--- 1/draft-ietf-roll-trickle-mcast-02.txt 2013-01-24 18:06:18.795707514 +0100 +++ 2/draft-ietf-roll-trickle-mcast-03.txt 2013-01-24 18:06:18.835707987 +0100 @@ -1,842 +1,1000 @@ ROLL J. Hui Internet-Draft Cisco Intended status: Standards Track R. Kelsey -Expires: April 22, 2013 Silicon Labs - October 19, 2012 +Expires: July 28, 2013 Silicon Labs + January 24, 2013 Multicast Protocol for Low power and Lossy Networks (MPL) - draft-ietf-roll-trickle-mcast-02 + draft-ietf-roll-trickle-mcast-03 Abstract This document specifies the Multicast Protocol for Low power and Lossy Networks (MPL) that provides IPv6 multicast forwarding in constrained networks. MPL avoids the need to construct or maintain any multicast forwarding topology, disseminating messages to all MPL - forwarders in an MPL domain. MPL uses the Trickle algorithm to drive - packet transmissions for both control and data-plane packets. - Specific Trickle parameter configurations allow MPL to trade between - dissemination latency and transmission efficiency. + forwarders in an MPL domain. MPL uses the Trickle algorithm to + manage message transmissions for both control and data-plane + messages. Different Trickle parameter configurations allow MPL to + trade between dissemination latency and transmission efficiency. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." - This Internet-Draft will expire on April 22, 2013. + This Internet-Draft will expire on July 28, 2013. Copyright Notice - Copyright (c) 2012 IETF Trust and the persons identified as the + Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 - 4. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 7 - 4.1. MPL Option . . . . . . . . . . . . . . . . . . . . . . . . 7 - 4.2. ICMPv6 MPL Message . . . . . . . . . . . . . . . . . . . . 8 - 4.2.1. MPL Window . . . . . . . . . . . . . . . . . . . . . . 9 - 5. MPL Forwarder Behavior . . . . . . . . . . . . . . . . . . . . 11 - 5.1. Multicast Packet Dissemination . . . . . . . . . . . . . . 11 - 5.1.1. Trickle Parameters and Variables . . . . . . . . . . . 12 - 5.1.2. Proactive Propagation . . . . . . . . . . . . . . . . 12 - 5.1.3. Reactive Propagation . . . . . . . . . . . . . . . . . 13 - 5.2. Sliding Windows . . . . . . . . . . . . . . . . . . . . . 13 - 5.3. Transmission of MPL Multicast Packets . . . . . . . . . . 15 - 5.4. Reception of MPL Multicast Packets . . . . . . . . . . . . 16 - 5.5. Transmission of ICMPv6 MPL Messages . . . . . . . . . . . 16 - 5.6. Reception of ICMPv6 MPL Messages . . . . . . . . . . . . . 17 - 6. MPL Parameters . . . . . . . . . . . . . . . . . . . . . . . . 19 - 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20 - 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 - 9. Security Considerations . . . . . . . . . . . . . . . . . . . 22 - 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23 - 10.1. Normative References . . . . . . . . . . . . . . . . . . . 23 - 10.2. Informative References . . . . . . . . . . . . . . . . . . 23 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24 + 3. Applicability Statement . . . . . . . . . . . . . . . . . . . 5 + 4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 6 + 4.1. Information Base Overview . . . . . . . . . . . . . . . . 6 + 4.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 6 + 4.3. Signaling Overview . . . . . . . . . . . . . . . . . . . . 7 + 5. MPL Constants . . . . . . . . . . . . . . . . . . . . . . . . 9 + 5.1. Multicast Addresses . . . . . . . . . . . . . . . . . . . 9 + 5.2. Message Types . . . . . . . . . . . . . . . . . . . . . . 9 + 5.3. MPL Forwarder Parameters . . . . . . . . . . . . . . . . . 9 + 5.4. Trickle Parameters . . . . . . . . . . . . . . . . . . . . 9 + 6. Protocol Message Formats . . . . . . . . . . . . . . . . . . . 11 + 6.1. MPL Option . . . . . . . . . . . . . . . . . . . . . . . . 11 + 6.2. MPL Control Message . . . . . . . . . . . . . . . . . . . 12 + 6.3. MPL Seed Info . . . . . . . . . . . . . . . . . . . . . . 13 + 7. Information Base . . . . . . . . . . . . . . . . . . . . . . . 15 + 7.1. Local Interface Set . . . . . . . . . . . . . . . . . . . 15 + 7.2. Domain Set . . . . . . . . . . . . . . . . . . . . . . . . 15 + 7.3. Seed Set . . . . . . . . . . . . . . . . . . . . . . . . . 15 + 7.4. Buffered Message Set . . . . . . . . . . . . . . . . . . . 15 + 8. MPL Domains . . . . . . . . . . . . . . . . . . . . . . . . . 17 + 9. MPL Seed Sequence Numbers . . . . . . . . . . . . . . . . . . 18 + 10. MPL Data Messages . . . . . . . . . . . . . . . . . . . . . . 19 + 10.1. MPL Data Message Generation . . . . . . . . . . . . . . . 19 + 10.2. MPL Data Message Transmission . . . . . . . . . . . . . . 19 + 10.3. MPL Data Message Processing . . . . . . . . . . . . . . . 20 + 11. MPL Control Messages . . . . . . . . . . . . . . . . . . . . . 22 + 11.1. MPL Control Message Generation . . . . . . . . . . . . . . 22 + 11.2. MPL Control Message Transmission . . . . . . . . . . . . . 22 + 11.3. MPL Control Message Processing . . . . . . . . . . . . . . 23 + 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25 + 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 + 13.1. MPL Option Type . . . . . . . . . . . . . . . . . . . . . 26 + 13.2. MPL ICMPv6 Type . . . . . . . . . . . . . . . . . . . . . 26 + 13.3. Well-known Multicast Addresses . . . . . . . . . . . . . . 26 + 14. Security Considerations . . . . . . . . . . . . . . . . . . . 27 + 15. Normative References . . . . . . . . . . . . . . . . . . . . . 28 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29 1. Introduction Low power and Lossy Networks typically operate with strict resource constraints in communication, computation, memory, and energy. Such resource constraints may preclude the use of existing IPv6 multicast - topology and forwarding mechanisms. Traditional IP multicast - forwarding typically relies on topology maintenance mechanisms to - forward multicast messages to all subscribers of a multicast group. - However, maintaining such topologies in LLNs is costly and may not be - feasible given the available resources. + routing and forwarding mechanisms. Traditional IP multicast delivery + typically relies on topology maintenance mechanisms to discover and + maintain routes to all subscribers of a multicast group. However, + maintaining such topologies in LLNs is costly and may not be feasible + given the available resources. Memory constraints may limit devices to maintaining links/routes to one or a few neighbors. For this reason, the Routing Protocol for LLNs (RPL) specifies both storing and non-storing modes [RFC6550]. The latter allows RPL routers to maintain only one or a few default routes towards a LLN Border Router (LBR) and use source routing to - forward packets away from the LBR. For the same reasons, a LLN - device may not be able to maintain a multicast forwarding topology - when operating with limited memory. + forward messages away from the LBR. For the same reasons, a LLN + device may not be able to maintain a multicast routing topology when + operating with limited memory. Furthermore, the dynamic properties of wireless networks can make the - cost of maintaining a multicast forwarding topology prohibitively + cost of maintaining a multicast routing topology prohibitively expensive. In wireless environments, topology maintenance may involve selecting a connected dominating set used to forward multicast messages to all nodes in an administrative domain. However, existing mechanisms often require two-hop topology information and the cost of maintaining such information grows polynomially with network density. This document specifies the Multicast Protocol for Low power and Lossy Networks (MPL), which provides IPv6 multicast forwarding in constrained networks. MPL avoids the need to construct or maintain - any multicast forwarding topology, disseminating multicast messages - to all MPL forwarders in an MPL domain. By using the Trickle - algorithm [RFC6206], MPL requires only small, constant state for each - MPL device that initiates disseminations. The Trickle algorithm also + any multicast routing topology, disseminating multicast messages to + all MPL forwarders in an MPL domain. By using the Trickle algorithm + [RFC6206], MPL requires only small, constant state for each MPL + device that initiates disseminations. The Trickle algorithm also allows MPL to be density-aware, allowing the communication rate to scale logarithmically with density. 2. 