ICN Research Group H. Asaeda
Internet-Draft X. Shao
Intended status: Experimental NICT
Expires: May 19, 2017 T. Turletti
Inria
November 15, 2016
Contrace: Traceroute Facility for Content-Centric Network
draft-asaeda-icnrg-contrace-01
Abstract
This document describes the traceroute facility for Content-Centric
Network (CCN), named "Contrace". Contrace investigates: 1) the
forwarding path information per name prefix, device name, and
function/application, 2) the Round-Trip Time (RTT) between content
forwarder and consumer, and 3) the states of in-network cache per
name prefix.
Status of This Memo
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This Internet-Draft will expire on May 19, 2017.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
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include Simplified BSD License text as described in Section 4.e of
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 6
3. Contrace Message Formats . . . . . . . . . . . . . . . . . . 7
3.1. Request Message . . . . . . . . . . . . . . . . . . . . . 8
3.1.1. Request Block . . . . . . . . . . . . . . . . . . . . 10
3.1.2. Report Block . . . . . . . . . . . . . . . . . . . . 12
3.2. Reply Message . . . . . . . . . . . . . . . . . . . . . . 14
3.2.1. Reply Block . . . . . . . . . . . . . . . . . . . . . 16
3.2.1.1. Reply Sub-Block . . . . . . . . . . . . . . . . . 16
4. Contrace User Behavior . . . . . . . . . . . . . . . . . . . 19
4.1. Sending Contrace Request . . . . . . . . . . . . . . . . 19
4.2. Receiving Contrace Reply . . . . . . . . . . . . . . . . 20
5. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 20
5.1. Receiving Contrace Request . . . . . . . . . . . . . . . 20
5.2. Forwarding Contrace Request . . . . . . . . . . . . . . . 21
5.3. Sending Contrace Reply . . . . . . . . . . . . . . . . . 22
5.4. Forwarding Contrace Reply . . . . . . . . . . . . . . . . 22
6. Publisher Behavior . . . . . . . . . . . . . . . . . . . . . 22
7. Contrace Termination . . . . . . . . . . . . . . . . . . . . 23
7.1. Arriving at Publisher or Gateway . . . . . . . . . . . . 23
7.2. Arriving at Router Having Cache . . . . . . . . . . . . . 23
7.3. No Route . . . . . . . . . . . . . . . . . . . . . . . . 23
7.4. No Information . . . . . . . . . . . . . . . . . . . . . 23
7.5. No Space . . . . . . . . . . . . . . . . . . . . . . . . 23
7.6. Fatal Error . . . . . . . . . . . . . . . . . . . . . . . 24
7.7. Contrace Reply Timeout . . . . . . . . . . . . . . . . . 24
7.8. Non-Supported Node . . . . . . . . . . . . . . . . . . . 24
7.9. Administratively Prohibited . . . . . . . . . . . . . . . 24
8. Configurations . . . . . . . . . . . . . . . . . . . . . . . 24
8.1. Contrace Reply Timeout . . . . . . . . . . . . . . . . . 24
8.2. HopLimit in Fixed Header . . . . . . . . . . . . . . . . 24
8.3. Access Control . . . . . . . . . . . . . . . . . . . . . 25
9. Diagnosis and Analysis . . . . . . . . . . . . . . . . . . . 25
9.1. Number of Hops . . . . . . . . . . . . . . . . . . . . . 25
9.2. Caching Router and Gateway Identification . . . . . . . . 25
9.3. TTL or Hop Limit . . . . . . . . . . . . . . . . . . . . 25
9.4. Time Delay . . . . . . . . . . . . . . . . . . . . . . . 25
9.5. Path Stretch . . . . . . . . . . . . . . . . . . . . . . 25
9.6. Cache Hit Probability . . . . . . . . . . . . . . . . . . 26
10. Security Considerations . . . . . . . . . . . . . . . . . . . 26
10.1. Policy-Based Information Provisioning for Request . . . 26
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10.2. Filtering of Contrace Users Located in Invalid Networks 26
10.3. Topology Discovery . . . . . . . . . . . . . . . . . . . 27
10.4. Characteristics of Content . . . . . . . . . . . . . . . 27
10.5. Shortening Contrace Reply Timeout . . . . . . . . . . . 27
10.6. Limiting Request Rates . . . . . . . . . . . . . . . . . 27
10.7. Limiting Reply Rates . . . . . . . . . . . . . . . . . . 27
10.8. Adjacency Verification . . . . . . . . . . . . . . . . . 27
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
11.1. Normative References . . . . . . . . . . . . . . . . . . 28
11.2. Informative References . . . . . . . . . . . . . . . . . 28
Appendix A. Contrace Command and Options . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction
In Content-Centric Network (CCN) or Named-Data Network (NDN),
publishers provide content through the network, and receivers
retrieve content by name. In this network architecture, routers
forward content requests by means of their Forwarding Information
Bases (FIBs), which are populated by name-based routing protocols.
