Malloc Working Group Roger Kermode Internet Engineering Task Force Motorola INTERNET-DRAFT 7 September 1999 Expires 7 March 2000 MADCAP Multicast Scope Nesting State Option 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 defines a new option to the Multicast Address Dynamic Client Allocation Protocol (MADCAP) to support nested scoping. The new option's purpose is to allow clients to learn which scopes nest inside each other, and hence may be used for expanding scope searches or hierarchical multicast transport. Copyright Notice Copyright (C) The Internet Society (1999). All Rights Reserved. Expires 7 March 2000 [Page 1] DRAFT 7 Sept 1999 Contents Abstract. . . . . . . . . . . . . . . . . . . . . . . . . 1 1. Introduction. . . . . . . . . . . . . . . . . . . . . 3 1.1 Time-To-Live (TTL) Scoping Split Horizon Effect. . 3 1.2 Eliminating the Split Horizion Effect with Administrative Scoping . . . . . . . . . . . . . 4 1.3 Terminology. . . . . . . . . . . . . . . . . . . . 5 2. Nested Scope Discovery. . . . . . . . . . . . . . . . 5 2.1 MADCAP processing of MZAP messages . . . . . . . . 6 2.1.1 Zone Nesting State . . . . . . . . . . . . . 6 2.1.2 Updating Scope Nesting State via the observation of NIMs. . . . . . . . . . . . . 7 2.1.3 Updating Scope Nesting State due to Timer Expiration . . . . . . . . . . . . . . 7 2.2 Multicast Scope List Option. . . . . . . . . . . . 8 2.3 Multicast Scope Nesting State Option . . . . . . . 8 2.3.1 Representing the Multicast Scope Nesting State. . . . . . . . . . . . . 8 2.3.2 Multicast Scope Nesting State Option Usage . 10 3. Multicast Scope Nesting State Option Format . . . . . 10 4. Constants . . . . . . . . . . . . . . . . . . . . . . 11 5. Security Considerations . . . . . . . . . . . . . . . 11 6. IANA Considerations . . . . . . . . . . . . . . . . . 11 7. Acknowledgements. . . . . . . . . . . . . . . . . . . 11 8. References. . . . . . . . . . . . . . . . . . . . . . 12 9. Author's Address. . . . . . . . . . . . . . . . . . . 12 10. Full Copyright Statement. . . . . . . . . . . . . . . 12 Expires 7 March 2000 [Page 2] DRAFT 7 Sept 1999 1. Introduction The Multicast Address Dynamic Client Allocation Protocol (MADCAP) [MADCAP] affords client applications the ability to request multicast address allocation services from multicast address allocation servers. As part of the Multicast Address Allocation Architecture [MAAA], MADCAP gives clients the ability to reserve, request, and extend leases on multicast addresses. A new MADCAP option, the "Multicast Scope Nesting State" option is proposed to allow clients to learn not only which scopes exist via the existing "Multicast Scope List" option, but how these scopes nest inside each other. This new option will also afford clients the ability to make better scope selections for a given session and also to construct hierarchies of administratively scoped zones. These hierarchies may then be used to perform expanding scope searches instead of the expanding ring or increasing-TTL searches. Expanding scope searches do not suffer from the Split-Horizon Effect present in expanding ring searches, and therefore both simplify protocol design and provide better localization. 1.1 Time-To-Live (TTL) Scoping Split Horizon Effect Multicast searching and localized recovery transport techniques that rely on TTL scoping are known to suffer when deployed in a wide scale manner. The failing lies in the split horizon effect shown below in Figure 1. Here a requestor and responder must each use a TTL that is sufficiently large that they will reach the other. When they are separated by many hops the TTL becomes large and the number of receivers within the multicast tree that only receive either the request or the response can become very large. ....... ******* ... *** *** A Only hears S .. ** .. ** B hears S and R . * . * C Only hears R . * . * . S<------->R * . TTL Boundary for S . * . * * TTL Boundary for R . A * B . C * .. ** .. ** ... *** *** ....... ******* Figure 1 : Split Horizon Problem from TLL scoping Expires 7 March 2000 [Page 3] DRAFT 7 Sept 1999 1.2 Eliminating the Split Horizon Effect with Administrative Scoping Ideally, a mechanism that either eliminates or minimizes the size of the A and C regions in Figure 1. as shown in Figure 2. is needed to solve this problem. One mechanism that affords this ability is administrative scoping [RFC2365], in which routers prevent the passing of packets within a certain range of multicast addresses. Routers that have this feature can be configured to provide a perimeter around a region of the network. This perimeter is said to encompass an administratively scoped zone inside of which traffic sent to that particular range of multicast addresses can neither leave nor enter. Routers can construct and manage administratively scoped zones using the MZAP [MZAP] protocol. ........................ . . . many hops . .S<------------------------>R. . . . . ........................ Figure 2 : Eliminating the Split Horizon Effect MZAP also includes the ability to determine whether or not administratively scoped regions nest inside one another. This allows hierarchies such as that shown in Figure 1. to be constructed. . . . . . . . . . . . . . . . . . . . scope a . Scope Boundaries . . . = scope a . _______________ ________________ . - = scopes b,c . / scope b \ / scope c \ . # = scopes d,e,f, & g .| | | |. .| ##### ##### | | ##### ##### |. .| #scope# #scope#| | #scope# #scope# |. .\ # d # # e #| | # f # # g # /. .\ #### #####/ \ ##### #### /. .\____________/ \_____________/. . . . . . . . . . . . . . . . . . Figure 3 : Admin Scope Zone Nesting Hierarchy example A generic expanding scope search algorithm [KERM] that exploits the existence of a hierarchy of administratively scoped zones is: Expires 7 March 2000 [Page 4] DRAFT 7 Sept 1999 1) Starting with the smallest known scope for the session, a requestor in that session issues a request and waits for a reply. 2) If a node within that scope hears a request at a certain scope that it can satisfy it sends a response at that same scope, possibly after some random delay to reduce duplicate responses. 3) Nodes that receive a response to a particular request while waiting to send a response to that request, suppress their own response. 4) If a requestor issues a request to a scope, and does not hear a response after specified amount of time, it retransmits its request at the same scope a small number of additional times. Should these retries fail to elicit a response, the requestor increases the scope to the next largest scope and tries again. 5) Requestors increase the scope of the request according to step 4 until either a response is received, or the largest legal scope for the session is reached. Should attempts to elicit a response at the largest possible scope for the session fail to yield a response, the requestor may conclude that the request cannot be met. 1.3. Terminology 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]. Throughout the rest of this document, the words "server" or "MADCAP server" refer to a host providing multicast address allocation services via MADCAP. The words "client" or "MADCAP client" refer to a host requesting multicast address allocation services via MADCAP. 2. Nested Scope Discovery The "Multicast Scope Nesting State" option is proposed to augment the "Multicast Scope List" option within the MADCAP protocol by providing additional information to applications about how scopes nest. MADCAP servers shall learn this additional information for their clients by noting the contents of Zone Not Inside Messages (ZNIM) that are periodically transmitted by the Zone Border Routers that enforce the boundaries of administratively scoped zones. Expires 7 March 2000 [Page 5] DRAFT 7 Sept 1999 2.1 MADCAP Server processing of MZAP messages MADCAP servers listen to MZAP traffic originated by ZBRs to learn which scopes exist (via Zone Announcement Messages, ZAMs) and which of these scopes do not nest (via Not Inside Messages, NIMs). This state must be cached within the MADCAP server. 2.1.1 Scope Nesting State Two scopes, X and Y, can be related in one of four possible ways. 1) X nests inside Y, 2) Y nests inside X, 3) X and Y do not nest (the overlap case), and 4) X and Y nest inside each other. The fourth case SHOULD be interpreted as meaning that X and Y have exactly the same border. This does not mean that X and Y are the same scope since X and Y may correspond to different ranges of the multicast address space. This state MUST be stored in the MADCAP servers which MUST allow the state to be updated as network conditions change. Each MADCAP server SHOULD therefore define two pieces of state that describe whether "scope X nests in scope Y" or vice versa. For the remainder of this document the nesting relationship shall be denoted as the "/" where X/Y defines the relation "X nests inside Y". This relation shall be understood to take one of the values "true", or "false." Nesting relationship state that is indeterminate is considered to be "false." Since the decision as to whether one scope nests inside another must be made in a collective fashion by all the routers for a scope, MADCAP servers MUST include mechanisms to allow for: a) whether the nesting decision is still under consideration or can be considered definitive, and therefore be announced to MADCAP clients. b) whether one or both scopes for a particular nesting state entry have been destroyed, and hence whether the nesting state should therefore be discarded. c) whether the scope boundaries have changed so that whereas scope X did or did not nest inside scope Y, the opposite is now true. Expires 7 March 2000 [Page 6] DRAFT 7 Sept 1999 To realize a) and b) MADCAP servers MUST implement the following two timers; NEST_NO_NIM_TIMER, SCOPES_EXIST_TIMER. The first timer, NEST_NO_NIM_TIMER, is used to mark time between a MADCAP server's first hearing of a scope and making a decision about its relationship to other zones. Up until the time this timer expires MADCAP servers MUST NOT conclude that the scope nests within another. The NEST_NO_NIM_TIMER timer will also be used to timeout X/Y = "false" state to allow X/Y to be reset to true in the event that the boundaries for zone X and zone Y change so that zone X now nests inside zone Y. The second timer SCOPES_EXIST_TIMER will be used to timeout the internal state between two scopes in the event that one or both scopes are destroyed. 