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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group Ross Finlayson 2 Internet-Draft LIVE.COM 3 Expire in six months 1999.08.22 5 An Abstract API for Multicast Address Allocation 7 9 1. Status of this Memo 11 This document is an Internet-Draft and is in full conformance 12 with all provisions of Section 10 of RFC2026. 14 Internet-Drafts are working documents of the Internet Engineering 15 Task Force (IETF), its areas, and its working groups. Note that 16 other groups may also distribute working documents as 17 Internet-Drafts. 19 Internet-Drafts are draft documents valid for a maximum of six 20 months and may be updated, replaced, or obsoleted by other 21 documents at any time. It is inappropriate to use Internet- 22 Drafts as reference material or to cite them other than as 23 "work in progress." 25 The list of current Internet-Drafts can be accessed at 26 http://www.ietf.org/ietf/1id-abstracts.txt 28 The list of Internet-Draft Shadow Directories can be accessed at 29 http://www.ietf.org/shadow.html. 31 2. Abstract 33 This document describes the ''abstract service interface'' for the dynamic 34 multicast address allocation service, as seen by applications. While it 35 does not describe a concrete API (i.e., for a specific programming 36 language), it describes - in abstract terms - the semantics of this 37 service, including the guarantees that it makes to applications. 39 Additional documents (not necessarily products of the IETF) would describe 40 concrete APIs for this service. 42 3. Introduction 44 Applications are the customers of a multicast address allocation service, 45 so a definition of this service should include not only the inter-node 46 network protocols that are used to implement it, but also the 'protocol' 47 that applications use to access the service. While APIs ("application 48 programming interfaces") for specific programming languages (or operating 49 systems) are outside the domain of the IETF, it is appropriate for us to 50 define - in abstract terms - the semantic interface that this service 51 presents to applications. Specific APIs would then be based upon this 52 abstract service interface. 54 Note that it is possible to implement the multicast address allocation 55 service in at least two different ways. The first (& perhaps most common) 56 way is for end nodes to allocate addresses by communicating with a separate 57 "Address Allocation Server" node, using the "Host to Address Allocation 58 Server" network protocol (MADCAP) [1][7]. Alternatively, an 59 "Address Allocation Server" implementation might be co-located (along 60 with one or more applications) on an end node, in which case some other, 61 internal, mechanism might be used to access the server. In either case, 62 however, the abstract service interface (and, presumably, any specific 63 APIs) would remain the same. 65 The remainder of this document describes the abstract interface. 67 Note that this interface is intended only for the allocation of dynamic 68 multicast addresses, as used by the traditional multicast service model [2]. 69 Future multicast service models might allocate or assign multicast 70 addresses in other ways, but this is outside the scope of this document. 72 4. Abstract Data Types 74 The interface described below uses the following abstract data types: 75 - AddressFamily: e.g., IPv4 or IPv6 76 - MulticastAddress: An actual multicast address (i.e., that could 77 subsequently 78 be used as the destination of a datagram) 79 - MulticastAddressSet: A set of "MulticastAddress"es 80 - LanguageTag: The code for a (human) language, as defined in [4] 81 - Scope: An "administrative scope" [3] from which multicast addresses 82 are to be allocated. Each scope is a "MulticastAddressSet", 83 with an associated set of (character-string) names - indexed by 84 "LanguageTag". (Each language tag has at most one corresponding 85 name, 86 per scope.) For each scope, a (language tag, name) pair may be 87 defined to be the 'default' name for this scope. (See the section 88 "Querying the name of a scope" below.) 89 (An implementation of this abstract data type might also include 90 other 91 information, such as a default TTL for the scope.) 92 - Time: An (absolute) event time. This is used for specifying the 93 "lifetime" of multicast addresses: the period of time during which 94 allocated multicast addresses are guaranteed to be available. 95 (It is also used to specify the desired start time for an 96 "advance allocation".) 97 Note that a concrete API might prefer to specify some of these 98 times as relative times (i.e., relative to the current time-of-day), 99 rather than absolute time. (Relative times have the advantage of 100 not requiring clock synchronization.) 101 - Lease: A compound data type that describes the result of a (successful) 102 multicast address allocation. It consists of: 103 - [MulticastAddressSet] The set of addresses that were allocated; 104 - [AddressFamily] The address family of these addresses 105 - [Time] The lifetime of these addresses (the same for each address) 106 - [Time] The "start time" of the allocation. (See the discussion of 107 "advance allocation" below.) 108 (A concrete API would likely also include a 109 MADCAP "Lease Identifier" [1].) 