GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc3618

Network Working Group B. Fenner, Ed. Request for Comments: 3618 D. Meyer, Ed. Category: Experimental October 2003

             Multicast Source Discovery Protocol (MSDP)

Status of this Memo

 This memo defines an Experimental Protocol for the Internet
 community.  It does not specify an Internet standard of any kind.
 Discussion and suggestions for improvement are requested.
 Distribution of this memo is unlimited.

Copyright Notice

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

Abstract

 The Multicast Source Discovery Protocol (MSDP) describes a mechanism
 to connect multiple IP Version 4 Protocol Independent Multicast
 Sparse-Mode (PIM-SM) 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.

Table of Contents

 1.  Introduction. . . . . . . . . . . . . . . . . . . . . . . . .   2
 2.  Overview. . . . . . . . . . . . . . . . . . . . . . . . . . .   3
 3.  Procedure . . . . . . . . . . . . . . . . . . . . . . . . . .   3
 4.  Caching . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
 5.  Timers. . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.1. SA-Advertisement-Timer . . . . . . . . . . . . . . . . .   5
     5.2. SA-Advertisement-Timer Processing. . . . . . . . . . . .   5
     5.3. SA Cache Timeout (SA-State Timer). . . . . . . . . . . .   5
     5.4. Peer Hold Timer. . . . . . . . . . . . . . . . . . . . .   5
     5.5. KeepAlive Timer. . . . . . . . . . . . . . . . . . . . .   6
     5.6. ConnectRetry Timer . . . . . . . . . . . . . . . . . . .   6
 6.  Intermediate MSDP Peers . . . . . . . . . . . . . . . . . . .   6
 7.  SA Filtering and Policy . . . . . . . . . . . . . . . . . . .   6
 8.  Encapsulated Data Packets . . . . . . . . . . . . . . . . . .   7
 9.  Other Scenarios . . . . . . . . . . . . . . . . . . . . . . .   7
 10. MSDP Peer-RPF Forwarding. . . . . . . . . . . . . . . . . . .   7
     10.1. Definitions . . . . . . . . . . . . . . . . . . . . . .   7
           10.1.1. Multicast RPF Routing Information Base. . . . .   8
           10.1.2. Peer-RPF Route. . . . . . . . . . . . . . . . .   8

Fenner & Meyer Experimental [Page 1] RFC 3618 MSDP October 2003

           10.1.3. Peer-RPF Forwarding Rules . . . . . . . . . . .   8
     10.2. MSDP mesh-group semantics . . . . . . . . . . . . . . .   9
 11. MSDP Connection State Machine . . . . . . . . . . . . . . . .   9
     11.1. Events. . . . . . . . . . . . . . . . . . . . . . . . .  10
     11.2. Actions . . . . . . . . . . . . . . . . . . . . . . . .  10
     11.3. Peer-specific Events. . . . . . . . . . . . . . . . . .  11
     11.4. Peer-independent Events . . . . . . . . . . . . . . . .  11
 12. Packet Formats. . . . . . . . . . . . . . . . . . . . . . . .  12
     12.1. MSDP TLV format . . . . . . . . . . . . . . . . . . . .  12
     12.2. Defined TLVs. . . . . . . . . . . . . . . . . . . . . .  12
           12.2.1. IPv4 Source-Active TLV. . . . . . . . . . . . .  13
           12.2.2. KeepAlive TLV . . . . . . . . . . . . . . . . .  14
 13. MSDP Error Handling . . . . . . . . . . . . . . . . . . . . .  15
 14. SA Data Encapsulation . . . . . . . . . . . . . . . . . . . .  15
 15. Applicability Statement . . . . . . . . . . . . . . . . . . .  15
     15.1. Between PIM Domains . . . . . . . . . . . . . . . . . .  15
     15.2. Between Anycast-RPs . . . . . . . . . . . . . . . . . .  15
 16. Intellectual Property . . . . . . . . . . . . . . . . . . . .  15
 17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  16
 18. Security Considerations . . . . . . . . . . . . . . . . . . .  16
 19. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     19.1. Allocated TLV Range . . . . . . . . . . . . . . . . . .  17
     19.2. Experimental TLV Range. . . . . . . . . . . . . . . . .  17
 20. References. . . . . . . . . . . . . . . . . . . . . . . . . .  17
     20.1. Normative References. . . . . . . . . . . . . . . . . .  17
     20.2. Informative References. . . . . . . . . . . . . . . . .  18
 21. Editors' Addresses. . . . . . . . . . . . . . . . . . . . . .  18
 22. Full Copyright Statement. . . . . . . . . . . . . . . . . . .  19

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.

Fenner & Meyer Experimental [Page 2] RFC 3618 MSDP October 2003

 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].

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 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.

Fenner & Meyer Experimental [Page 3] RFC 3618 MSDP October 2003

 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.

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.

Fenner & Meyer Experimental [Page 4] RFC 3618 MSDP October 2003

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).

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

Fenner & Meyer Experimental [Page 5] RFC 3618 MSDP October 2003

 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.