2.1.2 Updating Scope Nesting State via the observation of NIMs When a MADCAP server S receives a NIM from a ZBR containing information that scope X does not nest in scope Y, it MUST update its internal state in the following manner. 1) S SHOULD update its internal X/Y state to "false". 2) S SHOULD restart NEST_NO_NIM_TIMER for the newly updated X/Y state. 2.1.3 Updating Scope Nesting State due to timer expiration. MADCAP servers will also update X/Y nesting state upon the expiration of timers. o If the NEST_NO_NIM_TIMER expires for a state entry X/Y AND no NIMs have been received that indicate scope X does not nest inside scope Y, a MADCAP Server, S, MAY conclude that scope X nests inside scope Y. As a result S will change X/Y from "false" to "true". When a state change from "false" to "true" occurs for X/Y, S must also start the ZONES_EXIST_TIMER timer for X/Y. The ZONES_EXIST_TIMER should only reset when a ZAM has been received for both zone X and zone Y since the last time it was restarted. This ensures that both zone X and zone Y are known to still exist. o If the ZONES_EXIST_TIMER expires for a state entry X/Y, S SHOULD conclude that either zone Y or zone X no longer exists and hence that both X/Y and Y/X state should be destroyed. Expires 7 March 2000 [Page 7] DRAFT 7 Sept 1999 2.2 Multicast Scope List Option To understand the "Multicast Scope Nesting State" option one must first understand the the "Multicast Scope List" option. The Multicast Scope List option in MADCAP is used by MADCAP servers to inform MADCAP clients of which zones are visible. Visible scopes are enumerated inside the option as successive tuples, where each tuple consists of the following information: o Scope ID: The smallest address for the range of multicast addresses covered by this scop o Last Address: The largest address for the range of multicast addresses covered by this scope. o TTL: The TTL to be used when sending message to this scope. o Name(s): One or more languages specific name for the scope. 2.3 Multicast Scope Nesting State Option Given a Multicast Scope List containing descriptions for n scopes one can form n(n-1)/2 pairings. As was shown in section 2.1.1 each pairing can take on one of four possible states. Thus, for a list of n scopes there exists 2 pieces of information for each pairing for a total of n(n-1) pieces of information regarding which scopes do and do not nest inside each other. This information is most easily and efficiently conveyed in the a compressed bit matrix as shown in section 2.4. 2.3.1 Representing the Multicast Scope Nesting State As was stated in section 2.3, the Multicast Nesting State option must convey a total of n(n-1) pieces of state, where n is the number of scopes listed in the preceding Multicast Scope List Option. This information will be sparse, since at most only a few scopes will nest. Expires 7 March 2000 [Page 8] DRAFT 7 Sept 1999 There are several ways to represent this information using full matricies, sparse-matricies, and using lists of variable length lists. In the interests of maximal efficiency and flexibility, the Multicast Nesting State Option uses a bit-packed matrix approach. In this approach a matrix constructed for each piece of X/Y state where X is the row and Y is the column. A "1" in the matrix means that the relationship "row nests inside column" is true, while a "0" means that this relationship is wither false or indeterminate. The diagonal of the matrix is removed, since this is the case where X is the same as Y, and each row is then zero-padded to the next byte boundary to give the final representation. An example of how a matrix would be constructed for the following scope nestings S1/S2, S2/S3, S2/S4, S3/S5, S4/S5, S5/S6, and S6/S7. Note that a number of additional nesting relationships are implied from this set. ________________________________ /............ \ \ \ /.S3 _________._____ \ \ \ |. /+--+ \ . \ | | | |. | |S1| S2 | . S4 | S5 | S6 | S7 | |. \+--+ / . | | | | \. \______/ . | | | | \....