CCN/NDN also enables receivers to retrieve content from an in-network
cache.
In CCN/NDN, while consumers do not generally need to know which
content forwarder is transmitting the content to them, operators and
developers may want to identify the content forwarder and observe the
forwarding path information per name prefix for troubleshooting or
investigating the network conditions.
Traceroute [5] is a useful tool for analyzing the routing conditions
in IP networks as it provides intermediate router addresses along the
path between source and destination and the Round-Trip Time (RTT) for
the path. However, this IP-based network tool cannot trace the name
prefix paths used in CCN/NDN. Moreover, given a source-rooted
forwarding path per name prefix, specifying a forwarding source
(i.e., router or publisher) for any content is difficult, because we
do not always know which branch of the source tree the consumer is
on. Additionally, it is not feasible to flood the entire source-
rooted tree to find the path from a source to a consumer.
Furthermore, such IP-based network tool does not allow the states of
the in-network cache to be discovered.
This document describes the specification of "Contrace", an active
network measurement tool for investigating the path and caching
condition in CCN. Contrace is designed based on the work originally
published in [4].
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Contrace consists of the Contrace user command and the Contrace
forwarding function implementation on a content forwarder (e.g.,
router). The Contrace user (e.g., consumer) invokes the contrace
command (described in Appendix A) with the name prefix of the
content, the device name, or the function (or application) name. The
Contrace command initiates the Contrace "Request" message (described
in Section 3.1). The Request message, for example, obtains
forwarding path and cache information. When an appropriate adjacent
neighbor router receives the Request message, it retrieves cache
information. If the router is not the content forwarder for the
request, it inserts its "Report" block (described in Section 3.1.2)
into the Request message and forwards the Request message to its
upstream neighbor router(s) decided by its FIB. These two message
types, Contrace Request and Reply messages, are encoded in the CCNx
TLV format [1].
In this way, the Contrace Request message is forwarded by routers
toward the content publisher, and the Contrace Report record is
inserted by each intermediate router. When the Request message
reaches the content forwarder (i.e., a router or the publisher who
has the specified cache or content), the content forwarder forms the
Contrace "Reply" message (described in Section 3.2) and sends it to
the downstream neighbor router. The Reply message is forwarded back
toward the Contrace user in a hop-by-hop manner. This request-reply
message flow, walking up the tree from a consumer toward a publisher,
is inspired by the design of the IP multicast traceroute facility
[6].
Contrace supports multipath forwarding. The Request messages can be
forwarded to multiple neighbor routers. When the Request messages
forwarded to multiple routers, the different Reply messages will be
forwarded from different routers or publisher. To support this case,
PIT entries initiated by Contrace remain until the defined timeout
value is expired.
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1. Request 2. Request 3. Request 4. Request
(+U) (U+A) (U+A+B) (U+A+B+C)
+----+ +----+ +----+ +----+
| | | | | | | |
| v | v | v | v
+--------+ +--------+ +--------+ +--------+ +---------+
|Contrace|----| Router |----| Router |----| Router |----|Publisher|
| user | | A | | B | | C | | |
+--------+ +--------+ +--------+ +--------+ +---------+
\
\ +-------+
3. Request \ | Cache |
(U+A+B) \ +---------+ |
v| Caching |----+
| router |
+---------+
Figure 1: Request messages forwarded by consumer and routers.
