MBONED Working Group H. Asaeda Internet-Draft NICT Intended status: Standards Track K. Meyer Expires: April 17, 2018 Cisco W. Lee, Ed. October 14, 2017 Mtrace Version 2: Traceroute Facility for IP Multicast draft-ietf-mboned-mtrace-v2-20 Abstract This document describes the IP multicast traceroute facility, named Mtrace version 2 (Mtrace2). Unlike unicast traceroute, Mtrace2 requires special implementations on the part of routers. This specification describes the required functionality in multicast routers, as well as how an Mtrace2 client invokes a query and receives a reply. 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 April 17, 2018. Copyright Notice Copyright (c) 2017 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 (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 Asaeda, et al. Expires April 17, 2018 [Page 1] Internet-Draft Mtrace2 October 2017 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. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 6 3. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . 7 3.1. Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . 8 3.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . 8 3.2.1. Mtrace2 Query . . . . . . . . . . . . . . . . . . . . 9 3.2.2. Mtrace2 Request . . . . . . . . . . . . . . . . . . . 11 3.2.3. Mtrace2 Reply . . . . . . . . . . . . . . . . . . . . 11 3.2.4. IPv4 Mtrace2 Standard Response Block . . . . . . . . 12 3.2.5. IPv6 Mtrace2 Standard Response Block . . . . . . . . 15 3.2.6. Mtrace2 Augmented Response Block . . . . . . . . . . 18 3.2.7. Mtrace2 Extended Query Block . . . . . . . . . . . . 19 4. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 20 4.1. Receiving Mtrace2 Query . . . . . . . . . . . . . . . . . 20 4.1.1. Query Packet Verification . . . . . . . . . . . . . . 20 4.1.2. Query Normal Processing . . . . . . . . . . . . . . . 21 4.2. Receiving Mtrace2 Request . . . . . . . . . . . . . . . . 21 4.2.1. Request Packet Verification . . . . . . . . . . . . . 21 4.2.2. Request Normal Processing . . . . . . . . . . . . . . 22 4.3. Forwarding Mtrace2 Request . . . . . . . . . . . . . . . 23 4.3.1. Destination Address . . . . . . . . . . . . . . . . . 24 4.3.2. Source Address . . . . . . . . . . . . . . . . . . . 24 4.3.3. Appending Standard Response Block . . . . . . . . . . 24 4.4. Sending Mtrace2 Reply . . . . . . . . . . . . . . . . . . 25 4.4.1. Destination Address . . . . . . . . . . . . . . . . . 25 4.4.2. Source Address . . . . . . . . . . . . . . . . . . . 25 4.4.3. Appending Standard Response Block . . . . . . . . . . 25 4.5. Proxying Mtrace2 Query . . . . . . . . . . . . . . . . . 25 4.6. Hiding Information . . . . . . . . . . . . . . . . . . . 26 Asaeda, et al. Expires April 17, 2018 [Page 2] Internet-Draft Mtrace2 October 2017 5. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 26 5.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 26 5.1.1. Destination Address . . . . . . . . . . . . . . . . . 27 5.1.2. Source Address . . . . . . . . . . . . . . . . . . . 27 5.2. Determining the Path . . . . . . . . . . . . . . . . . . 27 5.3. Collecting Statistics . . . . . . . . . . . . . . . . . . 27 5.4. Last Hop Router (LHR) . . . . . . . . . . . . . . . . . . 27 5.5. First Hop Router (FHR) . . . . . . . . . . . . . . . . . 28 5.6. Broken Intermediate Router . . . . . . . . . . . . . . . 28 5.7. Non-Supported Router . . . . . . . . . . . . . . . . . . 28 5.8. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 28 5.8.1. Arriving at Source . . . . . . . . . . . . . . . . . 28 5.8.2. Fatal Error . . . . . . . . . . . . . . . . . . . . . 29 5.8.3. No Upstream Router . . . . . . . . . . . . . . . . . 29 5.8.4. Reply Timeout . . . . . . . . . . . . . . . . . . . . 29 5.9. Continuing after an Error . . . . . . . . . . . . . . . . 29 6. Protocol-Specific Considerations . . . . . . . . . . . . . . 29 6.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . 30 6.2. Bi-Directional PIM . . . . . . . . . . . . . . . . . . . 30 6.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . 30 6.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . 30 7. Problem Diagnosis . . . . . . . . . . . . . . . . . . . . . . 31 7.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . 31 7.2. TTL or Hop Limit Problems . . . . . . . . . . . . . . . . 31 7.3. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 31 7.4. Link Utilization . . . . . . . . . . . . . . . . . . . . 32 7.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . 32 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 8.1. "Mtrace2 Forwarding Codes" Registry . . . . . . . . . . . 32 8.2. "Mtrace2 TLV Types" registry . . . . . . . . . . . . . . 32 8.3. UDP Destination Port . . . . . . . . . . . . . . . . . . 33 9. Security Considerations . . . . . . . . . . . . . . . . . . . 33 9.1. Addresses in Mtrace2 Header . . . . . . . . . . . . . . . 33 9.2. Filtering of Clients . . . . . . . . . . . . . . . . . . 33 9.3. Topology Discovery . . . . . . . . . . . . . . . . . . . 33 9.4. Characteristics of Multicast Channel . . . . . . . . . . 33 9.5. Limiting Query/Request Rates . . . . . . . . . . . . . . 33 9.6. Limiting Reply Rates . . . . . . . . . . . . . . . . . . 34 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 34 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 34 11.1. Normative References . . . . . . . . . . . . . . . . . . 34 11.2. Informative References . . . . . . . . . . . . . . . . . 35 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35 Asaeda, et al. Expires April 17, 2018 [Page 3] Internet-Draft Mtrace2 October 2017 1. Introduction Given a multicast distribution tree, tracing from a multicast source to a receiver is difficult, since we do not know which branch of the multicast tree the receiver lies. This means that we have to flood the whole tree to find the path from a source to a receiver. On the other hand, walking up the tree from a receiver to a source is easy, as most existing multicast routing protocols know the upstream router for each source. Tracing from a receiver to a source can involve only the routers on the direct path. This document specifies the multicast traceroute facility named Mtrace version 2 or Mtrace2 which allows the tracing of an IP multicast routing path. Mtrace2 is usually initiated from an Mtrace2 client by sending an Mtrace2 Query to a Last Hop Router (LHR) or to a Rendezvous Point (RP). The RP is a special router where sources and receivers meet in PIM-SM [5]. From the LHR/RP receiving the query, the tracing is directed towards a specified source if a source address is specified and source specific state exists on the receiving router. If no source address is specified or if no source specific state exists on a receiving LHR, the tracing is directed toward the RP for the specified group address. Moreover, Mtrace2 provides additional information such as the packet rates and losses, as well as other diagnostic information. Mtrace2 is primarily intended for the following purposes: o To trace the path that a packet would take from a source to a receiver. o To isolate packet loss problems (e.g., congestion). o To isolate configuration problems (e.g., TTL threshold). Figure 1 shows a typical case on how Mtrace2 is used. FHR represents the first-hop router, LHR represents the last-hop router, and the arrow lines represent the Mtrace2 messages that are sent from one node to another. The numbers before the Mtrace2 messages represent the sequence of the messages that would happen. Source, Receiver and Mtrace2 client are typically hosts. Asaeda, et al. Expires April 17, 2018 [Page 4] Internet-Draft Mtrace2 October 2017 2. Request 2. Request +----+ +----+ | | | | v | v | +--------+ +-----+ +-----+ +----------+ | Source |----| FHR |----- The Internet -----| LHR |----| Receiver | +--------+ +-----+ | +-----+ +----------+ \ | ^ \ | / \ | / \ | / 3. Reply \ | / 1. Query \ | / \ | / \ +---------+ / v | Mtrace2 |/ | client | +---------+ Figure 1 When an Mtrace2 client initiates a multicast trace, it sends an Mtrace2 Query packet to the LHR or RP for a multicast group and, optionally, a source address. The LHR/RP turns the Query packet into a Request. The Request message type enables each of the upstream routers processing the message to apply different packet and message validation rules than those required for handling of a Query message. The LHR/RP then appends a standard response block containing its interface addresses and packet statistics to the Request packet, then forwards the