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   Internet Draft                                           B. Nickless 
   Document: draft-ietf-mboned-ipv4-mcast-bcp-         Argonne National 
   01.txt                                                    Laboratory 
   Expires: December 2003                                     June 2003 
 
 
                   IPv4 Multicast Best Current Practice 
 
 
Status of this Memo 
 
   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. 
    
    
Abstract 
    
   This document describes best current practices for IPv4 multicast 
   deployment, both within and between PIM Domains and Autonomous 
   Systems. 
 
 
Table of Contents 
    
   Status of this Memo................................................1 
   Abstract...........................................................1 
   Conventions used in this document..................................2 
   Scope..............................................................2 
   Introduction and Terminology.......................................2 
   Packet Forwarding..................................................3 
   Any Source Multicast...............................................3 
   Source Specific Multicast..........................................4 
   Multiprotocol BGP..................................................4 
   PIM Sparse Mode....................................................5 
   Internet Group Management Protocol.................................6 
   Multicast Source Discovery Protocol................................6 
     
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   Model IPv4 Multicast-Capable BGPv4 Configuration...................7 
   Model IPv4 Multicast Inter-domain PIM Sparse Mode Configuration....7 
   Model PIM Sparse Mode Rendezvous Point Location....................8 
   Model MSDP Configuration Between Autonomous Systems................9 
   Advanced Configurations............................................9 
   Security Considerations...........................................10 
   Acknowledgements..................................................10 
   Normative References..............................................10 
   Non-Normative References..........................................11 
   Author's Address..................................................12 
 
 
Overview 
    
   Current best practice for IPv4 multicast service provision uses four 
   different protocols: Internet Group Management Protcol, Protocol 
   Independent Multicast (Sparse Mode), Border Gateway Protocol with 
   multiprotocol extensions, and the Multicast Source Discovery 
   Protocol.  This document outlines how these protocols work together 
   to provide end-to-end IPv4 multicast service.  In addition, this 
   document describes best current practices for configuring these 
   protocols, individually and in combination. 
    
Conventions used in this document 
    
   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 RFC-2119 [RFC2119]. 
    
Scope 
 
   This document is intended to provide basic information on how IPv4 
   Multicast routing is accomplished.  It discusses the IPv4 Multicast 
   Service model based in IGMP; how PIM Sparse Mode is used to route 
   traffic within an Autonomous System; and how the Multiprotocol 
   extensions to BGPv4, PIM Sparse Mode, and the Multicast Source 
   Discovery Protocol are used to route traffic between Autonomous 
   Systems.  Pointers to more sophisticated uses of these protocols are 
   provided. 
    
Introduction and Terminology 
 
   IPv4 multicast [MCAST] is an internetwork service that allows IPv4 
   datagrams sent from a source to be delivered to one or more 
   interested receiver(s).  That is, a given source sends a packet to 
   the network with a destination address in the 224.0.0.0/4 CIDR 
   [CIDR] range.  The network transports this packet to all receivers 
   (replicated where necessary) that have registered their interest in 
   receiving these packets.  The set of interested receivers is known 
   as a Host Group [RFC966]. 
    
     
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   The letter S is used to represent the IPv4 address of a given 
   source.  The letter G is used to represent a given IPv4 group 
   address (within the 224/4 CIDR range).  A packet, or series of 
   packets, sent by a sender with a given address S to a given Host 
   Group G is represented as (S,G).  A set of packets sent to Host 
   Group G by multiple senders is represented as (*,G). 
    
Packet Forwarding 
 
   Routers do multicast packet forwarding.  In order to know from where 
   to accept packets, and where to send them (duplicated if necessary), 
   each router maintains forwarding state.  This forwarding state might 
   be source specific (S,G) or source-generic/group-specific (*,G).  
   Each element of forwarding state defines an Input Interface (IIF) 
   and a set of Output Interfaces, known as an Output Interface List 
   (OIL). 
    
