Internet Engineering Task Force P. Savola Internet-Draft CSC/FUNET Obsoletes: 2908,2909 (if approved)
November 29, 2004February 18, 2005 Expires: May 30,August 19, 2005 Overview of the Internet Multicast Addressing Architecture draft-ietf-mboned-addrarch-00.txtdraft-ietf-mboned-addrarch-01.txt Status of this Memo This document is an Internet-Draft and is subject to all provisions of sectionSection 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668. 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 Internet-Draft will expire on May 30,August 19, 2005. Copyright Notice Copyright (C) The Internet Society (2004).(2005). Abstract The lack of up-to-date documentation on IP multicast address allocation and assignment procedures has caused a great deal of confusion. To clarify the situation, this memo describes the allocation and assignment techniques and mechanisms currently (as of this writing) in use. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Terminology: Allocation or Assignment . . . . . . . . . . 3 2. Multicast Address Allocation . . . . . . . . . . . . . . . . . 4 2.1 Derived Allocation . . . . . . . . . . . . . . . . . . . . 4 2.1.1 GLOP Allocation . . . . . . . . . . . . . . . . . . . 4 2.1.2 Unicast-prefix -based Allocation . . . . . . . . . . . 4 2.2 Scope-relative Allocation . . . . . . . . . . . . . . . . 5 2.3 Static IANA Allocation . . . . . . . . . . . . . . . . . . 6 2.4 Dynamic Allocation . . . . . . . . . . . . . . . . . . . . 6 3. Multicast Address Assignment . . . . . . . . . . . . . . . . . 6 3.1 Derived Assignment . . . . . . . . . . . . . . . . . . . . 6 3.2 SSM Assignment inside the Node . . . . . . . . . . . . . . 7 3.3 Manually Configured Assignment . . . . . . . . . . . . . . 7 3.4 Static IANA Assignment . . . . . . . . . . . . . . . . . . 7 3.5 Dynamic Assignments . . . . . . . . . . . . . . . . . . . 8 3.6 Future Developments . . . . . . . . . . . . . . . . . . . 84. Multicast Address Discovery . . . . . . . . . . . . . . . . . 9 5.Summary and Future Directions . . . . . . . . . . . . . . . . 10 5.19 4.1 Prefix Allocation . . . . . . . . . . . . . . . . . . . . 10 5.29 4.2 Address Assignment . . . . . . . . . . . . . . . . . . . . 11 5.310 4.3 Future Actions . . . . . . . . . . . . . . . . . . . . . . 11 6.10 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 7.11 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 8.11 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 9.11 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 9.18.1 Normative References . . . . . . . . . . . . . . . . . . . .12 9.28.2 Informative References . . . . . . . . . . . . . . . . . . . 1312 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 1514 A. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 14 B. Multicast Address Discovery . . . . . . . . . . . . . . . . . 15 Intellectual Property and Copyright Statements . . . . . . . . 16 1. Introduction Good, up-to-date documentation of IP multicast is close to non-existent. Particularly, this is an issue with multicast address allocations (to networks and sites) and assignments (to hosts and applications). This problem is stressed by the fact that there exists confusing or misleading documentation on the subject [RFC2908]. The consequence is that those who wish to learn of IP multicast and how the addressing works do not get a clear view of the current situation. The aim of this document is to provide a brief overview of multicast addressing and allocation techniques. The term 'addressing architecture' refers to the set of addressing mechanisms and methods in an informal manner. It is important to note that Source-specific Multicast (SSM) [I-D.ietf-ssm-arch] does not have these addressing problems; hence, this document focuses on Any Source Multicast (ASM) model. The applicability of SSM has been briefly discussed in [I-D.ietf-mboned-ipv6-multicast-issues]. This memo obsoletes RFC 2908 and RFC 2909 and re-classifies them Historic. 1.1 Terminology: Allocation or Assignment Almost all multicast documents and many other RFCs (such as DHCPv4 [RFC2131] and DHCPv6 [RFC3315]) have used the terms address "allocation" and "assignment" interchangeably. However, the operator and address management communities use these for two conceptually different processes. In unicast operations, address allocations refer to leasing a large block of addresses from Internet Assigned Numbers Authority (IANA) to a Regional Internet Registry (RIR), from RIR to a Local Internet Registry (LIR) possibly through a National Internet Registry (NIR). Address assignments, on the other hand, are the leases of smaller address blocks or even single addresses to the end-user sites or end-users