packet towards the source/RP. The Request packet is either unicasted to its upstream router towards the source/RP, or multicasted to the group if the upstream router's IP address is not known. In a similar fashion, each router along the path to the source/RP appends a standard response block to the end of the Request packet before forwarding it to its upstream router. When the FHR receives the Request packet, it appends its own standard response block, turns the Request packet into a Reply, and unicasts the Reply back to the Mtrace2 client. The Mtrace2 Reply may be returned before reaching the FHR under some circumstances. This can happen if a Request packet is received at an RP or gateway, or when any of several types of error or exception conditions occur which prevent sending of a request to the next upstream router. The Mtrace2 client waits for the Mtrace2 Reply message and displays the results. When not receiving an Mtrace2 Reply message due to network congestion, a broken router (see Section 5.6), or a non- Asaeda, et al. Expires April 17, 2018 [Page 5] Internet-Draft Mtrace2 October 2017 responding router (see Section 5.7), the Mtrace2 client may resend another Mtrace2 Query with a lower hop count (see Section 3.2.1), and repeat the process until it receives an Mtrace2 Reply message. The details are Mtrace2 client specific, and it is outside the scope of this document. Note that when a router's control plane and forwarding plane are out of sync, the Mtrace2 Requests might be forwarded based on the control states instead. In which case, the traced path might not represent the real path the data packets would follow. Mtrace2 supports both IPv4 and IPv6. Unlike the previous version of Mtrace, which implements its query and response as IGMP messages [8], all Mtrace2 messages are UDP-based. Although the packet formats of IPv4 and IPv6 Mtrace2 are different because of the address families, the syntax between them is similar. This document describes the base specification of Mtrace2 that can serve as a basis for future proposals such as Mtrace2 for AMT [9] and Mtrace2 for MVPN [10]. They are therefore out of the scope of this document. 2. Terminology In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in RFC 2119 [1], and indicate requirement levels for compliant Mtrace2 implementations. 2.1. Definitions Since Mtrace2 Queries and Requests flow in the opposite direction to the data flow, we refer to "upstream" and "downstream" with respect to data, unless explicitly specified. Incoming interface The interface on which data is expected to arrive from the specified source and group. Outgoing interface This is one of the interfaces to which data from the source or RP is expected to be transmitted for the specified source and group. It is also the interface on which the Mtrace2 Request was received. Upstream router Asaeda, et al. Expires April 17, 2018 [Page 6] Internet-Draft Mtrace2 October 2017 The router, connecting to the Incoming interface of the current router, which is responsible for forwarding data for the specified source and group to the current router. First-hop router (FHR) The router that is directly connected to the source the Mtrace2 Query specifies. Last-hop router (LHR) A router that is directly connected to a receiver. It is also the router that receives the Mtrace2 Query from an Mtrace2 client. Group state It is the state a shared-tree protocol, such as PIM-SM [5], uses to choose the upstream router towards the RP for the specified group. In this state, source-specific state is not available for the corresponding group address on the router. Source-specific state It is the state that is used to choose the path towards the source for the specified source and group. ALL-[protocol]-ROUTERS group It is a link-local multicast address for multicast routers to communicate with their adjacent routers that are running the same routing protocol. For instance, the IPv4 'ALL-PIM-ROUTERS' group is '224.0.0.13', and the IPv6 'ALL-PIM-ROUTERS' group is 'ff02::d' [5]. 3. Packet Formats This section describes the details of the packet formats for Mtrace2 messages. All Mtrace2 messages are encoded in TLV format (see Section 3.1). The first TLV of a message is a message header TLV specifying the type of message and additional context information required for processing of the message and for parsing of subsequent TLVs in the message. Subsequent TLVs in a message, referred to as Blocks, are appended after the header TLV to provide additional information associated with the message. If an implementation receives an unknown TLV type for the first TLV in a message, it SHOULD ignore and silently discard the TLV and any subsequent TLVs in the packet containing the TLV. If an implementation receives an unknown TLV type for a subsequent TLV within a message, it SHOULD ignore and silently discard the TLV. If the length of a TLV exceeds the available space in the containing packet, the implementation MUST ignore and silently discard the TLV and any remaining portion of the Asaeda, et al. Expires April 17, 2018 [Page 7] Internet-Draft Mtrace2 October 2017 containing packet. Any data in the packet after the specified TLV length is considered to be outside the boundary of the TLV and MUST be ignored during processing of the TLV. All Mtrace2 messages are UDP packets. For IPv4, Mtrace2 Query and Request messages MUST NOT be fragmented. For IPv6, the packet size for the Mtrace2 messages MUST NOT exceed 1280 bytes, which is the smallest MTU for an IPv6 interface [2]. The source port is uniquely selected by the local host operating system. The destination port is the IANA reserved Mtrace2 port number (see Section 8). All Mtrace2 messages MUST have a valid UDP checksum. Additionally, Mtrace2 supports both IPv4 and IPv6, but not mixed. For example, if an Mtrace2 Query or Request message arrives in as an IPv4 packet, all addresses specified in the Mtrace2 messages MUST be IPv4 as well. Same rule applies to IPv6 Mtrace2 messages. 3.1. Mtrace2 TLV 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 | Length | Value .... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 8 bits Describes the format of the Value field. For all the available types, please see Section 3.2 Length: 16 bits Length of Type, Length, and Value fields in octets. Minimum length required is 3 octets. The maximum TLV length is not defined; however the entire Mtrace2 packet length SHOULD NOT exceed the available MTU. Value: variable length The format is based on the Type value. The length of the value field is Length field minus 3. All reserved fields in the Value field MUST be transmitted as zeros and ignored on receipt. 3.2. Defined TLVs The following TLV Types are defined: Asaeda, et al. Expires April 17, 2018 [Page 8] Internet-Draft Mtrace2 October 2017 Code Type ==== ================================ 0x01 Mtrace2 Query 0x02 Mtrace2 Request 0x03 Mtrace2 Reply 0x04 Mtrace2 Standard Response Block 0x05 Mtrace2 Augmented Response Block 0x06 Mtrace2 Extended Query Block Each Mtrace2 message MUST begin with either a Query, Request or Reply TLV. The first TLV determines the type of each Mtrace2 message. Following a Query TLV, there can be a sequence of optional Extended Query Blocks. In the case of a Request or a Reply TLV, it is then followed by a sequence of Standard Response Blocks, each from a multicast router on the path towards the source or the RP. In the case more information is needed, a Standard Response Block can be followed by one or multiple Augmented Response Blocks. We will describe each message type in detail in the next few sections. 