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]. + "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and + "OPTIONAL" in this document are to be interpreted as described in + [RFC2119]. The following terms are used throughout this document: - MPL forwarder An IPv6 router that subscribes to the MPL - multicast group and participates in disseminating - MPL multicast packets. + MPL Forwarder - A router that implements this protocol. A MPL + Forwarder is equipped with at least one MPL + Interface. - MPL multicast scope The multicast scope that MPL uses when forwarding - MPL multicast packets. In other words, the - multicast scope of the IPv6 Destination Address - of an MPL multicast packet. + MPL Interface - An MPL Forwarder's attachment to a + communications medium, over which it transmits + and receives MPL Data Messages and MPL Control + Messages according to this specification. An MPL + Interface is assigned one or more unicast + addresses and is subscribed to one or more MPL + Domain Addresses. - MPL domain A connected set of MPL forwarders that define the - extent of the MPL dissemination process. As a - form of flood, all MPL forwarders in an MPL - domain will receive MPL multicast packets. The - MPL domain MUST be composed of at least one MPL - multicast scope and MAY be composed of multiple - MPL multicast scopes. + MPL Domain Address - A multicast address that identifies the set of + MPL Interfaces within an MPL Domain. MPL Data + Messages disseminated in an MPL Domain have the + associated MPL Domain Address as their + destination address. - MPL seed A MPL forwarder that begins the dissemination - process for an MPL multicast packet. The MPL - seed may be different than the source of the - original multicast packet. + MPL Domain - A scope zone, as defined in [RFC4007], in which + MPL Interfaces subscribe to the same MPL Domain + Address and participate in disseminating MPL Data + Messages. - MPL seed identifier An identifier that uniquely identifies an MPL - forwarder within its MPL domain. + MPL Data Message - A multicast message that is used to communicate + a multicast payload between MPL Forwarders and + contains an MPL Option in the IPv6 header. A MPL + Data Message has its destination address set to + the MPL Domain Address. - original multicast packet An IPv6 multicast packet that is - disseminated using MPL. + MPL Control Message - A link-local multicast message that is used to + communicate information about recently received + MPL Data Messages to neighboring MPL Forwarders. - MPL multicast packet An IPv6 multicast packet that contains an MPL - Hop-by-Hop Option. When either source or - destinations are beyond the MPL multicast scope, - the MPL multicast packet is an IPv6-in-IPv6 - packet that contains an MPL Hop-by-Hop Option in - the outer IPv6 header and encapsulates an - original multicast packet. When both source and - destinations are within the MPL multicast scope, - the MPL Hop-by-Hop Option may be included - directly within the original multicast packet. + MPL Seed - An MPL Forwarder that generates MPL Data + Messages and serves as an entry point into an MPL + Domain. -3. Overview +3. Applicability Statement - MPL delivers IPv6 multicast packets by disseminating them to all MPL - forwarders within an MPL domain. MPL dissemination is a form of - flood. An MPL forwarder may broadcast/multicast an MPL multicast - packet out of the same physical interface on which it was received. - Using link-layer broadcast/multicast allows MPL to forward multicast - packets without explicitly identifying next-hop destinations. An MPL - forwarder may also broadcast/multicast MPL multicast packets out - other interfaces to disseminate the message across different links. - MPL does not build or maintain a multicast forwarding topology to - forward multicast packets. + This protocol is an IPv6 multicast forwarding protocol for Low-Power + and Lossy Networks. By implementing a controlled dissemination using + the Trickle algorithm, this protocol is designed for networks that + communicate using low-power and lossy links with widely varying + topologies in both the space and time dimensions. - Any MPL forwarder may initiate the dissemination process by serving - as an MPL seed for an original multicast packet. The MPL seed may or - may not be the same device as the source of the original multicast - packet. When the original multicast packet's source is outside the - LLN, the MPL seed may be the ingress router. Even if an original - multicast packet source is within the LLN, the source may first - forward the multicast packet to the MPL seed using IPv6-in-IPv6 - tunneling. Because MPL state requirements grows with the number of - active MPL seeds, limiting the number of MPL seeds reduces the amount - of state that MPL forwarders must maintain. +4. Protocol Overview - Because MPL typically broadcasts/multicasts MPL packets out of the - same interface on which they were received, MPL forwarders are likely - to receive an MPL multicast packet more than once. The MPL seed tags - each original multicast packet with an MPL seed identifier and a - sequence number. The sequence number provides a total ordering of - MPL multicast packets disseminated by the MPL seed. + The goal of MPL is to deliver multicast messages to all interfaces + that subscribe to the multicast messages' destination address within + an MPL Domain. - MPL defines a new IPv6 Hop-by-Hop Option, the MPL Option, to include - MPL-specific information along with the original multicast packet. - Each IPv6 multicast packet that MPL disseminates includes the MPL - Option. Because the original multicast packet's source and the MPL - seed may not be the same device, the MPL Option may be added to the - original multicast packet en-route. To allow Path MTU discovery to - work properly, MPL encapsulates the original multicast packet in - another IPv6 header that includes the MPL Option. +4.1. Information Base Overview - Upon receiving a new MPL multicast packet for forwarding, the MPL - forwarder may proactively transmit the MPL multicast packet packet a - limited number of times and then falls back into an optional reactive - mode. In maintenance mode, an MPL forwarder buffers recently - received MPL multicast packets and advertises a summary of recently - received MPL multicast packets from time to time, allowing - neighboring MPL forwarders to determine if they have any new - multicast packets to offer or receive. + A node records necessary protocol state in the following information + sets: - MPL forwarders schedule their packet (control and data) transmissions - using the Trickle algorithm [RFC6206]. Trickle's adaptive - transmission interval allows MPL to quickly disseminate messages when - there are new MPL multicast packets, but reduces transmission - overhead as the dissemination process completes. Trickle's - suppression mechanism and transmission time selection allow MPL's - communication rate to scale logarithmically with density. + o The Local Interface Set records the set of local MPL Interfaces + and the unicast addresses assigned to those MPL Interfaces. -4. Message Formats + o The Domain Set records the set of MPL Domain Addresses and the + local MPL Interfaces that subscribe to those addresses. -4.1. MPL Option + o The Seed Set records information about received MPL Data Messages + received from an MPL Seed. The Seed Set maintains the minimum + sequence number that the MPL Forwarder is willing to receive or + has buffered in its Buffered Message Set. MPL uses the Seed Set + and Buffered Message Set to determine when to accept an MPL Data + Message, process its payload, and retransmit it. - The MPL Option is carried in an IPv6 Hop-by-Hop Options header, - immediately following the IPv6 header. The MPL Option has the - following format: + o The Buffered Message Set records recently received MPL Data + Messages from an MPL Seed. MPL Data Messages resident in the + Buffered Message Set have sequence numbers that are greater than + or equal to the minimum threshold maintained in the Seed Set. MPL + uses the Buffered Message Set to store MPL Data Messages that may + be transmitted by the MPL Forwarder for forwarding. + +4.2. Overview + + MPL achieves its goal by implementing a controlled flood that + attempts to disseminate the multicast data message to all interfaces + within an MPL Domain. MPL performs the following tasks to + disseminate a multicast message: + + o When having a multicast message to forward into an MPL Domain, the + MPL Seed generates an MPL Data Message that includes the MPL Seed + Identifier, a newly generated sequence number, and the multicast + message. If the multicast destination address is not the MPL + Domain Address, IP-in-IP [RFC2473] is used to encapsulate the + multicast message in the MPL Data Message. + + o Upon receiving an MPL Data Message, the MPL Forwarder extracts the + MPL Seed and sequence number and determines whether or not the MPL + Data Message was previously received using the Seed Set and + Buffered Message Set. + + * If the sequence number is