   When a packet is received on an IIF, the router performs a Reverse 
   Path Forwarding (RPF) check on that packet.  If that RPF check 
   succeeds, the packet is forwarded to the interfaces in the OIL. 
    
   The forwarding state in each router is a node on a singly rooted 
   tree.  In the case of shared trees using (*,G) forwarding state, the 
   root of the tree is the PIM Sparse Mode Rendezvous Point.  In the 
   case of source-specific trees using (S,G) forwarding state, the root 
   of the tree is the PIM Designated Router for the source S sending to 
   group G. 
    
Any Source Multicast 
 
   Any Source Multicast (ASM) is the traditional IPv4 multicast [MCAST] 
   model.  IPv4 multicast sources send IPv4 datagrams to the network, 
   with the destination address of each IPv4 datagram set to a specific 
   ôgroupö address in the Class D address space (224/4).  IPv4 
   multicast receivers register their interest in packets addressed to 
   a group address, and the internetwork delivers packets from all 
   sources in the internetwork to the interested receivers. 
    
   It is the responsibility of the internetwork to keep track of all 
   the sources transmitting to a particular group (identified by the 
   group address).  When a receiver wishes traffic sent to a group the 
   network forwards traffic from all group sources. 
    
   There is no requirement that a source be a member of the destination 
   Host Group.  In terms of [RFC966], IPv4 ASM groups are ôopenö. 
    
   IPv4 multicast receivers register their interest in packets sent to 
   group addresses through the Internet Group Management Protocol 
   Version 2 (IGMPv2) [IGMPV2].  IGMPv2 does not have any facility for 
   receivers to specify which sources the receiver wants to receive 
   from.  That is, IGMPv2 only allows (*,G) registrations.   
    
   The Internet Group Management Protocol Version 3 (IGMPv3) [IGMPV3] 
   can also be used in Any Source Multicast mode. 
     
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Source Specific Multicast 
 
   Source Specific Multicast (SSM) [SSM] is another IPv4 multicast 
   model.  IPv4 multicast sources send IPv4 datagrams to the network, 
   with the destination address of each IPv4 datagram set to a specific 
   ôgroupö address in the Class D address space (224/4).  IPv4 
   multicast receivers register their interest in packets from a 
   specific source that have been addressed to a group address, and the 
   internetwork delivers packets from that source to the interested 
   receivers. 
    
   It is the responsibility of each receiver to specify which sources, 
   sending to which groups, the receiver wishes to receive datagrams 
   from. 
    
   IPv4 multicast receivers register their interest in packets sent by 
   specific sources to group addresses through IGMPv3.  That is, IGMPv3 
   supports (S,G) registrations. 
    
   Sources that send packets to group addresses in the 232/8 range (the 
   SSM-specific range) can only be received by IGMPv3/SSM speaking 
   receivers and networks. 
    
Multiprotocol BGP 
 
   The topology of inter-domain IPv4 multicast forwarding is determined 
   by BGPv4 [BGPV4] policy, as is IPv4 unicast forwarding.  BGP 
   provides reachability information.  Reachability information for 
   IPv4 Unicast and IPv4 Multicast prefixes can be advertised 
   separately.  (See [MBGP] for details and the definition of Network 
   Layer Reachability Information (NLRI) and Subsequent Address Family 
   Information (SAFI).) The practical definition of reachability is 
   different for IPv4 unicast (NLRI=unicast, SAFI=1) and IPv4 multicast 
   (NLRI=Multicast, SAFI=2). 
    
   In current practice for BGP unicast advertisements (NLRI=Unicast, 
   SAFI=1), reachability is interpreted to mean that IPv4 datagrams 
   will be forwarded towards their destination host if sent to the 
   NEXT_HOP address in the advertisement. 
    
   In the case of BGP multicast advertisements (NLRI=Multicast, 
   SAFI=2), reachability is interpreted to mean two things 
   simultaneously: 
    
   First, IPv4 datagrams can be requested from sources within the 
   advertised prefix range.  Such requests are made to the advertised 
   NEXT_HOP by means of the PIM Sparse Mode [PIM-SM] protocol, or 
   (rarely) any other mutually agreed upon protocol that supports (S,G) 
   requests. 
    