3.2.1. Mtrace2 Query An Mtrace2 Query is usually originated by an Mtrace2 client which sends an Mtrace2 Query message to the LHR. When tracing towards the source or the RP, the intermediate routers MUST NOT modify the Query message except the Type field. If the actual number of hops is not known, an Mtrace2 client could send an initial Query message with a large # Hops (e.g., 0xffffffff), in order to try to trace the full path. An Mtrace2 Query message is shown as follows: Asaeda, et al. Expires April 17, 2018 [Page 9] Internet-Draft Mtrace2 October 2017 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 | Length | # Hops | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Multicast Address | | | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | | | Source Address | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Mtrace2 Client Address | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Query ID | Client Port # | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2 # Hops: 8 bits This field specifies the maximum number of hops that the Mtrace2 client wants to trace. If there are some error conditions in the middle of the path that prevent an Mtrace2 Reply from being received by the client, the client MAY issue another Mtrace2 Query with a lower number of hops until it receives a Reply. Multicast Address: 32 bits or 128 bits This field specifies an IPv4 or IPv6 address, which can be either: m-1: a multicast group address to be traced; or, m-2: all 1's in case of IPv4 or the unspecified address (::) in case of IPv6 if no group-specific information is desired. Source Address: 32 bits or 128 bits This field specifies an IPv4 or IPv6 address, which can be either: s-1: an unicast address of the source to be traced; or, s-2: all 1's in case of IPv4 or the unspecified address (::) in case of IPv6 if no source-specific information is desired. For example, the client is tracing a (*,g) group state. Asaeda, et al. Expires April 17, 2018 [Page 10] Internet-Draft Mtrace2 October 2017 Note that it is invalid to have a source-group combination of (s-2, m-2). If a router receives such combination in an Mtrace2 Query, it MUST silently discard the Query. Mtrace2 Client Address: 32 bits or 128 bits This field specifies the Mtrace2 client's IPv4 address or IPv6 global address. This address MUST be a valid unicast address, and therefore, MUST NOT be all 1's or an unspecified address. The Mtrace2 Reply will be sent to this address. Query ID: 16 bits This field is used as a unique identifier for this Mtrace2 Query so that duplicate or delayed Reply messages may be detected. Client Port #: 16 bits This field specifies the destination UDP port number for receiving the Mtrace2 Reply packet. 3.2.2. Mtrace2 Request The format of an Mtrace2 Request message is similar to an Mtrace2 Query except the Type field is 0x02. When a LHR receives an Mtrace2 Query message, it would turn the Query into a Request by changing the Type field of the Query from 0x01 to 0x02. The LHR would then append an Mtrace2 Standard Response Block (see Section 3.2.4) of its own to the Request message before sending it upstream. The upstream routers would do the same without changing the Type field until one of them is ready to send a Reply. 3.2.3. Mtrace2 Reply The format of an Mtrace2 Reply message is similar to an Mtrace2 Query except the Type field is 0x03. When a FHR or a RP receives an Mtrace2 Request message which is destined to itself, it would append an Mtrace2 Standard Response Block (see Section 3.2.4) of its own to the Request message. Next, it would turn the Request message into a Reply by changing the Type field of the Request from 0x02 to 0x03. The Reply message would then be unicasted to the Mtrace2 client specified in the Mtrace2 Client Address field. There are a number of cases an intermediate router might return a Reply before a Request reaches the FHR or the RP. See Section 4.1.1, Section 4.2.2, Section 4.3.3, and Section 4.5 for more details. Asaeda, et al. Expires April 17, 2018 [Page 11] Internet-Draft Mtrace2 October 2017 3.2.4. IPv4 Mtrace2 Standard Response Block This section describes the message format of an IPv4 Mtrace2 Standard Response Block. The Type field is 0x04. 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 | Length | MBZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Query Arrival Time | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Incoming Interface Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Outgoing Interface Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Upstream Router Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Input packet count on incoming interface . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Output packet count on outgoing interface . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Total number of packets for this source-group pair . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Rtg Protocol | Multicast Rtg Protocol | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Fwd TTL | MBZ |S| Src Mask |Forwarding Code| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ MBZ: 8 bits This field MUST be zeroed on transmission and ignored on reception. Query Arrival Time: 32 bits The Query Arrival Time is a 32-bit NTP timestamp specifying the arrival time of the Mtrace2 Query or Request packet at this router. The 32-bit form of an NTP timestamp consists of the middle 32 bits of the full 64-bit form; that is, the low 16 bits of the integer part and the high 16 bits of the fractional part. The following formula converts from a UNIX timeval to a 32-bit NTP timestamp: Asaeda, et al. Expires April 17, 2018 [Page 12] Internet-Draft Mtrace2 October 2017 query_arrival_time = ((tv.tv_sec + 32384) << 16) + ((tv.tv_nsec << 7) / 1953125) The constant 32384 is the number of seconds from Jan 1, 1900 to Jan 1, 1970 truncated to 16 bits. ((tv.tv_nsec << 7) / 1953125) is a reduction of ((tv.tv_nsec / 1000000000) << 16). Note that Mtrace2 does not require all the routers on the path to have synchronized clocks in order to measure one-way latency. Additionally, Query Arrival Time is useful for measuring the packet rate. For example, suppose that a client issues two queries, and the corresponding requests R1 and R2 arrive at router X at time T1 and T2, then the client would be able to compute the packet rate on router X by using the packet count information stored in the R1 and R2, and the time T1 and T2. Incoming Interface Address: 32 bits This field specifies the address of the interface on which packets from the source or the RP are expected to arrive, or 0 if unknown or unnumbered. Outgoing Interface Address: 32 bits This field specifies the address of the interface on which packets from the source or the RP are expected to transmit towards the receiver, or 0 if unknown or unnumbered. This is also the address of the interface on which the Mtrace2 Query or Request arrives. Upstream Router Address: 32 bits This field specifies the address of the upstream router from which this router expects packets from this source. This may be a multicast group (e.g., ALL-[protocol]-ROUTERS group) if the upstream router is not known because of the workings of the multicast routing protocol. However, it should be 0 if the incoming interface address is unknown or unnumbered. Input packet count on incoming interface: 64 bits This field contains the number of multicast packets received for all groups and sources on the incoming interface, or all 1's if no count can be reported. This counter may have the same value as ifHCInMulticastPkts from the IF-MIB [12] for this interface. Output packet count on outgoing interface: 64 bit This field contains the number of multicast packets that have been transmitted or queued for transmission for all groups and sources on the outgoing interface, or all 1's if no count can be reported. This counter may have the same value as ifHCOutMulticastPkts from the IF-MIB [12] for this interface. Asaeda, et al. Expires April 17, 2018 [Page 13] Internet-Draft Mtrace2 October 2017 Total number of packets for this source-group pair: 64 bits This field counts the number of packets from the specified source forwarded by the router to the specified group, or all 1's if no count can be reported. If the S bit is set (see below), the count is for the source network, as specified by the Src Mask field (see below). If the S bit is set and the Src Mask field is 127, indicating no source-specific state, the count is for all sources sending to this group. This counter should have the same value as ipMcastRoutePkts from the IPMROUTE-STD-MIB [13] for this forwarding entry. Rtg Protocol: 16 bits This field describes the unicast routing protocol running between this router and the upstream router, and it is used to determine the RPF interface for the specified source or RP. This value should have the same value as ipMcastRouteRtProtocol from the IPMROUTE-STD-MIB [13] for this entry. If the router is not able to obtain this value, all 0's must be specified. Multicast Rtg Protocol: 16 bits This field describes the multicast routing protocol in use between the router and the upstream router. This value should have the same value as ipMcastRouteProtocol from the IPMROUTE-STD-MIB [13] for this entry. If the router cannot obtain this value, all 0's must be specified. Fwd TTL: 8 bits This field contains the configured multicast TTL threshold, if any, of the outgoing interface. S: 1 bit If this bit is set, it indicates that the packet count for the source-group pair is for the source network, as determined by masking the source address with the Src Mask field. Src Mask: 7 bits This field contains the number of 1's in the netmask the router has for the source (i.e. a value of 24 means the netmask is 0xffffff00). If the router is forwarding solely on group state, this field is set to 127 (0x7f). Forwarding Code: 8 bits This field contains a forwarding information/error code. Values with the high order bit set (0x80-0xff) are intended for use as error or exception codes. Section 4.1 and Section 4.2 explain how and when the Forwarding Code is filled. Defined values are as follows: Asaeda, et al. Expires April 17, 2018 [Page 14] Internet-Draft Mtrace2 October 2017 Value Name Description ----- -------------- ---------------------------------------------- 0x00 NO_ERROR No error 0x01 WRONG_IF Mtrace2 Request arrived on an interface to which this router would not forward for the specified group towards the source or RP. 0x02 PRUNE_SENT This router has sent a prune upstream which applies to the source and group in the Mtrace2 Request. 