Contrace user and routers (i.e., Router A,B,C) insert their own
Report blocks into the Request message and forward the message toward
the content forwarder (i.e., caching router and publisher)
3. Reply(C) 2. Reply(C)
4. Reply(P) 3. Reply(P) 2. Reply(P) 1. Reply(P)
+----+ +----+ +----+ +----+
| | | | | | | |
v | v | v | v |
+--------+ +--------+ +--------+ +--------+ +---------+
|Contrace|----| Router |----| Router |----| Router |----|Publisher|
| user | | A | | B | | C | | |
+--------+ +--------+ +--------+ +--------+ +---------+
^
\ +-------+
1. Reply(C) \ | Cache |
\ +---------+ |
\| Caching |----+
| router |
+---------+
Figure 2: Reply messages forwarded by publisher and routers. Each
router forwards the Reply message, and finally the Contrace user
receives two Reply messages: one from the publisher and the other
from the caching router.
Contrace facilitates the tracing of a routing path and provides: 1)
the RTT between content forwarder (i.e., caching router or publisher)
and consumer, 2) the states of in-network cache per name prefix, and
3) the forwarding path information per name prefix.
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In addition, Contrace identifies the states of the cache, such as the
following metrics for Content Store (CS) in the content forwarder: 1)
size of the cached content, 2) number of the cached chunks of the
content, 3) number of the accesses (i.e., received Interests) per
cache or chunk, and 4) lifetime and expiration time per cache or
chunk. The number of received Interests per cache or chunk on the
routers indicates the popularity of the content.
Furthermore, Contrace implements policy-based information
provisioning that enables administrators to "hide" secure or private
information, but does not disrupt the forwarding of messages. This
policy-based information provisioning reduces the deployment barrier
faced by operators in installing and running Contrace on their
routers.
2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [2],
and indicate requirement levels for compliant Contrace
implementations.
2.1. Definitions
Since Contrace requests flow in the opposite direction to the data
flow, we refer to "upstream" and "downstream" with respect to data,
unless explicitly specified.
Router
It is a router facilitating name-based content/device/function
name or characteristic retrieval in the path between consumer and
publisher.
Scheme name
It indicates a URI and protocol such as "ccnx:/" and "ndn:/".
This document considers the protocol for name-based
content/device/function name or characteristic retrieval.
Gateway
It is a router supporting multiple scheme names in the path
between consumer and publisher. The router may have multiple
(different) FIBs.
Node
It is a router, gateway, publisher, or consumer.
Content forwarder
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It is either a router or a publisher that holds the cache (or
content) and forwards it to consumers.
Contrace user
It is a node that invokes the contrace command and initiates the
Contrace Request.
Incoming face
The face on which data is expected to arrive from the specified
name prefix.
Outgoing face
The face to which data from the publisher or router is expected to
transmit for the specified name prefix. It is also the face on
which the Contrace Request messages are received.
3. Contrace Message Formats
Contrace uses two message types: Request and Reply. Both messages
are encoded in the CCNx TLV format ([1], Figure 3). The Request
message consists of a fixed header, Request block TLV Figure 7, and
Report block TLV(s) Figure 11. The Reply message consists of a fixed
header, Request block TLV, Report block TLV(s), and Reply block/sub-
block TLV(s) Figure 14.
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
+---------------+---------------+---------------+---------------+
| Version | PacketType | PacketLength |
+---------------+---------------+---------------+---------------+
| PacketType specific fields | HeaderLength |
+---------------+---------------+---------------+---------------+
/ Optional Hop-by-hop header TLVs /
+---------------+---------------+---------------+---------------+
/ PacketPayload TLVs /
+---------------+---------------+---------------+---------------+
/ Optional CCNx ValidationAlgorithm TLV /
+---------------+---------------+---------------+---------------+
/ Optional CCNx ValidationPayload TLV (ValidationAlg required) /
+---------------+---------------+---------------+---------------+
Figure 3: Packet format [1]
The Request and Reply Type values in the fixed header are
PT_TRACE_REQ and PT_TRACE_REPLY, respectively (Figure 4). These
messages are forwarded in a hop-by-hop manner. When the Request
message reaches the content forwarder, the content forwarder turns
the Request message into a Reply message by changing the Type field
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value in the fixed header from PT_TRACE_REQ to PT_TRACE_REPLY and
forwards back to the node that has initiated the Request message.
Code Type name
======== =====================
1 PT_INTEREST [1]
2 PT_CONTENT [1]
3 PT_RETURN [1]
4 PT_TRACE_REQ
5 PT_TRACE_REPLY
Figure 4: Packet Type Namespace
Each Contrace message MUST begin with a fixed header with either a
Request or Reply type value to specify whether it is a Request
message or Reply message. Following a fixed header, there can be a
sequence of optional hop-by-hop header TLV(s) for a Request message.