110 - NestingRelationship: A binary data type that describes whether 111 or not two scopes nest. Two scopes nest if traffic sent 112 sent to a multicast group within one scope could be seen 113 by all hosts present within the other scope were they to 114 join the multicast group within the first scope. This value 115 would be "False" for overlapping scopes where only some 116 (or none) of the hosts within the second scope could see 117 traffic sent to an address due to the presence of an 118 administratively scoped boundary. In cases where the first 119 and second scopes are topologically identical this value 120 would be "True." 121 - Status: A result code. 123 5. The Abstract Interface 125 5.1 Allocating multicast addresses: 126 alloc_multicast_addr(in AddressFamily family, 127 in Scope scope, 128 in Integer minDesiredAddresses, 129 in Integer maxDesiredAddresses, 130 in Time minDesiredStartTime, 131 in Time maxDesiredStartTime, 132 in Time minDesiredLifetime, 133 in Time maxDesiredLifetime, 134 out Lease multicastAddressSetLease, 135 out Status status) 136 This operation attempts to allocate a set of multicast addresses 137 (the size of this set is in the range 138 [minDesiredAddresses, maxDesiredAddresses]) within the given address 139 family and scope, and within a given range of desired 140 lifetimes. ("minDesiredStartTime" and "maxDesiredStartTime" are 141 used to specify "advance allocation"; this is described in more 142 detail below.) 144 If the address allocation succeeds, the result is returned in 145 "multicastAddressSetLease" (with "status" = OK). 147 During the lifetime of this lease, the allocation service will 148 make a "best-effort" attempt to not allocate any of these addresses 149 to others. (However, once the lease's lifetime has expired, any of 150 its addresses can be allocated to others.) 152 Multicast addresses are allocated for a limited lifetime. 153 An application may attempt to extend this lifetime, but this 154 operation may fail. Therefore, an application must be prepared 155 for the possibility it will not be able to use the same addresses 156 for as long as it desires. In particular, the application must 157 be prepared to either quit early (because its original multicast 158 address assignments have expired), or, alternatively, to 159 occasionally 160 'renumber' its multicast addresses (in some application or 161 higher-level-protocol dependent way), by making a new allocation. 162 However, if an application needs to consider 'renumbering', it will 163 always know this in advance, at the time it acquired its current 164 address(es) - by checking the lifetime in the returned lease. 165 An application will never need to be notified asynchronously of 166 the need to 'renumber'. 168 Possible errors: 169 - bad address family 170 - bad scope 171 - bad desired number of addresses (e.g., max < min) 172 - bad desired lifetimes (e.g., max < min) 173 - errors with the two "start time" parameters (see 174 "Advance allocation" below) 175 - no addresses can be allocated (for the requested 176 parameters) 178 An allocation attempt can also fail with a result "status" code 179 of TRY_LATER, indicating that the requested allocation cannot 180 be made at this time, but that it might succeed if the caller 181 retries the attempt at some future time. (This future time is 182 returned in the "start time" field of the 183 "multicastAddressSetLease"; 184 the other parts of this lease are undefined.) 186 Note that a concrete (i.e., programming language-specific) API for 187 multicast address allocation will probably include additional, 188 specialized variants of this general allocation operation. For 189 instance, it may include separate operations for: 190 - allocating only a single address 191 (i.e., minDesiredAddresses = maxDesiredAddresses = 1); 192 - (attempting to) allocate an address with a single, fixed 193 lifetime (i.e., minDesiredLifetime = maxDesiredLifetime); 194 - (attempting to) allocate an address for immediate use 195 (i.e., minDesiredStartTime = maxDesiredStartTime = 'now') 197 5.2 Changing multicast addresses' lifetime: 198 change_multicast_addr_lifetime(in Lease multicastAddressSetLease, 199 in Time minDesiredLifetime, 200 in Time maxDesiredLifetime, 201 out Time lifetime) 202 This operation attempts to change the lifetime of previously 203 allocated multicast addresses. Unless an error occurs, it returns 204 the new lifetime (which might remain unchanged). 206 Possible errors: 207 - bad address family 208 - bad durations (e.g., max < min) 209 - the addresses' lifetime could not be changed 210 (and the existing lifetime was not in the requested range 211 [minDesiredLifetime,maxDesiredLifetime]) 212 - the addresses were not ones that we had allocated 213 (see section 5.9) - or they have already expired 215 5.3 Deallocating multicast addresses: 216 deallocate_multicast_addr(in Lease multicastAddressSetLease) 217 This operation attempts to deallocate previously allocated 218 multicast addresses. 220 Possible errors: 221 - bad address family 222 - the addresses were not ones that we had allocated 223 (or they have already expired) 225 5.4 Querying the set of usable multicast address scopes: 226 get_multicast_addr_scopes(in AddressFamily family, 227 out "set of" Scope) 228 This operation returns the set of administrative multicast address 229 scopes that are defined for this node. 231 Possible errors: 232 - bad address family 234 5.5 Querying the name of a scope: 235 get_scope_name(in Scope scope, 236 in LanguageTag language, 237 out String name, 238 out LanguageTag languageForName) 239 This operation returns a character-string name for a given scope. 240 If the scope has a name in the specified "language", then this name 241 (and language) is returned. Otherwise, the scope's default 242 (language, name) pair is returned. 244 Possible errors: 245 - bad scope 247 5.6 Querying the nesting state of known usable multicast address scopes: 248 get_scope_nesting_state(in "set of" Scope, 249 out "matrix of" NestingRelationship) 251 Possible errors: 252 - bad scope. 