   Second, the MSDP [MSDP] speaker associated with the NEXT_HOP address 
   will provide MSDP Source Active messages from PIM Rendevous Points 
   within the advertised prefix range. 
     
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   These two interpretations of BGP NLRI=Multicast flow from the use of 
   BGP to replace the topology discovery portion of the Distance Vector 
   Multicast Routing Protocol [DVMRP].  DVMRP is a ôdenseö routing 
   protocol, which means traffic is flooded outwards from the sources 
   to all possible receivers.  In this situation, an IPv4 multicast 
   router has to decide which incoming interface may accept IPv4 
   datagrams from a given source (to avoid forwarding loops).  When the 
   switch was made to use a ôsparseö forwarding model (requiring 
   specific (S,G) requests for traffic to flow) both interpretations of 
   BGP NLRI=Multicast became necessary for interoperability with the 
   DVMRP-based model. 
    
   Note that while MSDP is not strictly necessary for Autonomous 
   Systems that only support Source Specific Multicast [SSM], MSDP 
   depends on the latter interpretation of BGP NLRI=Multicast to avoid 
   MSDP SA forwarding loops.  There is a real danger of causing MSDP SA 
   forwarding ôblack holesö unless MSDP peerings are set up at the same 
   time as BGP NLRI=Multicast peerings. 
    
   Some MBGP implementations also support combined multicast and 
   unicast advertisements (SAFI=3).  Current practice is to interpret 
   these advertisements to include all three meanings listed above: 
   unicast forwarding, availability of traffic from multicast sources, 
   and MSDP Source Active availability. 
    
PIM Sparse Mode 
 
   The PIM Sparse Mode protocol [PIM-SM] is widely used to create 
   forwarding state from IPv4 multicast sources to interested 
   receivers. 
    
   The term ôPIM Sparse Mode domainö generally refers to the hosts and 
   routers that share a PIM Sparse Mode Rendezvous Point. 
    
   In current practice, there is generally one PIM Sparse Mode domain 
   per Autonomous System.  Some Autonomous Systems choose to have 
   multiple PIM Sparse Mode domains for scalability and reliability 
   reasons. 
    
   Within a PIM Sparse Mode domain, the standard PIM Sparse Mode 
   mechanisms are used to build shared forwarding trees.  Interested 
   IPv4 multicast receivers make their group interest known through the 
   Internet Group Management Protocol, and the associated PIM 
   Designated Router (DR) sends (*,G) PIM Join messages towards the RP 
   to build the appropriate shared forwarding tree.  IPv4 multicast 
   sources are registered with the PIM Rendezvous Point (RP).  When 
   enough traffic from a given source is flowing down the shared tree, 
   PIM routers will create and join source-specific (S,G) trees rooted 
   at the source.  This is known as the SPT Threshold. 
    
   Best current practice is to configure routers to join the source-
   rooted tree on the first packet sent down the shared tree.  That is, 
   the SPT Threshold should be zero. 
     
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   In the ASM model, PIM Sparse Mode Rendezvous Points have to co-
   operate in order to discover active sources and set up forwarding 
   trees.  MSDP is used to spread the knowledge of active sources 
   within a multicast group.  Source-specific (S,G) joins are used to 
   set up forwarding from sources towards the interested receivers.  No 
   inter-PIM-domain shared forwarding tree is created. 
    
   In the SSM model, there is no need for PIM Sparse Mode Rendezvous 
   Points because each receiver explicitly identifies the sources from 
   which it desires traffic.  Thus, the local PIM Designated Router 
   that receives an IGMPv3 request for traffic can initiate the PIM-
   Sparse Mode source-specific (S,G) requests directly towards the 
   source.  Packets sent to group addresses within the 232.0.0.0/8 
   range SHOULD NOT be encapsulated into PIM Register messages and 
   forwarded to the PIM Rendezvous Point. 
    
