RFC 8487
Mtrace Version 2: Traceroute Facility for IP Multicast
Pages: 41
Proposed Standard
Proposed Standard
Part 1 of 2 – Pages 1 to 22
Internet Engineering Task Force (IETF) H. Asaeda Request for Comments: 8487 NICT Category: Standards Track K. Meyer ISSN: 2070-1721 Dell EMC W. Lee, Ed. October 2018 Mtrace Version 2: Traceroute Facility for IP MulticastAbstract
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 is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8487.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 7 3. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . 8 3.1. Mtrace2 TLV Format . . . . . . . . . . . . . . . . . . . 9 3.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . 10 3.2.1. Mtrace2 Query . . . . . . . . . . . . . . . . . . . . 10 3.2.2. Mtrace2 Request . . . . . . . . . . . . . . . . . . . 12 3.2.3. Mtrace2 Reply . . . . . . . . . . . . . . . . . . . . 12 3.2.4. IPv4 Mtrace2 Standard Response Block . . . . . . . . 13 3.2.5. IPv6 Mtrace2 Standard Response Block . . . . . . . . 18 3.2.6. Mtrace2 Augmented Response Block . . . . . . . . . . 20 3.2.7. Mtrace2 Extended Query Block . . . . . . . . . . . . 21 4. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 22 4.1. Receiving an Mtrace2 Query . . . . . . . . . . . . . . . 22 4.1.1. Query Packet Verification . . . . . . . . . . . . . . 22 4.1.2. Query Normal Processing . . . . . . . . . . . . . . . 23 4.2. Receiving an Mtrace2 Request . . . . . . . . . . . . . . 23 4.2.1. Request Packet Verification . . . . . . . . . . . . . 24 4.2.2. Request Normal Processing . . . . . . . . . . . . . . 24 4.3. Forwarding Mtrace2 Request . . . . . . . . . . . . . . . 26 4.3.1. Destination Address . . . . . . . . . . . . . . . . . 26 4.3.2. Source Address . . . . . . . . . . . . . . . . . . . 26 4.3.3. Appending Standard Response Block . . . . . . . . . . 26 4.4. Sending Mtrace2 Reply . . . . . . . . . . . . . . . . . . 27 4.4.1. Destination Address . . . . . . . . . . . . . . . . . 27 4.4.2. Source Address . . . . . . . . . . . . . . . . . . . 27 4.4.3. Appending Standard Response Block . . . . . . . . . . 27 4.5. Proxying Mtrace2 Query . . . . . . . . . . . . . . . . . 28 4.6. Hiding Information . . . . . . . . . . . . . . . . . . . 28 5. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 29 5.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 29 5.1.1. Destination Address . . . . . . . . . . . . . . . . . 29 5.1.2. Source Address . . . . . . . . . . . . . . . . . . . 29 5.2. Determining the Path . . . . . . . . . . . . . . . . . . 29 5.3. Collecting Statistics . . . . . . . . . . . . . . . . . . 29 5.4. Last-Hop Router (LHR) . . . . . . . . . . . . . . . . . . 30 5.5. First-Hop Router (FHR) . . . . . . . . . . . . . . . . . 30 5.6. Broken Intermediate Router . . . . . . . . . . . . . . . 30 5.7. Non-supported Router . . . . . . . . . . . . . . . . . . 30 5.8. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 31 5.8.1. Arriving at Source . . . . . . . . . . . . . . . . . 31 5.8.2. Fatal Error . . . . . . . . . . . . . . . . . . . . . 31 5.8.3. No Upstream Router . . . . . . . . . . . . . . . . . 31 5.8.4. Reply Timeout . . . . . . . . . . . . . . . . . . . . 31 5.9. Continuing after an Error . . . . . . . . . . . . . . . . 31
6. Protocol-Specific Considerations . . . . . . . . . . . . . . 32 6.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . 32 6.2. Bidirectional PIM . . . . . . . . . . . . . . . . . . . . 32 6.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . 32 6.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . 33 7. Problem Diagnosis . . . . . . . . . . . . . . . . . . . . . . 33 7.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . 33 7.2. TTL or Hop-Limit Problems . . . . . . . . . . . . . . . . 33 7.3. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 33 7.4. Link Utilization . . . . . . . . . . . . . . . . . . . . 34 7.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . 34 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34 8.1. "Mtrace2 Forwarding Codes" Registry . . . . . . . . . . . 35 8.2. "Mtrace2 TLV Types" Registry . . . . . . . . . . . . . . 35 8.3. UDP Destination Port . . . . . . . . . . . . . . . . . . 35 9. Security Considerations . . . . . . . . . . . . . . . . . . . 35 9.1. Addresses in Mtrace2 Header . . . . . . . . . . . . . . . 35 9.2. Verification of Clients and Peers . . . . . . . . . . . . 35 9.3. Topology Discovery . . . . . . . . . . . . . . . . . . . 36 9.4. Characteristics of Multicast Channel . . . . . . . . . . 36 9.5. Limiting Query/Request Rates . . . . . . . . . . . . . . 37 9.6. Limiting Reply Rates . . . . . . . . . . . . . . . . . . 37 9.7. Specific Security Concerns . . . . . . . . . . . . . . . 37 9.7.1. Request and Response Bombardment . . . . . . . . . . 37 9.7.2. Amplification Attack . . . . . . . . . . . . . . . . 37 9.7.3. Leaking of Confidential Topology Details . . . . . . 38 9.7.4. Delivery of False Information (Forged Reply Messages) 38 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 39 10.1. Normative References . . . . . . . . . . . . . . . . . . 39 10.2. Informative References . . . . . . . . . . . . . . . . . 40 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 41 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41