\....... / / / / \ \___________/ / / / \___________________/ / / \ Y \______________________/ / X \ 1 2 3 4 5 6 7 \_________________________/ +-+-+-+-+-+-+-+ 1 |1 1 1 1 1 1 1| *111111 1111 1100 0xfc 2 |0 1 1 1 1 1 1| 0*11111 0111 1100 0x7c 3 |0 0 1 0 1 1 1| 00*0111 0001 1100 0x1c 4 |0 0 0 1 1 1 1| => 000*111 => 0001 1100 => 0x1c 5 |0 0 0 0 1 1 1| 0000*11 0000 1100 0x0c 6 |0 0 0 0 0 1 1| 00000*1 0000 0100 0x04 7 |0 0 0 0 0 0 1| 000000* 0000 0000 0x00 +-+-+-+-+-+-+-+ ^^ * = X/Y where zero padding X == Y Final Representation: 0xfc 0x7c 0x1c 0x1c 0x0c 0x04 0x00 Figure 4. Scope Nesting Example Expires 7 March 2000 [Page 9] DRAFT 7 Sept 1999 2.3.2 Multicast Scope Nesting State Option Usage The "Multicast Scope Nesting State" option is dependent upon the "Multicast Scope List" option. This decision was made according to the following reasoning. The Multicast Nest State Option requires that the scopes be identified along with their nesting properties. Since the information needed to describe a scope is contained in the Multicast Scope List option and this information can change, the MADCAP messages that contain the Multicast Scope Nesting State option must be atomic and therefore must include the "Multicast Scope List Option." Thus, the "Multicast Scope Nesting State" option MAY only be used in messages that carry the "Multicast Scope List" option, specifically: DISCOVER, OFFER, ACK (in response to RENEW) The "Multicast Scope Nesting State" option MUST NOT be used in messages that do not carry the "Multicast Scope List" option, specifically: INFORM, ACK (in response to INFORM), RENEW, RELEASE, ACK (in response to RELEASE), NAK, any DISCOVER/OFFER/ACK (in response to RENEW) that does not carry the "Multicast Scope List" Since the Multicast Nest State option is dependent upon the Multicast Scope List option, it MUST follow, and NEVER precede, the Multicast Scope List option. 3. Multicast Scope Nesting State Option Format Code Len Count Nest State Matrix +-----+-----+-----+-----+-----+-----+-...-+-----+ | OPTID | p | m | N1 | | Nm | +-----+-----+-----+-----+-----+-----+-...-+-----+ Code: 16 bits Option identifier (OPTID), to be assigned by IANA. Len: 16 bits The length of the option in bytes. Count: 8 bits The number of zones present in the Nest State Matrix. This value MUST be identical to the Count field in the preceding Multicast State List option. Expires 7 March 2000 [Page 10] DRAFT 7 Sept 1999 Nest State Matrix: The compressed bit-packed representation of the matrix, derived in the same manner as shown in Figure 4. Note for N scopes the compressed matrix will be Nxceil((N-1)/8) bytes long. The scopes corresponding to the rows and columns of this matrix list in the same order as they appear in the Multicast Scope List Option. 4. Constants [OPTID] The option identifier for the Mutlicast Scope Nesting State option, to be assigned by IANA. 5. Security Considerations Since this draft proposes an extension to the MADCAP protocol via the addition of a new option, the same set of security concerns apply. In addition to these concerns are those that would arise were the information in the Multicast Scope Nesting State option to be falsified. In this case the clients would be misinformed as to which scopes nest inside one another. In this event, the client would then make incorrect decisions regarding the order in which to use the scopes. The effect of this would be to use larger scopes than necessary, which would effectively flatten any scope hierarchy present and nullify the advantage afforded by the hierarchy's presence. Thus a malformed or tampered Multicast Scope Nesting option may cause protocols that rely upon the existence of a scoping hierarchy to scale less well, but it would not prevent them from working. 6. IANA Considerations The Multicast Nesting State Option will require the assignment of an additional option code to the MADCAP [MADCAP] protocol. 7. Acknowledgments The Author would like to acknowledge Mark Handley and Dave Thaler for the helpful discussions and feedback which helped shape and refine this document. Expires 7 March 2000 [Page 11] DRAFT 7 Sept 1999 8. References [KERM] Kermode, R., "Smart Network Caches: Localized Content and Application Negotiated Recovery Mechanisms for Multicast Media Distribution", Ph.D. Thesis, MIT Media Laboratory, June 1998. [MAAA] Handley, M., Thaler, D., and D. Estrin, "The Internet Multicast Address Allocation Architecture", Internet Draft, December 1997. [MADCAP] Patel. B.V., Shah, M., Hanna, S.R., "Multicast Address Dynamic Client Allocation Protocol (MADCAP)", Internet Draft, draft-ietf-malloc-madcap-03.txt [MZAP] Handley, M., Thaler, D., Kermode, R., "Multicast-Scope Zone Announcement Protocol (MZAP)", draft-ietf-mboned-mzap-03.txt, Internet-Draft, February, 1999. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP, RFC 2119, March 1997. [RFC2365] Meyer, D., "Administratively Scoped IP Multicast", BCP, RFC 2365, July 1998. 9. Author's Address Roger Kermode Motorola Australian Research Centre Locked Bag 5028 Botany, NSW 1455 Australia Email: Roger_Kermode@email.mot.com 10. Full Copyright Statement Copyright (C) The Internet Society (1999). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of Expires 7 March 2000 [Page 12] DRAFT 7 Sept 1999 developing Internet standards in which case the procedures for copyrights defined in the Internet languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." Expires 7 March 2000 [Page 13]