Internet Group Management Protocol 
 
   The Internet Group Management Protocol was designed to be used by 
   hosts to notify the network that the hosts want to receive traffic 
   on an IPv4 multicast group.   
    
   The IGMP design originally assumed a shared media network like 
   Ethernet.  When IEEE 802.1 bridging (layer 2) switches became 
   available, many vendors built in IGMP ôsnoopingö so as to avoid 
   flooding IP multicast traffic to all ports.   
    
   There are two alternative best current practices for IPv4 multicast 
   deployment in a network that has many IEEE 802 segments.  Both 
   practices are intended to constrain unwanted flooding of multicast 
   traffic to segments that have no intended receivers.  One is to use 
   nominally IEEE 802.1 bridges enhanced with IGMP snooping.  Another 
   is to avoid IEEE 802.1 bridges altogether, in favor of small subnets 
   and multicast-aware IP routers. 
    
   IGMPv2 [IGMPV2] supports the ASM model.  IGMPv3 [IGMPV3] supports 
   the ASM model as well as the SSM model. 
    
   Some wide area network access servers support IGMP and IPv4 
   Multicast over PPP connections.  Host implementations also support 
   the IGMP over PPP connections, even those that use dial-up modems.  
   Such support contributes to the availability and utility of IPv4 
   multicast service, but only when configured by network operators. 
    
Multicast Source Discovery Protocol 
    
   The Multicast Source Discovery Protocol (MSDP) supports the Any 
   Source Multicast model.  It SHOULD NOT be used in a Source Specific 
   Multicast context. 
    
   Current best practice is for Autonomous Systems to ask each other 
   for traffic from specific sources transmitting to specific groups.  
   It follows that inter-AS IP multicast forwarding trees are all 
     
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   source-specific.  Thus, when a receiver registers an interest in 
   datagrams addressed to a multicast group G (generally through an 
   IGMPv2 (*,G) join) it is necessary for the associated PIM Sparse 
   Mode Rendezvous Point (or other intra-AS protocol element, such as a 
   Core Based Trees [CBT] Core Router) to arrange (S,G) joins towards 
   each sender.  Each inter-AS (S,G) join creates a branch of the 
   forwarding tree towards the sender. 
    
   The Multicast Source Discovery Protocol [MSDP] is used to 
   communicate the availability of sources between Autonomous Systems.  
   MSDP-speaking PIM Sparse Mode Rendezvous Points (or other designated 
   MSDP speakers with knowledge of all sources within an Autonomous 
   System) flood knowledge of active sources to each other. 
    
   MSDP-speaking RPs communicate by way of a TCP session.  The Source 
   Active messages transmitted over the TCP session contain a packet of 
   data, which the MSDP-speaking RPs can forward down their group-
   specific shared trees.  This is how PIM speakers within a PIM domain 
   learn of the external sources. 
    
   Generally, with the SPT Threshold set to zero, PIM speakers within 
   the domain will then join the source-rooted distribution tree.  
   Thus, the persistent packet flow may bypass the RP altogether. 
    
Model IPv4 Multicast-Capable BGPv4 Configuration 
 
   IPv4 multicast reachability is communicated between Autonomous 
   Systems by BGPv4 prefix announcements.  That is, prefixes are 
   advertised with NLRI=Multicast (SAFI in {2,3}).  As outlined above, 
   the semantics of a BGPv4 advertisement of an IPv4 NLRI=Multicast 
   prefix are currently interpreted to mean two things: 
    
   First, such an advertisement means that the router with the NEXT_HOP 
   address of that advertisement will supply packets from any 
   transmitting source S whose address matches the prefix advertised.  
   In order to fulfill this expectation, any two BGPv4 speakers that 
   communicate NLRI=Multicast advertisements must be able to ask each 
   other for (S,G) traffic.  That is, they must have some protocol 
   (most often PIM Sparse Mode) configured between them. 
    