less than the lower-bound sequence + number maintained in the Seed Set or a message with the same + sequence number exists within the Buffered Message Set, the MPL + Forwarder marks the MPL Data Message as old. + + * Otherwise, the MPL Forwarder marks the MPL Data Message as new. + + o For each newly received MPL Data Message, an MPL Forwarder updates + the Seed Set, adds the MPL Data Message into the Buffered Message + Set, processes its payload, and multicasts the MPL Data Message a + number of times on all MPL Interfaces participating in the same + MPL Domain to forward the message. + + o Each MPL Forwarder may periodically link-local multicast MPL + Control Messages on MPL Interfaces to communicate information + contained in the MPL Forwarder's Seed Set and Buffered Message + Sets. + + o Upon receiving an MPL Control Message, an MPL Forwarder determines + whether there are any new MPL Data Messages that have yet to be + received by the MPL Control Message's source and multicasts those + MPL Data Messages. + + MPL's configuration parameters allow two forwarding strategies for + disseminating MPL Data Messages. + + Proactive Forwarding - With proactive forwarding, an MPL Forwarder + schedules transmissions of MPL Data Messages using the Trickle + algorithm, without any prior indication that neighboring nodes + have yet to receive the message. After transmitting the MPL Data + Message a limited number of times, the MPL forwarder may terminate + proactive forwarding for the MPL Data Message message. + + Reactive Forwarding - With reactive forwarding, an MPL Forwarder + link-local multicasts MPL Control Messages using the Trickle + algorithm [RFC6206]. MPL Forwarders use MPL Control Messages to + discover new MPL Data Messages that have not yet been received. + When discovering that a neighboring MPL Forwarder has not yet + received a new MPL Data Message, the MPL Forwarder schedules those + MPL Data Messages for transmission using the Trickle algorithm. + +4.3. Signaling Overview + + This protocol generates and processes the following messages: + + MPL Data Message - Generated by an MPL Seed to deliver a multicast + message across an MPL Domain. The MPL Data Message's source is an + address in the Local Interface Set of the MPL Seed that generated + the message and is valid within the MPL Domain. The MPL Data + Message's destination is the MPL Domain Address corresponding to + the MPL Domain. An MPL Data Message contains: + + * The Seed Identifier of the MPL Seed that generated the MPL Data + Message. + + * The sequence number of the MPL Seed that generated the MPL Data + Message. + + * The original multicast message. + + MPL Control Message - Generated by an MPL Forwarder to communicate + information contained in the Seed Set and Buffered Message Set to + neighboring MPL Forwarders. An MPL Control Message contains a + list of tuples for each entry in the Seed Set. Each tuple + contains: + + * The minimum sequence number maintained in the Seed Set for the + MPL Seed. + + * A bit-vector indicating the sequence numbers of MPL Data + Messages resident in the Buffered Message Set for the MPL Seed, + where the first bit represents a sequence number equal to the + minimum threshold maintained in the Seed Set. + + * The length of the bit-vector. + +5. MPL Constants + + This section describes various program and networking constants used + by MPL. + +5.1. Multicast Addresses + + MPL makes use of MPL Domain Addresses to identify MPL Interfaces of + an MPL Domain. By default, MPL Forwarders subscribe to the + ALL_MPL_FORWARDERS multicast address with a scope value of 3 (subnet- + local). + + For each MPL Domain Address that an MPL Interface subscribes to, the + MPL Interface MUST also subscribe to the MPL Domain Address with a + scope value of 2 (link-local) when reactive forwarding is in use. + MPL Forwarders use the link-scoped MPL Domain Address to communicate + MPL Control Messages to neighboring (i.e. on-link) MPL Forwarders. + +5.2. Message Types + + MPL defines an IPv6 Option for carrying an MPL Seed Identifier and a + sequence number within an MPL Data Message. The IPv6 Option Type has + value MPL_OPT_TYPE. + + MPL defines an ICMPv6 Message (MPL Control Message) for communicating + information contained in its Seed Set and Buffered Message Set to + neighboring MPL Forwarders. The MPL Control Message has ICMPv6 Type + MPL_ICMP_TYPE. + +5.3. MPL Forwarder Parameters + + PROACTIVE_FORWARDING A boolean value that indicates whether the MPL + Forwarder should schedule MPL Data Message transmissions after + receiving them for the first time. + + SEED_SET_LIFETIME The minimum lifetime for an entry in the Seed Set. + +5.4. Trickle Parameters + + As specified in [RFC6206], a Trickle timer runs for a defined + interval and has three configuration parameters: the minimum interval + size Imin, the maximum interval size Imax, and a redundancy constant + k. + + This specification defines a fourth Trickle configuration parameter, + TimerExpirations, which indicates the number of Trickle timer + expiration events that occur before terminating the Trickle + algorithm. + + Each MPL forwarder maintains a separate Trickle parameter set for MPL + Data Message and MPL Control Message transmissions. The Trickle + parameters are listed below: + + DATA_MESSAGE_IMIN The minimum Trickle timer interval, as defined in + [RFC6206], for MPL Data Message transmissions. + + DATA MESSAGE_IMAX The maximum Trickle timer interval, as defined in + [RFC6206], for MPL Data Message transmissions. + + DATA_MESSAGE_K The redundancy constant, as defined in [RFC6206], for + MPL Data Message transmissions. + + DATA_MESSAGE_TIMER_EXPIRATIONS The number of Trickle timer + expirations that occur before terminating the Trickle algorithm + for MPL Data Message transmissions. + + CONTROL_MESSAGE_IMIN The minimum Trickle timer interval, as defined + in [RFC6206], for MPL Control Message transmissions. + + CONTROL_MESSAGE_IMAX The maximum Trickle timer interval, as defined + in [RFC6206], for MPL Control Message transmissions. + + CONTROL_MESSAGE_K The redundancy constant, as defined in [RFC6206], + for MPL Control Message transmissions. + + CONTROL_MESSAGE_TIMER_EXPIRATIONS The number of Trickle timer + expirations that occur before terminating the Trickle algorithm + for MPL Control Message transmissions. + + It is RECOMMENDED that all MPL Forwarder within an MPL Domain use the + same values for the Trickle Parameters above, as specified in + [RFC6206]. + +6. Protocol Message Formats + + The protocol messages generated and processed by an MPL Forwarder are + described in this section. + +6.1. MPL Option + + The MPL Option is carried in MPL Data Messages in an IPv6 Hop-by-Hop + Options header, immediately following the IPv6 header. The MPL + Option has the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type | Opt Data Len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - | S |M| rsv | sequence | seed-id (optional) | + | S |M|V| rsv | sequence | seed-id (optional) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - Option Type XX (to be confirmed by IANA). + Option Type MPL_OPT_TYPE - Opt Data Len Length of the Option Data field in octets. MUST - be set to either 2 or 4. + Opt Data Len Length of the Option Data field in octets. S 2-bit unsigned integer. Identifies the length of - seed-id. 0 indicates that the seed-id is 0 and - not included in the MPL Option. 1 indicates that - the seed-id is a 16-bit unsigned integer. 2 - indicates that the seed-id is a 64-bit unsigned - integer. 3 indicates that the seed-id is a 128- - bit unsigned integer. + seed-id. 0 indicates that the seed-id is the IPv6 + Source Address and not included in the MPL + Option. 1 indicates that the seed-id is a 16-bit + unsigned integer. 2 indicates that the seed-id is + a 64-bit unsigned integer. 