, including
   possible next TLV's in the same message, SHOULD be ignored, and the
   MSDP session should not be reset.



12.1.  MSDP TLV format



       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    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.



Fenner and Meyer                                Section 12.1.  [Page 17]

INTERNET-DRAFT           Expires: November 2003                 May 2003


       Minimum length required is 4 octets, except for
       Keepalive messages.  The maximum TLV length is 9192.

      Value (variable length)
       Format is based on the Type value. See below. The length of
       the value field is Length field minus 3. All reserved fields
       in the Value field MUST be transmitted as zeros and ignored on
       receipt.



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                  Reserved (Previously: Notification)


   Each TLV is described below.

   In addition, the following TLV Types are assigned but not described
   in this memo:

    Code                        Type
    ====================================================
      6                  MSDP traceroute in progress
      7                  MSDP traceroute reply




12.2.1.  IPv4 Source-Active TLV



   The maximum size SA message that can be sent is 9192 octets. The 9192
   octet size does not include the TCP, IP, layer-2 headers.







Fenner and Meyer                              Section 12.2.1.  [Page 18]

INTERNET-DRAFT           Expires: November 2003                 May 2003


       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       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 value of the total length field
       in the header of the encapsulated IP packet. If there are
       multiple (S,G) entries in an SA message, only the last entry
       may have encapsulated data and it must reflect the source and
       destination addresses in the header of the encapsulated IP
       packet.

      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.  An
       SA message containing encapsulated data typically has an
       entry count of 1 (i.e. only contains a single entry, for
       the (S,G) representing the encapsulated packet).

      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 MUST be
       ignored by a receiver.

      Sprefix Len



Fenner and Meyer                              Section 12.2.1.  [Page 19]

INTERNET-DRAFT           Expires: November 2003                 May 2003


       The route prefix length associated with source address.
       This field MUST be transmitted as 32 (/32).

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

      Source Address
       The IP address of the active source.

      Multiple (S,G) entries MAY appear in the same SA 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.  KeepAlive TLV


   A KeepAlive TLV is sent to an MSDP peer if and only if there were no
   MSDP messages sent to the peer within [KeepAlive-Period] seconds.
   This message is necessary to keep the MSDP connection alive.


       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       4       |             3                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The length of the message is 3 octets which encompasses the one octet
   Type field and the two octet Length field.




13.  MSDP Error Handling


   If an MSDP message is received with a TLV format error, the session
   SHOULD be reset with that peer. MSDP messages with other errors, such
   as unrecognized type code, received from MSDP peers, SHOULD be
   silently discarded and the session SHOULD not be reset.







Fenner and Meyer                                  Section 13.  [Page 20]

INTERNET-DRAFT           Expires: November 2003                 May 2003


14.  SA Data Encapsulation


   As discussed earlier, TCP encapsulation of data in SA messages MAY be
   supported for backwards compatibility with legacy MSDP peers.


15.  Applicability Statement


   MSDP is used primarily in two deployment scenarios:



15.1.  Between PIM Domains


   MSDP can be used between PIM domains to convey information about
   active sources available in other domains.  MSDP peering used in such
   cases is generally one to one peering, and utilizes the deterministic
   peer-RPF rules described in this spec (i.e., does not use mesh-
   groups). Peerings can be aggregated on a single MSDP peer, typically
   from one to hundreds of peerings, similar in scale, although not
   necessarily consistent, with BGP peerings.



15.2.  Between Anycast-RPs


   MSDP is also used between Anycast-RPs [RFC3446] within a PIM domain
   to synchronize information about the active sources being served by
   each Anycast-RP peer (by virtue of IGP reachability). MSDP peering
   used in this scenario is typically based on MSDP mesh groups, where
   anywhere from two to tens of peers can comprise a given mesh group,
   although more than ten is not typical. One or more of these mesh-
   group peers may then also have additional one-to-one peering with
   msdp peers outside that PIM domain as described in scenario A, for
   discovery of external sources. MSDP for anycast-RP without external
   MSDP peering is a valid deployment option and common.


16.  Intellectual Property


   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in



Fenner and Meyer                                  Section 16.  [Page 21]

INTERNET-DRAFT           Expires: November 2003                 May 2003


   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.  Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
   obtain a general license or permission for the use of such
   proprietary rights by implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive
   Director.