   Second, such an advertisement means that the router with the 
   NEXT_HOP address of that advertisement will supply MSDP Source 
   Active messages from any (e.g.) PIM Sparse Mode Rendezvous Point 
   whose address matches the prefix advertised.  To avoid MSDP ôblack 
   holesö, Autonomous Systems with BGPv4 speakers that exchange 
   NLRI=Multicast advertisements must also have appropriate MSDP 
   peerings configured. 
    
Model IPv4 Multicast Inter-domain PIM Sparse Mode Configuration 
 
   As outlined above, current practice is that each IPv4 BGPv4 
   NLRI=Multicast capable peering is capable of making (S,G) requests 
   for traffic.  Autonomous Systems predominantly use PIM Sparse Mode 
   for this purpose.  The rest of this section describes how PIM Sparse 
     
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   Mode is widely configured, but the principles can be applied to any 
   other (S,G) request protocol between Autonomous Systems. 
    
   The minimum TTL Threshold for traffic crossing an Autonomous System 
   peering is generally set to be 32.  This value follows earlier 
   practice [FAQ] that sets inter-institution TTL barriers at 16-32.  
   It also provides a reasonable number of values both above and below 
   the (maximum 255) barrier. 
    
   The PIM Sparse Mode Adjacency should not make requests for traffic 
   across the peering for sources in these groups: 
    
   224.0.1.39/32: CiscoÆs Rendezvous Point Announcement Protocol 
   224.0.1.40/32: CiscoÆs Rendezvous Point Discovery Protocol 
   239.0.0.0/8:   Administratively Scoped IPv4 Group Addresses (with 
   possible exceptions) 
    
   The first two groups are used to determine where PIM Sparse Mode 
   Rendezvous Points can be found within an Autonomous System.  The 
   latter group range is defined by RFC 2365 [RFC2365].  RFC 2365 has 
   been generally interpreted to equate ôorganizationsö (see section 
   6.2) with Autonomous Systems.  Some Autonomous Systems choose to 
   interpret this differently. 
    
Model PIM Sparse Mode Rendezvous Point Location 
 
   In order to participate in current-practice inter-Autonomous System 
   IPv4 multicast routing, a PIM Sparse Mode Rendezvous Point (or other 
   such MSDP-speaker) should have access to the full BGP NLRI=Multicast 
   reachability table so as to arrange for (S,G) joins to the 
   appropriate external peer networks.  This need arises when a (*,G)  
   request comes in from a host.  Access to the BGPv4 NLRI=Multicast 
   reachability table is also important so that the (e.g.) PIM Sparse 
   Mode Rendezvous Point will perform MSDP Reverse-Path-Forwarding 
   (RPF) checks correctly. 
    
   PIM Sparse Mode Rendezvous Points are often located at the border 
   router of an Autonomous System where the BGPv4 NLRI=Multicast 
   reachability table is already maintained.  If necessary, an MSDP 
   Mesh Group can be created if there are multiple BGPv4 NLRI=Multicast 
   speakers within an Autonomous System.  (See Section 14.3 of [MSDP] 
   as well as [ANYCASTRP].) 
    
   The IPv4 address of each PIM Sparse Mode Rendezvous Point (or other 
   such MSDP-speaker) must be chosen so that it is within an advertised 
   BGPv4 NLRI=Multicast prefix.  The MSDP RPF checks operate on the so-
   called ôRP-Addressö within the MSDP Source Active message, not the 
   advertised source S.  In the most widely deployed case, the RP-
   Address is set by the MSDP-speaker to be the PIM Sparse Mode 
   Rendezvous Point address. 
    
     
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Model MSDP Configuration Between Autonomous Systems 
 
   MSDP peerings are configured between Autonomous Systems.  These 
   peerings are statically defined.  Thus, in practice, such MSDP-
   speaking (e.g.) PIM Sparse Mode Rendezvous Point(s) must be ôtied 
   downö to known addresses and routers for the inter-AS peerings to 
   operate correctly. 
    