themselves. Therefore, in this memo, we will separate the two different functions: "allocation" describes how larger blocks of addresses are obtained by the network operators, and "assignment" describes how applications, nodes or sets of nodes obtain a multicast address for their use. [[ NOTE IN DRAFT: is this choice of terminology too confusing? ]]2. Multicast Address Allocation Multicast address allocation, i.e., how a network operator might be able to obtain a larger block of addresses, can be handled in a number of ways as described below. Note that these are all only pertinent to ASM -- SSM requires no address block allocation because the group address has only local significance (however, the address assignment inside the node is still an issue discussed in Section 3.2). 2.1 Derived Allocation Derived allocations take the unicast prefix or some other properties of the network to determine unique multicast address allocations. 2.1.1 GLOP Allocation GLOP address allocation [RFC3180] inserts the 16-bit public Autonomous System (AS) number in the middle of the IPv4 multicast prefix 126.96.36.199/8, so that each AS number can get a /24 worth of multicast addresses. While this is sufficient for multicast testing or small scale use, it might not be sufficient in all cases for extensive multicast use. A minor operational debugging issue with GLOP addresses is that the connection between the AS and the prefix is not apparent from the prefix, but has to be calculated (e.g., from [RFC3180], AS 5662 maps to 188.8.131.52/24). A usage issue is that GLOP addresses are not tied to any prefix but to routing domains, so they cannot be used or calculated automatically. 2.1.2 Unicast-prefix -based Allocation RFC 3306 [RFC3306] describes a mechanism which embeds up to 64 first bits of an IPv6 unicast address in the prefix part of the IPv6 multicast address, leaving at least 32 bits of group-id space available after the prefix mapping. A similar mapping has been proposed for IPv4 [I-D.ietf-mboned-ipv4-uni-based-mcast], but it provides a rather low amount of addresses (e.g., 1 per an IPv4 /24 block). While there exist large networks without an AS number of their own, this has not been seen to add sufficient value compared to GLOP addressing. The IPv6 unicast-prefix -based allocations are an extremely useful way to allow each network operator, even each subnet, obtain multicast addresses easily, through an easy computation. Further, as the IPv6 multicast header also includes the scope value [RFC3513], multicast groups of smaller scope can also be used with the same mapping. The IPv6 Embedded RP technique [RFC3956], used with Protocol Independent Multicast - Sparse Mode (PIM-SM), further leverages the unicast prefix based allocations, by embedding the unicast prefix and interface identifier of the PIM-SM Rendezvous Point (RP) in the prefix. This provides all the necessary information needed to the routing systems to run the group in either inter- or intra-domain operation. A difference to RFC 3306 is, however, that the hosts cannot calculate their "multicast prefix" automatically, as the prefix depends on the decisions of the operator setting up the RP but rather needs to be communicated somehow.requires an assignment method. All the IPv6 unicast-prefix -based allocation techniques provide sufficient amount of multicast address space for the network operators. 2.2 Scope-relative Allocation Administratively scoped multicast [RFC2365] is provided by two different means: under 184.108.40.206/8 in IPv4 or by 4-bit encoding in the IPv6 multicast address prefix [RFC3513]. As IPv6 scope-relative allocations can be handled with unicast-prefix -based multicast addressing as described in Section 2.1.2, and there is no need for separate scope-relative allocations, we'll just discuss IPv4 in this section. The IPv4 scope-relative prefix 220.127.116.11/8 is further divided to Local Scope (18.104.22.168/16) and Organization Local Scope (22.214.171.124/14); other parts of the administrative scopes are either reserved for expansion or undefined [RFC2365]. Topologies which act under a single administration can easily use the scoped multicast addresses for their internal groups. Groups which need to be shared between multiple routing domains (but not propagated through Internet) are more problematic and typically need an assignment of a global multicast address because their scope is undefined. There is a large number of multicast applications (such as "Norton Ghost") which are restricted either to a link or a site, but it is extremely undesirable to propagate them further (either to the rest of the site, or beyond the site). Typically many such applications have been given a static IANA address assignment; this makes it challenging to implement proper propagation limiting -- which could be easier if such applications could have been assigned specific scope-relative addresses instead. This is an area of further future work -- it might be able to mitigate this issue if there was more coordination inside the scope-relative allocation block. 