1. Introduction
Given a multicast distribution tree, tracing hop-by-hop downstream from a multicast source to a given multicast receiver is difficult because there is no efficient and deterministic way to determine the branch of the multicast routing tree on which that receiver lies. 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 Protocol Independent Multicast - Sparse Mode (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 a 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., Time to live (TTL) threshold). The following figure shows a typical case of 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. The source, receiver, and Mtrace2 client are typically hosts.
2. Request 2. Request
+----+ +----+
| | | |
v | v |
+--------+ +-----+ +-----+ +----------+
| Source |----| FHR |----- The Internet -----| LHR |----| Receiver |
+--------+ +-----+ | +-----+ +----------+
\ | ^
\ | /
\ | /
\ | /
3. Reply \ | / 1. Query
\ | /
\ | /
\ +---------+ /
v | Mtrace2 |/
| Client |
+---------+
When an Mtrace2 client initiates a multicast trace, it sends an
Mtrace2 Query packet to an 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 the 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 that prevent the 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-
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 specific to the Mtrace2 client and 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 this 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 Internet Group Management Protocol (IGMP) messages [10], 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 Automatic Multicast Tunneling (AMT) [16] and Mtrace2 for Multicast in MPLS/BGP IP VPNs (known as Multicast VPN (MVPN)) [15]. They are, therefore, out of the scope of this document.2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [1] [7] when, and only when, they appear in all capitals, as shown here. The key words 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:
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:
The state a shared-tree protocol, such as Protocol Independent
Multicast - Sparse Mode (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:
The state that is used to choose the path towards the source for
the specified source and group.
ALL-[protocol]-ROUTERS group:
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 the Type/Length/Value (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 any TLV in a message,
it SHOULD ignore and silently discard the entire packet. 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 containing packet.
All Mtrace2 messages are UDP packets. For IPv4, Mtrace2 Query/Request/Reply messages MUST NOT be fragmented. Therefore, Mtrace2 clients and LHRs/RPs MUST set the IP header do-not-fragment (DF) bit for all Mtrace2 messages. For IPv6, the packet size for the Mtrace2 messages MUST NOT exceed 1280 bytes, which is the smallest Maximum Transmission Unit (MTU) for an IPv6 interface [8]. 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 when mixed. For example, if an Mtrace2 Query or Request message arrives as an IPv4 packet, all addresses specified in the Mtrace2 messages MUST be IPv4 as well. The 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 4 octets. The length MUST be a multiple of 4 octets. The maximum TLV length is not defined; however, the entire Mtrace2 packet length MUST NOT exceed the available MTU. Value: variable length The format is based on the Type value. The length of the Value field is the 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: Code Type ==== ================================ 0x00 Reserved 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, a Request, or a 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 where 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 originated by an Mtrace2 client, which sends an Mtrace2 Query message to the LHR. The LHR modifies only the Type field of the Query TLV (to turn it into a "Request") before appending a Standard Response Block and forwarding it upstream. The LHR and intermediate routers handling the Mtrace2 message when tracing upstream MUST NOT modify any other fields within the Query/Request TLV. Additionally, intermediate routers handling the message after the LHR has converted the Query into a Request MUST NOT modify the Type field of the Request TLV. If the actual number of hops is not known, an Mtrace2 client could send an initial Query message with a large # Hops (e.g., 0xff), in order to try to trace the full path.