   The so-called ôRP-addressö in MSDP Source Active messages must be 
   addressed within prefixes announced by BGPv4 NLRI=Multicast 
   advertisements.  (Otherwise the RP-Address Reverse Path Forwarding 
   checks done by peer MSDP-speaking Autonomous Systems will fail, and 
   the MSDP Source Active messages will be discarded.)  The most common 
   RP-address in MSDP Source Active messages is the PIM Rendezvous 
   Point IPv4 address. 
    
   In practice, MSDP speakers are configured to not advertise sources 
   to external peers that are operating in certain groups, as outlined 
   in [UNUSABLE].  Also see [FILTERLIST] for more information.  Some 
   sites block all groups in 224.0.0.0/24, due to a lack of interdomain 
   groups in that range. 
    
   MSDP speakers are configured to not accept or advertise sources to 
   or from external peers with Private Internet addresses [RFC1918]. 
    
   MSDP-speakers are configured, wherever possible, to only advertise 
   sources within prefixes that they are advertising as BGPv4 
   NLRI=Multicast (SAFI in {2,3}) announcements.  That is, a non-
   transit Autonomous System would only advertise sources within the 
   prefixes it advertises to its peers. 
    
   Based on recent events, MSDP peerings are configured with reasonable 
   rate limits to dampen explosions of MSDP SA advertisements.  These 
   explosions can occur when malicious software generates packets 
   addressed to many IPv4 multicast groups in a very short period of 
   time.  What ôappropriateö means for these rate limits will vary over 
   time with the number of active IPv4 multicast sources in the 
   Internet.  To determine an initial approximation for these rate 
   limits, configure MSDP without rate limits initially, and then set 
   the rate limits at some small multiple of the observed steady state 
   rate.  Another approach would be to set rate limits based on a small 
   multiple of the current number of active sources in the Internet.  
   The Mantra Project [MANTRA] maintains MSDP statistics, as well as 
   other IPv4 multicast statistics. 
    
Advanced Configurations 
 
   Often an organization may wish to have multiple PIM RPs for 
   scalability reasons.  The Anycast-RP [ANYCASTRP] draft outlines one 
   way how this can be accomplished. 
    
   When an organization has multiple border routers, it makes sense for 
   the organization to move the PIM Rendezvous Point off of the border 
   and to an internal router.  Note that the MSDP-speaking PIM RP will 
     
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   need to be a part of the iBGP mesh so as to have BGPv4 
   NLRI=Multicast topology information. 
    
Security Considerations 
    
   Autonomous Systems often configure router filters or firewall rules 
   to discard mis-forwarded IPv4 datagrams.  Such rules may explicitly 
   list the IPv4 address ranges that are acceptable for incoming IPv4 
   datagrams.  When IPv4 multicast is enabled, these rules need to be 
   updated to disallow incoming IPv4 datagrams with addresses in the 
   239/8 CIDR range, but otherwise to allow incoming IPv4 datagrams 
   with destination addresses in the 224/4 CIDR range. 
    
   PIM Sparse Mode Rendezvous Points are particularly vulnerable to 
   Denial of Service attacks.  As outlined above, it is important to 
   put rate limits on MSDP peerings so as to protect your PIM Sparse 
   Mode Rendezvous Points from explosions in the size of the cached 
   MSDP Source Active table.  Other denial of service attacks include 
   sending excessive Register-encapsulated packets towards the 
   Rendezvous Point and flooding the Rendezvous Point with large 
   numbers of (S,G) joins originated as IGMP Group Reports. 
    
Acknowledgements 
    
   Dino Farinacci created the (S,G) notation used throughout this 
   document. 
    
   Kevin Almeroth, Tony Ballardie, H…vard Eidnes, David Farmer, Leonard 
   Giuliano, John Heasley, Marty Hoag, Milan J, Simon Leinen, Michael 
   Luby, David Meyer, John Meylor, Stephen Sprunk and Dave Thaler 
   provided information, pointed out mistakes and made suggestions for 
   improvement. 
    
   Marshall Eubanks described the vulnerability of PIM Sparse Mode 
   Rendezvous Points to various denial of service attacks. 
 