3 indicates that the + seed-id is a 128-bit unsigned integer. - M 1-bit flag. 0 indicates that the value in - sequence is not the greatest sequence number that - was received from the MPL seed. + M 1-bit flag. 1 indicates that the value in + sequence is known to be the largest sequence + number that was received from the MPL Seed. - rsv 5-bit reserved field. MUST be set to zero and - incoming MPL multicast packets in which they are - not zero MUST be dropped. + V 1-bit flag. 0 indicates that the MPL Option + conforms to this specification. MPL Options + received in which this flag is 1 MUST be dropped. + + rsv 4-bit reserved field. MUST be set to 0 on + transmission and ignored on reception. sequence 8-bit unsigned integer. Identifies relative - ordering of MPL multicast packets from the source + ordering of MPL Data Messages from the MPL Seed identified by seed-id. - seed-id Uniquely identifies the MPL seed that initiated - dissemination of the MPL multicast packet. The - size of seed-id is indicated by the S field. + seed-id Uniquely identifies the MPL Seed that initiated + dissemination of the MPL Data Message. The size + of seed-id is indicated by the S field. - The Option Data of the Trickle Multicast option MUST NOT change as - the MPL multicast packet is forwarded. Nodes that do not understand - the Trickle Multicast option MUST discard the packet. Thus, - according to [RFC2460] the three high order bits of the Option Type - must be set to '010'. The Option Data length is variable. + The Option Data (in particular the M flag) of the MPL Option is + updated by MPL Forwarders as the MPL Data Message is forwarded. + Nodes that do not understand the MPL Option MUST discard the MPL Data + Message. Thus, according to [RFC2460] the three high order bits of + the Option Type are set to '011'. The Option Data length is + variable. - The seed-id uniquely identifies an MPL seed within the MPL domain. - When seed-id is 128 bits (S=3), the MPL seed MAY use an IPv6 address - assigned to one of its interfaces that is unique within the MPL - domain. Managing MPL seed identifiers is not within scope of this - document. + The seed-id uniquely identifies an MPL Seed. When seed-id is 128 + bits (S=3), the MPL seed MAY use an IPv6 address assigned to one of + its interfaces that is unique within the MPL domain. Managing MPL + Seed Identifiers is not within scope of this document. - The sequence field establishes a total ordering of MPL multicast - packets from the same MPL seed. The MPL seed MUST increment the - sequence field's value on each new MPL multicast packet that it - disseminates. Implementations MUST follow the Serial Number - Arithmetic as defined in [RFC1982] when incrementing a sequence value - or comparing two sequence values. + The sequence field establishes a total ordering of MPL Data Messages + generated by an MPL Seed for an MPL Domain. The MPL Seed MUST + increment the sequence field's value on each new MPL Data Message + that it generates for an MPL Domain. Implementations MUST follow the + Serial Number Arithmetic as defined in [RFC1982] when incrementing a + sequence value or comparing two sequence values. Future updates to this specification may define additional fields following the seed-id field. -4.2. ICMPv6 MPL Message +6.2. MPL Control Message - The MPL forwarder uses ICMPv6 MPL messages to advertise information - about recently received MPL multicast packets. The ICMPv6 MPL - message has the following format: + An MPL Forwarder uses ICMPv6 messages to communicate information + contained in its Seed Set and Buffered Message Set to neighboring MPL + Forwarders. The MPL Control Message has the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Code | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | - . MPL Window[1..n] . + . MPL Seed Info[1..n] . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IP Fields: Source Address A link-local address assigned to the sending interface. - Destination Address The link-local all-nodes MPL forwarders multicast - address (FF02::TBD). + Destination Address The link-scoped MPL Domain Address corresponding + to the MPL Domain. Hop Limit 255 ICMPv6 Fields: - Type XX (to be confirmed by IANA). + Type MPL_ICMP_TYPE Code 0 Checksum The ICMP checksum. See [RFC4443]. - MPL Window[1..n] List of one or more MPL Windows (defined in - Section 4.2.1). + MPL Seed Info[1..n] List of one or more MPL Seed Info entries. - An MPL forwarder transmits an ICMPv6 MPL message to advertise - information about buffered MPL multicast packets. More explicitly, - the ICMPv6 MPL message encodes the sliding window state (described in - Section 5.2) that the MPL forwarder maintains for each MPL seed. The - advertisement serves to indicate to neighboring MPL forwarders - regarding newer messages that it may send or the neighboring MPL - forwarders have yet to receive. + The MPL Control Message indicates the sequence numbers of MPL Data + Messages that are within the Buffered Message Set. The MPL Control + Message also indicates the sequence numbers of MPL Data Messages that + an MPL Forwarder is willing to receive. The MPL Control Message + allows neighboring MPL Forwarders to determine whether there are any + new MPL Data Messages to exchange. -4.2.1. MPL Window +6.3. MPL Seed Info - An MPL Window encodes the sliding window state (described in - Section 5.2 that the MPL forwarder maintains for an MPL seed. Each - MPL Window has the following format: + An MPL Seed Info encodes the minimum sequence number for the MPL Seed + maintained in the Seed Set. The MPL Seed Info also indicates the + sequence numbers of MPL Data Messages generated by the MPL Seed + within the Buffered Message Set. The MPL Seed Info has the following + format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - | w-min | w-len | S | seed-id (0, 2 or 16 octets) | + | min-seqno | bm-len | S | seed-id (0/2/8/16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | - . buffered-mpl-packets (0 to 8 octets) . + . buffered-mpl-messages (variable length) . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - w-min 8-bit unsigned integer. Indicates the first - sequence number associated with the first bit in - buffered-mpl-packets. + min-seqno 8-bit unsigned integer. The lower-bound sequence + number for the MPL Seed. - w-len 6-bit unsigned integer. Indicates the size of - the sliding window and the number of valid bits - in buffered-mpl-packets. The sliding window's - upper bound is the sum of w-min and w-len. + bm-len 6-bit unsigned integer. The size of buffered- + mpl-messages in octets. S 2-bit unsigned integer. Identifies the length of - seed-id. 0 indicates that the seed-id value is 0 - and not included in the MPL Option. 1 indicates - that the seed-id value is a 16-bit unsigned - integer. 2 indicates that the seed-id value is a - 128-bit unsigned integer. 3 is reserved. + seed-id. 0 indicates that the seed-id value is + the IPv6 Source Address and not included in the + MPL Seed Info. 1 indicates that the seed-id value + is a 16-bit unsigned integer. 2 indicates that + the seed-id value is a 64-bit unsigned integer. 3 + indicates that the seed-id is a 128-bit unsigned + integer. - seed-id Indicates the MPL seed associated with this - sliding window. + seed-id Variable-length unsigned integer. Indicates the + MPL Seed associated with this MPL Seed Info. - buffered-mpl-packets Variable-length bit vector. Identifies the - sequence numbers of MPL multicast packets that - the MPL forwarder has buffered. The sequence - number is determined by w-min + i, where i is the - offset within buffered-mpl-packets. + buffered-mpl-messages Variable-length bit vector. Identifies the + sequence numbers of MPL Data Messages maintained + in the Buffered Message Set for the MPL Seed. + The sequence number is determined by min-seqno + + i, where i is the bit offset within buffered-mpl- + messages. - The MPL Window does not have any octet alignment requirement. + The MPL Seed Info does not have any octet alignment requirement. -5. MPL Forwarder Behavior +7. Information Base - An MPL forwarder implementation needs to manage sliding windows for - each active MPL seed. The sliding window allows the MPL forwarder to - determine what multicast packets to accept and what multicast packets - are buffered. An MPL forwarder must also manage MPL packet - transmissions. +7.1. Local Interface Set -5.1. Multicast Packet Dissemination + The Local Interface Set records the local MPL Interfaces of an MPL + Forwarder. The Local Interface Set consists of Local Interface + Tuples, one per MPL Interface: (AddressSet). - MPL uses the Trickle algorithm to control packet transmissions when - disseminating MPL multicast packets [RFC6206]. MPL provides two - propagation mechanisms for disseminating MPL multicast packets. + AddressSet - a set of unicast addresses assigned to the MPL + Interface. - 1. With proactive propagation, an MPL forwarder transmits buffered - MPL multicast packets using the Trickle algorithm. This method - is called proactive propagation since an MPL forwarder actively - transmits MPL multicast packets without discovering that a - neighboring MPL forwarder has yet to receive the message. +7.2. Domain Set - 2. With reactive propagation, an MPL forwarder transmits ICMPv6 MPL - messages using the Trickle algorithm. An MPL forwarder only - transmits buffered MPL multicast packets upon discovering that - neighboring devices have not yet to receive the corresponding MPL - multicast packets. + The Domain Set records the MPL Interfaces that subscribe to each MPL + Domain Address. The Domain Set consists of MPL Domain Tuples, one + per MPL Domain: (MPLInterfaceSet). - When receiving a new multicast