0x03 PRUNE_RCVD This router has stopped forwarding for this source and group in response to a request from the downstream router. 0x04 SCOPED The group is subject to administrative scoping at this router. 0x05 NO_ROUTE This router has no route for the source or group and no way to determine a potential route. 0x06 WRONG_LAST_HOP This router is not the proper LHR. 0x07 NOT_FORWARDING This router is not forwarding this source and group out the outgoing interface for an unspecified reason. 0x08 REACHED_RP Reached the Rendezvous Point. 0x09 RPF_IF Mtrace2 Request arrived on the expected RPF interface for this source and group. 0x0A NO_MULTICAST Mtrace2 Request arrived on an interface which is not enabled for multicast. 0x0B INFO_HIDDEN One or more hops have been hidden from this trace. 0x0C REACHED_GW Mtrace2 Request arrived on a gateway (e.g., a NAT or firewall) that hides the information between this router and the Mtrace2 client. 0x0D UNKNOWN_QUERY A non-transitive Extended Query Type was received by a router which does not support the type. 0x80 FATAL_ERROR A fatal error is one where the router may know the upstream router but cannot forward the message to it. 0x81 NO_SPACE There was not enough room to insert another Standard Response Block in the packet. 0x83 ADMIN_PROHIB Mtrace2 is administratively prohibited. 3.2.5. IPv6 Mtrace2 Standard Response Block This section describes the message format of an IPv6 Mtrace2 Standard Response Block. The Type field is also 0x04. Asaeda, et al. Expires April 17, 2018 [Page 15] Internet-Draft Mtrace2 October 2017 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 | Length | MBZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Query Arrival Time | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Incoming Interface ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Outgoing Interface ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | * Local Address * | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | * Remote Address * | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Input packet count on incoming interface . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Output packet count on outgoing interface . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Total number of packets for this source-group pair . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Rtg Protocol | Multicast Rtg Protocol | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MBZ 2 |S|Src Prefix Len |Forwarding Code| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ MBZ: 8 bits This field MUST be zeroed on transmission and ignored on reception. Query Arrival Time: 32 bits Same definition as in IPv4. Incoming Interface ID: 32 bits This field specifies the interface ID on which packets from the source or RP are expected to arrive, or 0 if unknown. This ID should be the value taken from InterfaceIndex of the IF-MIB [12] for this interface. Asaeda, et al. Expires April 17, 2018 [Page 16] Internet-Draft Mtrace2 October 2017 Outgoing Interface ID: 32 bits This field specifies the interface ID to which packets from the source or RP are expected to transmit, or 0 if unknown. This ID should be the value taken from InterfaceIndex of the IF-MIB [12] for this interface Local Address: 128 bits This field specifies a global IPv6 address that uniquely identifies the router. An unique local unicast address [11] SHOULD NOT be used unless the router is only assigned link-local and unique local addresses. If the router is only assigned link- local addresses, its link-local address can be specified in this field. Remote Address: 128 bits This field specifies the address of the upstream router, which, in most cases, is a link-local unicast address for the upstream router. Although a link-local address does not have enough information to identify a node, it is possible to detect the upstream router with the assistance of Incoming Interface ID and the current router address (i.e., Local Address). Note that this may be a multicast group (e.g., ALL-[protocol]- ROUTERS group) if the upstream router is not known because of the workings of a multicast routing protocol. However, it should be the unspecified address (::) if the incoming interface address is unknown. Input packet count on incoming interface: 64 bits Same definition as in IPv4. Output packet count on outgoing interface: 64 bits Same definition as in IPv4. Total number of packets for this source-group pair: 64 bits Same definition as in IPv4, except if the S bit is set (see below), the count is for the source network, as specified by the Src Prefix Len field. If the S bit is set and the Src Prefix Len field is 255, indicating no source-specific state, the count is for all sources sending to this group. This counter should have the same value as ipMcastRoutePkts from the IPMROUTE-STD-MIB [13] for this forwarding entry. Rtg Protocol: 16 bits Same definition as in IPv4. Asaeda, et al. Expires April 17, 2018 [Page 17] Internet-Draft Mtrace2 October 2017 Multicast Rtg Protocol: 16 bits Same definition as in IPv4. MBZ 2: 15 bits This field MUST be zeroed on transmission and ignored on reception. S: 1 bit Same definition as in IPv4, except the Src Prefix Len field is used to mask the source address. Src Prefix Len: 8 bits This field contains the prefix length this router has for the source. If the router is forwarding solely on group state, this field is set to 255 (0xff). Forwarding Code: 8 bits Same definition as in IPv4. 3.2.6. Mtrace2 Augmented Response Block In addition to the Standard Response Block, a multicast router on the traced path can optionally add one or multiple Augmented Response Blocks before sending the Request to its upstream router. The Augmented Response Block is flexible for various purposes such as providing diagnosis information (see Section 7) and protocol verification. Its Type field is 0x05, and its format is as follows: 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 | Length | MBZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Augmented Response Type | Value .... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ MBZ: 8 bits This field MUST be zeroed on transmission and ignored on reception. Augmented Response Type: 16 bits This field specifies the type of various responses from a multicast router that might need to communicate back to the Mtrace2 client as well as the multicast routers on the traced path. The Augmented Response Type is defined as follows: Asaeda, et al. Expires April 17, 2018 [Page 18] Internet-Draft Mtrace2 October 2017 Code Type ==== =============================================== 0x01 # of the returned Standard Response Blocks When the NO_SPACE error occurs on a router, the router should send the original Mtrace2 Request received from the downstream router as a Reply back to the Mtrace2 client, and continue with a new Mtrace2 Request. In the new Request, the router would add a Standard Response Block followed by an Augmented Response Block with 0x01 as the Augmented Response Type, and the number of the returned Mtrace2 Standard Response Blocks as the Value. Each upstream router would recognize the total number of hops the Request has been traced so far by adding this number and the number of the Standard Response Block in the current Request message. This document only defines one Augmented Response Type in the Augmented Response Block. The description on how to provide diagnosis information using the Augmented Response Block is out of the scope of this document, and will be addressed in separate documents. Value: variable length The format is based on the Augmented Response Type value. The length of the value field is Length field minus 6. 