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Savola 3 Internet-Draft CSC/FUNET 4 Expires: August 16, 2005 February 12, 2005 6 Lightweight Multicast Address Discovery Problem Space 7 draft-savola-mboned-address-discovery-problems-00.txt 9 Status of this Memo 11 This document is an Internet-Draft and is subject to all provisions 12 of Section 3 of RFC 3667. By submitting this Internet-Draft, each 13 author represents that any applicable patent or other IPR claims of 14 which he or she is aware have been or will be disclosed, and any of 15 which he or she become aware will be disclosed, in accordance with 16 RFC 3668. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as 21 Internet-Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on August 16, 2005. 36 Copyright Notice 38 Copyright (C) The Internet Society (2005). 40 Abstract 42 Typically applications developers have requested static IANA 43 assignments for the applications, even if the applications would 44 typically be only used within a site, between consenting sites, or 45 would not eventually even use multicast at all. This memo describes 46 this problem space, and summarizes a number of proposed approaches to 47 mitigating these problems. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 52 2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3 53 3. Mitigation Techniques . . . . . . . . . . . . . . . . . . . . 4 54 3.1 Locally Scoped Address Assignment by IANA . . . . . . . . 5 55 3.2 Single Administration Address Discovery with Server 56 Configuration . . . . . . . . . . . . . . . . . . . . . . 5 57 3.3 Zero-configuration Single Administration Address 58 Discovery . . . . . . . . . . . . . . . . . . . . . . . . 6 59 3.4 Global Multiple Administration Address Discovery . . . . . 6 60 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 61 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 62 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 63 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 64 7.1 Normative References . . . . . . . . . . . . . . . . . . . 8 65 7.2 Informative References . . . . . . . . . . . . . . . . . . 8 66 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 8 67 Intellectual Property and Copyright Statements . . . . . . . . 9 69 1. Introduction 71 Many applications have been written which leverage or could leverage 72 multicast routing infrastructures, in one or more of the following 73 scopes: (We'll get back to these later.) 75 1. link-local scope, 77 2. [geographical] site scope, 79 3. organization-local scope, 81 4. global scope, used between consenting sites/enterprises, also 82 including cases like "inside a country", or 84 5. truly a global scope. 86 Multicast-leveraging applications are often designed such that each 87 multicast group has a "server", "session creator" or some other 88 node(s) (or persons operating the nodes) which are in some way in 89 control of the application. 91 Both the "server" and "client end" of an application are currently 92 typically provisioned with the group address using static IANA 93 assignment [I-D.ietf-mboned-addrarch]. Only rarely these apps are 94 manually configured e.g. with locally scoped addresses, especially 95 the ones with a large number of clients. 97 It would be highly desirable that the applications could easily use 98 more dynamic, and more scoping-friedly mechanisms for discovering the 99 appropriate addresses to use. 101 All of these issues are only relevant to Any Source Multicast (ASM), 102 as SSM requires this information is known a priori. 104 2. Problem Statement 106 The current IANA static assignment for these applications is a 107 problem for multiple reasons: 109 o This messes up the multicast scoping plans which the site may 110 have. Each application's global address must be individually 111 scoped and filtered in all the routers and in their access lists. 112 Scoping should be easier. 114 o Static IANA assignments are required for each application; a 115 permanant global assignment for each application which could use 116 multicast depletes the resource quickly. 118 o This has issues with IPv6, because such IPv6 addresses can not be 119 scalably routed in inter-domain routing; in intra-domain, this 120 requires manual configuration or running BSR (for ff01::/16 or 121 ff02::/16 or the like) 123 o "Intended for local only use" applications typically leak through 124 to the IPv4 MSDP because there is no clear logic which ones should 125 be global and which ones are local. 127 There are at least four different proposed ways to mitigate this, 128 from the least to most extensive: 130 a. Smaller-than-global single-administration address assignment by 131 IANA (from 239/8 or elsewhere). 133 b. Smaller-than-global single-administration discovery, with the 134 expectation that a locally scoped address is manually configured 135 on the "server end". 137 c. Smaller-than-global single-administration discovery with complete 138 zero-configuration. 140 d. Global (but restricted) multi-administration discovery with some 141 amount of manual configuration. 143 We'll outline each proposed mitigation technique briefly below. 145 NOTE: David Meyer's experience from being the designated expert for 146 IANA assignments is that almost all of the requested multicast 147 addresses have been such that the requestors would not have been 148 satisfied if their application would only be restricted to operate 149 within a site. 151 If people agree on this, the first three mitigation techniques won't 152 have significant impact, because the application developers won't 153 implement the discovery in any case. They will _still_ want to get 154 the globally scoped addresses from IANA, instead of implementing the 155 "service discovery inside an organization" -shim. 157 3. Mitigation Techniques 159 The generic goals from the application/deployment perspective are: 161 o Not depending on any uncommon external infrastructure besides the 162 application itself (e.g., a MADCAP [RFC2730] server), so that the 163 application can be deployed where MADCAP server is not present. 164 I.e., this should be sufficiently lightweight to be coded in the 165 application or be used by a simple application shim library. 167 o The application should "just work" from perspective of "client 168 end" without any configuration. "Server end" may or may not 169 require configuration of an address. 171 o The presence of applications should be easily filterable at least 172 at the edges of the network. 174 o Preferably it should also be easy to segment the use of 175 application into the smallest possible scopes within the network, 176 to avoid undue state and confusion in the network. 178 3.1 Locally Scoped Address Assignment by IANA 180 If we ignore the first problem about local scoping, the easiest 181 mitigation technique might be having IANA assign locally scoped 182 addresses on FCFS basis (like UDP/TCP port numbers). This could be 183 done inside or outside of 239/8. 185 This way the local applications could easily get a local assignment 186 which could be easily filtered by site administrators at site 187 borders. 