In the case of a Request message, it is followed by a sequence of
Report blocks, each from a router on the path toward the publisher or
caching router.
At the beginning of PacketPayload TLVs, one top-level TLV type,
T_TRACE (Figure 5), exists at the outermost level of a CCNx protocol
message. This TLV indicates that the Name segment TLV(s) and Reply
block TLV(s) would follow in the Request or Reply message.
Code Type name
======== =========================
1 T_INTEREST [1]
2 T_OBJECT [1]
3 T_VALIDATION_ALG [1]
4 T_VALIDATION_PAYLOAD [1]
5 T_TRACE
Figure 5: Top-Level Type Namespace
3.1. Request Message
When a Contrace user initiates a trace request (e.g., by contrace
command described in Appendix A), a Contrace Request message is
created and forwarded to its upstream router through the Incoming
face(s) determined by its FIB.
The packet format of the Contrace Request message is as shown in
Figure 6. It consists of a fixed header, Request block TLV
(Figure 7), Report block TLV(s) (Figure 11), and Name TLV. The Type
value of Top-Level type namespace is T_TRACE (Figure 5). The Type
value for the Report message is PT_TRACE_REQ.
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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
+---------------+---------------+---------------+---------------+
| Version | PT_TRACE_REQ | PacketLength |
+---------------+---------------+---------------+---------------+
| HopLimit | ReturnCode |Reserved (MBZ) | HeaderLength |
+===============+===============+===============+===============+
| |
+ Request block TLV +
| |
+---------------+---------------+---------------+---------------+
/ Report block TLV 1 /
+---------------+---------------+---------------+---------------+
/ Report block TLV 2 /
+---------------+---------------+---------------+---------------+
/ . /
/ . /
+---------------+---------------+---------------+---------------+
/ Report block TLV n /
+===============+===============+===============+===============+
| T_TRACE | MessageLength |
+---------------+---------------+---------------+---------------+
| T_NAME | Length |
+---------------+---------------+---------------+---------------+
/ Name segment TLVs (name prefix specified by contrace command) /
+---------------+---------------+---------------+---------------+
Figure 6: Packet format of the Request message
HopLimit: 8 bits
HopLimit is a counter that is decremented with each hop. It
limits the distance a Request may travel on the network.
ReturnCode: 8 bits
ReturnCode is used for the Reply message. This value is replaced
by the content forwarder when the Request message is returned as
the Reply message (see Section 3.2). Until then, this field MUST
be transmitted as zeros and ignored on receipt.
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Value Name Description
----- --------------- ----------------------------------------------
0x00 NO_ERROR No error
0x01 WRONG_IF Contrace Request arrived on an interface
to which this router would not forward for
the specified name/function toward the
publisher.
0x02 INVALID_REQUEST Invalid Contrace Request is received.
0x03 NO_ROUTE This router has no route for the named prefix
and no way to determine a potential route.
0x04 NO_INFO This router has no cache information for the
specified name prefix, device information, or
function.
0x05 NO_SPACE There was not enough room to insert another
Report block in the packet.
0x06 INFO_HIDDEN Information is hidden from this trace because
of some policy.
0x0E ADMIN_PROHIB Contrace Request is administratively
prohibited.
0x0F UNKNOWN_REQUEST This router does not support/recognize the
Request message.
0x80 FATAL_ERROR A fatal error is one where the router may
know the upstream router but cannot forward
the message to it.
Reserved (MBZ): 8 bits
The reserved fields in the Value field MUST be transmitted as
zeros and ignored on receipt.
3.1.1. Request Block
When a Contrace user transmits the Request message, it MUST insert
the Request block TLV (Figure 7) and the Report block TLV (Figure 11)
of its own to the Request message before sending it through the
Incoming face(s).