253 - nesting state undetermined at this time. 255 This operation would return a matrix that shows the 256 current nesting relationships between the supplied 257 set of scopes which would have previously been supplied 258 via the get_multicast_addr_scopes(...) function. 260 5.7 Querying the set of scopes that a given scope is known to nest inside: 261 get_larger_scopes(in Scope, 262 out "set of" Scope) 264 This operation returns the set of administrative multicast 265 address scopes that are known to encompass the supplied 266 Scope. 268 Possible errors: 269 - bad scope. 270 - nesting state undetermined at this time. 272 5.8 Querying the set of scopes that are known to nest inside a given scope: 273 get_smaller_scopes(in Scope, 274 out "set of" Scope) 276 This operation returns the set of administrative multicast 277 address scopes that are known to nest inside the supplied 278 Scope (NB this would include those scopes that are 279 topologically identical to the supplied scope). 281 Possible errors: 282 - bad scope. 283 - nesting state undetermined at this time. 285 5.9 Note: 286 The decision as to who is allowed to deallocate (or change the lifetime 287 of) a previously allocated multicast address set lease is 288 implementation-specific, and depends upon the security policy of the host 289 system. Thus it is not specified in this abstract API. One possible 290 starting point, however, is the following: 291 A previously allocated multicast address can be deallocated (or have 292 its lifetime queried or changed) by the same "principal", and on the 293 same node, as that which originally allocated it. ("principal" 294 might, 295 for example, be a "user" in the host operating system.) 297 5.10 Advance allocation 298 ======================= 299 By specifying "minDesiredStartTime = maxDesiredStartTime = 'now'", 300 the address allocation operation - "alloc_multicast_addr" - described above 301 can be used to request a set of multicast addresses that can be used 302 *immediately* (and until their lifetime expires). During this whole time, 303 the addresses are not available for allocation to others. 305 It is also possible - using the "minDesiredStartTime" and 306 "maxDesiredStartTime" parameters - to allocate multicast addresses 307 *in advance* - i.e., so that they have a future "start time" as well as 308 an expiration time. Before the start time, the multicast addresses may 309 be allocated to others. 311 Advance allocation is convenient for allocating addresses for events that 312 begin far in the future - e.g., several weeks or months away. Without 313 advance allocation, it would be necessary to allocate addresses for a long 314 period of time - even when it will not be used. Such a request would not 315 only be a wasteful use of the multicast address space, but it may also be 316 difficult to implement (especially since address allocations are expected 317 to remain valid in spite of topology changes). 319 Advance allocation requests can produce the following errors (in addition to 320 those defined earlier): 321 - bad start time durations (e.g., max < min) 322 - requested start times conflict with requested lifetimes 323 (i.e., min start time > max lifetime) 325 The following operation is also defined: 327 change_multicast_addr_start_time(in Lease multicastAddressSetLease, 328 in Time minDesiredStartTime, 329 in Time maxDesiredStartTime, 330 out Time startTime) 331 This operation attempts to change the start time of previously 332 allocated multicast addresses. Unless an error occurs, it returns 333 the new start time (which might remain unchanged). 335 Possible errors: the same as "change_multicast_addr_lifetime" 337 6. Security Considerations 339 As noted in section 5.9 above, each implementation of this abstract API 340 should define a security policy that specifies when (and by whom) 341 previously allocated multicast addresses can be deallocated (or queried, 342 or have their lifetime changed). 344 Because multicast addresses are a finite resource, there is a potential for 345 a "denial of service" attack by allocating a large number of multicast 346 addresses without deallocating them. Preventing such an attack, however, 347 is not the role of the API, but rather by the underlying MAAS ("Multicast 348 Address Allocation Server(s)" [6]). 350 7. Acknowledgements 352 Many thanks to other participants in the "MALLOC" working group 353 - in particular Steve Hanna, Dave Thaler, Roger Kermode, 354 and Pavlin Radoslavov - for their valuable comments. 356 8. References 358 [1] Patel, B., Shah, M., Hanna, S., 359 "Multicast Address Dynamic Client Allocation Protocol (MADCAP)", 360 Work-in-Progress, Internet-Draft "draft-ietf-malloc-madcap-06.txt", 361 August, 1999. 362 [2] Deering, S., "Host Extensions for IP Multicasting", 363 RFC 1112, August 1989. 364 [3] Meyer, D., "Administratively Scoped IP Multicast", 365 RFC 2365 (BCP 23), July, 1998. 366 [4] Alvestrand, H., "Tags for the Identification of Languages", 367 RFC 1766, March 1995. 368 [5] Handley, M., Jacobson, V., "SDP: Session Description Protocol", 369 RFC 2327, April 1998. 370 [6] Estrin, D., Handley, M., Thaler, D., 371 "The Internet Multicast Address Allocation Architecture", 372 Work-in-Progress, Internet-Draft "draft-ietf-malloc-arch-01.txt", 373 May 1999. 374 [7] Kermode, R. "MADCAP Multicast Scope Nesting State Option," 375 Work-In-Progress, Internet-Draft 376 "draft-ietf-malloc-madcap-nest-opt-01.txt", April 1999. 378 9. Author's Address 380 Ross Finlayson, 381 Live Networks, Inc. (LIVE.COM) 382 email: finlayson@live.com 383 WWW: http://www.live.com/