3.2.7. Mtrace2 Extended Query Block There may be a sequence of optional Extended Query Blocks that follow an Mtrace2 Query to further specify any information needed for the Query. For example, an Mtrace2 client might be interested in tracing the path the specified source and group would take based on a certain topology. In which case, the client can pass in the multi-topology ID as the Value for an Extended Query Type (see below). The Extended Query Type is extensible and the behavior of the new types will be addressed by separate documents. The Mtrace2 Extended Query Block's Type field is 0x06, and is formatted as follows: 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 | Length | MBZ |T| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extended Query Type | Value .... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Asaeda, et al. Expires April 17, 2018 [Page 19] Internet-Draft Mtrace2 October 2017 MBZ: 7 bits This field MUST be zeroed on transmission and ignored on reception. T-bit (Transitive Attribute): 1 bit If the TLV type is unrecognized by the receiving router, then this TLV is either discarded or forwarded along with the Query, depending on the value of this bit. If this bit is set, then the router MUST forward this TLV. If this bit is clear, the router MUST send an Mtrace2 Reply with an UNKNOWN_QUERY error. Extended Query Type: 16 bits This field specifies the type of the Extended Query Block. Value: 16 bits This field specifies the value of this Extended Query. 4. Router Behavior This section describes the router behavior in the context of Mtrace2 in detail. 4.1. Receiving Mtrace2 Query An Mtrace2 Query message is an Mtrace2 message with no response blocks filled in, and uses TLV type of 0x01. 4.1.1. Query Packet Verification Upon receiving an Mtrace2 Query message, a router MUST examine whether the Multicast Address and the Source Address are a valid combination as specified in Section 3.2.1, and whether the Mtrace2 Client Address is a valid IP unicast address. If either one is invalid, the Query MUST be silently ignored. Mtrace2 supports a non-local client to the LHR/RP. A router SHOULD, however, support a mechanism to filter out queries from clients beyond a specified administrative boundary. The potential approaches are described in Section 9.2. In the case where a local LHR client is required, the router must then examine the Query to see if it is the proper LHR/RP for the destination address in the packet. It is the proper local LHR if it has a multicast-capable interface on the same subnet as the Mtrace2 Client Address and is the router that would forward traffic from the given (S,G) or (*,G) onto that subnet. It is the proper RP if the multicast group address specified in the query is 0 and if the IP header destination address is a valid RP address on this router. Asaeda, et al. Expires April 17, 2018 [Page 20] Internet-Draft Mtrace2 October 2017 If the router determines that it is not the proper LHR/RP, or it cannot make that determination, it does one of two things depending on whether the Query was received via multicast or unicast. If the Query was received via multicast, then it MUST be silently discarded. If it was received via unicast, the router turns the Query into a Reply message by changing the TLV type to 0x03 and appending a Standard Response Block with a Forwarding Code of WRONG_LAST_HOP. The rest of the fields in the Standard Response Block MUST be zeroed. The router then sends the Reply message to the Mtrace2 Client Address on the Client Port # as specified in the Mtrace2 Query. Duplicate Query messages as identified by the tuple (Mtrace2 Client Address, Query ID) SHOULD be ignored. This MAY be implemented using a cache of previously processed queries keyed by the Mtrace2 Client Address and Query ID pair. The duration of the cached entries is implementation specific. Duplicate Request messages MUST NOT be ignored in this manner. 4.1.2. Query Normal Processing When a router receives an Mtrace2 Query and it determines that it is the proper LHR/RP, it turns the Query to a Request by changing the TLV type from 0x01 to 0x02, and performs the steps listed in Section 4.2. 4.2. Receiving Mtrace2 Request An Mtrace2 Request is an Mtrace2 message that uses TLV type of 0x02. With the exception of the LHR, whose Request was just converted from a Query, each Request received by a router should have at least one Standard Response Block filled in. 4.2.1. Request Packet Verification If the Mtrace2 Request does not come from an adjacent router, or if the Request is not addressed to this router, or if the Request is addressed to a multicast group which is not a link-scoped group (i.e., 224.0.0.0/24 for IPv4, FFx2::/16 [3] for IPv6), it MUST be silently ignored. GTSM [14] SHOULD be used by the router to determine whether the router is adjacent or not. If the sum of the number of the Standard Response Blocks in the received Mtrace2 Request and the value of the Augmented Response Type of 0x01, if any, is equal or more than the # Hops in the Mtrace2 Request, it MUST be silently ignored. Asaeda, et al. Expires April 17, 2018 [Page 21] Internet-Draft Mtrace2 October 2017 4.2.2. Request Normal Processing When a router receives an Mtrace2 Request message, it performs the following steps. Note that it is possible to have multiple situations covered by the Forwarding Codes. The first one encountered is the one that is reported, i.e. all "note Forwarding Code N" should be interpreted as "if Forwarding Code is not already set, set Forwarding Code to N". Note that in the steps described below the "Outgoing Interface" is the one on which the Mtrace2 Request message arrives. 1. Prepare a Standard Response Block to be appended to the packet, setting all fields to an initial default value of zero. 2. If Mtrace2 is administratively prohibited, note the Forwarding Code of ADMIN_PROHIB and skip to step 4. 3. In the Standard Response Block, fill in the Query Arrival Time, Outgoing Interface Address (for IPv4) or Outgoing Interface ID (for IPv6), Output Packet Count, and Fwd TTL (for IPv4). 4. Attempt to determine the forwarding information for the specified source and group, using the same mechanisms as would be used when a packet is received from the source destined for the group. A state need not be instantiated, it can be a "phantom" state created only for the purpose of the trace, such as "dry-run." If using a shared-tree protocol and there is no source-specific state, or if no source-specific information is desired (i.e., all 1's for IPv4 or unspecified address (::) for IPv6), group state should be used. If there is no group state or no group- specific information is desired, potential source state (i.e., the path that would be followed for a source-specific Join) should be used. 5. If no forwarding information can be determined, the router notes a Forwarding Code of NO_ROUTE, sets the remaining fields that have not yet been filled in to zero, and then sends an Mtrace2 Reply back to the Mtrace2 client. 6. If a Forwarding Code of ADMIN_PROHIB has been set, skip to step 7. Otherwise, fill in the Incoming Interface Address (or Incoming Interface ID and Local Address for IPv6), Upstream Router Address (or Remote Address for IPv6), Input Packet Count, Total Number of Packets, Routing Protocol, S, and Src Mask (or Src Prefix Len for IPv6) using the forwarding information determined in step 4. Asaeda, et al. Expires April 17, 2018 [Page 22] Internet-Draft Mtrace2 October 2017 7. If the Outgoing interface is not enabled for multicast, note Forwarding Code of NO_MULTICAST. If the Outgoing interface is the interface from which the router would expect data to arrive from the source, note forwarding code RPF_IF. If the Outgoing interface is not one to which the router would forward data from the source or RP to the group, a Forwarding code of WRONG_IF is noted. In the above three cases, the router will return an Mtrace2 Reply and terminate the trace. 8. If the group is subject to administrative scoping on either the Outgoing or Incoming interfaces, a Forwarding Code of SCOPED is noted. 