packet, an MPL forwarder first - utilizes proactive propagation to forward the MPL multicast packet. - Proactive propagation reduces dissemination latency since it does not - require discovering that neighboring devices have not yet received - the MPL multicast packet. MPL forwarders utilize proactive - propagation for newly received MPL multicast packets since they can - assume that some neighboring MPL forwarders have yet to receive the - MPL multicast packet. After a limited number of MPL multicast packet - transmissions, the MPL forwarder may terminate proactive propagation - for the MPL multicast packet. + MPLInterfaceSet - a set of MPL Interfaces that subscribe to the MPL + Domain Address that identifies the MPL Domain. - An MPL forwarder may optionally use reactive propagation to continue - the dissemination process with lower communication overhead. With - reactive propagation, neighboring MPL forwarders use ICMPv6 MPL - messages to discover new MPL multicast messages that have not yet - been received. When discovering that a neighboring MPL forwarder has - not yet received a new MPL multicast packet, the MPL forwarder - enables proactive propagation again. +7.3. Seed Set -5.1.1. Trickle Parameters and Variables + The Seed Set records a sliding window used to determine the sequence + numbers of MPL Data Messages that an MPL Forwarder is willing to + accept generated by the MPL Seed. It consists of MPL Seed Tuples: + (SeedID, MinSequence, Lifetime). - As specified in RFC 6206 [RFC6206], a Trickle timer runs for a - defined interval and has three configuration parameters: the minimum - interval size Imin, the maximum interval size Imax, and a redundancy - constant k. + SeedID - the identifier for the MPL Seed. - MPL defines a fourth configuration parameter, TimerExpirations, which - indicates the number of Trickle timer expiration events that occur - before terminating the Trickle algorithm. + MinSequence - a lower-bound sequence number that represents the + sequence number of the oldest MPL Data Message the MPL Forwarder + is willing to receive or transmit. An MPL Forwarder MUST ignore + any MPL Data Message that has sequence value less than than + MinSequence. - Each MPL forwarder maintains a separate Trickle parameter set for the - proactive and reactive propagation methods. TimerExpirations MUST be - greater than 0 for proactive propagation. TimerExpirations MAY be - set to 0 for reactive propagation, which effectively disables - reactive propagation. + Lifetime - indicates the minimum lifetime of the Seed Set entry. An + MPL Forwarder MUST NOT free a Seed Set entry before its expires. - As specified in RFC 6206 [RFC6206], a Trickle timer has three - variables: the current interval size I, a time within the current - interval t, and a counter c. +7.4. Buffered Message Set - MPL defines a fourth variable, e, which counts the number of Trickle - timer expiration events since the Trickle timer was last reset. + The Buffered Message Set records recently received MPL Data Messages + from an MPL Seed. An MPL Forwarder uses the Buffered Message Set to + buffer MPL Data Messages while the MPL Forwarder is forwarding the + MPL Data Messages. The Buffered Message Set consists of Buffered + Message Tuples: (SeedID, SequenceNumber, DataMessage). -5.1.2. Proactive Propagation + SeedID - the identifier for the MPL Seed that generated the MPL Data + Message. - With proactive propagation, the MPL forwarder transmits buffered MPL - multicast packets using the Trickle algorithm. Each buffered MPL - multicast packet that is proactively being disseminated with - proactive propagation has an associated Trickle timer. Adhering to - Section 5 of RFC 6206 [RFC6206], this document defines the following: + SequenceNumber - the sequence number for the MPL Data Message. - o This document defines a "consistent" transmission for proactive - propagation as receiving an MPL multicast packet that has the same - MPL seed identifier and sequence number as a buffered MPL packet. + DataMessage - the MPL Data Message. - o This document defines an "inconsistent" transmission for proactive - propagation as receiving an MPL multicast packet that has the same - MPL seed identifier, the M flag set, and has a sequence number - less than the buffered MPL multicast packet's sequence number. + All MPL Data Messages within the Buffered Message Set MUST have a + sequence number greater than or equal to MinSequence for the + corresponding SeedID. When increasing MinSequence for an MPL Seed, + the MPL Forwarder MUST delete any MPL Data Messages from the Buffered + Message Set that have sequence numbers less than MinSequence. - o This document does not define any external "events". +8. MPL Domains - o This document defines both MPL multicast packets and ICMPv6 MPL - multicast packets as Trickle messages. These messages are defined - in the sections below. + An MPL Domain is a scope zone, as defined in [RFC4007], in which MPL + Interfaces subscribe to the same MPL Domain Address and participate + in disseminating MPL Data Messages. - o The actions outside the Trickle algorithm that the protocol takes - involve managing sliding window state, and is specified in - Section 5.2. + By default, an MPL Forwarder MUST participate in an MPL Domain + identified by the ALL_MPL_FORWARDERS multicast address with a scope + value of 3 (subnet-local). -5.1.3. Reactive Propagation + An MPL Forwarder MAY participate in additional MPL Domains identified + by other multicast addresses. An MPL Interface MUST subscribe to the + MPL Domain Addresses for the MPL Domains that it participates in. + The allocation of other multicast addresses is out of scope. - With reactive propagation, the MPL forwarder transmits ICMPv6 MPL - messages using the Trickle algorithm. A MPL forwarder maintains a - single Trickle timer for reactive propagation with each MPL domain. - When REACTIVE_TIMER_EXPIRATIONS is 0, the MPL forwarder does not - execute the Trickle algorithm for reactive propagation and reactive - propagation is disabled. Adhering to Section 5 of RFC 6206 - [RFC6206], this document defines the following: + For each MPL Domain Address that an MPL Interface subscribes to, the + MPL Interface MUST also subscribe to the same MPL Domain Address with + a scope value of 2 (link-local) when reactive forwarding is in use + (i.e. when communicating MPL Control Messages). - o This document defines a "consistent" transmission for reactive - propagation as receiving an ICMPv6 MPL message that indicates - neither the receiving nor transmitting node has new MPL multicast - packets to offer. +9. MPL Seed Sequence Numbers - o This document defines an "inconsistent" transmission for reactive - propagation as receiving an ICMPv6 MPL message that indicates - either the receiving or transmitting node has at least one new MPL - multicast packet to offer. + Each MPL Seed maintains a sequence number for each MPL Domain that it + serves. The sequence numbers are included in MPL Data Messages + generated by the MPL Seed. The MPL Seed MUST increment the sequence + number for each MPL Data Message that it generates for an MPL Domain. + Implementations MUST follow the Serial Number Arithmetic as defined + in [RFC1982] when incrementing a sequence value or comparing two + sequence values. This sequence number is used to establish a total + ordering of MPL Data Messages generated by an MPL Seed for an MPL + Domain. - o This document defines an "event" for reactive propagation as - updating any sliding window (i.e. changing the value of WindowMin, - WindowMax, or the set of buffered MPL multicast packets) in - response to receiving an MPL multicast packet. +10. MPL Data Messages - o This document defines both MPL multicast packets and ICMPv6 MPL - multicast packets as Trickle messages. These messages are defined - in the sections below. +10.1. MPL Data Message Generation - o The actions outside the Trickle algorithm that the protocol takes - involve managing sliding window state, and is specified in - Section 5.2. + MPL Data Messages are generated by MPL Seeds when they enter the MPL + Domain. All MPL Data messages have the following properties: -5.2. Sliding Windows + o The IPv6 Source Address MUST be an address in the AddressSet of a + corresponding MPL Interface and MUST be valid within the MPL + Domain. - Every MPL forwarder MUST maintain a sliding window of sequence - numbers for each MPL seed of recently received MPL packets. The - sliding window performs two functions: + o The IPv6 Destination Address MUST be set to the MPL Domain Address + corresponding to the MPL Domain. - 1. Indicate what MPL multicast packets the MPL forwarder should - accept. + o A MPL Data Message MUST contain an MPL Option in its IPv6 Header + to identify the