189 This is slightly inflexible as the application developers could only 190 tell whether the application's scope is link-local (there are very 191 few of these), global, or something in between. "Expanding ring 192 search" inside the site-local scopes would not be possible. 194 NOTE, based on DaveM's experience, it is not clear why the 195 application designers would accept a local range instead of a global 196 assignment, even if the application would primarily be used within a 197 local scope. 199 3.2 Single Administration Address Discovery with Server Configuration 201 The second mitigation technique would be to specify and implement a 202 mechanism, requiring no infrastructure in the network, where the 203 "server end" would be manually configured with appropriately selected 204 locally-scoped addresses which the clients would use to discover the 205 group address. 207 The client ends should discover the smallest possible scope where the 208 application is supported. 210 A few notes on this method: 212 o One could characterize a potential solution as an easily 213 implementable server shim at "server end" listening to a set 214 well-known locally-scoped multicast addresses, which would respond 215 to queries by "client end". 217 o How can the servers demultiplex "queries" sent to these addresses? 218 Are these messages in SAP format or something simpler? The query 219 must have an identifier (e.g., done by hashing a name?) which the 220 server uses to know the client is interested in the server's 221 multicast transmission. 223 o How should the servers communicate back to the clients? By 224 replying with unicast (issues after bootup with lots of nodes) or 225 do the clients also join the address (DoS potential, a very 226 crowded group which all the servers at least need to subscribe 227 to)? 229 Again, this does not solve the root problem; why would an application 230 designer implement this mechanism when he/she wants to support global 231 scoping as well? IANA assignment will be requested in any case. 233 3.3 Zero-configuration Single Administration Address Discovery 235 A slightly more extensive problem is the same as above, but assuming 236 that the application must be completely zero-configurable. That is, 237 it must work without having to manually configure anything on the 238 server end. 240 This could be achieved e.g., by adding to the above a SAP-like 241 address segments from which the addresses could be dynamically 242 reserved. This might not sit well on the organization's local 243 scoping plans, however. 245 However, it is worth considering whether this is really needed. For 246 link-local scope, this may be desirable as such requires no set-up of 247 multicast routing. But for larger scopes, is this really useful? If 248 there is no administrator to configure the address, likely there is 249 no multicast infrastructure in the first place, or desire to run the 250 application in multicast mode! 252 Again, this does not solve the root problem. 254 3.4 Global Multiple Administration Address Discovery 256 Most applications are such that they _can_ be run over 257 site/organization boundaries (even if they typically would not be), 258 so the application developers will want to support the most extensive 259 scope. There is no common local scope (even between 260 organization-local and global) which could cover these disjoint 261 global interconnections, so the applications must use global scope 262 addresses. 264 To get away from static IANA assignments, there should be a 265 lightweight multicast address discovery function which could be used 266 e.g., in the embedded devices to discover the appropriate multicast 267 address they should use. 269 Obviously, the result could also be that the application should be 270 restricted to a local scope, and use local scope addresses, but wider 271 discovery should also be supported. 273 This approach has a number of challenges, however. It's difficult to 274 visualize how multiple administrative domains could perform discovery 275 in a desired manner automatically -- we have to assume that the sites 276 might not want to tell about all of their local sessions to all the 277 other sites (i.e., you may want to allow site A to discover session 278 1, and site B to discover session 2, but not mix these). In other 279 words, there will likely need to be some manual control of what gets 280 seen to the outside and what not. This makes the mechanism more 281 complicated, and requires more network operator management. 283 Further attributes and requirements for this kind of approach remain 284 to be figured out. 286 4. Acknowledgements 288 This memo grew out of the discussions in MBONED WG, where the 289 participants were, among others, Beau Williamson, Albert Manfredi, 290 Marshall Eubanks, John Kristoff, David Meyer, Stig Venaas, Rami 291 Lehtonen, and Leonard Giuliano. 293 5. IANA Considerations 295 This memo includes no request to IANA. 297 [[Note to the RFC-Editor: this section should be removed prior to 298 publication.]] 300 6. Security Considerations 302 As section Section 3.4 describes, the organizations will not want to 303 expose all their sessions, or even knowledge that the organization is 304 using a particular application, to the outside. The confidentiality 305 needs must be considered. 307 7. References 308 7.1 Normative References 310 [I-D.ietf-mboned-addrarch] 311 Savola, P., "Overview of the Internet Multicast Addressing 312 Architecture", 313 Internet-Draft draft-ietf-mboned-addrarch-00, November 314 2004. 316 7.2 Informative References 318 [RFC2730] Hanna, S., Patel, B. and M. Shah, "Multicast Address 319 Dynamic Client Allocation Protocol (MADCAP)", RFC 2730, 320 December 1999. 322 Author's Address 324 Pekka Savola 325 CSC/FUNET 326 Espoo 327 Finland 329 Email: psavola@funet.fi 331 Intellectual Property Statement 333 The IETF takes no position regarding the validity or scope of any 334 Intellectual Property Rights or other rights that might be claimed to 335 pertain to the implementation or use of the technology described in 336 this document or the extent to which any license under such rights 337 might or might not be available; nor does it represent that it has 338 made any independent effort to identify any such rights. 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Please address the information to the IETF at 353 ietf-ipr@ietf.org. 355 Disclaimer of Validity 357 This document and the information contained herein are provided on an 358 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 359 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 360 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 361 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 362 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 363 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 365 Copyright Statement 367 Copyright (C) The Internet Society (2005). This document is subject 368 to the rights, licenses and restrictions contained in BCP 78, and 369 except as set forth therein, the authors retain all their rights. 371 Acknowledgment 373 Funding for the RFC Editor function is currently provided by the 374 Internet Society.