An Mtrace2 Query message is shown 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 | # Hops |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Multicast Address |
| |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| |
| Source Address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Mtrace2 Client Address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Query ID | Client Port # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Length: 16 bits
The Length field MUST be either 20 (i.e., 8 + 3 * 4 (IPv4
addresses)) or 56 (i.e., 8 + 3 * 16 (IPv6 addresses)); if the
length is 20, then IPv4 addresses MUST be assumed, and if the
length is 56, then IPv6 addresses MUST be assumed.
# 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 ones 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: a unicast address of the source to be traced or
s-2: all ones 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.
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;
therefore, it MUST NOT be all ones 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 Mtrace2 Request TLV is exactly the same as an Mtrace2 Query
except for identifying the Type field of 0x02.
When an LHR receives an Mtrace2 Query message, it turns the Query
into a Request by changing the Type field of the Query from 0x01 to
0x02. The LHR then appends an Mtrace2 Standard Response Block (see
Section 3.2.4) of its own to the Request message before sending it
upstream. The upstream routers do the same without changing the Type
field until one of them is ready to send a Reply.
3.2.3. Mtrace2 Reply
The Mtrace2 Reply TLV is exactly the same as an Mtrace2 Query except
for identifying the Type field of 0x03.
When an FHR or an RP receives an Mtrace2 Request message that is
destined to itself, it appends an Mtrace2 Standard Response Block
(see Section 3.2.4) of its own to the Request message. Next, it
turns the Request message into a Reply by changing the Type field of
the Request from 0x02 to 0x03 and by changing the UDP destination port to the port number specified in the Client Port Number field in the Request. It then unicasts the Reply message to the Mtrace2 client specified in the Mtrace2 Client Address field. There are a number of cases in which an intermediate router might return a Reply before a Request reaches the FHR or the RP. See Sections 4.1.1, 4.2.2, 4.3.3, and 4.5 for more details.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 Network Time Protocol (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 timespec (fractional part in
nanoseconds) to a 32-bit NTP timestamp:
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), where "<<"
denotes a logical left shift.
Note that synchronized clocks are required on the traced routers
to estimate propagation and queuing delays between successive
hops. Nevertheless, even without this synchronization, an
application can still estimate an upper bound on cumulative one-
way latency by measuring the time between sending a Query and
receiving a Reply.
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 using 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 MUST 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 ones if
no count can be reported. This counter may have the same value as
ifHCInMulticastPkts from the Interfaces Group MIB (IF-MIB) [9] for
this interface.
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 ones if no count can be
reported. This counter may have the same value as
ifHCOutMulticastPkts from the IF-MIB [9] for this interface.
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 ones 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 IP Multicast MIB [14] 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 Reverse Path Forwarding (RPF) interface for the specified
source or RP. This value should have the same value as
ipMcastRouteRtProtocol from the IP Multicast MIB [14] 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 IP Multicast MIB [14]
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 with
conditions that are transitory or automatically recovered. Other
Forwarding Code values indicate a need to fix a problem in the
Query or a need to redirect the Query. Sections 4.1 and 4.2
explain 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
for which this router does not perform
forwarding for the specified group to the
source or RP.
0x02 PRUNE_SENT This router has sent a prune upstream that
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
that 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 that 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. 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 [9]
for this interface.
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 [9]
for this interface.
Local Address: 128 bits
This field specifies a global IPv6 address that uniquely
identifies the router. A unique local unicast address [12] 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 the 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 IP Multicast MIB [14]
for this forwarding entry.
Rtg Protocol: 16 bits
Same definition as in IPv4.
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:
Code Type
====== ==============================================
0x0001 # 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 adds 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 recognizes the total number of hops the
Request has 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 this 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 .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.
(page 22 continued on part 2)