MBONED Working Group H. Asaeda Internet-Draft Keio University Intended status: Standards Track T. Jinmei Expires: July 11, 2011 ISC W. Fenner Arastra, Inc. S. Casner Packet Design, Inc. January 7, 2011 Mtrace Version 2: Traceroute Facility for IP Multicast draft-ietf-mboned-mtrace-v2-08 Abstract This document describes the IP multicast traceroute facility. Unlike unicast traceroute, multicast traceroute requires special implementations on the part of routers. This specification describes the required functionality in multicast routers, as well as how management applications can use the router functionality. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on July 11, 2011. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents Asaeda, et al. Expires July 11, 2011 [Page 1] Internet-Draft Mtrace2 January 2011 carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. 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. Asaeda, et al. Expires July 11, 2011 [Page 2] Internet-Draft Mtrace2 January 2011 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 10 4.1. Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . . 10 4.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . . 10 5. Mtrace2 Query Header . . . . . . . . . . . . . . . . . . . . . 12 5.1. # hops: 8 bits . . . . . . . . . . . . . . . . . . . . . . 12 5.2. Multicast Address . . . . . . . . . . . . . . . . . . . . 13 5.3. Source Address . . . . . . . . . . . . . . . . . . . . . . 13 5.4. Mtrace2 Client Address . . . . . . . . . . . . . . . . . . 13 5.5. Query ID: 16 bits . . . . . . . . . . . . . . . . . . . . 13 5.6. Client Port # . . . . . . . . . . . . . . . . . . . . . . 13 6. IPv4 Mtrace2 Standard Response Block . . . . . . . . . . . . . 14 6.1. MBZ: 8 bit . . . . . . . . . . . . . . . . . . . . . . . . 14 6.2. Query Arrival Time: 32 bits . . . . . . . . . . . . . . . 14 6.3. Incoming Interface Address: 32 bits . . . . . . . . . . . 15 6.4. Outgoing Interface Address: 32 bits . . . . . . . . . . . 15 6.5. Previous-Hop Router Address: 32 bits . . . . . . . . . . . 15 6.6. Input packet count on incoming interface: 64 bits . . . . 15 6.7. Output packet count on outgoing interface: 64 bits . . . . 16 6.8. Total number of packets for this source-group pair: 64 bits . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 6.9. Rtg Protocol: 16 bits . . . . . . . . . . . . . . . . . . 16 6.10. Multicast Rtg Protocol: 16 bits . . . . . . . . . . . . . 16 6.11. Fwd TTL: 8 bits . . . . . . . . . . . . . . . . . . . . . 16 6.12. S: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . . 16 6.13. Src Mask: 7 bits . . . . . . . . . . . . . . . . . . . . . 17 6.14. Forwarding Code: 8 bits . . . . . . . . . . . . . . . . . 17 7. IPv6 Mtrace2 Standard Response Block . . . . . . . . . . . . . 19 7.1. MBZ: 8 bit . . . . . . . . . . . . . . . . . . . . . . . . 19 7.2. Query Arrival Time: 32 bits . . . . . . . . . . . . . . . 20 7.3. Incoming Interface ID: 32 bits . . . . . . . . . . . . . . 20 7.4. Outgoing Interface ID: 32 bits . . . . . . . . . . . . . . 20 7.5. Local Address . . . . . . . . . . . . . . . . . . . . . . 20 7.6. Remote Address . . . . . . . . . . . . . . . . . . . . . . 20 7.7. Input packet count on incoming interface . . . . . . . . . 20 7.8. Output packet count on outgoing interface . . . . . . . . 21 7.9. Total number of packets for this source-group pair . . . . 21 7.10. Rtg Protocol: 16 bits . . . . . . . . . . . . . . . . . . 21 7.11. Multicast Rtg Protocol: 16 bits . . . . . . . . . . . . . 21 7.12. S: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . . 21 7.13. Src Prefix Len: 8 bits . . . . . . . . . . . . . . . . . . 21 7.14. Forwarding Code: 8 bits . . . . . . . . . . . . . . . . . 21 8. Mtrace2 Augmented Response Block . . . . . . . . . . . . . . . 22 9. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 23 Asaeda, et al. Expires July 11, 2011 [Page 3] Internet-Draft Mtrace2 January 2011 9.1. Receiving Mtrace2 Query . . . . . . . . . . . . . . . . . 23 9.1.1. Packet Verification . . . . . . . . . . . . . . . . . 23 9.1.2. Normal Processing . . . . . . . . . . . . . . . . . . 23 9.1.3. Mtrace2 Query Received by Non-Supported Router . . . . 23 9.2. Receiving Mtrace2 Request . . . . . . . . . . . . . . . . 24 9.2.1. Packet Verification . . . . . . . . . . . . . . . . . 24 9.2.2. Normal Processing . . . . . . . . . . . . . . . . . . 24 9.2.3. Mtrace2 Request Received by Non-Supported Router . . . 26 9.3. Forwarding Mtrace2 Request . . . . . . . . . . . . . . . . 26 9.3.1. Destination Address . . . . . . . . . . . . . . . . . 26 9.3.2. Source Address . . . . . . . . . . . . . . . . . . . . 26 9.4. Sending Mtrace2 Reply . . . . . . . . . . . . . . . . . . 27 9.4.1. Destination Address . . . . . . . . . . . . . . . . . 27 9.4.2. Source Address . . . . . . . . . . . . . . . . . . . . 27 9.5. Proxying Mtrace2 Query . . . . . . . . . . . . . . . . . . 27 9.6. Hiding Information . . . . . . . . . . . . . . . . . . . . 28 10. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 29 10.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 29 10.1.1. Destination Address . . . . . . . . . . . . . . . . . 29 10.1.2. Source Address . . . . . . . . . . . . . . . . . . . . 29 10.2. Determining the Path . . . . . . . . . . . . . . . . . . . 29 10.3. Collecting Statistics . . . . . . . . . . . . . . . . . . 29 10.4. Last Hop Router . . . . . . . . . . . . . . . . . . . . . 29 10.5. First Hop Router . . . . . . . . . . . . . . . . . . . . . 30 10.6. Broken Intermediate Router . . . . . . . . . . . . . . . . 30 10.7. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 30 10.7.1. Arriving at source . . . . . . . . . . . . . . . . . . 30 10.7.2. Fatal error . . . . . . . . . . . . . . . . . . . . . 30 10.7.3. No previous hop . . . . . . . . . . . . . . . . . . . 30 10.7.4. Traceroute shorter than requested . . . . . . . . . . 30 10.8. Continuing after an error . . . . . . . . . . . . . . . . 31 11. Protocol-Specific Considerations . . . . . . . . . . . . . . . 32 11.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . . 32 11.2. Bi-Directional PIM . . . . . . . . . . . . . . . . . . . . 32 11.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . . 32 11.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . . 32 11.5. AMT . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 12. Problem Diagnosis . . . . . . . . . . . . . . . . . . . . . . 34 12.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . . 34 12.2. TTL or Hop Limit Problems . . . . . . . . . . . . . . . . 34 12.3. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 34 12.4. Link Utilization . . . . . . . . . . . . . . . . . . . . . 35 12.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . . 35 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36 13.1. Forwarding Codes . . . . . . . . . . . . . . . . . . . . . 36 13.2. UDP Destination Port and IPv6 Address . . . . . . . . . . 36 14. Security Considerations . . . . . . . . . . . . . . . . . . . 37 14.1. Topology Discovery . . . . . . . . . . . . . . . . . . . . 37 Asaeda, et al. Expires July 11, 2011 [Page 4] Internet-Draft Mtrace2 January 2011 14.2. Traffic Rates . . . . . . . . . . . . . . . . . . . . . . 37 14.3. Limiting Query/Request Rates . . . . . . . . . . . . . . . 37 15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 38 16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39 16.1. Normative References . . . . . . . . . . . . . . . . . . . 39 16.2. Informative References . . . . . . . . . . . . . . . . . . 39 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41 Asaeda, et al. Expires July 11, 2011 [Page 5] Internet-Draft Mtrace2 January 2011 1. Introduction This document specifies the multicast traceroute facility named mtrace version 2 or mtrace2. Mtrace2 allows the tracing of an IP multicast routing paths. Mtrace2 provides additional information about packet rates and losses, or other diagnosis information. For instance, mtrace2 is used for the following purposes. o To trace the path that a packet would take from some source to some destination. o To isolate packet loss problems (e.g., congestion). o To isolate configuration problems (e.g., TTL threshold). Mtrace2 consists of the client and router programs. The mtrace2 client program is invoked from somewhere in the multicast tree, on a host, router, or proxy such as IGMP/MLD proxy [8]. The node invoking the program is called the mtrace2 client. The mtrace2 client program creates the mtrace2 Query message, which includes a source and multicast address specified by the client, and forwards the message to its neighbor router or proxy. This initiates a trace of a multicast routing path from the client toward the specified source, or if no source address is specified, toward a core router if such a router exists. In the case of PIM-SM [6], the core router is an RP maintaining the specified multicast address. When a router or proxy receives an mtrace2 Query message and has the corresponding routing state regarding the source and multicast addresses specified in the Query, the router or proxy invokes the mtrace2 router program. The mtrace2 router program creates an mtrace2 Request message corresponding to the query and forwards the Request toward the specified source or the core router. When a first-hop router or proxy (a single hop from the source specified in the request) or the core router receives an mtrace2 Query or Request message, the router or proxy invokes the mtrace2 router program. The mtrace2 router program creates an mtrace2 Reply message. The Reply message is forwarded to the mtrace2 client, thus completing the mtrace2 Request. The mtrace2 client program waits for the mtrace2 Reply message and displays the results. When an mtrace2 Reply message does not come due to network congestion, a broken router (see Section 10.6) or a non-responding router (see Section 10.8), the mtrace2 client program can resend an mtrace2 Query with a lower hop count (see Section 5.1) and repeat the process until it receives an mtrace2 Reply message. Asaeda, et al. Expires July 11, 2011 [Page 6] Internet-Draft Mtrace2 January 2011 The mtrace2 client should also be aware that the mtrace2 Query may follow the control path on the routers, in the case of a router's control plane and forwarding plane are not synchronized, e.g., a buggy implementation. In this case, mtrace2 Requests will be forwarded toward the specified source or the core router because the router does not have any forwarding state for the query. The mtrace2 supports both IPv4 and IPv6 multicast traceroute facility. The protocol design, concept, and program behavior are same between IPv4 and IPv6 mtrace2. While the original IPv4 multicast traceroute, mtrace, the query and response messages are implemented as IGMP messages [10], all mtrace2 messages are carried on UDP. The packet formats of IPv4 and IPv6 mtrace2 are different because of the different address families, but the syntax is similar. Asaeda, et al. Expires July 11, 2011 [Page 7] Internet-Draft Mtrace2 January 2011 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT","SHOULD", "SHOULD NOT", "RECOMMENDED","MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [1]. Since multicast traceroutes 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 traffic is expected from the specified source and group. Outgoing interface: The interface on which traffic is forwarded from the specified source and group toward the destination. It is the interface on which the mtrace2 Query or Request was received. Previous-hop router: The router that is on the link attached to the Incoming interface and is responsible for forwarding traffic for the specified source and group. Last-hop router: The router that is on the link attached to the Outgoing interface and receives the mtrace2 Query from the adjacent mtrace2 client. Group state: It is the state in which a shared-tree protocol (e.g., PIM-SM [6]) running on a router chooses the previous-hop router toward the core router or Rendezvous Point (RP) as its parent router. In this state, source-specific state is not available for the corresponding multicast address on the router. Source-specific state: It is the state in which a routing protocol running on a router chooses the path that would be followed for a source-specific join. ALL-[protocol]-ROUTERS.MCAST.NET: It is a dedicated multicast address for a multicast router to communicate with other routers that are working with the same routing protocol. For instance, the address of ALL-PIM-ROUTERS.MCAST.NET [6] is '224.0.0.13' for IPv4 and 'ff02::d' for IPv6. Asaeda, et al. Expires July 11, 2011 [Page 8] Internet-Draft Mtrace2 January 2011 3. Overview Given a multicast distribution tree, tracing from a source to a multicast destination is hard, since you do not know down which branch of the multicast tree the destination lies. This means that you have to flood the whole tree to find the path from one source to one destination. However, walking up the tree from destination to source is easy, as most existing multicast routing protocols know the previous hop for each source. Tracing from destination to source can involve only routers on the direct path. The party requesting the multicast traceroute sends a traceroute Query packet to the last-hop multicast router for the given multicast address. The last-hop router turns the Query into a Request packet by changing the packet type and adding a response data block containing its interface addresses and packet statistics, and then forwards the Request packet via unicast to the router that the last- hop router believes is the proper previous hop for the given source and group. Each hop adds its response data to the end of the Request packet, then unicast forwards it to the previous hop. The first-hop router (the router that believes that packets from the source originate on one of its directly connected networks) changes the packet type to indicate a Reply packet and sends the completed Reply to the mtrace2 client address specified in the Query header. The Reply may be returned before reaching the first-hop router if a fatal error condition such as "no route" is encountered along the path or hop count is exceeded. Multicast traceroute uses any information available to it in the router to attempt to determine a previous hop to forward the trace towards. Multicast routing protocols vary in the type and amount of state they keep; multicast traceroute endeavors to work with all of them by using whatever is available. For example, if a PIM-SM router is on the (*,G) tree, it chooses the parent towards the RP as the previous hop. In these cases, no source/group-specific state is available, but the path may still be traced. Asaeda, et al. Expires July 11, 2011 [Page 9] Internet-Draft Mtrace2 January 2011 4. Packet Formats The mtrace2 message is carried as a UDP packet. The destination address of mtrace2 Query messages is either the last-hop router unicast address or multicast address if the mtrace2 client does not know the proper last-hop router address. The destination address of mtrace2 Report messages is the address specified in Previous-Hop Router Address field in the last appended mtrace2 Standard Response Block, which is either the previous-hop router unicast address or multicast address. Detailed in Section 9.3. Mtrace2 message is encoded in TLV format. If an implementation receives a TLV whose length exceeds the TLV length specified in the Length field, the TLV SHOULD be accepted but any additional data SHOULD be ignored. If an implementation receives a TLV whose type value is unknown, the mtrace2 message SHOULD be ignored and silently dropped. 4.1. 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) Length (16 bits) Value (variable length) 4.2. Defined TLVs The following TLV Types are defined: Code Type ====== ====================================== 1 Mtrace2 Query 2 Mtrace2 Request 3 Mtrace2 Reply 4 Mtrace2 Standard Response Block 5 Mtrace2 Augmented Response Block An mtrace2 message MUST contain exactly one Mtrace2 Query header. A multicast router that sends an mtrace2 Request or Reply message MUST add one mtrace2 Standard Response block to given mtrace2 message but MUST NOT add multiple mtrace2 Standard Response blocks to it. A Asaeda, et al. Expires July 11, 2011 [Page 10] Internet-Draft Mtrace2 January 2011 multicast router that adds one mtrace2 Standard Response block to given mtrace2 message MAY append one or multiple Augmented Response blocks. The TLV type field is defined to be "0x1" and "0x2" for mtrace2 Queries and Requests, respectively. An mtrace2 message containing the type "0x1" is an mtrace2 Query. It is sent by an mtrace2 querier (i.e., an mtrace2 client). It is changed to "0x2" by the proper last-hop router. The type field is changed to "0x3" when the packet is completed and sent as an mtrace2 Reply from the first-hop router to the querier. Asaeda, et al. Expires July 11, 2011 [Page 11] Internet-Draft Mtrace2 January 2011 5. Mtrace2 Query Header The mtrace2 supports both IPv4 and IPv6. If the mtrace2 Query or Reply arrives in an IPv4 packet, all addresses specified in the mtrace2 messages must be with IPv4 addresses. The mtrace2 message is carried as a UDP packet. The UDP source port is uniquely selected by the local host operating system. The UDP destination port is the IANA reserved mtrace2 port number (see Section 13). The UDP checksum MUST be valid in mtrace2 messages. The mtrace2 message includes the common mtrace2 Query header as follows. The header is only filled in by the originator of the mtrace2 Query; intermediate routers MUST NOT modify any of the fields. 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 +-+-+-+-+-+-+-+-+ | # hops | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Multicast Address | | | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | | | Source Address | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Mtrace2 Client Address | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Query ID | Client Port # | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1 5.1. # hops: 8 bits This field specifies the maximum number of hops that the mtrace2 client wants to trace. If there is some error condition in the middle of the path that prevents an mtrace2 Reply from being received by the client, the client issues another mtrace2 Query with the lower number of hops until it receives a Reply from the first-hop router. Asaeda, et al. Expires July 11, 2011 [Page 12] Internet-Draft Mtrace2 January 2011 5.2. Multicast Address This field specifies the 32 bits length IPv4 or 128 bits length IPv6 multicast address to be traced, or is filled with "all 1" in case of IPv4 or with the unspecified address (::) in case of IPv6 if no group-specific information is desired. Note that non-group-specific mtrace2 MUST specify source address. 5.3. Source Address This field specifies the 32 bits length IPv4 or 128 bits length IPv6 address of the multicast source for the path being traced, or is filled with "all 1" in case of IPv4 or with the unspecified address (::) in case of IPv6 if no source-specific information such as a trace for RPT in PIM-SM is desired. Note that non-source-specific traceroutes may not be possible with certain multicast routing protocols. 5.4. Mtrace2 Client Address This field specifies the 32 bits length IPv4 or 128 bits length IPv6 global address of the mtrace2 client. The trace starts at this client address and proceeds toward the traffic source. 5.5. Query ID: 16 bits This field is used as a unique identifier for this mtrace2 Request so that duplicate or delayed Replies may be detected. 5.6. Client Port # Mtrace2 Reply is sent back to the address specified in an Mtrace2 Client Address field. This field specifies the UDP port number the router will send Mtrace2 Reply. This client port number MUST NOT be changed by any router. Asaeda, et al. Expires July 11, 2011 [Page 13] Internet-Draft Mtrace2 January 2011 6. IPv4 Mtrace2 Standard Response Block Each intermediate IPv4 router in a trace path appends "response data block" to the forwarded trace packet. The standard response data block looks 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 +-+-+-+-+-+-+-+-+ | MBZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Query Arrival Time | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Incoming Interface Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Outgoing Interface Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Previous-Hop 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| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 6.1. MBZ: 8 bit Must be zeroed on transmission and ignored on reception. 6.2. Query Arrival Time: 32 bits The Query Arrival Time is a 32-bit NTP timestamp specifying the arrival time of the mtrace2 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. Asaeda, et al. Expires July 11, 2011 [Page 14] Internet-Draft Mtrace2 January 2011 The following formula converts from a UNIX timeval to a 32-bit NTP timestamp: query_arrival_time = (tv.tv_sec + 32384) << 16 + ((tv.tv_usec << 10) / 15625) The constant 32384 is the number of seconds from Jan 1, 1900 to Jan 1, 1970 truncated to 16 bits. ((tv.tv_usec << 10) / 15625) is a reduction of ((tv.tv_usec / 100000000) << 16). However, mtrace2 does not require synchronizing NTP timestamp among all routers along paths to measure one-way latency. The use of Query Arrival Time is useful to measure the packets per second (PPS). Suppose that a client issues two queries Q1 and Q2, and the corresponding requests R1 and R2 arrive at router X at t1 and t2, then the client would be able to calculate the PPS at router X by using the packet count results at t1 and t2. 6.3. Incoming Interface Address: 32 bits This field specifies the address of the interface on which packets from this source and group are expected to arrive, or 0 if unknown or unnumbered. 6.4. Outgoing Interface Address: 32 bits This field specifies the address of the interface on which packets from this source and group flow to the specified destination, or 0 if unknown or unnumbered. 6.5. Previous-Hop Router Address: 32 bits This field specifies the router from which this router expects packets from this source. This may be a multicast group (e.g. ALL- [protocol]-ROUTERS.MCAST.NET) if the previous hop 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. 6.6. 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" if no count can be reported. This counter may have the same value as ifHCInMulticastPkts from the IF-MIB [12] for this interface. Asaeda, et al. Expires July 11, 2011 [Page 15] Internet-Draft Mtrace2 January 2011 6.7. Output packet count on outgoing interface: 64 bits 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" if no count can be reported. This counter may have the same value as ifHCOutMulticastPkts from the IF- MIB for this interface. 6.8. Total number of packets for this source-group pair: 64 bits This field counts the number of packets from the specified source forwarded by this router to the specified group, or "all 1" if no count can be reported. If the S bit is set, the count is for the source network, as specified by the Src Mask field. If the S bit is set and the Src Mask field is 63, 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. 6.9. Rtg Protocol: 16 bits This field describes the routing protocol used to decide an RPF interface for the requested source. 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" must be specified. 6.10. Multicast Rtg Protocol: 16 bits This field describes the multicast routing protocol in use between this router and the previous-hop router. This value should have the same value as ipMcastRouteProtocol from the IPMROUTE-STD-MIB [13] for this entry. If the router does not able to obtain this value, "all 0" must be specified. 6.11. Fwd TTL: 8 bits This field contains the TTL that a packet is required to have before it will be forwarded over the outgoing interface. 6.12. S: 1 bit This S bit 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. Asaeda, et al. Expires July 11, 2011 [Page 16] Internet-Draft Mtrace2 January 2011 6.13. Src Mask: 7 bits This field contains the number of 1's in the netmask this 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). 6.14. Forwarding Code: 8 bits This field contains a forwarding information/error code. Section 9.2 explains how and when the forwarding code is filled. Defined values are as follows; 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 this source, group, destination. 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 next hop router. 0x04 SCOPED The group is subject to administrative scoping at this hop. 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 last-hop router. 0x07 NOT_FORWARDING This router is not forwarding this source, group out the outgoing interface for an unspecified reason. 0x08 REACHED_RP Reached Rendezvous Point or Core 0x09 RPF_IF Mtrace2 Request arrived on the expected Asaeda, et al. Expires July 11, 2011 [Page 17] Internet-Draft Mtrace2 January 2011 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 querier 0x81 NO_SPACE There was not enough room to insert another response data block in the packet. 0x82 ADMIN_PROHIB Mtrace2 is administratively prohibited. Note that if a router discovers there is not enough room in a packet to insert its response, it puts the NO_SPACE code value in the previous router's Forwarding Code field, overwriting any error the previous router placed there. After the router sends the Reply to the Mtrace2 Client Address in the header, the router continues the mtrace2 Query by sending an mtrace2 Request containing the same mtrace2 Query header. Section 9.3 and Section 10.8 include the details. The 0x80 bit of the Forwarding Code is used to indicate a fatal error. A fatal error is one where the router may know the previous hop but cannot forward the message to it. Asaeda, et al. Expires July 11, 2011 [Page 18] Internet-Draft Mtrace2 January 2011 7. IPv6 Mtrace2 Standard Response Block Each intermediate IPv6 router in a trace path appends "response data block" to the forwarded trace packet. The standard response data block looks 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 +-+-+-+-+-+-+-+-+ | 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 |S|Src Prefix Len |Forwarding Code| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7.1. MBZ: 8 bit Must be zeroed on transmission and ignored on reception. Asaeda, et al. Expires July 11, 2011 [Page 19] Internet-Draft Mtrace2 January 2011 7.2. Query Arrival Time: 32 bits Same definition described in Section 6.2 7.3. Incoming Interface ID: 32 bits This field specifies the interface ID on which packets from this source and group 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. This field is carried in network byte order. 7.4. Outgoing Interface ID: 32 bits This field specifies the interface ID on which packets from this source and group flow to the specified destination, or 0 if unknown. This ID should be the value taken from InterfaceIndex of the IF-MIB for this interface. This field is carried in network byte order. 7.5. Local Address This field specifies a global IPv6 address that uniquely identifies the router. A 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. 7.6. Remote Address This field specifies the address of the previous-hop router, which, in most cases, is a link-local unicast address for the queried source and destination addresses. Although a link-local address does not have enough information to identify a node, it is possible to detect the previous-hop router with the assistance of Incoming Interface ID and the current router address (i.e., Local Address). This may be a multicast group (e.g., ALL-[protocol]- ROUTERS.MCAST.NET) if the previous hop is not known because of the workings of the multicast routing protocol. However, it should be the unspecified address (::) if the incoming interface address is unknown. 7.7. Input packet count on incoming interface Same definition described in Section 6.6 Asaeda, et al. Expires July 11, 2011 [Page 20] Internet-Draft Mtrace2 January 2011 7.8. Output packet count on outgoing interface Same definition described in Section 6.7 7.9. Total number of packets for this source-group pair This field counts the number of packets from the specified source forwarded by this router to the specified group, or "all 1" if no count can be reported. If the S bit is set, 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 for this forwarding entry. 7.10. Rtg Protocol: 16 bits Same definition described in Section 6.9 7.11. Multicast Rtg Protocol: 16 bits Same definition described in Section 6.10 7.12. S: 1 bit This S bit 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 Prefix Len field. 7.13. 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) 7.14. Forwarding Code: 8 bits Same definition described in Section 6.14 Asaeda, et al. Expires July 11, 2011 [Page 21] Internet-Draft Mtrace2 January 2011 8. Mtrace2 Augmented Response Block In addition to the standard response block, a multicast router on the path will be able to add "augumented response block" when it sends the mtrace2 Request to its upstream router or sends the Reply to the Mtrace2 Client Address. This augmented response block is flexible to add various information. 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 +-+-+-+-+-+-+-+-+ | MBZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Value .... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The augmented response block is always appended to mtrace2 TLV header (0x04). The 16 bits Type filed of the augmented response block is defined for various purposes, such as diagnosis (as in Section 12) and protocol verification. The packet length of the augmented response block is specified in the augmented response block TLV header as seen in Section 4.1. The following augmented response block type is defined: Code Type ====== ================================================= 0x01 # Mtrace2 Standard Response Blocks Returned When the NO_SPACE error occurs, the router sends back the mtrace2 Reply with contained data (i.e., all appended response blocks), and continues the mtrace2 Query by sending an mtrace2 Request as will be described in Section 9.3. In this mtrace2 Request, the router appends the augmented response block with the code "0x01" and the number of returned mtrace2 response blocks. Every router between this router and the first-hop router can recognize the limit number of hops by referring this number and the # hops in the header. This document only defines the above augmented response block type and does not define other augmented response block types. Specifing how to deal with diagnosis information will be also described in separate documents. Asaeda, et al. Expires July 11, 2011 [Page 22] Internet-Draft Mtrace2 January 2011 9. Router Behavior All of these actions are performed in addition to (NOT instead of) forwarding the packet, if applicable. E.g. a multicast packet that has TTL or the hop limit remaining MUST be forwarded normally, as MUST a unicast packet that has TTL or the hop limit remaining and is not addressed to this router. 9.1. Receiving Mtrace2 Query An mtrace2 Query message is an mtrace2 message with no response blocks filled in, and uses TLV type 0x1 for IPv4 and IPv6 mtrace2. 9.1.1. Packet Verification Upon receiving an mtrace2 Query message, a router must examine the Query to see if it is the proper last-hop router for the destination address in the packet. It is the proper last-hop router 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. If the router determines that it is not the proper last-hop router, or it cannot make that determination, it does one of two things depending if the Query was received via multicast or unicast. If the Query was received via multicast, then it MUST be silently dropped. If it was received via unicast, a forwarding code of WRONG_LAST_HOP is noted and processing continues as in Section 9.2. Duplicate Query messages as identified by the tuple (Mtrace2 Client Address, Query ID) SHOULD be ignored. This MAY be implemented using a simple 1-back cache (i.e. remembering the Mtrace2 Client Address and Query ID of the previous Query message that was processed, and ignoring future messages with the same Mtrace2 Client Address and Query ID). Duplicate Request messages MUST NOT be ignored in this manner. 9.1.2. Normal Processing When a router receives an mtrace2 Query and it determines that it is the proper last-hop router, it it changes the TLV type to 0x2 and treats it like an mtrace2 Request and performs the steps listed in Section 9.2. 9.1.3. Mtrace2 Query Received by Non-Supported Router When a router that does not support mtrace2 receives an mtrace2 Query message whose destination address is multicast, the router will Asaeda, et al. Expires July 11, 2011 [Page 23] Internet-Draft Mtrace2 January 2011 silently discard the message. When the router receives an mtrace2 Query message whose destination address is the router's interface address, the router returns an ICMP Port unreachable to the Mtrace2 Client Address. 9.2. Receiving Mtrace2 Request An mtrace2 Request is a traceroute message with some number of response blocks filled in, and uses TLV type 0x2 for IPv4 and IPv6 mtrace2. 9.2.1. Packet Verification If the mtrace2 Request does not come from an adjacent host or router, it MUST be silently ignored. If the mtrace2 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. 224/24 for IPv4, FFx2::/16 [3] for IPv6), it MUST be silently ignored. GTSM [14] SHOULD be used by the router to determine whether the host or router is adjacent or not. 9.2.2. Normal Processing When a router receives an mtrace2 Request, 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". 1. If there is room in the current buffer (or the router can efficiently allocate more space to use), insert a new response block into the packet and fill in the Query Arrival Time, Outgoing Interface Address (for IPv4 mtrace2) or Outgoing Interface ID (for IPv6 mtrace2), Output Packet Count, and Fwd TTL (for IPv4 mtrace2). If there was no room, fill in the forwarding code "NO_SPACE" in the *previous* hop's response block, and forward the packet to the address specified in the Mtrace2 Client Address field and continue the trace as described in Section 9.3. 2. Attempt to determine the forwarding information for the source and group specified, 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 "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 Asaeda, et al. Expires July 11, 2011 [Page 24] Internet-Draft Mtrace2 January 2011 state, or if no source-specific information is desired (i.e., "all 1" 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. If this router is the Core or RP and no source- specific state is available (e.g., this router has been receiving PIM Register messages from the first-hop router), note a code of REACHED_RP. 3. 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 forwards the packet to the mtrace2 client as described in Section 9.3. 4. Fill in the Incoming Interface Address, Previous-Hop Router Address, Input Packet Count, Total Number of Packets, Routing Protocol, S, and Src Mask from the forwarding information that was determined. 5. If mtrace2 is administratively prohibited, note the appropriate forwarding code (ADMIN_PROHIB). If mtrace2 is administratively prohibited and any of the fields as filled in step 4 are considered private information, zero out the applicable fields. Then the packet is forwarded to the mtrace2 client as described in Section 9.3. 6. If the reception interface is not enabled for multicast, note forwarding code NO_MULTICAST. If the reception interface is the interface from which the router would expect data to arrive from the source, note forwarding code RPF_IF. Otherwise, if the reception interface is not one to which the router would forward data from the source to the group, a forwarding code of WRONG_IF is noted. 7. If the group is subject to administrative scoping on either the Outgoing or Incoming interfaces, a forwarding code of SCOPED is noted. 8. If this router is the Rendezvous Point or Core for the group, a forwarding code of REACHED_RP is noted. 9. If this router has sent a prune upstream which applies to the source and group in the mtrace2 Request, it notes forwarding code PRUNE_SENT. If the router has stopped forwarding downstream in response to a prune sent by the next hop router, it notes forwarding code PRUNE_RCVD. If the router should normally forward traffic for this source and group downstream Asaeda, et al. Expires July 11, 2011 [Page 25] Internet-Draft Mtrace2 January 2011 but is not, it notes forwarding code NOT_FORWARDING. 10. If this router is a gateway (e.g., a NAT or firewall) that hides the information between this router and the mtrace2 querier, it notes forwarding code REACHED_GW. 11. The packet is then sent on to the previous hop or the Mtrace2 Client Address as described in Section 9.3. 9.2.3. Mtrace2 Request Received by Non-Supported Router When a router that does not understand mtrace2 Request messages receives an mtrace2 Request message whose destination address is multicast, the router will silently discard the message. When the router receives an mtrace2 Request message whose destination address is the router's interface address, the router returns an ICMP Port unreachable to the Mtrace2 Client Address, and the mtrace2 client may then issue another mtrace2 Query with the lower number of # hops. 9.3. Forwarding Mtrace2 Request 9.3.1. Destination Address If the Previous-hop router for the mtrace2 Request is known for this request and the number of response blocks is less than the number requested (i.e., the "# hops" field in the mtrace2 Query header), the packet is sent to that router. If the Incoming Interface is known but the Previous-hop router is not known, the packet is sent to an appropriate multicast address on the Incoming Interface. The appropriate multicast address may depend on the routing protocol in use, MUST be a link-scoped group (i.e. 224/24 for IPv4, FF02::/16 for IPv6), MUST NOT be ALL-SYSTEMS.MCAST.NET (224.0.0.1) for IPv4 and All Nodes Address (FF02::1) for IPv6, and MAY be ALL-ROUTERS.MCAST.NET (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 group. Otherwise, it is sent to the Mtrace2 Client Address in the header. 9.3.2. Source Address An mtrace2 Request should be sent with the address of the router's reception interface. However, if the router's interface address is unnumbered, the router can use one of its numbered interface address as the source address. When the REACHED_GW code is noted, the router sends back the mtrace2 Reply as in Section 9.4. In addition to that, it must continue the mtrace2 Query by proxying the original querier as in Section 9.5. Asaeda, et al. Expires July 11, 2011 [Page 26] Internet-Draft Mtrace2 January 2011 When the NO_SPACE error occurs, the router sends back the mtrace2 Reply with contained data and the NO_SPACE error code as in Section 9.4, and continues the mtrace2 Query by sending an mtrace2 Request containing the same mtrace2 Query header and its standard and augmented response blocks. The corresponding augmented response block type is "# Mtrace2 Response Blocks Returned" described in Section 8. 9.4. Sending Mtrace2 Reply 9.4.1. Destination Address An mtrace2 Reply must be sent to the address specified in the Mtrace2 Client Address field in the mtrace2 Query header. 9.4.2. Source Address An mtrace2 Reply should be sent with the address of the router's reception interface. However, if the router's interface address is unnumbered, the router can use one of its numbered interface address as the source address. 9.5. Proxying Mtrace2 Query When a gateway (e.g., a NAT or firewall) that needs to block unicast packets to the mtrace2 querier or hide information between the gateway and the mtrace2 querier receives mtrace2 Query from an adjacent host or mtrace2 Request from an adjacent router, it sends back the mtrace2 Reply with contained data and the REACHED_GW code to the address specified in the Mtrace2 Client Address field in the mtrace2 Query header. At the same time, the gateway prepares a new mtrace2 Query message. The gateway uses the original mtrace2 Query header as the base for the new mtrace2 Query; it sets the Mtrace2 Client Address to its Incoming Interface address and the Client Port # to its own port (which may be the same as the mtrace2 port as the gateway is listening on that port), and decreases # hops according to the number of standard response blocks in the returned mtrace2 Reply from the gateway. The mtrace2 Query message is sent to the previous-hop router or to an appropriate multicast address on the Incoming Interface. When the gateway receives the mtrace2 Reply from the first-hop router or any intermediate router, it MUST forward the mtrace2 Reply back to the mtrace2 querier with the original mtrace2 Query header. Asaeda, et al. Expires July 11, 2011 [Page 27] Internet-Draft Mtrace2 January 2011 9.6. Hiding Information Information about a domain's topology and connectivity may be hidden from mtrace2 Requests. The INFO_HIDDEN forwarding code may be used to note that, for example, the incoming interface address and packet count are for the entrance to the domain and the outgoing interface address and packet count are the exit from the domain by specifying "all 1". The source-group packet count (Section 6.8 and Section 7.9) is from router, but may be "all 1" if it is hidden. Asaeda, et al. Expires July 11, 2011 [Page 28] Internet-Draft Mtrace2 January 2011 10. Client Behavior 10.1. Sending Mtrace2 Query 10.1.1. Destination Address Mtrace2 Query packet can be sent to the ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All Routers Address (FF02::2) for IPv6. This will ensure that the packet is received by the last-hop router on the subnet. Otherwise, if the proper last-hop router is known for the mtrace2 destination, the Query is unicasted to that router. See also Section 10.4 on determining the last-hop router. 10.1.2. Source Address An mtrace2 Query must be sent with the address of the mtrace2 querier's reception interface, which would be the Mtrace2 Client Address. 10.2. Determining the Path The client could send a small number of initial query messages with a large "# hops" field, 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 a user-defined timeout has occurred. See also Section 10.6 on receiving the results of a trace. 10.3. Collecting Statistics After a client has determined that it has traced the whole path or as much as it can expect to (see Section 10.7), 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 12.3 and Section 12.4. 10.4. Last Hop Router The mtrace2 querier 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 ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All Routers Address (FF02::2) for IPv6. All routers except the correct Asaeda, et al. Expires July 11, 2011 [Page 29] Internet-Draft Mtrace2 January 2011 last-hop router SHOULD ignore any mtrace2 Request received via multicast. 10.5. First Hop Router The IANA assigned 224.0.1.32, MTRACE.MCAST.NET as the default multicast group for old IPv4 mtrace (v1) responses, in order to support mtrace queriers that are not unicast reachable from the first-hop router. However, mtrace2 does not reserve any IPv4/IPv6 multicast addresses for mtrace2 Replies. Every mtrace2 Reply is sent to the unicast address specified in the Mtrace2 Client Address field of the mtrace2 Query header. 10.6. Broken Intermediate Router A broken intermediate router might simply not understand mtrace2 packets, and drop them. The querier would then get no Reply at all from its mtrace2 Requests. It should then perform a hop-by-hop search by setting the number of hops field until it gets a Reply (both linear and binary search are options, but binary is likely to be slower because a failure requires waiting for a timeout). 10.7. Mtrace2 Termination When performing an expanding hop-by-hop trace, it is necessary to determine when to stop expanding. 10.7.1. 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 Previous-hop router is zero. 10.7.2. Fatal error A trace has encountered a fatal error if the last Forwarding Error in the trace has the 0x80 bit set. 10.7.3. No previous hop A trace can not continue if the last Previous-hop in the trace is set to 0. 10.7.4. Traceroute shorter than requested If the trace that is returned is shorter than requested (i.e. the number of response blocks is smaller than the "# hops" field), the trace encountered an error and could not continue. Asaeda, et al. Expires July 11, 2011 [Page 30] Internet-Draft Mtrace2 January 2011 10.8. Continuing after an error When the NO_SPACE error occurs, as described in Section 9.3, the multicast routers sends back the mtrace2 Reply to the address specified in the Mtrace2 Client Address field in the mtrace2 Query header. In this case, the mtrace2 client may receive multiple mtrace2 Replies from different routers (along the path). After the client receives multiple mtrace2 Reply messages, it integrates (i.e. constructs) them as a single mtrace2 Reply message. If a trace times out, it is likely to be because a router in the middle of the path does not support mtrace2. That router's address will be in the Previous-hop router field of the last entry in the last response packet received. 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 a previous-hop 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. Asaeda, et al. Expires July 11, 2011 [Page 31] Internet-Draft Mtrace2 January 2011 11. Protocol-Specific Considerations 11.1. 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 trace Query may be unicasted to the RP. 11.2. Bi-Directional PIM Bi-directional PIM [7] 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 sources to the RPA (Rendezvous Point Address) and from the RPA to receivers without requiring source-specific state. In contrast to PIM-SM, RP always has the state to trace. A Designated Forwarder (DF) for a given RPA is in charge of forwarding downstream traffic onto its link, and forwarding upstream traffic from its link towards the RPL (Rendezvous Point Link) that the RPA belongs to. Hence mtrace2 reports DF addresses or RPA along the path. 11.3. 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 previous hop router is known, but the last-hop router 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 last-hop forwarder for the link (because they won or lost an Assert battle) and know who the previous hop is (because it won an Assert battle). Therefore, mtrace2 is always able to follow the proper path when traffic is flowing. 11.4. IGMP/MLD Proxy When an mtrace2 Query packet reaches an incoming interface of IGMP/ MLD Proxy [8], it puts a WRONG_IF (0x01) value in Forwarding Code of Asaeda, et al. Expires July 11, 2011 [Page 32] Internet-Draft Mtrace2 January 2011 mtrace2 standard response block (as in Section 6.14) and sends the mtrace2 Reply back to the Mtrace2 Client Address. When an mtrace2 Query packet reaches an outgoing interface of IGMP/MLD proxy, it is forwarded through its incoming interface towards the upstream router. 11.5. AMT AMT [9] provides the multicast connectivity to the unicast-only inter-network. To do this, multicast packets being sent to or from a site are encapsulated in unicast packets. When an mtrace2 Query packet reaches an AMT pseudo-interface of an AMT gateway, the AMT gateway encapsulats it to a particular AMT relay reachable across the unicast-only infrastructure. Then the AMT relay decapsulates the mtrace2 Query packet and forwards the mtrace2 Request to the appropriate multicast router. Asaeda, et al. Expires July 11, 2011 [Page 33] Internet-Draft Mtrace2 January 2011 12. Problem Diagnosis 12.1. Forwarding Inconsistencies The forwarding error code can tell if a group is unexpectedly pruned or administratively scoped. 12.2. TTL or Hop Limit Problems By taking the maximum of hops (from source + forwarding TTL (or hop limit) threshold) over all hops, it is possible to discover the TTL or hop limit required for the source to reach the destination. 12.3. 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 Query 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 response data 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 queue of one hop, perhaps due to priority dropping, or in the input queue at the next hop. The counters in the response data 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. Asaeda, et al. Expires July 11, 2011 [Page 34] Internet-Draft Mtrace2 January 2011 12.4. 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. 12.5. 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. Asaeda, et al. Expires July 11, 2011 [Page 35] Internet-Draft Mtrace2 January 2011 13. IANA Considerations The following new assignments can only be made via a Standards Action as specified in [4]. 13.1. Forwarding Codes New Forwarding codes must only be created by an RFC that modifies this document's Section 10, fully describing the conditions under which the new forwarding code is used. The IANA may act as a central repository so that there is a single place to look up forwarding codes and the document in which they are defined. 13.2. UDP Destination Port and IPv6 Address The IANA should allocate UDP destination port for multicast traceroute version 2 upon publication of the first RFC. Asaeda, et al. Expires July 11, 2011 [Page 36] Internet-Draft Mtrace2 January 2011 14. Security Considerations 14.1. 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. 14.2. Traffic Rates 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. 14.3. Limiting Query/Request Rates Routers should limit mtrace2 Queries and Requests by ignoring the received messages. Routers MAY randomly ignore the received messages to minimize the processing overhead, i.e., to keep fairness in processing queries. The rate limit is left to the router's implementation. Asaeda, et al. Expires July 11, 2011 [Page 37] Internet-Draft Mtrace2 January 2011 15. 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, extensive comments were received from Ronald Bonica, Yiqun Cai, Liu Hui, Bharat Joshi, Pekka Savola, Shinsuke Suzuki, Dave Thaler, Achmad Husni Thamrin, and Cao Wei. Asaeda, et al. Expires July 11, 2011 [Page 38] Internet-Draft Mtrace2 January 2011 16. References 16.1. 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 2460, December 1998. [3] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 2373, July 1998. [4] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 2434, October 1998. [5] Braden, B., Borman, D., and C. Partridge, "Computing the Internet Checksum", RFC 1071, September 1988. [6] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", RFC 4601, August 2006. [7] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, "Bidirectional Protocol Independent Multicast (BIDIR-PIM)", RFC 5015, October 2007. [8] 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. [9] Thaler, D., Talwar, M., Aggarwal, A., Vicisano, L., and T. Pusateri, "Automatic IP Multicast Without Explicit Tunnels (AMT)", draft-ietf-mboned-auto-multicast-08.txt (work in progress), October 2007. 16.2. Informative References [10] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. Thyagarajan, "Internet Group Management Protocol, Version 3", RFC 3376, October 2002. [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. Asaeda, et al. Expires July 11, 2011 [Page 39] Internet-Draft Mtrace2 January 2011 [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. Asaeda, et al. Expires July 11, 2011 [Page 40] Internet-Draft Mtrace2 January 2011 Authors' Addresses Hitoshi Asaeda Keio University Graduate School of Media and Governance Fujisawa, Kanagawa 252-0882 Japan Email: asaeda@wide.ad.jp URI: http://www.sfc.wide.ad.jp/~asaeda/ Tatuya Jinmei Internet Systems Consortium Redwood City, CA 94063 US Email: Jinmei_Tatuya@isc.org William C. Fenner Arastra, Inc. Menlo Park, CA 94025 US Email: fenner@fenron.net Stephen L. Casner Packet Design, Inc. Palo Alto, CA 94304 US Email: casner@packetdesign.com Asaeda, et al. Expires July 11, 2011 [Page 41]