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.

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

Fenner & Meyer Experimental [Page 6] RFC 3618 MSDP October 2003

 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 [RFC2858].  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.

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:

Fenner & Meyer Experimental [Page 7] RFC 3618 MSDP October 2003

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
 [RFC2858].

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.
            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
 (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 [RFC2328] 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.

Fenner & Meyer Experimental [Page 8] RFC 3618 MSDP October 2003

 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.
 (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 & Meyer Experimental [Page 9] RFC 3618 MSDP October 2003

  1. ————–>+———-+

/ | 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

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)

Fenner & Meyer Experimental [Page 10] RFC 3618 MSDP October 2003

 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:
    1. > Send KeepAlive TLV
    2. > Set KeepAlive timer to [KeepAlive-Period]
  • ) KeepAlive TLV received:
    1. > Set Hold Timer to [HoldTime-Period]
  • ) Source-Active TLV received:
    1. > Set Hold Timer to [HoldTime-Period]
    2. > Run Peer-RPF Forwarding algorithm
    3. > Set KeepAlive timer to [KeepAlive-Period] for those peers

the Source-Active TLV is forwarded to

  1. > Send information to PIM-SM
  2. > Store information in cache

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:
    1. > Start periodic transmission of Source-Active TLV(s)
    2. > 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):

  1. > Send Source-Active TLV
  2. > Set KeepAlive timer to [KeepAlive-Period]
  • ) SG-State-Timer expired (one timer per cache entry):

Fenner & Meyer Experimental [Page 11] RFC 3618 MSDP October 2003

  1. > 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.  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)

Fenner & Meyer Experimental [Page 12] RFC 3618 MSDP October 2003

 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.

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

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ /

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.

Fenner & Meyer Experimental [Page 13] RFC 3618 MSDP October 2003

 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
  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.

Fenner & Meyer Experimental [Page 14] RFC 3618 MSDP October 2003

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.

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
 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

Fenner & Meyer Experimental [Page 15] RFC 3618 MSDP October 2003

 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 document.

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.
 If follow-on work is done in this area, a more robust integrity
 mechanism, such as HMAC-SHA1 [RFC2104, RFC2202] ought to be employed.

Fenner & Meyer Experimental [Page 16] RFC 3618 MSDP October 2003

19. IANA Considerations

 This document creates a new namespace called "MSDP TLV Values" that
 the IANA will manage.  The initial 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.

20. References

20.1. Normative References

 [RFC1142]       Oran, D., Ed., "OSI IS-IS Intra-domain Routing
                 Protocol", RFC 1142, February 1990.
 [RFC2119]       Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2328]       Moy, J., "OSPF Version 2", STD 54, RFC 2328, April
                 1998.
 [RFC2858]       Bates, T., Rekhter, Y., Chandra, R. and D. Katz,
                 "Multiprotocol Extensions for BGP-4", RFC 2858, June
                 2000.
 [RFC2362]       Estrin, D., Farinacci, D., Helmy, A., Thaler, D.,
                 Deering, S., Handley, M., Jacobson, V., Lin, C.,
                 Sharma, P. and L. Wei, "Protocol Independent
                 Multicast - Sparse Mode (PIM-SM):  Protocol
                 Specification", RFC 2362, June 1998.
 [RFC2365]       Meyer, D., "Administratively Scoped IP Multicast",
                 BCP 23, RFC 2365, July 1998.
 [RFC2385]       Heffernan, A., "Protection of BGP Sessions via the
                 TCP MD5 Signature Option", RFC 2385, August 1998.

Fenner & Meyer Experimental [Page 17] RFC 3618 MSDP October 2003

 [RFC2434]       Narten, T. and H. Alvestrand, "Guidelines for Writing
                 an IANA Considerations Section in RFCs", BCP 26, RFC
                 2434, October 1998.
 [RFC3446]       Kim, D., Meyer, D., Kilmer, H. and D. Farinacci,
                 "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., Meylor, J. and D. Meyer, "Multicast
                 Source Discovery Protocol (MSDP) Deployment
                 Scenarios", Work in Progress, July 2003.
 [RFC2104]       Krawczyk, H., Bellare, M. and R.  Canetti, "HMAC:
                 Keyed-Hashing for Message Authentication", RFC 2104,
                 February 1997.
 [RFC2202]       Cheng, P. and R. Glenn, "Test Cases for HMAC-MD5 and
                 HMAC-SHA-1", RFC 2202, September 1997.

21. Editors' Addresses

 Bill Fenner
 AT&T Labs -- Research
 75 Willow Road
 Menlo Park, CA 94025
 EMail: fenner@research.att.com
 David Meyer
 EMail: dmm@1-4-5.net

Fenner & Meyer Experimental [Page 18] RFC 3618 MSDP October 2003

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 assignees.
 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.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Fenner & Meyer Experimental [Page 19]

/data/webs/external/dokuwiki/data/pages/rfc/rfc3618.txt · Last modified: 2003/10/17 18:20 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki