PIM Y. Liu, Ed. Internet-Draft China Mobile Intended status: Standards Track M. McBride Expires: 19 August 2023 T. Eckert, Ed. Futurewei Z. Zhang ZTE Corporation 15 February 2023 PIM Assert Message Packing draft-ietf-pim-assert-packing-08 Abstract LANs often have more than one upstream router. When PIM Sparse Mode (PIM-SM), including PIM-SSM, is used, this can lead to duplicate IP multicast packets being forwarded by these PIM routers. PIM Assert messages are used to elect a single forwarder for each IP multicast traffic flow between these routers. This document defines a mechanism to send and receive information for multiple IP multicast flows in a single PackedAssert message. This optimization reduces the total number of PIM packets on the LAN and can therefore speed up the election of the single forwarder, reducing the number of duplicate IP multicast packets incurred. 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 https://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 19 August 2023. Copyright Notice Copyright (c) 2023 IETF Trust and the persons identified as the document authors. All rights reserved. Liu, et al. Expires 19 August 2023 [Page 1] Internet-Draft assert-packing February 2023 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. Problem statement . . . . . . . . . . . . . . . . . . . . . . 4 3. Specification . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. PIM Hello Assert Packing Option . . . . . . . . . . . . . 5 3.2. Assert Packing Message Formats . . . . . . . . . . . . . 5 3.3. PackedAssert Mechanism . . . . . . . . . . . . . . . . . 6 3.3.1. Sending PackedAssert messages . . . . . . . . . . . . 6 3.3.2. Receiving PackedAssert messages . . . . . . . . . . . 9 4. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . 9 4.1. PIM Assert Packing Hello Option . . . . . . . . . . . . . 9 4.2. Assert Message Format . . . . . . . . . . . . . . . . . . 10 4.3. Simple PackedAssert Message Format . . . . . . . . . . . 10 4.4. Aggregated PackedAssert Message Format . . . . . . . . . 12 4.4.1. Source Aggregated Assert Record . . . . . . . . . . . 13 4.4.2. RP Aggregated Assert Record . . . . . . . . . . . . . 14 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 6. Security Considerations . . . . . . . . . . . . . . . . . . . 17 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 8. Working Group considerations . . . . . . . . . . . . . . . . 17 8.1. Open Issues . . . . . . . . . . . . . . . . . . . . . . . 18 8.2. Changelog . . . . . . . . . . . . . . . . . . . . . . . . 18 8.2.1. draft-ietf-pim-assert-packing-08 . . . . . . . . . . 18 8.2.2. draft-ietf-pim-assert-packing-07 . . . . . . . . . . 18 8.2.3. draft-ietf-pim-assert-packing-06 . . . . . . . . . . 18 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 9.1. Normative References . . . . . . . . . . . . . . . . . . 18 9.2. Informative References . . . . . . . . . . . . . . . . . 19 Appendix A. Use case examples . . . . . . . . . . . . . . . . . 19 A.1. Enterprise network . . . . . . . . . . . . . . . . . . . 19 A.2. Video surveillance . . . . . . . . . . . . . . . . . . . 19 A.3. Financial Services . . . . . . . . . . . . . . . . . . . 19 A.4. IPTV broadcast Video . . . . . . . . . . . . . . . . . . 20 A.5. MVPN MDT . . . . . . . . . . . . . . . . . . . . . . . . 20 A.6. Special L2 services . . . . . . . . . . . . . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 Liu, et al. Expires 19 August 2023 [Page 2] Internet-Draft assert-packing February 2023 1. Introduction In PIM-SM shared LAN networks, there is typically more than one upstream router. When duplicate data packets appear on the LAN, from different upstream routers, assert packets are sent from these routers to elect a single forwarder according to [RFC7761]. The PIM assert messages are sent periodically to keep the assert state. The PIM assert message carries information about a single multicast source and group, along with the corresponding metric-preference and metric of the route towards the source or RP. This document defines a mechanism to encode the information of multiple PIM Assert messages into a single PackedAssert message. This allows to send and receive information for multiple IP multicast flows in a single PackedAssert message without changing the PIM Assert state machinery. It reduces the total number of PIM packets on the LAN and can therefore speed up the election of the single forwarder, reducing the number of duplicate IP multicast packets. This can particularly be helpful when there is traffic for a large number of multicast groups or SSM channels and PIM packet processing performance of the routers is slow. 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 1.2. Terminology The reader is expected to be familiar with the terminology of [RFC7761]. The following lists the abbreviations repeated in this document. AT: Assert Timer RP: Rendezvous Point RPF: Reverse Path Forwarding SPT: Shortest Path Tree RPT: RP Tree DR: Designated Router Liu, et al. Expires 19 August 2023 [Page 3] Internet-Draft assert-packing February 2023 2. Problem statement PIM Assert occur in many deployments. See Appendix A for some explicit examples. PIM assert state depends mainly on the network topology. As long as there is a layer 2 network with more than 2 PIM routers, there may be multiple upstream routers, which can cause duplicate multicast traffic to be forwarded and assert process to occur. As the multicast services become widely deployed, the number of multicast entries increases, and a large number of assert messages may be sent in a very short period when multicast data packets trigger PIM assert processing in the shared LAN networks. The PIM routers need to process a large number of PIM assert small packets in a very short time. As a result, the device load is very large. The assert packet may not be processed in time or even discarded, thus extending the time of traffic duplication in the network. The PIM Assert mechanism can only be avoided by designing the network to be without transit subnets with multiple upstream routers. For example, an L2 ring between routers can sometimes be reconfigured to be a ring of point-to-point subnets connected by the routers. These L2/L3 topology changes are undesirable though, when they are only done to enable IP multicast with PIM because they increase the cost of introducing IP multicast with PIM. These designs are also not feasible when specific L2 technologies are needed. For example various L2 technologies for rings provide sub 50msec failover mechanisms, something not possible equally with an L3 subnet based ring. Likewise, IEEE Time Sensitive Networking mechanisms would require an L2 topology that can not simply be replaced by an L3 topology. L2 sub-topologies can also significantly reduce the cost of deployment. 3. Specification This document defines three elements in support of PIM assert packing: 1. The PIM Hello Assert Packing Option. 2. The encoding of PackedAssert messages. 3. How to send and receive PackedAssert messages. Liu, et al. Expires 19 August 2023 [Page 4] Internet-Draft assert-packing February 2023 3.1. PIM Hello Assert Packing Option The PIM Assert Packing Hello Option (Section 4.1) is used to announce support for the assert packing mechanisms specified in this document. PackedAssert messages (Section 3.2) MUST NOT be used unless all PIM routers in the same subnet announce this option. 3.2. Assert Packing Message Formats The PIM Assert message, as defined in Section 4.9.6 of [RFC7761], describes the parameters of a (*,G) or (S,G) assert through the following information elements: Rendezvous Point Tree flag (R), Source Address, Group Address, Metric and Metric Preference. This document calls this information an assert record. Assert packing introduces two new PIM Assert message encodings through the allocation and use of two flags in the PIM Assert message header [RFC8736], the Packed (P) and the Aggregated (A) flags. If the P)acked flag is 0, the message is a (non-packed) PIM Assert message as specified in [RFC7761]. See Section 4.2. In this case, the (A) flag MUST be set to 0, and MUST be ignored on receipt. If the (P) flag is 2, then the message is called a PackedAssert message and the type and hence encoding format of the payload is determined by the (A) flag. If A=0, then the message body is a sequence of assert records preceeded by a count. This is called a "Simple PackedAssert" message. See Section 4.3. If A=1, then the message body is a sequence of aggregated assert records preceeded by a count. This is called an "Aggregated PackedAssert". See Section 4.4. Two aggregated assert record types are specified. The "Source Aggregated Assert Record", see Section 4.4.1, encodes one (common) Source Address, Metric and Metric Preference as well as a list of one or more Group Addresses with a Count. Source Aggregated Assert Records provide a more compact encoding than the Simple PackedAssert message format when multiple (S,G) flows share the same source S. A single Source Aggregated Assert Record with n Group Addresses represents the information of assert records for (S,G1)...(S,Gn). The "RP Aggregated Assert Record", see Section 4.4.2, encodes one common Metric and Metric Preference as well as a list of "Group Records", each of which encodes a Group Address and a list of zero or Liu, et al. Expires 19 August 2023 [Page 5] Internet-Draft assert-packing February 2023 more Source Addresses with a count. This is called an "RP Aggregated Assert Record", because with standard RPF according to ([RFC7761]), all the Group Addresses that use the same RP will have the same Metric and Metric Preference. RP Aggregation Records provide a more compact encoding than the Simple PackedAssert message format for (*,G) flows. The Source Address is optionally used by [RFC7761] assert procedures to indicate the source(s) that triggered the assert, otherwise it is 0. Both Source Aggregated Assert Records and RP Aggregated Assert Records also include the R flag which maintains its semantic from [RFC7761] but also distinguishes the encodings. Source Aggregated Assert Records have R=0, as (S,G) assert records do in [RFC7761]. RP Aggregated Assert Records have R=1, as (*,G) assert records do in [RFC7761]. 3.3. PackedAssert Mechanism PackedAsserts do not change the [RFC7761] PIM assert state machine specification. Instead, sending and receiving of PackedAssert messages as specified in the following subsections is logically a layer in between sending/receiving of Assert messages and serialization/deserialization of their respective packets. There is no change in the information elements of the transmitted information elements constituting the assert records nor their semantics. Only the compactness of their encoding. 3.3.1. Sending PackedAssert messages When using assert packing, the regular [RFC7761] Assert message encoding with A=0 and P=0 is still allowed to be sent. Routers are free to choose which PackedAssert message type they send. It is out of scope of this specification for which conditions, such as data-triggered asserts or Assert Timer (AT) expiry based asserts, an implementation should generate PackedAsserts instead of Asserts. Instead, * Implementations are expected to specify in documentation and/or management interfaces (such as a YANG model), which PackedAssert message types they can send and under which conditions they will. * Implementation SHOULD NOT send only Asserts, but no PackedAsserts under all conditions, when all routers on the LAN do support Assert Packing. Liu, et al. Expires 19 August 2023 [Page 6] Internet-Draft assert-packing February 2023 When a PIM router has an assert record ready to send according to [RFC7761], it calls send Assert(S,G) / send Assert(_,G) (Section 4.2), Send Assert(S,G) / SendAssertCancel(S,G) (Section 4.6.1), Send Assert(_,G) / Send AssertCancel(*,G) (Section 4.6.2) and send Assert(S,G) (Section 4.8.2). Each of these calls will send an Assert message. When sending of PackedAsserts is possible on the network, any of these calls is permitted to not send an Assert message, but only remember the assert record, and let PIM continue with further processing for other flows that may result in additional assert records - to finally packe PackedAssert messages from the remembered assert records and send them. The following text discusses several conditions to be taken into account for this further processing and how to create and schedule PackedAssert messages. Avoiding possible additional and relevant delay because of further processing is most critical for assert records that are triggered by reception of data or reception of asserts against which the router is in the "I am Assert Winner" state. In these cases the router SHOULD send out an Assert or PackedAssert message containing this assert record as soon as possible to minimize the time in which duplicate IP multicast packets can occur. To avoid additional delay in this case, the router should employ appropriate assert packing and scheduling mechanisms, such as for example the following. Asserts/PackedAsserts in this case are scheduled for serialization with highest priority, such that they bypass any potentially earlier scheduled other packets. When there is no such Assert/PacketAssert message scheduled for or being serialized, the router immediately serializes an Assert or PackedAssert message without further assert packing. If there are one or more Assert/PackedAssert messages serialized and/or scheduled to be serialized, then the router can pack assert records into new PackedAssert messages until shortly before the last of those Assert/PackedAssert packets has finished serializing. Asserts triggered by expiry of the AT on an assert winner are not time-critical because they can be scheduled in advance and because the Assert_Override_Interval parameter of [RFC7761] already creates a 3 second window in which such assert records can be sent, received, and processed before an assert losers state would expire and duplicate IP multicast packets could occur. Liu, et al. Expires 19 August 2023 [Page 7] Internet-Draft assert-packing February 2023 An example mechanism to allow packing of AT expiry triggered assert records on assert winners is to round the AT to an appropriate granularity such as 100msec. This will cause AT for multiple (S,G) and/or (*,G) states to expire at the same time, thus allowing them to be easily packed without changes to the assert state machinery. AssertCancel messages have assert records with an infinite metric and can use assert packing as any other Assert. They are sent on Override Timer (OT) expiry and can be packed for example with the same considerations as AT expiry triggered assert records. Additional delay is not "relevant" when it still causes the overall amount of (possible) duplicate IP multicast packets to decrease in a condition with large number of (S,G) and/or (*,G), compared to the situation in which no delay is added by the implementation. This can simply be the case because the implementation can not afford to implement the (more advanced) mechanisms described above, and some simpler mechanism that does introduce some additional delay still causes more overall reduction in duplicate IP multicast packets than not sending PackedAsserts at all, but only Asserts. "Relevant" is a highly implementation dependent metric and can typically only be measured against routers of the same type as receivers, and performance results with other routers will likely differ. Therefore it is optional. When Asserts are sent, a single packet loss will result only in continued or new duplicates from a single IP multicast flow. Loss of (non AssertCancel) PackedAssert impacts duplicates for all flows packed into the PackedAssert and may result in the need for re- sending more than one Assert/PacketAssert, because of the possible inability to pack the assert records in this condition. Threrefore, routers SHOULD support mechanisms allowing for PackedAsserts and Asserts to be sent with an appropriate DSCP, such as Expedited Forwarding (EF), to minimize their loss, especially when duplicate IP multicast packets could cause congestion and loss. Routers MAY support a configurable option for sending PackedAssert messages twice in short order (such as 50msec apart), to overcome possible loss, but only when the following two conditions are met. 1. The total size of the two PackedAsserts is less than the total size of equivalent Assert messages, Liu, et al. Expires 19 August 2023 [Page 8] Internet-Draft assert-packing February 2023 2. The condition of the assert records flows in the PackedAssert is such that the router can expect that their reception by PIM routers will not trigger Assert/PackedAsserts replies. This condition is true for example when sending an assert record while becoming or being Assert Winner (Action A1/A3 in [RFC7761]). It is "sufficient" that assert records are not packed up to MTU size, but to a size that allows the router to achieve the required operating scale of (S,G) and (*,G) flows with minimum duplicates. This packing size may be larger when the network is operating with the maximum number of supported multicast flows, and it can be a smaller packing size when operating with fewer multicast flows. Larger than "sufficient" packets may then not provide additional benefits, because they only reduce the performance requirements for packet sending and reception, and other performance limiting factors may take over once a "sufficient" size is reached. And larger packets can incur more duplicates on loss. Routers MAY support a "sufficient" amount of packing to minimize the negative impacts of loss of PackedAssert packets without loss of performance of minimizing IP multicast packet duplication. 3.3.2. Receiving PackedAssert messages Upon reception of a PackedAssert message, the PIM router logically converts its payload into a sequence of assert records that are then processed as if an equivalent sequence of Assert messages where received according to [RFC7761]. 4. Packet Formats This section describes the format of new PIM extensions introduced by this document. 4.1. PIM Assert Packing Hello Option 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OptionType = TBD | OptionLength = 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: PIM Assert Packing Hello Option The PIM Assert Packing Hello Option is a new option for PIM Hello Messages according to Section 4.9.2 of [RFC7761]. * OptionType TBD: PIM Packed Assert Capability Hello Option Liu, et al. Expires 19 August 2023 [Page 9] Internet-Draft assert-packing February 2023 Including the PIM OptionType TBD indicates support for the ability to receive and process all the PackedAssert encodings defined in this document. 4.2. Assert Message 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |PIM Ver| Type |7 6 5 4 3 2|A|P| Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Group Address (Encoded-Group format) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Address (Encoded-Unicast format) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |R| Metric Preference | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Assert Figure 2 shows a PIM Assert message as specified in Section 4.9.6 of [RFC7761] with the common header showing the Flag Bits defined in [RFC8736] and the location of the P and A flags. As specified in Section 3.2, both flags in a (non-packed) PIM Assert message are required to be set to 0. 4.3. Simple PackedAssert Message Format Liu, et al. Expires 19 August 2023 [Page 10] Internet-Draft assert-packing February 2023 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |PIM Ver| Type |7 6 5 4 3 2|A|P| Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Count | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . Assert Record [1] . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . Assert Record [2] . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . | . . . | . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . Assert Record [M] . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: Simple PackedAssert * PIM Version, Type, Checksum: As specified in Section 4.9.6 of [RFC7761]. * 7 6 5 4 3 2: Flag bits according to Section 4 of [RFC8736]. * Reserved: Set to zero on transmission. Ignored upon receipt. * P: packed flag. MUST be 1. * A: aggregated flag. MUST be 0. * Count The number of packed Assert Records in the message. Liu, et al. Expires 19 August 2023 [Page 11] Internet-Draft assert-packing February 2023 The format of each Assert Record is the same as the PIM assert message body as specified in Section 4.9.6 of [RFC7761]. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Group Address (Encoded-Group format) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Address (Encoded-Unicast format) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |R| Metric Preference | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: Assert Record 4.4. Aggregated PackedAssert Message 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |PIM Ver| Type |7 6 5 4 3 2|A|P| Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Count (M) | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . Aggregated Assert Record [1] . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . Aggregated Assert Record [2] . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . | . . . | . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . Aggregated Assert Record [M] . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Liu, et al. Expires 19 August 2023 [Page 12] Internet-Draft assert-packing February 2023 Figure 5: Aggregated PackedAssert * PIM Version, Type, Reserved, Checksum: As specified in Section 4.9.6 of [RFC7761]. * 7 6 5 4 3 2: Flag bits according to Section 4 of [RFC8736]. * P: packed flag. MUST be 1. * A aggregated flag. MUST be 1. * Count: The number of Aggregated Assert Records following in the message. Each of these records can either be a Source Aggregated or RP aggregated Assert Record. 4.4.1. Source Aggregated Assert Record 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |R| Metric Preference | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Address (Encoded-Unicast format) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Number of Groups (N) | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Group Address 1 (Encoded-Group format) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Group Address 2 (Encoded-Group format) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . | | . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Group Address N (Encoded-Group format) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 6: Source Aggregated Assert Record * Reserved: Set to zero on transmission. Ignored upon receipt. * R: MUST be 0. Liu, et al. Expires 19 August 2023 [Page 13] Internet-Draft assert-packing February 2023 R indicates both that the encoding format of the record is that of a Source Aggregated Assert Record, but also that all assert records represented by the Source Aggregated Assert Record have R=0 and are therefore (S,G) assert records according to the definition of R in [RFC7761], Section 4.9.6. * Source Address, Metric Preference, Metric: As specified in Section 4.9.6 of [RFC7761]. Source Address MUST NOT be zero. * Number of Groups: The number of Group Address fields. * Group Address: As specified in Section 4.9.6 of [RFC7761]. 4.4.2. RP Aggregated Assert Record An RP Aggregation Assert record aggregates (*,G) assert records with the same Metric Preference and Metric. Typically this is the case for all (*,G) using the same RP, but the encoding is not limited to only (*,G) using the same RP because the RP address is not encoded as it is also not present in [RFC7761] assert records. Liu, et al. Expires 19 August 2023 [Page 14] Internet-Draft assert-packing February 2023 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |R| Metric Preference | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Number of Group Records (K) | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . Group Record [1] . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . Group Record [2] . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . | . . . | . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . Group Record [K] . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 7: RP Aggregated Assert Record * R: MUST be 1. R indicates both that the encoding format of the record is that of an RP Aggregated Assert Record, and that all assert records represented by the RP Aggregated Assert Record have R=1 and are therefore (*,G) assert records according to the definition of R in [RFC7761], Section 4.9.6. * Metric Preference, Metric: As specified in Section 4.9.6 of [RFC7761]. * Reserved: Set to zero on transmission. Ignored upon receipt. Liu, et al. Expires 19 August 2023 [Page 15] Internet-Draft assert-packing February 2023 * Number of Group Records: The number of packed Group Records. A record consists of a Group Address and a Source Address list with a number of sources. The format of each Group Record is: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Group Address (Encoded-Group format) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Number of Sources (P) | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Address 1 (Encoded-Unicast format) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Address 2 (Encoded-Unicast format) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . | | . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Address P (Encoded-Unicast format) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 8: Group Record * Group Address and Reserved: As specified in Section 4.9.6 of [RFC7761]. * Reserved: Set to zero on transmission. Ignored upon receipt. * Number of Sources: The Number of Sources is corresponding to the number of Source Address fields in the Group Record. If this number is 0, the Group Record indicates one assert record with a Source Address of 0. If this number is not 0 and one of the (*,G) assert records to be encoded should have the Source Address 0, then 0 needs to be encoded as one of the Source Address fields. * Source Address: As specified in Section 4.9.6 of [RFC7761]. But there can be multiple Source Address fields in the Group Record. Liu, et al. Expires 19 August 2023 [Page 16] Internet-Draft assert-packing February 2023 5. IANA Considerations IANA is requested to assign a new code point from the "PIM-Hello Options" registry for the Packed Assert Capability as follows: +=======+========+=========================+================+ | Value | Length | Name | Reference | +=======+========+=========================+================+ | TBD | 0 | Packed Assert Capability| [This Document]| +=======+========+=========================+================+ Figure 9 IANA is requested to assign two Flag Bits in the Assert message from the "PIM Message Types" registry as follows: +======+========+=================+====================+ | Type | Name | Flag Bits | Reference | +======+========+=================+====================+ | 5 | Assert | 2-7: Reserved | [RFC3973][RFC7761] | | | | 1: Aggregated | [This Document] | | | | 0: Packed | [This Document] | +======+========+=================+====================+ Figure 10 6. Security Considerations The security considerations of [RFC7761] apply to the extensions defined in this document. This document packs multiple assert records in a single message. As described in Section 6.1 of [RFC7761], a forged Assert message could cause the legitimate designated forwarder to stop forwarding traffic to the LAN. The effect may be amplified when using a PackedAssert message. 7. Acknowledgments The authors would like to thank: Stig Venaas for the valuable contributions of this document, Alvaro Retana for his thorough and constructive RTG AD review. 8. Working Group considerations [RFC-Editor: please remove this section]. Liu, et al. Expires 19 August 2023 [Page 17] Internet-Draft assert-packing February 2023 8.1. Open Issues 8.2. Changelog This document is hosted starting with -06 on https://github.com/toerless/pim-assert-packing. 8.2.1. draft-ietf-pim-assert-packing-08 Included changes from review of Alvaro Retana (https://mailarchive.ietf.org/arch/msg/pim/ GsKq9bB2a6yDdM9DvAUGCWthdEI) Please see the following emails discussing the changes: https://raw.githubusercontent.com/toerless/pim-assert-packing/main/ emails/07-alvaro-review-reply.txt 8.2.2. draft-ietf-pim-assert-packing-07 Included changes from review of Alvaro Retana (https://mailarchive.ietf.org/arch/msg/pim/ Cp4o5glUFge2b84X9CQMwCWZjAk/) Please see the following emails discussing the changes: https://raw.githubusercontent.com/toerless/pim-assert-packing/main/ emails/05-alvaro-review-reply.txt https://raw.githubusercontent.com/toerless/pim-assert-packing/main/ emails/07-pim-wg-announce.txt 8.2.3. draft-ietf-pim-assert-packing-06 This version was converted from txt format into markdown for better editing later, but is otherwise text identical to -05. It was posted to DataTracker to make diffs easier. Functional changes: 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . Liu, et al. Expires 19 August 2023 [Page 18] Internet-Draft assert-packing February 2023 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 2016, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8736] Venaas, S. and A. Retana, "PIM Message Type Space Extension and Reserved Bits", RFC 8736, DOI 10.17487/RFC8736, February 2020, . 9.2. Informative References [RFC6037] Rosen, E., Ed., Cai, Y., Ed., and IJ. Wijnands, "Cisco Systems' Solution for Multicast in BGP/MPLS IP VPNs", RFC 6037, DOI 10.17487/RFC6037, October 2010, . Appendix A. Use case examples A.1. Enterprise network When an Enterprise network is connected through a layer-2 network, the intra-enterprise runs layer-3 PIM multicast. The different sites of the enterprise are equivalent to the PIM connection through the shared LAN network. Depending upon the locations and amount of groups there could be many asserts on the first-hop routers. A.2. Video surveillance Video surveillance deployments have migrated from analog based systems to IP-based systems oftentimes using multicast. In the shared LAN network deployments, when there are many cameras streaming to many groups there may be issues with many asserts on first-hop routers. A.3. Financial Services Financial services extensively rely on IP Multicast to deliver stock market data and its derivatives, and current multicast solution PIM is usually deployed. As the number of multicast flows grow, there are many stock data with many groups may result in many PIM asserts on a shared LAN network from publisher to the subscribers. Liu, et al. Expires 19 August 2023 [Page 19] Internet-Draft assert-packing February 2023 A.4. IPTV broadcast Video PIM DR deployments are often used in host-side network for IPTV broadcast video services. Host-side access network failure scenario may be benefitted by assert packing when many groups are being used. According to [RFC7761] the DR will be elected to forward multicast traffic in the shared access network. When the DR recovers from a failure, the original DR starts to send traffic, and the current DR is still forwarding traffic. In the situation multicast traffic duplication maybe happen in the shared access network and can trigger the assert progress. A.5. MVPN MDT As described in [RFC6037], MDT (Multicast Distribution Tree) is used as tunnels for MVPN. The configuration of multicast-enabled VRF (VPN routing and forwarding) or interface that is in a VRF changing may cause many assert packets to be sent in a same time. A.6. Special L2 services Additionally, future backhaul, or fronthaul, networks may want to connect L3 across an L2 underlay supporting Time Sensitive Networks (TSN). The infrastructure may run DetNet over TSN. These transit L2 LANs would have multiple upstreams and downstreams. This document is taking a proactive approach to prevention of possible future assert issues in these types of environments. Authors' Addresses Yisong Liu (editor) China Mobile China Email: liuyisong@chinamobile.com Mike McBride Futurewei United States of America Email: michael.mcbride@futurewei.com Toerless Eckert (editor) Futurewei United States of America Email: tte@cs.fau.de Liu, et al. Expires 19 August 2023 [Page 20] Internet-Draft assert-packing February 2023 Zheng(Sandy) Zhang ZTE Corporation China Email: zhang.zheng@zte.com.cn Liu, et al. Expires 19 August 2023 [Page 21]