   This work was supported by the Mathematical, Information, and 
   Computational Sciences Division subprogram of the Office of Advanced 
   Scientific Computing Research, U.S. Department of Energy, under 
   Contract W-31-109-Eng-38. 
 
Normative References 
    
   [RFC2119] RFC 2119: Key Words for use in RFCs to Indicate 
      Requirement Levels.  S. Bradner.  March 1997. 
    
   [MCAST] RFC 1112: Host extensions for IP multicasting. S.E. Deering. 
      August 1989. 
         
   [CIDR] RFC 1519: Classless Inter-Domain Routing (CIDR): an Address 
      Assignment and Aggregation Strategy. V. Fuller, T. Li, J. Yu, K. 
      Varadhan. September 1993. 
 
     
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   [RFC966] RFC 966: Host Groups: A Multicast Extension to the Internet 
      Protocol.  S. E. Deering, D. R. Cheriton.  December 1985. 
    
   [IGMPV2] RFC 2236: Internet Group Management Protocol, Version 2. W. 
      Fenner.  November 1997. 
    
   [IGMPV3] RFC 3376: Internet Group Management Protocol, Version 3.  
      B. Cain, S. Deering, B. Fenner, I Kouvelas, A. Thyagarajan.  
      October 2002. 
    
   [SSM] draft-ietf-ssm-arch-00.txt: Source-Specific Multicast for IP.  
      H. Holbrook, B. Cain.  21 November 2001. 
    
   [BGPV4] RFC 1771: A Border Gateway Protocol 4 (BGP-4).  Y. Rekhter, 
      T. Li.  March 1995. 
    
   [MBGP] RFC 2858: Multiprotocol Extensions for BGP-4.  T. Bates, Y. 
      Rekhter, R. Chandra, D. Katz.  June 2000. 
    
   [PIM-SM] RFC 2117: Protocol Independent Multicast-Sparse Mode (PIM-
      SM): Protocol Specification.  D. Estrin, D. Farinacci, A. Helmy, 
      D. Thaler, S. Deering, M. Handley, V. Jacobson, C. Liu, P. 
      Sharma, L. Wei.  June 1997. 
    
   [MSDP] draft-ietf-msdp-spec-13.txt: Multicast Source Discovery 
      Protocol (MSDP).  D. Meyer (Editor), B. Fenner (Editor).  
      November 2001. 
    
 
   [RFC2365] RFC 2365: Administratively Scoped IP Multicast.  D. Meyer.  
      July 1998. 
    
   [UNUSABLE] IPv4 Multicast Unusable Group Addresses.  B. Nickless.  
      draft-nickless-ipv4-mcast-unusable-02.txt.  June 2003. 
    
   [RFC1918] RFC 1918: Address Allocation for Private Internets.  Y. 
      Rekhter, B. Moskowitz, D. Karrenberk, G. J. de Groot, E. Lear.  
      February 1996. 
    
    
   [ANYCASTRP] RFC 3446: Anycast RP mechanism using PIM and MSDP.  D. 
      Kim, D. Meyer, H. Kilmer, D. Farinacci.  January 2003. 
    
Non-Normative References 
 
   [DVMRP] RFC 1075: Distance Vector Multicast Routing Protocol.  D. 
      Waitzman, C. Partridge, S.E. Deering.  November 1988. 
    
   [FAQ] http://netlab.gmu.edu/mbone_installation.htm 
    
     
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                 IPv4 Multicast Best Current Practice        June 2003 
    
   [FILTERLIST] ftp://ftpeng.cisco.com/ipmulticast/config-notes/msdp-
      sa-filter.txt 
    
   [MANTRA] http://www.caida.org/tools/measurement/mantra 
    
    
Author's Address 
    
   Bill Nickless 
   Argonne National Laboratory 
   9700 South Cass Avenue #221     Phone:  +1 630 252 7390 
   Argonne, IL 60439               Email:  nickless@mcs.anl.gov 
     
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