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
+---------------+---------------+---------------+---------------+
| T_TRACE_REQ | Length |
+---------------+---------------+---------------+---------------+
| SchemeName | SkipHopCount | Timeout |Reserved (MBZ) |
+---------------+---------------+---------------+---------------+
| Request ID | Flags |
+---------------+---------------+---------------+---------------+
Figure 7: Request block TLV (hop-by-hop header)
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Code Type name
============= =====================
1 T_INTLIFE [1]
2 T_CACHETIME [1]
3 T_MSGHASH [1]
4 - 7 Reserved [1]
8 T_TRACE_REQ
9 T_TRACE_REPORT
%x0FFE T_PAD [1]
%x0FFF T_ORG [1]
%x1000-%x1FFF Reserved [1]
Figure 8: Hop-by-Hop Type Namespace
Type: 16 bits
Format of the Value field. For the single Request block TLV, the
type value MUST be T_TRACE_REQ. For all the available types for
hop-by-hop type namespace, please see Figure 8.
Length: 16 bits
Length of Value field in octets. For the Request block, it MUST
be 4 in the current specification.
SchemeName: 8 bits
Currently, the following scheme names are defined.
Code Scheme name
============= ===============
0 ccnx:/
1 ndn:/
%x02-%FF Not assigned
Figure 9: Scheme Names
SkipHopCount: 8 bits
Number of skipped routers. This value MUST be lower than the
value of HopLimit at the fixed header.
Timeout: 8 bits
It is a [Contrace Reply Timeout] value later described in
Section 8.1. A Contrace user requests routers along the path to
keep the PIT entry for the Request until this timeout value
expires. Note that, because of some security concern
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(Section 10.5), a router along the path may configure the shorter
timeout value than this requested timeout value. In that case,
the Request may be timed out and the Contrace user may not receive
the Reply as expected.
Request ID: 16 bits
This field is used as a unique identifier for this Contrace
Request so that duplicate or delayed Reply messages can be
detected.
Flags: 16 bits
The trace conditions specified as the contrace command options
(described in Appendix A) are transferred in the Flags field. The
trace conditions depend on the specified name (i.e., name_prefix,
device_name, or function_name) as shown in Figure 10. Note that
code %x01 and %x02 are exclusive options; that is, only one of
them should be turned on at once.
Code Type name
============ =====================================================
%x01 Cache retrieval allowing partial match (name_prefix)
%x02 No cache information required (name_prefix)
%x04 Publisher reachability (name_prefix and device_name)
%x08 Discovery of gateway supporting specified scheme
name (name_prefix, device_name, and function_name)
%x16 Function's or application's version number retrieval
(function_name)
%x32-%x32768 Not assigned
Figure 10: Codes and types specified in Flags field
3.1.2. Report Block
A Contrace user and each upstream router along the path would insert
its own Report block TLV without changing the Type field of the fixed
header of the Request message until one of these routers is ready to
send a Reply. In the Report block TLV (Figure 11), the Request
Arrival Time and the Node Identifier MUST be inserted.
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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
+---------------+---------------+---------------+---------------+
| T_TRACE_REPORT | Length |
+---------------+---------------+---------------+---------------+
| Request Arrival Time |
+---------------+---------------+---------------+---------------+
/ Node Identifier /
+---------------+---------------+---------------+---------------+
Figure 11: Report block TLV (hop-by-hop header)
Type: 16 bits
Format of the Value field. For the Request block TLV(s), the type
value(s) MUST be T_TRACE_REPORT.
Length: 16 bits
Length of Value field in octets.
Request Arrival Time: 32 bits
The Request Arrival Time is a 32-bit NTP timestamp specifying the
arrival time of the Contrace Request packet at this router. The
32-bit form of an NTP timestamp consists of the middle 32 bits of
the full 64-bit form; that is, the low 16 bits of the integer part
and the high 16 bits of the fractional part.
The following formula converts from a UNIX timeval to a 32-bit NTP
timestamp:
request_arrival_time
= ((tv.tv_sec + 32384) << 16) + ((tv.tv_nsec << 7) / 1953125)
The constant 32384 is the number of seconds from Jan 1, 1900 to
Jan 1, 1970 truncated to 16 bits. ((tv.tv_nsec << 7) / 1953125)
is a reduction of ((tv.tv_nsec / 1000000000) << 16).
Note that all the routers on the path may not have synchronized
clocks. In that case, the Contrace user measures the RTT between
Contrace user and content forwarder. See Section 9.4.
Node Identifier: variable length
This field specifies the Contrace user or the router identifier
(e.g., IPv4 address) of the Incoming face on which packets from
the publisher are expected to arrive, or 0 if unknown or
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unnumbered. Note that although it would be necessary to define
the identifier uniqueness (e.g., by specifying the protocol
family) for this field, defining such uniqueness is [TBD] as we
may not always rely on the IP addressing architecture.