MPL Seed that generated the message and the + ordering relative to other MPL Data Messages generated by the MPL + Seed. - 2. Indicate what MPL multicast packets are buffered and may be - transmitted to neighboring MPL forwarders. + When the source address is in the AddressList of an MPL Interface + corresponding to the MPL Domain Address and the destination address + is the MPL Domain Address, the application message and the MPL Data + Message MAY be identical. In other words, the MPL Data Message may + contain a single IPv6 header that includes the MPL Option. - Each sliding window logically consists of: + Otherwise, IPv6-in-IPv6 encapsulation MUST be used to satisfy the MPL + Data Message requirements listed above [RFC2473]. The complete IPv6- + in-IPv6 message forms an MPL Data Message. The outer IPv6 header + conforms to the MPL Data Message requirements listed above. The + encapsulated IPv6 datagram encodes the multicast data message that is + communicated beyond the MPL Domain. - 1. A lower-bound sequence number, WindowMin, that represents the - sequence number of the oldest MPL multicast packet the MPL - forwarder is willing to receive or has buffered. An MPL - forwarder MUST ignore any MPL multicast packet that has sequence - value less than than WindowMin. +10.2. MPL Data Message Transmission - 2. An upper-bound sequence value, WindowMax, that represents the - sequence number of the next MPL multicast packet that the MPL - forwarder expects to receive. An MPL forwarder MUST accept any - MPL multicast packet that has sequence number greater than or - equal to WindowMax. + An MPL Forwarder manages transmission of MPL Data Messages in the + Buffered Message set using the Trickle algorithm [RFC6206]. An MPL + Forwarder MUST use a separate Trickle timer for each MPL Data Message + that it is actively forwarding. In accordance with Section 5 of RFC + 6206 [RFC6206], this document defines the following: - 3. A list of MPL multicast packets, BufferedPackets, buffered by the - MPL forwarder. Each entry in BufferedPackets MUST have a - sequence number in the range [WindowMin, WindowMax). + o This document defines a "consistent" transmission as receiving an + MPL Data Message that has the same seed-id and sequence value as + the MPL Data Message managed by the Trickle timer. - 4. A timer, HoldTimer, that indicates the minimum lifetime of the - sliding window. The MPL forwarder MUST NOT free a sliding window - before HoldTimer expires. + o This document defines an "inconsistent" transmission as receiving + an MPL Data Message that has the same seed-id value and the M flag + set, but has a sequence value less than MPL Data Message managed + by the Trickle timer. - When receiving an MPL multicast packet, if no existing sliding window - exists for the MPL seed, the MPL forwarder MUST create a new sliding - window before accepting the MPL multicast packet. The MPL forwarder - may reclaim memory resources by freeing a sliding window for another - MPL seed if its HoldTimer has expired. If, for any reason, the MPL - forwarder cannot create a new sliding window, it MUST discard the - packet. + o This document does not define any external "events". - If a sliding window exists for the MPL seed, the MPL forwarder MUST - ignore the MPL multicast packet if the packet's sequence number is - less than WindowMin or appears in BufferedPackets. Otherwise, the - MPL forwarder MUST accept the packet and determine whether or not to - forward the packet and/or pass the packet to the next higher layer. + o This document defines MPL Data Messages as Trickle messages. - When accepting an MPL multicast packet, the MPL forwarder MUST update - the sliding window based on the packet's sequence number. If the - sequence number is not less than WindowMax, the MPL forwarder MUST - set WindowMax to 1 greater than the packet's sequence number. If - WindowMax - WindowMin > MPL_MAX_WINDOW_SIZE, the MPL forwarder MUST - increment WindowMin such that WindowMax - WindowMin <= - MPL_MAX_WINDOW_SIZE. At the same time, the MPL forwarder MUST free - any entries in BufferedPackets that have a sequence number less than - WindowMin. + o The actions outside the Trickle algorithm that the protocol takes + involve managing Seed Set and Buffered Message Set - If the MPL forwarder has available memory resources, it MUST buffer - the MPL multicast packet for proactive propagation. If not enough - memory resources are available to buffer the packet, the MPL - forwarder MUST increment WindowMin and free entries in - BufferedPackets that have a sequence number less than WindowMin until - enough memory resources are available. Incrementing WindowMin will - ensure that the MPL forwarder does not accept previously received - packets. + As specified in [RFC6206], a Trickle timer has three variables: the + current interval size I, a time within the current interval t, and a + counter c. MPL defines a fourth variable, e, which counts the number + of Trickle timer expiration events since the Trickle timer was last + reset. - An MPL forwarder MAY reclaim memory resources from sliding windows - for other MPL seeds. If a sliding window for another MPL seed is - actively disseminating messages and has more than one entry in its - BufferedPackets, the MPL forwarder may free entries for that MPL seed - by incrementing WindowMin as described above. + After DATA_MESSAGE_TIMER_EXPIRATIONS Trickle timer events, the MPL + Forwarder MUST disable the Trickle timer. When a buffered MPL Data + Message does not have an associated Trickle timer, the MPL Forwarder + MAY delete the message from the Buffered Message Set by advancing + MinSequence of the corresponding MPL Seed in the Seed Set. When the + MPL Forwarder no longer buffers any messages for an MPL Seed, the MPL + Forwarder MUST NOT increment MinSequence for that MPL Seed. - If the MPL forwarder cannot free enough memory resources to buffer - the MPL multicast packet, the MPL forwarder MUST set WindowMin to 1 - greater than the packet's sequence number. + When transmitting an MPL Data Message, the MPL Forwarder MUST either + set the M flag to zero or set it to a level that indicates whether or + not the message's sequence number is the largest value that has been + received from the MPL Seed. - When memory resources are available, an MPL forwarder SHOULD buffer a - MPL multicast packet until the proactive propagation completes (i.e. - the Trickle algorithm stops execution) and MAY buffer for longer. - After proactive propagation completes, the MPL forwarder may advance - WindowMin to the packet's sequence number to reclaim memory - resources. When the MPL forwarder no longer buffers any packets, it - MAY set WindowMin equal to WindowMax. When setting WindowMin equal - to WindowMax, the MPL forwarder MUST initialize HoldTimer to - WINDOW_HOLD_TIME and start HoldTimer. After HoldTimer expires, the - MPL forwarder MAY free the sliding window to reclaim memory - resources. +10.3. MPL Data Message Processing -5.3. Transmission of MPL Multicast Packets + Upon receiving an MPL Data Message, the MPL Forwarder first processes + the MPL Option and updates the Trickle timer associated with the MPL + Data Message if one exists. - The MPL forwarder manages buffered MPL multicast packet transmissions - using the Trickle algorithm. When adding a packet to - BufferedPackets, the MPL forwarder MUST create a Trickle timer for - the packet and start execution of the Trickle algorithm. + Upon receiving an MPL Data Message, an MPL Forwarder MUST perform one + of the following actions: - After PROACTIVE_TIMER_EXPIRATIONS Trickle timer events, the MPL - forwarder MUST stop executing the Trickle algorithm. When a buffered - MPL multicast packet does not have an active Trickle timer, the MPL - forwarder MAY free the buffered packet by advancing WindowMin to 1 - greater than the packet's sequence number. + o Accept the message and enter the MPL Data Message in the Buffered + Message Set. - Each interface that supports MPL is configured with exactly one MPL - multicast scope. The MPL multicast scope MUST be site-local or - smaller and defaults to link-local. A scope larger than link-local - MAY be used only when that scope corresponds exactly to the MPL - domain. + o Accept the message and update the corresponding MinSequence in the + Seed Set to 1 greater than the message's sequence number. - An MPL domain may therefore be composed of one or more MPL multicast - scopes. For example, the MPL domain may be composed of a single MPL - multicast scope when using a site-local scope. Alternatively, the - MPL domain may be composed of multiple MPL multicast scopes when - using a link-local scope. + o Discard the message without any change to the MPL Information + Base. - IPv6-in-IPv6 encapsulation