2.3 Static IANA Allocation In some rare cases, some organizations may have been able to obtain static multicast address allocations directly from IANA. Typically these have been meant as a block of static assignments to multicast applications, as described in Section 3.4. In principle, IANA does not allocate multicast address blocks to the operators but GLOP or Unicast-prefix -based allocations should be used instead. 2.4 Dynamic Allocation RFC 2908 [RFC2908] proposed three different layers of multicast address allocation and assignment, where layers 3 (inter-domain allocation) and layer 2 (intra-domain allocation) could be applicable here. Multicast Address-Set Claim Protocol (MASC) [RFC2909] is an example of the former, and Multicast Address Allocation Protocol (AAP) [I-D.ietf-malloc-aap] (abandoned in 2000 due lack of interest and technical problems) is an example of the latter. Both of the proposed allocation protocols were quite complex, and have never been deployed or seriously implemented. It can be concluded that there are no dynamic multicast address allocation protocols, and other methods such as GLOP or unicast-prefix -based addressing should be used instead. 3. Multicast Address Assignment For multicast address assignment, i.e., how an application learns the address it can use, or a node (or a set of nodes) learns an address it could use for an application, has a number of options as described below. Any IPv6 address assignment method should be aware of the guidelines for the assignment of the group-IDs for IPv6 multicast addresses [RFC3307]. 3.1 Derived Assignment There are significantly fewer options for derived address assignment compared to derived allocation. Derived multicast assignment is only being specified for IPv6 link-scoped multicast [I-D.ietf-ipv6-link-scoped-mcast], where the EUI64 is embedded in the multicast address, providing a node with unique multicast addresses for link-local ASM communications. 3.2 SSM Assignment inside the Node While the SSM multicast addresses have only local (to the node) significance, there is still a minor issue on how to assign the addresses between the applications running on the same node (or more precisely, an IP address). This assignment is not considered to be a problem because typically the addresses for the applications are selected manually or statically, but if done using an API, the API could check that the addresses do not conflict prior to assigning one. 3.3 Manually Configured Assignment With manually configured assignment, the network operator which has a multicast address prefix assigns the multicast group addresses to the requesting nodes using a manual process. Typically the user or administrator which wants to use a multicast address for particular application requests an address from the network operator using phone, email, or similar means, and the network operator provides the user with a multicast address. Then the user/administrator of the node or application manually configures the application to use the assigned multicast address. This is a relatively simple processprocess; it has been sufficient for certain applications which require manual configuration in any case, or which cannot or do not want to justify a static IANA assignment. The manual assignment works when the beginning, but would become unscalable if the multicast usage would get onnumber of participants in a serious rise (fortunately, we have dynamic assignment, see Section 3.5). Another, separate issuegroup is small, as each participant has to ensure that the users wishing to use that application are able to locate the configured multicast address ("rendezvous" or "service discovery"); in this particular case, this might call for e.g., DNS-based discovery of the multicast address.be manually configured. This is the most commonly used technique when the multicast application does not have a static IANA assignment. 