9. If this router is the RP for the group for a non-source-specific query, note a Forwarding Code of REACHED_RP. The router will send an Mtrace2 Reply and terminate the trace. 10. If this router is directly connected to the specified source or source network on the Incoming interface, it sets the Upstream Router Address (for IPv4) or the Remote Address (for IPv6) of the response block to zero. The router will send an Mtrace2 Reply and terminate the trace. 11. If this router has sent a prune upstream which applies to the source and group in the Mtrace2 Request, it notes a Forwarding Code of PRUNE_SENT. If the router has stopped forwarding downstream in response to a prune sent by the downstream router, it notes a Forwarding Code of PRUNE_RCVD. If the router should normally forward traffic downstream for this source and group but is not, it notes a Forwarding Code of NOT_FORWARDING. 12. If this router is a gateway (e.g., a NAT or firewall) that hides the information between this router and the Mtrace2 client, it notes a Forwarding Code of REACHED_GW. The router continues the processing as described in Section 4.5. 13. If the total number of the Standard Response Blocks, including the newly prepared one, and the value of the Augmented Response Type of 0x01, if any, is less than the # Hops in the Request, the packet is then forwarded to the upstream router as described in Section 4.3; otherwise, the packet is sent as an Mtrace2 Reply to the Mtrace2 client as described in Section 4.4. 4.3. Forwarding Mtrace2 Request This section describes how an Mtrace2 Request should be forwarded. Asaeda, et al. Expires April 17, 2018 [Page 23] Internet-Draft Mtrace2 October 2017 4.3.1. Destination Address If the upstream router for the Mtrace2 Request is known for this request, the Mtrace2 Request is sent to that router. If the Incoming interface is known but the upstream router is not, the Mtrace2 Request is sent to an appropriate multicast address on the Incoming interface. The multicast address SHOULD depend on the multicast routing protocol in use, such as ALL-[protocol]-ROUTERS group. It MUST be a link-scoped group (i.e., 224.0.0.0/24 for IPv4, FF02::/16 for IPv6), and MUST NOT be the all-systems multicast group (224.0.0.1) for IPv4 and All Nodes Address (FF02::1) for IPv6. It MAY also be the all-routers multicast group (224.0.0.2) for IPv4 or All Routers Address (FF02::2) for IPv6 if the routing protocol in use does not define a more appropriate multicast address. 4.3.2. Source Address An Mtrace2 Request should be sent with the address of the Incoming interface. However, if the Incoming interface is unnumbered, the router can use one of its numbered interface addresses as the source address. 4.3.3. Appending Standard Response Block An Mtrace2 Request MUST be sent upstream towards the source or the RP after appending a Standard Response Block to the end of the received Mtrace2 Request. The Standard Response Block includes the multicast states and statistics information of the router described in Section 3.2.4. If appending the Standard Response Block would make the Mtrace2 Request packet longer than the MTU of the Incoming Interface, or, in the case of IPv6, longer than 1280 bytes, the router MUST change the Forwarding Code in the last Standard Response Block of the received Mtrace2 Request into NO_SPACE. The router then turns the Request into a Reply, and sends the Reply as described in Section 4.4. The router will continue with a new Request by copying from the old Request excluding all the response blocks, followed by the previously prepared Standard Response Block, and an Augmented Response Block with Augmented Response Type of 0x01 and the number of the returned Standard Response Blocks as the value. The new Request is then forwarded upstream. Asaeda, et al. Expires April 17, 2018 [Page 24] Internet-Draft Mtrace2 October 2017 4.4. Sending Mtrace2 Reply An Mtrace2 Reply MUST be returned to the client by a router if any of the following conditions occur: 1. The total number of the traced routers are equal to the # of hops in the request (including the one just added) plus the number of the returned blocks, if any. 2. Appending the Standard Response Block would make the Mtrace2 Request packet longer than the MTU of the Incoming interface. (In case of IPv6 not more than 1280 bytes; see Section 4.3.3 for additional details on handling of this case.) 3. The request has reached the RP for a non source specific query or has reached the first hop router for a source specific query (see Section 4.2.2, items 9 and 10 for additional details). 4.4.1. Destination Address An Mtrace2 Reply MUST be sent to the address specified in the Mtrace2 Client Address field in the Mtrace2 Request. 4.4.2. Source Address An Mtrace2 Reply SHOULD be sent with the address of the router's Outgoing interface. However, if the Outgoing interface address is unnumbered, the router can use one of its numbered interface addresses as the source address. 4.4.3. Appending Standard Response Block An Mtrace2 Reply MUST be sent with the prepared Standard Response Block appended at the end of the received Mtrace2 Request except in the case of NO_SPACE forwarding code. 4.5. Proxying Mtrace2 Query When a gateway (e.g., a NAT or firewall), which needs to block unicast packets to the Mtrace2 client, or hide information between the gateway and the Mtrace2 client, receives an Mtrace2 Query from an adjacent host or Mtrace2 Request from an adjacent router, it appends a Standard Response Block with REACHED_GW as the Forwarding Code. It turns the Query or Request into a Reply, and sends the Reply back to the client. Asaeda, et al. Expires April 17, 2018 [Page 25] Internet-Draft Mtrace2 October 2017 At the same time, the gateway originates a new Mtrace2 Query message by copying the original Mtrace2 header (the Query or Request without any of the response blocks), and makes the changes as follows: o sets the RPF interface's address as the Mtrace2 Client Address; o uses its own port number as the Client Port #; and, o decreases # Hops by ((number of the Standard Response Blocks that were just returned in a Reply) - 1). The "-1" in this expression accounts for the additional Standard Response Block appended by the gateway router. The new Mtrace2 Query message is then sent to the upstream router or to an appropriate multicast address on the RPF interface. When the gateway receives an Mtrace2 Reply whose Query ID matches the one in the original Mtrace2 header, it MUST relay the Mtrace2 Reply back to the Mtrace2 client by replacing the Reply's header with the original Mtrace2 header. If the gateway does not receive the corresponding Mtrace2 Reply within the [Mtrace Reply Timeout] period (see Section 5.8.4), then it silently discards the original Mtrace2 Query or Request message, and terminates the trace. 4.6. Hiding Information Information about a domain's topology and connectivity may be hidden from the Mtrace2 Requests. The Forwarding Code of INFO_HIDDEN may be used to note that. For example, the incoming interface address and packet count on the ingress router of a domain, and the outgoing interface address and packet count on the egress router of the domain can be specified as all 1's. Additionally, the source-group packet count (see Section 3.2.4 and Section 3.2.5) within the domain may be all 1's if it is hidden. 5. Client Behavior This section describes the behavior of an Mtrace2 client in detail. 5.1. Sending Mtrace2 Query An Mtrace2 client initiates an Mtrace2 Query by sending the Query to the LHR of interest. Asaeda, et al. Expires April 17, 2018 [Page 26] Internet-Draft Mtrace2 October 2017 5.1.1. Destination Address If an Mtrace2 client knows the proper LHR, it unicasts an Mtrace2 Query packet to that router; otherwise, it MAY send the Mtrace2 Query packet to the all-routers multicast group (224.0.0.2) for IPv4 or All Routers Address (FF02::2) for IPv6. This will ensure that the packet is received by the LHR on the subnet. See also Section 5.4 on determining the LHR. 5.1.2. Source Address An Mtrace2 Query MUST be sent with the client's interface address, which would be the Mtrace2 Client Address. 5.2. Determining the Path An Mtrace2 client could send an initial Query messages with a large # Hops, in order to try to trace the full path. If this attempt fails, one strategy is to perform a linear search (as the traditional unicast traceroute program does); set the # Hops field to 1 and try to get a Reply, then 2, and so on. If no Reply is received at a certain hop, the hop count can continue past the non-responding hop, in the hopes that further hops may respond. These attempts should continue until the [Mtrace Reply Timeout] timeout has occurred. See also Section 5.6 on receiving the results of a trace. 