MUST be used when using MPL to forward an - original multicast packet whose source or destination address is - outside the MPL multicast scope. IPv6-in-IPv6 encapsulation is - necessary to support Path MTU discovery when the MPL forwarder is not - the source of the original multicast packet. IPv6-in-IPv6 - encapsulation also allows an MPL forwarder to remove the MPL Option - when forwarding the original multicast packet over a link that does - not support MPL. The destination address scope for the outer IPv6 - header MUST be the MPL multicast scope. + If a Seed Set entry exists for the MPL Seed, the MPL Forwarder MUST + discard the MPL Data Message if its sequence number is less than + MinSequence or exists in the Buffered Message Set. - When an MPL domain is composed of multiple MPL multicast scopes (e.g. - when the MPL multicast scope is link-local), an MPL forwarder MUST - decapsulate and encapsulate the original multicast packet when - crossing between different MPL multicast scopes. In doing so, the - MPL forwarder MUST duplicate the MPL Option, unmodified, in the new - outer IPv6 header. + If a Seed Set entry does not exist for the MPL Seed, the MPL + Forwarder MUST create a new entry for the MPL Seed before accepting + the MPL Data Message. - The IPv6 destination address of the MPL multicast packet is the all- - MPL-forwarders multicast address (TBD). The scope of the IPv6 - destination address is set to the MPL multicast scope. + If memory is limited, an MPL Forwarder SHOULD reclaim memory + resources by: -5.4. Reception of MPL Multicast Packets + o Incrementing MinSequence entries in the Seed Set and deleting MPL + Data Messages in the Buffered Message Set that fall below the + corresponding MinSequence value. - Upon receiving an MPL multicast packet, the MPL forwarder first - determines whether or not to accept and buffer the MPL multicast - packet based on its MPL seed and sequence value, as specified in - Section 5.2. + o Deleting other Seed Set entries that have expired and the + corresponding MPL Data Messages in the Buffered Message Set. - If the MPL forwarder accepts the MPL multicast packet, the MPL - forwarder determines whether or not to deliver the original multicast - packet to the next higher layer. For example, if the MPL multicast - packet uses IPv6-in-IPv6 encapsulation, the MPL forwarder removes the - outer IPv6 header, which also removes MPL Option. + If the MPL Forwarder accepts the MPL Data Message, the MPL Forwarder + MUST perform the following actions: -5.5. Transmission of ICMPv6 MPL Messages + o If PROACTIVE_PROPAGATION is true, the MPL Forwarder MUST + initialize and start a Trickle timer for the MPL Data Message. - The MPL forwarder generates and transmits a new ICMPv6 MPL message - whenever Trickle requests a transmission. The MPL forwarder includes - an encoding of each sliding window in the ICMPv6 MPL message. + o If the MPL Control Message Trickle timer is not running and + CONTROL_MESSAGE_TIMER_EXPIRATIONS is non-zero, the MPL Forwarder + MUST initialize and start the MPL Control Message Trickle timer. - Each sliding window is encoded using an MPL Window entry, defined in - Section 5.2. The MPL forwarder sets the MPL Window fields as - follows: + o If the MPL Control Message Trickle timer is running, the MPL + Forwarder MUST reset the MPL Control Message Trickle timer. - S If the MPL seed identifier is 0, set S to 0. If the MPL seed - identifier is within the range [1, 65535], set S to 2. Otherwise, - set S to 3. +11. MPL Control Messages - w-min Set to the lower bound of the sliding window (i.e. - WindowMin). +11.1. MPL Control Message Generation - w-len Set to the length of the window (i.e. WindowMax - WindowMin). + An MPL Forwarder generates MPL Control Messages to communicate its + Seed Set and Buffered Message Set to neighboring MPL Forwarders. + Each MPL Control Message is generated according to Section 6.2, with + an MPL Seed Info for each entry in Seed Set. Each MPL Seed Info entry + has the following content: - seed-id If S is non-zero, set to the MPL seed identifier. + o S set to the size of the seed-id field in the MPL Seed Info entry. - buffered-mpl-packets Set each bit that represents a sequence number - of a packet in BufferedPackets to 1. Set all other bits to 0. - The i'th bit in buffered-mpl-packets represents a sequence number - of w-min + i. + o min-seqno set to MinSequence of the MPL Seed. -5.6. Reception of ICMPv6 MPL Messages + o bm-len set to the size of buffered-mpl-messages in octets. - An MPL forwarder processes each ICMPv6 MPL message that it receives - to determine if it has any new MPL multicast packets to receive or - offer. + o seed-id set to the MPL seed identifier. - An MPL forwarder determines if a new MPL multicast packet has not - been received from a neighboring node if any of the following - conditions hold true: + o buffered-mpl-messages with each bit representing whether or not an + MPL Data Message with the corresponding sequence number exists in + the Buffered Message Set. The i'th bit represents a sequence + number of min-seqno + i. '0' indicates that the corresponding MPL + Data Message does not exist in the Buffered Message Set. '1' + indicates that the corresponding MPL Data Message does exist in + the Buffered Message Set. - 1. The ICMPv6 MPL message includes an MPL Window for an MPL seed - that does not have a corresponding sliding window entry on the - MPL forwarder. +11.2. MPL Control Message Transmission - 2. The neighbor has a packet in its BufferedPackets that has - sequence value greater than or equal to WindowMax (i.e. w-min + - w-len >= WindowMax). + An MPL Forwarder transmits MPL Control Messages using the Trickle + algorithm. A MPL forwarder maintains a single Trickle timer for each + MPL Domain. When CONTROL_MESSAGE_TIMER_EXPIRATIONS is 0, the MPL + Forwarder does not execute the Trickle algorithm and does not + transmit MPL Control Messages. In accordance with Section 5 of RFC + 6206 [RFC6206], this document defines the following: - 3. The neighbor has a packet in its BufferedPackets that has - sequence number within range of the sliding window but is not - included in BufferedPackets (i.e. the i'th bit in buffered-mpl- - packets is set to 1, where the sequence number is w-min + i). + o This document defines a "consistent" transmission as receiving an + MPL Control Message that indicates neither the receiving nor + transmitting node has new MPL Data Message. - When an MPL forwarder determines that it has not yet received a new - MPL multicast packet buffered by a neighboring device, the MPL - forwarder resets the Trickle timer associated with reactive - propagation. + o This document defines an "inconsistent" transmission as receiving + an MPL Control Message that indicates either the receiving or + transmitting node has at least one new MPL Data Message to offer. - An MPL forwarder determines if an entry in BufferedPackets has not - been received by a neighboring MPL forwarder if any of the following - conditions hold true: + o This document defines an "event" as increasing MinSequence of any + entry in the Seed Set or adding a message to the Buffered Message + Set. - 1. The ICMPv6 MPL message does not include an MPL Window for the - packet's MPL seed. + o This document defines an MPL Control Message as a Trickle message. - 2. The packet's sequence number is greater than or equal to the - neighbor's WindowMax value (i.e. the packet's sequence number is - greater than or equal to w-min + w-len). + As specified in [RFC6206], a Trickle timer has three variables: the + current interval size I, a time within the current interval t, and a + counter c. MPL defines a fourth variable, e, which counts the number + of Trickle timer expiration events since the Trickle timer was last + reset. After CONTROL_MESSAGE_TIMER_EXPIRATIONS Trickle timer events, + the MPL Forwarder MUST disable the Trickle timer. - 3. The packet's sequence number is within the range of the - neighbor's sliding window [WindowMin, WindowMax), but not - included in the neighbor's BufferedPacket (i.e. the packet's - sequence number is greater than or equal to w-min, strictly less - than w-min + w-len, and the corresponding bit in buffered-mpl- - packets is set to 0. +11.3. MPL Control Message Processing - When an MPL forwarder determines that it has at least one buffered - MPL multicast packet that has not yet been received by a neighbor, - the MPL forwarder resets the Trickle timer associated with reactive - propagation. Additionally, for each buffered MPL multicast packet - that should be transferred, the MPL forwarder MUST reset the Trickle - timer and reset e to 0 for proactive propagation. If the Trickle - timer for proactive propagation has already stopped execution, the - MPL forwarder MUST initialize a new Trickle timer and start execution - of the Trickle algorithm. + An MPL Forwarder processes each MPL Control Message that it receives + to determine if it has any new MPL Data Messages to receive or offer. -6. MPL Parameters + An MPL Forwarder determines if a new MPL Data Message has not been + received from a neighboring node if any of the following conditions + hold true: - An MPL forwarder maintains two sets of Trickle parameters for the - proactive and reactive methods. The Trickle parameters are listed - below: + o The MPL Control Message includes an MPL Seed that does not exist + in the Seed Set. - PROACTIVE_IMIN The minimum Trickle timer interval, as defined in - [RFC6206] for proactive propagation. + o The MPL Control Message indicates that the neighbor has an MPL + Data Message in its Buffered Message Set with sequence number + greater than MinSequence (i.e. the i-th bit is set to 1 and min- + seqno + i > MinSequence) and is not included in the MPL + Forwarder's Buffered Message Set. - PROACTIVE_IMAX The maximum Trickle timer interval, as defined in - [RFC6206] for proactive propagation. + When an MPL Forwarder determines that it has not yet received an MPL + Data Message buffered by a neighboring device, the MPL Forwarder MUST + reset its Trickle timer associated with MPL Control Message + transmissions. If an MPL Control Message Trickle timer is not + running, the MPL Forwarder MUST initialize and start a new Trickle + timer. - PROACTIVE_K The redundancy constant, as defined in [RFC6206] for - proactive propagation. + An MPL Forwarder determines if an MPL Data Message in the Buffered + Message Set has not yet been received by a neighboring MPL Forwarder + if any of the following conditions hold true: - PROACTIVE_TIMER_EXPIRATIONS The number of Trickle timer expirations - that occur before terminating the Trickle algorithm. MUST be set - to a value greater than 0. + o The MPL Control Message does not include an MPL Seed for the MPL + Data Message. - REACTIVE_IMIN The minimum Trickle timer interval, as defined in - [RFC6206] for reactive propagation. + o The MPL Data Message's sequence number is greater than or equal to + min-seqno and not included in the neighbor's Buffered Message Set + (i.e. the MPL Data Message's sequence number does not have a + corresponding bit in buffered-mpl-messages set to 1). - REACTIVE_IMAX The maximum Trickle timer interval, as defined in - [RFC6206] for reactive propagation. + When an MPL Forwarder determines that it has at least one MPL Data + Message in its Buffered Message Set that has not yet been received by + a neighbor, the MPL Forwarder MUST reset the MPL Control Message + Trickle timer. Additionally, for each of those entries in the + Buffered Message Set, the MPL Forwarder MUST reset the Trickle timer + and reset e to 0. If a Trickle timer is not associated with the MPL + Data Message, the MPL Forwarder MUST initialize and start a new + Trickle timer. - REACTIVE_K The redundancy constant, as defined in [RFC6206] for - reactive propagation. +12. Acknowledgements - REACTIVE_TIMER_EXPIRATIONS The number of Trickle timer expirations - that occur before terminating the Trickle algorithm. MAY be set - to 0, which disables reactive propagation. + The authors would like to acknowledge the helpful comments of Robert + Cragie, Esko Dijk, Ralph Droms, Paul Duffy, Ulrich Herberg, Owen + Kirby, Joseph Reddy, Don Sturek, Dario Tedeschi, and Peter van der + Stok, which greatly improved the document. - WINDOW_HOLD_TIME The minimum lifetime for sliding window state. +13. IANA Considerations -7. Acknowledgements + This document defines one IPv6 Option, a type that must be allocated + from the IPv6 "Destination Options and Hop-by-Hop Options" registry + of [RFC2780]. - The authors would like to acknowledge the helpful comments of Robert - Cragie, Esko Dijk, Ralph Droms, Paul Duffy, Owen Kirby, Joseph Reddy, - Dario Tedeschi, and Peter van der Stok, which greatly improved the - document. + This document defines one ICMPv6 Message, a type that must be + allocated from the "ICMPv6 "type" Numbers" registry of [RFC4443]. -8. IANA Considerations + This document registers two well-known multicast addresses from the + IPv6 multicast address space. - The Trickle Multicast option requires an IPv6 Option Number. +13.1. MPL Option Type - HEX act chg rest - --- --- --- ----- - C 01 0 TBD + IANA is requested to allocate an IPv6 Option Type from the IPv6 + "Destination Options and Hop-by-Hop Options" registry of [RFC2780], + as specified in Table 1 below: - The first two bits indicate that the IPv6 node MUST discard the - packet if it doesn't recognize the option type, and the third bit - indicates that the Option Data MUST NOT change en-route. + +--------------+-----+-----+--------------+-------------+-----------+ + | Mnemonic | act | chg | rest | Description | Reference | + +--------------+-----+-----+--------------+-------------+-----------+ + | MPL_OPT_TYPE | 01 | 1 | TBD | MPL Option | This | + | | | | (suggested | | Document | + | | | | value 01101) | | | + +--------------+-----+-----+--------------+-------------+-----------+ -9. Security Considerations + Table 1: IPv6 Option Type Allocation - TODO. +13.2. MPL ICMPv6 Type -10. References + IANA is requested to allocate an ICMPv6 Type from the "ICMPv6 "type" + Numbers" registry of [RFC4443], as specified in Table 2 below: -10.1. Normative References + +---------------+------+---------------------+---------------+ + | Mnemonic | Type | Name | Reference | + +---------------+------+---------------------+---------------+ + | MPL_ICMP_TYPE | TBD | MPL Control Message | This Document | + +---------------+------+---------------------+---------------+ + + Table 2: IPv6 Option Type Allocation + +13.3. Well-known Multicast Addresses + + IANA is requested to allocate an IPv6 multicast address + "ALL_MPL_FORWARDERS" from the "Variable Scope Multicast Addresses" + sub-registry of the "INTERNET PROTOCOL VERSION 6 MULTICAST ADDRESSES" + registry. + +14. Security Considerations + + MPL uses sequence numbers to maintain a total ordering of MPL Data + Messages from an MPL Seed. The use of sequence numbers allows a + denial-of-service attack where an attacker can spoof a message with a + sufficiently large sequence number to: (i) flush messages from the + Buffered Message List and (ii) increase the MinSequence value for an + MPL Seed in the Seed Set. The former side effect allows an attacker + to halt the forwarding process of any MPL Data Messages being + disseminated. The latter side effect allows an attacker to prevent + MPL Forwarders from accepting new MPL Data Messages that an MPL Seed + generates while the sequence number is less than MinSequence. + + More generally, the basic ability to inject messages into a Low-power + and Lossy Network can be used as a denial-of-service attack + regardless of what forwarding protocol is used. For these reasons, + Low-power and Lossy Networks typically employ link-layer security + mechanisms to disable an attacker's ability to inject messages. + + To prevent attackers from injecting packets through an MPL Forwarder, + the MPL Forwarder MUST NOT accept or forward MPL Data Messages from a + communication interface that does not subscribe to the MPL Domain + Address identified in message's destination address. + + MPL uses the Trickle algorithm to manage message transmissions and + the security considerations described in [RFC6206] apply. + +15. Normative References [RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982, August 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. - [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. - [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in IPv6 Specification", RFC 2473, December 1998. + [RFC2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For + Values In the Internet Protocol and Related Headers", + BCP 37, RFC 2780, March 2000. + + [RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and + B. Zill, "IPv6 Scoped Address Architecture", RFC 4007, + March 2005. + [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", RFC 4443, March 2006. [RFC6206] Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko, "The Trickle Algorithm", RFC 6206, March 2011. [RFC6550] Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, JP., and R. Alexander, "RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks", RFC 6550, March 2012. -10.2. Informative References - - [I-D.ietf-roll-terminology] - Vasseur, J., "Terminology in Low power And Lossy - Networks", draft-ietf-roll-terminology-06 (work in - progress), September 2011. - Authors' Addresses Jonathan W. Hui Cisco 170 West Tasman Drive San Jose, California 95134 USA Phone: +408 424 1547 Email: jonhui@cisco.com