3.4 Static IANA Assignment In contrast to manually configured assignment, as described above, static IANA assignment refers to getting a globally unique assignment for the particular application directly from IANA. Guidelines for IANA are described in [I-D.ietf-mboned-rfc3171bis]. This is seen as lucrative because it's the simplest approach for application developers because they can then hard-code the multicast address, requiring no lease of the usable multicast address, and likewise the client applications do not need to perform any kind of service discovery (but depending on hard-coded addresses). However, this is a bad approach architecturally, as we should focus on enhancing and deploying service discovery and address assignment (as needed) instead of encouraging a "land-grab" of multicast addresses. In summary, there are applications which have obtained a static IANA assignment, some of which are really needed, and some of which probably should not have been granted. 3.5 Dynamic Assignments The layer 1 of RFC 2908 [RFC2908] described dynamic assignment from Multicast Address Allocation Servers (MAAS) to applications and nodes, with Multicast Address Dynamic Client Allocation Protocol (MADCAP) [RFC2730] andas examples. Since then, there has been a proposal for DHCPv6 assignments [I-D.jdurand-assign-addr-ipv6-multicast-dhcpv6] as examples.assignment [I-D.jdurand-assign-addr-ipv6-multicast-dhcpv6]. Based on a multicast prefix, it would be rather straightforward to deploy a dynamic assignment protocol which would lease group addresses to the applications wishing to use multicast. For example, only few have implemented MADCAP, and it's not significantly deployed. Moreover, it is not clear how widely for example the APIs for communication between the multicast application and the MADCAP client operating at the host have been implemented [RFC2771]. Based on that, a conclusion is that multicastAn entirely different approach is that either: 1.Session Announcement Protocol (SAP) [RFC2974]. In addition to advertising global multicast is not significantly attractive insessions, the first place, 2. manually configured assignments are sufficientprotocol also has associated ranges of addresses for now, or 3. that there are other gaps why dynamic assignments are not seenboth IPv4 and IPv6 which can be used by SAP-aware applications to create new groups and new group addresses. It is a rather tedious process to create a session (and obtain an address) this way which is why it isn't done all that often. (Note that the IPv6 SAP address is unroutable in the inter-domain multicast.) A conclusion about dynamic assignment protocols is that: 1. multicast is not significantly attractive in the first place, 2. very many applications have a static IANA assignment and thus require no dynamic or manual assignment, 3. those that cannot be easily satisfied with IANA or manual assignment (i.e., where dynamic assignment would be desirable) are rather marginal, or 4. that there are other gaps why dynamic assignments are not seen as a useful approach (for example, issues related to service discovery/rendezvous). In consequence, more work on rendezvous/service discovery will be needed to make dynamic assignment more useful. 3.64. Summary and Future Developments IPv6 could offer an alternative to dynamic assignments due to its larger address space: if a multicast prefix (e.g., about 2^32 bits worth of group-id's) is allocated to a subnet, it would be sufficient to ensure that multiple applications running on that subnet do not try to use the same address (selected e.g., using a random process).Directions This could call for a Duplicate Address Detection process, and/or a way for the RPs to inform the hosts about the prefix that could be used on each subnet (assuming Embedded-RP would be used). 4. Multicast Address Discovery [[ NOTE IN DRAFT: it is not clear whether thissection belongssummarizes the mechanisms and analysis discussed in this document at all; it is somewhat related, but could bear a more extensive discussion elsewhere. It should likely go in a separate document (if there was one discussing these problems!), or in an appendix. Feedbackmemo, and presents some potential future directions. 4.1 Prefix Allocation Summary of prefix allocation methods for ASM is appreciated. ]] As was notedin Section 3, multicast address discovery (i.e., service discovery or "rendezvous") is a problem with multicast address assignment. In particular, an acceptable mechanism (mechanisms such as Service Location Protocol (SLP) [RFC2608] seem toFigure 1. +-------+--------------------------------+--------+--------+ | Sect. | Prefix allocation method | IPv4 | IPv6 | +-------+--------------------------------+--------+--------+ | 2.1.1 | Derived: GLOP | Yes | NoNeed*| | 2.1.2 | Derived: Unicast-prefix -based |No -yet | Yes | | 2.2 | Separate Scope-relative | Yes | NoNeed*| | 2.3 | Static IANA allocation | No | No | | 2.4 | Dynamic allocation protocols | No | No | +-------+--------------------------------+--------+--------+ * = the need satisfied by IPv6 unicast-prefix -based allocation. Figure 1 o Only ASM is