17.  Acknowledgments


   The editors would like to thank the original authors, Dino Farinacci,
   Yakov Rehkter, Peter Lothberg, Hank Kilmer, and Jermey Hall for their
   original contribution to the MSDP specification. In addition, Bill
   Nickless, John Meylor, Liming Wei, Manoj Leelanivas, Mark Turner,
   John Zwiebel, Cristina Radulescu-Banu, Brian Edwards, Selina
   Priestley, IJsbrand Wijnands, Tom Pusateri, Kristofer Warell, Henning
   Eriksson, Thomas Eriksson, Dave Thaler, and Ravi Shekhar provided
   useful and productive design feedback and comments. Toerless Eckert,
   Leonard Giuliano, Mike McBride, David Meyer, John Meylor, Pekka
   Savola, Ishan Wu, and Swapna Yelamanchi contributed to the final
   version of the draft.


















Fenner and Meyer                                  Section 17.  [Page 22]

INTERNET-DRAFT           Expires: November 2003                 May 2003


18.  Security Considerations


   An MSDP implementation MUST implement Keyed MD5 [RFC2385] to secure
   control messages, and MUST be capable of interoperating with peers
   that do not support it. However, if one side of the connection is
   configured with Keyed MD5 and the other side is not, the connection
   SHOULD NOT be established.

   In addition, to mitigate state explosion during denial of service and
   other attacks, SA filters and limits SHOULD be used with MSDP to
   limit the sources and  groups that will be passed between RPs
   [DEPLOY]. These filtering and limiting functions may include, for
   example, access lists of source or group addresses which should not
   be propagated to other domains using MSDP, the absolute highest
   acceptable number of SA-state entries or a rate-limit of for the
   creation of new SA-state entries after the connection has been
   established.



19.  IANA Considerations


   This document creates a new namespace called "MSDP TLV Values" that
   the IANA should manage. The intial seven MSDP TLV values are
   specified in Section 12.2. The following two sections describe the
   rules for allocating new MSDP TLV values.



19.1.  IANA Allocated TLV Range


   MSDP TLV values in the range [8,200] (inclusive) are to be allocated
   using an IESG Approval or Standards Action process [RFC2434].



19.2.  Experimental TLV Range


   TLV values in the range [201,255] (inclusive) are allocated for
   experimental use.







Fenner and Meyer                                Section 19.2.  [Page 23]

INTERNET-DRAFT           Expires: November 2003                 May 2003


20.  References

20.1.  Normative References


   [RFC1142]       Oran, D. "OSI IS-IS Intra-domain Routing
                   Protocol", RFC 1142, February 1990.

   [RFC2178]       Moy, J., "OSPF Version 2", RFC 2178, April, 1998.

   [RFC2283]       Bates, T., R. Chandra, and D. Katz, 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.

   [RFC2385]       Heffernan. A, "Protection of BGP Sessions via the
                   TCP MD5 Signature Option", August, 1998.

   [RFC2434]       Narten, T., and H. Alvestrand, "Guidelines for
                   Writing an IANA Considerations Section in
                   RFCs", RFC2434/BCP0026, October, 1998.

   [RFC3446]       Kim, D., et al., "Anycast Rendezvous Point (RP)
                   Mechanism using Protocol Independent Multicast
                   (PIM) and Multicast Source Discovery Protocol
                   (MSDP)", RFC 3446, January, 2003.



20.2.  Informative References


   [DEPLOY]        McBride, M., J. Meylor, and D. Meyer, "Multicast
                   Source Discovery Protocol (MSDP) Deployment
                   Scenarios", draft-ietf-mboned-msdp-deploy-02.txt,
                   Work in Progress.

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





Fenner and Meyer                                Section 20.2.  [Page 24]

INTERNET-DRAFT           Expires: November 2003                 May 2003


21.  Editor's Addresses


   Bill Fenner
   AT&T Labs -- Research
   75 Willow Road
   Menlo Park, CA 94025
   Email: fenner@research.att.com

   David Meyer
   Email: dmm@maoz.com



22.  Full Copyright Statement

   Copyright (C) The Internet Society (2003). All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.










Fenner and Meyer                                  Section 22.  [Page 25]


Html markup produced by rfcmarkup 1.107, available from http://tools.ietf.org/tools/rfcmarkup/