5.3. Collecting Statistics After a client has determined that it has traced the whole path or as much as it can expect to (see Section 5.8), it might collect statistics by waiting a short time and performing a second trace. If the path is the same in the two traces, statistics can be displayed as described in Section 7.3 and Section 7.4. 5.4. Last Hop Router (LHR) The Mtrace2 client may not know which is the last-hop router, or that router may be behind a firewall that blocks unicast packets but passes multicast packets. In these cases, the Mtrace2 Request should be multicasted to the all-routers multicast group (224.0.0.2) for IPv4 or All Routers Address (FF02::2) for IPv6. All routers except the correct last-hop router SHOULD ignore any Mtrace2 Request received via multicast. Asaeda, et al. Expires April 17, 2018 [Page 27] Internet-Draft Mtrace2 October 2017 5.5. First Hop Router (FHR) The IANA assigned 224.0.1.32 as the default multicast group for old IPv4 mtrace (v1) responses, in order to support mtrace clients that are not unicast reachable from the first-hop router. Mtrace2, however, does not require any IPv4/IPv6 multicast addresses for the Mtrace2 Replies. Every Mtrace2 Reply is sent to the unicast address specified in the Mtrace2 Client Address field of the Mtrace2 Reply. 5.6. Broken Intermediate Router A broken intermediate router might simply not understand Mtrace2 packets, and drop them. The Mtrace2 client will get no Reply at all as a result. It should then perform a hop-by-hop search by setting the # Hops field until it gets an Mtrace2 Reply. The client may use linear or binary search; however, the latter is likely to be slower because a failure requires waiting for the [Mtrace Reply Timeout] period. 5.7. Non-Supported Router When a non-supported router receives an Mtrace2 Query or Request message whose destination address is a multicast address, the router will silently discard the message. When the router receives an Mtrace2 Query which is destined to itself, the router would return an ICMP port unreachable to the Mtrace2 client. On the other hand, when the router receives an Mtrace2 Request which is destined to itself, the router would return an ICMP port unreachable to its adjacent router from which the Request receives. Therefore, the Mtrace2 client needs to terminate the trace when the [Mtrace Reply Timeout] timeout has occurred, and may then issue another Query with a lower number of # Hops. 5.8. Mtrace2 Termination When performing an expanding hop-by-hop trace, it is necessary to determine when to stop expanding. 5.8.1. Arriving at Source A trace can be determined to have arrived at the source if the Incoming Interface of the last router in the trace is non-zero, but the Upstream Router is zero. Asaeda, et al. Expires April 17, 2018 [Page 28] Internet-Draft Mtrace2 October 2017 5.8.2. Fatal Error A trace has encountered a fatal error if the last Forwarding Error in the trace has the 0x80 bit set. 5.8.3. No Upstream Router A trace can not continue if the last Upstream Router in the trace is set to 0. 5.8.4. Reply Timeout This document defines the [Mtrace Reply Timeout] value, which is used to time out an Mtrace2 Reply as seen in Section 4.5, Section 5.2, and Section 5.7. The default [Mtrace Reply Timeout] value is 10 (seconds), and can be manually changed on the Mtrace2 client and routers. 5.9. Continuing after an Error When the NO_SPACE error occurs, as described in Section 4.2, a router will send back an Mtrace2 Reply to the Mtrace2 client, and continue with a new Request (see Section 4.3.3). In which case, the Mtrace2 client may receive multiple Mtrace2 Replies from different routers along the path. When this happens, the client MUST treat them as a single Mtrace2 Reply message. If a trace times out, it is very likely that a router in the middle of the path does not support Mtrace2. That router's address will be in the Upstream Router field of the last Standard Response Block in the last received Reply. A client may be able to determine (via mrinfo or SNMP [11][13]) a list of neighbors of the non-responding router. If desired, each of those neighbors could be probed to determine the remainder of the path. Unfortunately, this heuristic may end up with multiple paths, since there is no way of knowing what the non-responding router's algorithm for choosing an upstream router is. However, if all paths but one flow back towards the non- responding router, it is possible to be sure that this is the correct path. 6. Protocol-Specific Considerations This section describes the Mtrace2 behavior with the presence of different multicast protocols. Asaeda, et al. Expires April 17, 2018 [Page 29] Internet-Draft Mtrace2 October 2017 6.1. PIM-SM When an Mtrace2 reaches a PIM-SM RP, and the RP does not forward the trace on, it means that the RP has not performed a source-specific join so there is no more state to trace. However, the path that traffic would use if the RP did perform a source-specific join can be traced by setting the trace destination to the RP, the trace source to the traffic source, and the trace group to 0. This Mtrace2 Query may be unicasted to the RP, and the RP takes the same actions as an LHR. 6.2. Bi-Directional PIM Bi-directional PIM [6] is a variant of PIM-SM that builds bi- directional shared trees connecting multicast sources and receivers. Along the bi-directional shared trees, multicast data is natively forwarded from the sources to the Rendezvous Point Link (RPL), and from which, to receivers without requiring source-specific state. In contrast to PIM-SM, Bi-directional PIM always has the state to trace. A Designated Forwarder (DF) for a given Rendezvous Point Address (RPA) is in charge of forwarding downstream traffic onto its link, and forwarding upstream traffic from its link towards the RPL that the RPA belongs to. Hence Mtrace2 Reply reports DF addresses or RPA along the path. 6.3. PIM-DM Routers running PIM Dense Mode [15] do not know the path packets would take unless traffic is flowing. Without some extra protocol mechanism, this means that in an environment with multiple possible paths with branch points on shared media, Mtrace2 can only trace existing paths, not potential paths. When there are multiple possible paths but the branch points are not on shared media, the upstream router is known, but the LHR may not know that it is the appropriate last hop. When traffic is flowing, PIM Dense Mode routers know whether or not they are the LHR for the link (because they won or lost an Assert battle) and know who the upstream router is (because it won an Assert battle). Therefore, Mtrace2 is always able to follow the proper path when traffic is flowing. 6.4. IGMP/MLD Proxy When an IGMP/MLD Proxy [7] receives an Mtrace2 Query packet on an incoming interface, it notes a WRONG_IF in the Forwarding Code of the last Standard Response Block (see Section 3.2.4), and sends the Asaeda, et al. Expires April 17, 2018 [Page 30] Internet-Draft Mtrace2 October 2017 Mtrace2 Reply back to the Mtrace2 client. On the other hand, when an Mtrace2 Query packet reaches an outgoing interface of the IGMP/MLD proxy, it is forwarded onto its incoming interface towards the upstream router. 7. Problem Diagnosis This section describes different scenarios Mtrace2 can be used to diagnose the multicast problems. 7.1. Forwarding Inconsistencies The Forwarding Error code can tell if a group is unexpectedly pruned or administratively scoped. 7.2. TTL or Hop Limit Problems By taking the maximum of hops from the source and forwarding TTL threshold over all hops, it is possible to discover the TTL or hop limit required for the source to reach the destination. 