affected by the assignment/allocation issues (however, both ASM and SSM have been considered too complex) seems to be missing whichroughly the hosts wishingsame address discovery issues). o GLOP allocations seem to participate inprovide a groupsufficient IPv4 multicast allocation mechanism for now, but could use to findbe extended in future. Scope-relative allocations provide the address of that group [MBONED-IETF59]. It is worth noting that as long as not deploying an address assignmentopportunity for internal IPv4 allocations. o Unicast-prefix -based addresses and service discovery protocols/mechanisms means that one can getthe derivatives provide good allocation strategy with IPv6, also for scoped multicast addresses. o Dynamic allocations are a statictoo complex and unnecessary mechanism. o Static IANA allocations are an architecturally unacceptable approach. 4.2 Address Assignment Summary of address assignment from IANA, theremethods is little interest from the application developers to actually do anything except try to get thein Figure 2. +-------+--------------------------------+----------+----------+ | Sect. | Address assignment from IANA. Conclusion: if we want to use non-IANA processes, the assignments must be either forbidden completely, or made sufficiently difficult that it's easier for the application developers to take another route if a feasible mechanism is available. There are two issues in the service discovery: 1. The session initiator being able to publish the session somehow, and 2. The session participants finding out about the session (rather than creating their own). When manually configured or static IANA assignments are used, 1) should be relatively straightforward (if something needs to be manually configured or statically assigned, putting it e.g., in DNS should not be a problem). However, this is still more complex for dynamic or derived assignments because it implies that the host or the application has the right to make that publication on its own, rather than through a manual process by an administrator. 2) is always a challenge, but could leverage for example DNS (e.g., by relying on using SRV records with the DNS search path, as described in [I-D.iab-dns-choices] and [I-D.palet-v6ops-tun-auto-disc]). 5. Summary and Future Directions This section summarizes the mechanisms and analysis discussed in this memo, and presents some potential future directions. 5.1 Prefix Allocation Summary of prefix allocation methods is in Figure 1. +-------+--------------------------------+--------+--------+ | Sect. | Prefix allocationmethod | IPv4 | IPv6 | +-------+--------------------------------+--------+--------++-------+--------------------------------+----------+----------+ | 23.1 | SSMDerived: link-scope addresses | NoNeedNo | NoNeedYes | | 126.96.36.199 | Derived: GLOPSSM (inside the node) | Yes | NoNeed*| | 2.1.2 | Derived: Unicast-prefix -based |No -yet |Yes | | 2.23.3 | Separate Scope-relativeManual assignment | Yes | NoNeed*|Yes | 2.3| 3.4 | Static IANA allocationassignment |LastResort|LastResort| | No3.5 | NoDynamic assignment protocols | | 2.4 | Dynamic allocation protocols | No | No | +-------+--------------------------------+--------+--------+ * = the need satisfied by IPv6 unicast-prefix -based allocation. Figure 1 o Only ASM is affected by the assignment/allocation issues (however, both ASM and SSM have roughly the same address discovery issues). o GLOP allocations seem to provide a sufficient IPv4 multicast allocation mechanism for now, but could be extended in future. Scope-relative allocations provide the opportunity for internal IPv4 allocations. o Unicast-prefix -based addresses and the derivatives provide good allocation strategy with IPv6, also for scoped multicast addresses. o Dynamic allocations are a too complex and unnecessary mechanism. o Static IANA allocations are an architecturally unacceptable approach. 5.2 Address Assignment Summary of address assignment methods is in Figure 2. +-------+--------------------------------+----------+----------+ | Sect. | Address assignment method | IPv4 | IPv6 | +-------+--------------------------------+----------+----------+ | 3.1 | Derived: link-scope addresses | No | Yes | | 3.2 | SSM (inside the node) | Yes | Yes | | 3.3 | Manual assignment | Yes | Yes | | 3.4 | Static IANA assignment |LastResort|LastResort| | 3.5 | Dynamic assignment protocols | YesYes | Yes | +-------+--------------------------------+----------+----------+ Figure 2 o Manually configured assignment is what's typically done today, and works to a sufficient degree in smaller scale. o Static IANA assignment has been done extensively in the past, but it needs to be tightened down to prevent problems caused by "land-grabbing". o Dynamic assignment, e.g., using MADCAP have been implemented, but there is no wide deployment, so a solution is there -- but either there are other gaps in the multicast architecture or there is no need for it in the first place, when manual configuration is possible, and static IANA assignments are still there. Assignments using SAP also exist but are not common; global SAP assignment is unfeasible with IPv6. o Derived assignments are only applicable in a fringe case of link-scoped multicast. 5.34.3 Future Actions o Multicast address discovery/"rendezvous" needs to be analyzed at more length, and an adequate solution provided; the result also needs to be written down to be shown to the IANA static assignment requestors. See [I-D.savola-mboned-address-discovery-problems] and Appendix B for more. o IPv6 multicast DAD and/or multicast prefix communication mechanisms should be analyzed:analyzed (e.g., [I-D.jdurand-ipv6-multicast-ra]): whether there is demand or not, and specify if so.yes. o The IETF should consider whether to specify more ranges of the IPv4 scope-relative address space for static allocation for applications which should not be routed over the Internet (such as backup software, etc. -- so that these wouldn't need to use global addresses which should never leak in any case). o The IETF should seriously consider its static IANA allocations policy, e.g., "locking it down" to a stricter policy (like "IETF Consensus") and looking at developing the discovery/rendezvous functions, if necessary. 6.5. Acknowledgements Tutoring a couple multicast-related papers, the latest by Kaarle Ritvanen [RITVANEN] convinced the author that the up-to-date multicast address assignment/allocation documentation is necessary. Multicast address allocations/assignments were discussed at the MBONED WG session at IETF59 [MBONED-IETF59]. Dave Thaler, James Lingard, and Beau Williamson provided useful feedback for the preliminary version of this memo. Myung-Ki Shin and Jerome Durand also suggested improvements. 7.6. IANA Considerations This memo includes no request to IANA, but as the allocation and assignment of multicast addresses are related to IANA functions, it wouldn't hurt if the IANA reviewed this entire memo. IANA considerations in sections 4.1.1 and 4.1.2 of [RFC2908] still apply to the administratively scoped prefixes. (RFC-editor: please remove this section at publication.) 8.7. Security Considerations This memo only describes different approaches to allocating and assigning multicast addresses, and this has no security considerations; the security analysis of the mentioned protocols is out of scope of this memo. Obviously, especially the dynamic assignment protocols are inherently vulnerable to resource exhaustion attacks, as discussed e.g., in [RFC2730]. 9.8. References 9.18.1 Normative References [I-D.ietf-ipv6-link-scoped-mcast] Park, J., Shin, M. and H. Kim,"Link Scoped IPv6 Multicast Addresses", draft-ietf-ipv6-link-scoped-mcast-06 (work in progress), OctoberInternet-Draft draft-ietf-ipv6-link-scoped-mcast-08, December 2004. [I-D.ietf-mboned-rfc3171bis] Albanna, Z., Almeroth, K., Cotton, M. and D. Meyer, "IANA Guidelines for IPv4 Multicast Address Assignments", draft-ietf-mboned-rfc3171bis-02 (work in progress),Internet-Draft draft-ietf-mboned-rfc3171bis-02, March 2004. [I-D.ietf-ssm-arch] Holbrook, H. and B. Cain, "Source-Specific Multicast for IP", draft-ietf-ssm-arch-06 (work in progress),Internet-Draft draft-ietf-ssm-arch-06, September 2004. [RFC2365] Meyer, D., "Administratively Scoped IP Multicast", BCP 23, RFC 2365, July 1998. [RFC3180] Meyer, D. and P. Lothberg, "GLOP Addressing in 233/8", BCP 53, RFC 3180, September 2001. [RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6 Multicast Addresses", RFC 3306, August 2002. [RFC3307] Haberman, B., "Allocation Guidelines for IPv6 Multicast Addresses", RFC 3307, August 2002. [RFC3513] Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6) Addressing Architecture", RFC 3513, April 2003. [RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous Point (RP) Address in an IPv6 Multicast Address", RFC 3956, November 2004. 9.28.2 Informative References [I-D.iab-dns-choices] Faltstrom, P. and R. Austein, "Design Choices When Expanding DNS", draft-iab-dns-choices-00 (work in progress),Internet-Draft draft-iab-dns-choices-00, October 2004. [I-D.ietf-malloc-aap] Handley, M. and S. Hanna, "Multicast Address Allocation Protocol (AAP)", June 2000. [I-D.ietf-mboned-ipv4-uni-based-mcast] Thaler, D., "Unicast-Prefix-based IPv4 Multicast Addresses", draft-ietf-mboned-ipv4-uni-based-mcast-02 (work in progress),Internet-Draft draft-ietf-mboned-ipv4-uni-based-mcast-02, October 2004. [I-D.ietf-mboned-ipv6-multicast-issues] Savola, P., "IPv6 Multicast Deployment Issues", draft-ietf-mboned-ipv6-multicast-issues-01 (work in progress),Internet-Draft draft-ietf-mboned-ipv6-multicast-issues-01, September 2004. [I-D.jdurand-assign-addr-ipv6-multicast-dhcpv6] Durand, J., "IPv6 multicast address assignment with DHCPv6", draft-jdurand-assign-addr-ipv6-multicast-dhcpv6-00 (work in progress),, June 2004. [I-D.jdurand-ipv6-multicast-ra] Durand, J. and P. Savola, "Route Advertisement Option for IPv6 Multicast Prefixes", Internet-Draft draft-jdurand-ipv6-multicast-ra-00, February 2005. [I-D.palet-v6ops-tun-auto-disc] Palet, J. and M. Diaz, "Analysis of IPv6 Tunnel End-point Discovery Mechanisms", draft-palet-v6ops-tun-auto-disc-02 (work in progress), October 2004.Internet-Draft draft-palet-v6ops-tun-auto-disc-03, January 2005. [I-D.savola-mboned-address-discovery-problems] Savola, P., "Lightweight Multicast Address Discovery Problem Space", , February 2005. [MBONED-IETF59] "MBONED WG session at IETF59", <http://www.ietf.org/proceedings/04mar/172.htm>. [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. [RFC2608] Guttman, E., Perkins, C., Veizades, J. and M. Day, "Service Location Protocol, Version 2", RFC 2608, June 1999. [RFC2730] Hanna, S., Patel, B. and M. Shah, "Multicast Address Dynamic Client Allocation Protocol (MADCAP)", RFC 2730, December 1999. [RFC2771] Finlayson, R., "An Abstract API for Multicast Address Allocation", RFC 2771, February 2000. [RFC2908] Thaler, D., Handley, M. and D. Estrin, "The Internet Multicast Address Allocation Architecture", RFC 2908, September 2000. [RFC2909] Radoslavov, P., Estrin, D., Govindan, R., Handley, M., Kumar, S. and D. Thaler, "The Multicast Address-Set Claim (MASC) Protocol", RFC 2909, September 2000. [RFC2974] Handley, M., Perkins, C. and E. Whelan, "Session Announcement Protocol", RFC 2974, October 2000. [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003. [RITVANEN] Ritvanen, K., "Multicast Routing and Addressing", HUT Report, Seminar on Internetworking, May 2004, <http://www.tml.hut.fi/Studies/T-110.551/2004/papers/>. Author's Address Pekka Savola CSC - Scientific Computing Ltd. Espoo Finland EMail:Email: firstname.lastname@example.org Appendix A. Open Issues (This section will be removed or merged with the rest before publication..) o Is the case for IPv4 Unicast-Prefix Base Multicast addressing sufficiently strong, or could those organizations just get an AS number themselves if they really wanted to do multicast? o ShouldAppendix B. Multicast Address Discovery [[ NOTE IN DRAFT: the intent of this section has been mostly superceded by [I-D.savola-mboned-address-discovery-problems] and therefore it is put in the appendix, with pending removal in the future. As was noted in Section 3, multicast address discovery (i.e., service discovery or "rendezvous") is a problem with multicast address assignment. In particular, an acceptable mechanism (mechanisms such as Service Location Protocol (SLP) [RFC2608] seem to have been considered too complex) seems to be missing which the hosts wishing to participate in a group could use to find the address of that group [MBONED-IETF59]. It is worth noting that as long as not deploying an address assignment and service discovery protocols/mechanisms means that one mergecan get a static address assignment from IANA, there is little interest from the routing architecture document's contents hereapplication developers to actually do anything except try to get the assignment from IANA. Conclusion: if we want to use non-IANA processes, the assignments must be either forbidden completely, or made sufficiently difficult that it's easier for the application developers to take another route if a feasible mechanism is available. There are two issues in the service discovery: 1. The session initiator being able to publish the session somehow, and 2. The session participants finding out about the session (rather than creating their own). When manually configured or static IANA assignments are used, 1) should be relatively straightforward (if something needs to be manually configured or statically assigned, putting it e.g., in DNS should not be a problem). However, this is still more complex for dynamic or derived assignments because it implies that the host or the application has the right to make that publication on its own, rather than through a manual process by an administrator. 2) is always a challenge, but could leverage for example DNS (e.g., by relying on using SRV records with the DNS search path, as well?described in [I-D.iab-dns-choices] and [I-D.palet-v6ops-tun-auto-disc]). 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