7.3. Packet Loss By taking two traces, it is possible to find packet loss information by comparing the difference in input packet counts to the difference in output packet counts for the specified source-group address pair at the previous hop. On a point-to-point link, any difference in these numbers implies packet loss. Since the packet counts may be changing as the Mtrace2 Request is propagating, there may be small errors (off by 1 or 2 or more) in these statistics. However, these errors will not accumulate if multiple traces are taken to expand the measurement period. On a shared link, the count of input packets can be larger than the number of output packets at the previous hop, due to other routers or hosts on the link injecting packets. This appears as "negative loss" which may mask real packet loss. In addition to the counts of input and output packets for all multicast traffic on the interfaces, the Standard Response Block includes a count of the packets forwarded by a node for the specified source-group pair. Taking the difference in this count between two traces and then comparing those differences between two hops gives a measure of packet loss just for traffic from the specified source to the specified receiver via the specified group. This measure is not affected by shared links. On a point-to-point link that is a multicast tunnel, packet loss is usually due to congestion in unicast routers along the path of that tunnel. On native multicast links, loss is more likely in the output Asaeda, et al. Expires April 17, 2018 [Page 31] Internet-Draft Mtrace2 October 2017 queue of one hop, perhaps due to priority dropping, or in the input queue at the next hop. The counters in the Standard Response Block do not allow these cases to be distinguished. Differences in packet counts between the incoming and outgoing interfaces on one node cannot generally be used to measure queue overflow in the node. 7.4. Link Utilization Again, with two traces, you can divide the difference in the input or output packet counts at some hop by the difference in time stamps from the same hop to obtain the packet rate over the link. If the average packet size is known, then the link utilization can also be estimated to see whether packet loss may be due to the rate limit or the physical capacity on a particular link being exceeded. 7.5. Time Delay If the routers have synchronized clocks, it is possible to estimate propagation and queuing delay from the differences between the timestamps at successive hops. However, this delay includes control processing overhead, so is not necessarily indicative of the delay that data traffic would experience. 8. IANA Considerations The following new registries are to be created and maintained under the "RFC Required" registry policy as specified in [4]. 8.1. "Mtrace2 Forwarding Codes" Registry This is an integer in the range 0-255. Assignment of a Forwarding Code requires specification of a value and a name for the Forwarding Code. Initial values for the forwarding codes are given in the table at the end of Section 3.2.4. Additional values (specific to IPv6) may also be specified at the end of Section 3.2.5. Any additions to this registry are required to fully describe the conditions under which the new Forwarding Code is used. 8.2. "Mtrace2 TLV Types" registry Assignment of a TLV Type requires specification of an integer value "Code" in the range 0-255 and a name ("Type"). Initial values for the TLV Types are given in the table at the beginning of Section 3.2. Asaeda, et al. Expires April 17, 2018 [Page 32] Internet-Draft Mtrace2 October 2017 8.3. UDP Destination Port The Mtrace2 UDP destination port is assigned when this document is published as RFC. 9. Security Considerations This section addresses some of the security considerations related to Mtrace2. 9.1. Addresses in Mtrace2 Header An Mtrace2 header includes three addresses, source address, multicast address, and Mtrace2 client address. These addresses MUST be congruent with the definition defined in Section 3.2.1 and forwarding Mtrace2 messages having invalid addresses MUST be prohibited. For instance, if Mtrace2 Client Address specified in an Mtrace2 header is a multicast address, then a router that receives the Mtrace2 message MUST silently discard it. 9.2. Filtering of Clients A router SHOULD support a mechanism to filter out queries from clients beyond a specified administrative boundary. Such a boundary could, for example, be specified via a list of allowed/disallowed client addresses or subnets. If a query is received from beyond the specified administrative boundary, the Query MUST NOT be processed. The router MAY, however, perform rate limited logging of such events. 9.3. Topology Discovery Mtrace2 can be used to discover any actively-used topology. If your network topology is a secret, Mtrace2 may be restricted at the border of your domain, using the ADMIN_PROHIB forwarding code. 9.4. Characteristics of Multicast Channel Mtrace2 can be used to discover what sources are sending to what groups and at what rates. If this information is a secret, Mtrace2 may be restricted at the border of your domain, using the ADMIN_PROHIB forwarding code. 9.5. Limiting Query/Request Rates A router may limit Mtrace2 Queries and Requests by ignoring some of the consecutive messages. The router MAY randomly ignore the received messages to minimize the processing overhead, i.e., to keep Asaeda, et al. Expires April 17, 2018 [Page 33] Internet-Draft Mtrace2 October 2017 fairness in processing queries, or prevent traffic amplification. The rate limit is left to the router's implementation. 9.6. Limiting Reply Rates The proxying and NO_SPACE behaviors may result in one Query returning multiple Reply messages. In order to prevent abuse, the routers in the traced path MAY need to rate-limit the Replies. The rate limit function is left to the router's implementation. 10. Acknowledgements This specification started largely as a transcription of Van Jacobson's slides from the 30th IETF, and the implementation in mrouted 3.3 by Ajit Thyagarajan. Van's original slides credit Steve Casner, Steve Deering, Dino Farinacci and Deb Agrawal. The original multicast traceroute client, mtrace (version 1), has been implemented by Ajit Thyagarajan, Steve Casner and Bill Fenner. The idea of the "S" bit to allow statistics for a source subnet is due to Tom Pusateri. For the Mtrace version 2 specification, the authors would like to give special thanks to Tatsuya Jinmei, Bill Fenner, and Steve Casner. Also, extensive comments were received from David L. Black, Ronald Bonica, Yiqun Cai, Liu Hui, Bharat Joshi, Robert Kebler, John Kristoff, Mankamana Mishra, Heidi Ou, Pekka Savola, Shinsuke Suzuki, Dave Thaler, Achmad Husni Thamrin, Stig Venaas, and Cao Wei. 11. References 11.1. Normative References [1] Bradner, S., "Key words for use in RFCs to indicate requirement levels", RFC 2119, March 1997. [2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 8200, July 2017. [3] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006. [4] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 8126, June 2017. Asaeda, et al. Expires April 17, 2018 [Page 34] Internet-Draft Mtrace2 October 2017 [5] 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)", RFC 7761, March 2016. [6] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, "Bidirectional Protocol Independent Multicast (BIDIR- PIM)", RFC 5015, October 2007. [7] Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet Group Management Protocol (IGMP) / Multicast Listener Discovery (MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")", RFC 4605, August 2006. 11.2. Informative References [8] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. Thyagarajan, "Internet Group Management Protocol, Version 3", RFC 3376, October 2002. [9] Bumgardner, G., "Automatic Multicast Tunneling", RFC 7450, February 2015. [10] Rosen, E. and R. Aggarwal, "Multicast in MPLS/BGP IP VPNs", RFC 6513, February 2012. [11] Draves, R. and D. Thaler, "Default Router Preferences and More-Specific Routes", RFC 4191, November 2005. [12] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB", RFC 2863, June 2000. [13] McWalter, D., Thaler, D., and A. Kessler, "IP Multicast MIB", RFC 5132, December 2007. [14] Gill, V., Heasley, J., Meyer, D., Savola, P., and C. Pignataro, "The Generalized TTL Security Mechanism (GTSM)", RFC 5082, October 2007. [15] Adams, A., Nicholas, J., and W. Siadak, "Protocol Independent Multicast - Dense Mode (PIM-DM): Protocol Specification (Revised)", RFC 3973, January 2005. Authors' Addresses Asaeda, et al. Expires April 17, 2018 [Page 35] Internet-Draft Mtrace2 October 2017 Hitoshi Asaeda National Institute of Information and Communications Technology 4-2-1 Nukui-Kitamachi Koganei, Tokyo 184-8795 Japan Email: asaeda@nict.go.jp Kerry Meyer Cisco Systems, Inc. 510 McCarthy Blvd. Milpitas, CA 95035 USA Email: kerrymey@cisco.com WeeSan Lee (editor) Email: weesan@weesan.com Asaeda, et al. Expires April 17, 2018 [Page 36]