Potentially, this field may be defined as a new TLV. Such
discussion is also [TBD].
3.2. Reply Message
When a content forwarder receives a Contrace Request message from the
appropriate adjacent neighbor router, it would insert a Reply block
TLV and Reply sub-block TLV(s) of its own to the Request message and
turn the Request into the Reply by changing the Type field of the
fixed header of the Request message from PT_TRACE_REQ to
PT_TRACE_REPLY. The Reply message (see Figure 12) would then be
forwarded back toward the Contrace user in a hop-by-hop manner.
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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
+---------------+---------------+---------------+---------------+
| Version |PT_TRACE_REPLY | PacketLength |
+---------------+---------------+---------------+---------------+
| HopLimit | ReturnCode |Reserved (MBZ) | HeaderLength |
+===============+===============+===============+===============+
| |
+ Request block TLV +
| |
+---------------+---------------+---------------+---------------+
/ . /
/ . /
/ n Report block TLVs /
/ . /
/ . /
+===============+===============+===============+===============+
| T_TRACE | MessageLength |
+---------------+---------------+---------------+---------------+
| T_NAME | Length |
+---------------+---------------+---------------+---------------+
/ Name segment TLVs (name prefix specified by contrace command) /
+---------------+---------------+---------------+---------------+
/ Reply block TLV /
+---------------+---------------+---------------+---------------+
/ Reply sub-block TLV 1 /
+---------------+---------------+---------------+---------------+
/ Reply sub-block TLV 2 /
+---------------+---------------+---------------+---------------+
/ . /
/ . /
+---------------+---------------+---------------+---------------+
/ Reply sub-block TLV k /
+---------------+---------------+---------------+---------------+
Figure 12: Reply message consists of a fixed header, Request block
TLV, Report block TLV(s), Name TLV, and Reply block/sub-block TLV(s)
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Code Type name
============= =====================
0 T_NAME [1]
1 T_PAYLOAD [1]
2 T_KEYIDRESTR [1]
3 T_OBJHASHRESTR [1]
5 T_PAYLDTYPE [1]
6 T_EXPIRY [1]
8 T_TRACE_REPLY
9 - 12 Reserved [1]
%x0FFE T_PAD [1]
%x0FFF T_ORG [1]
%x1000-%x1FFF Reserved [1]
Figure 13: CCNx Message Type Namespace
3.2.1. Reply Block
The Reply block TLV is an envelope for Reply sub-block TLV(s)
(explained in Section 3.2.1.1).
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
+---------------+---------------+---------------+---------------+
| T_TRACE_REPLY | Length |
+---------------+---------------+---------------+---------------+
Figure 14: Reply block TLV (packet payload)
Type: 16 bits
Format of the Value field. For the Report block TLV, the type
value MUST be T_TRACE_REPLY.
Length: 16 bits
Length of Value field in octets. This length is a total length of
Reply sub-block(s).
3.2.1.1. Reply Sub-Block
In addition to the Reply block, a router on the traced path will add
one or multiple Reply sub-blocks followed by the Reply block before
sending the Reply to its neighbor router.
The Reply sub-block is flexible for various purposes. For instance,
operators and developers may want to obtain various characteristics
of content such as content's ownership and copyright, or other cache
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states and conditions. Various information about device or function
(or application) may be also retrieved by the variety of Reply sub-
blocks. In this document, Reply sub-block TLVs for T_TRACE_CONTENT
and T_TRACE_CONTENT_OWNER (Figure 15) and for T_TRACE_GATEWAY
(Figure 16) are defined; other Reply sub-block TLVs are [TBD].
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 |
+---------------+---------------+---------------+---------------+
| Content Size |
+---------------+---------------+---------------+---------------+
| Object Count |
+---------------+---------------+---------------+---------------+
| # Received Interest |
+---------------+---------------+---------------+---------------+
| First Seqnum |
+---------------+---------------+---------------+---------------+
| Last Seqnum |
+---------------+---------------+---------------+---------------+
| Cache Lifetime |
+---------------+---------------+---------------+---------------+
| Remain Cache Lifetime |
+---------------+---------------+---------------+---------------+
| T_NAME | Length |
+---------------+---------------+---------------+---------------+
/ Name segment TLVs (name prefix partially/exactly matched) /
+---------------+---------------+---------------+---------------+
Figure 15: Reply sub-block TLV for T_TRACE_CONTENT and
T_TRACE_CONTENT_OWNER (packet payload)
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 |
+---------------+---------------+---------------+---------------+
| Scheme Name | Reserved (MBZ) |
+---------------+---------------+---------------+---------------+
Figure 16: Reply sub-block TLV for T_TRACE_GATEWAY (packet payload)
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Code Type name
============= ===========================
0 T_TRACE_CONTENT
1 T_TRACE_CONTENT_OWNER
2 T_TRACE_GATEWAY
3 T_TRACE_DEVICE
4 T_TRACE_FUNCTION
%x0FFF T_ORG
%x1000-%x1FFF Reserved (Experimental Use)
Figure 17: Contrace Reply Type Namespace
Type: 16 bits
Format of the Value field. For the Reply sub-block TLV, the type
value MUST be one of the type value defined in the Contrace Reply
Type Namespace (Figure 17). T_TRACE_CONTENT is specified when the
cache information is replied from a caching router.
T_TRACE_CONTENT_OWNER is specified when the content information is
replied from a publisher. T_TRACE_GATEWAY is used to discover a
gateway that has a FIB for the specified scheme name.
Length: 16 bits
Length of Value field in octets.
Scheme Name: 8 bits
The code of the scheme name defined in Figure 9.
Content Size: 32 bits
The total size (MB) of the (cached) content objects. Note that
the maximum size expressed by 32 bit field is 65 GB.
Object Count: 32 bits
The number of the (cached) content objects.
# Received Interest: 32 bits
The number of the received Interest messages to retrieve the
content.
First Seqnum: 32 bits
The first sequential number of the (cached) content objects.
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Last Seqnum: 32 bits
The last sequential number of the (cached) content objects. Above
First Seqnum and this Last Seqnum do not guarantee the
consecutiveness of the cached content objects.
Cache Lifetime: 32 bits
The elapsed time after the oldest content object in the cache is
stored. The Cache Lifetime is a 32-bit NTP timestamp, and the
formula converts from a UNIX timeval to a 32-bit NTP timestamp is
same as that of Section 3.1.2.
Remain Cache Lifetime: 32 bits
The lifetime of a content object, which is removed first among the
cached content objects. The Remain Cache Lifetime is a 32-bit NTP
timestamp.
4. Contrace User Behavior
4.1. Sending Contrace Request
A Contrace user initiates a Contrace Request by sending the Request
message to the adjacent neighbor router(s) of interest. As a typical
example, a Contrace user invokes the contrace command (detailed in
Appendix A) that forms a Request message and sends it to the user's
adjacent neighbor router(s).
When the Contrace user's program initiates a Request message, it MUST
insert the necessary values, the "Request ID" (in the Request block)
and the "Node Identifier" (in the Report block), in the Request and
Report blocks. Contrace user's program MUST also record the Request
ID at the corresponding PIT entry. The Request ID is a unique
identifier for the Contrace Request.
A Contrace Request with a scheme name (e.g., ccnx:/, ndn:/) is used
to discover a router that has the FIB of the specified scheme name.
In other words, a Contrace user can discover gateway(s) that support
different protocols such as CCN and NDN. (Note that defining the way
to interoperate different protocols is [TBD].) A Contrace Request
with a scheme name may be forwarded to upstream routers being far
from the Contrace user (see Section 5.2); therefore, it is
RECOMMENDED that the number of traced routers is limited for the
Request (e.g., contrace command with "-r" option with small hops, and
repeated by incrementing the hop count if needed). It does not
provide other information, e.g., cache information.
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After the Contrace user's program sends the Request message, until
the Reply times out, the Contrace user's program MUST keep the
following information; Request ID and Flags specified in the Request
block, Node Identifier and Request Arrival Time specified in the
Report block, and HopLimit specified in the fixed header.
4.2. Receiving Contrace Reply
A Contrace user's program will receive one or multiple Contrace Reply
messages from the adjacent neighbor router that has previously
received and forwarded the Request message(s). When the program
receives the Reply, it MUST compare the kept Request ID and the
Request ID noted in the Reply. If they do not match, the Reply
message SHOULD be silently discarded.
If the number of the Report blocks in the received Reply is more than
the initial HopLimit value (which was inserted in the original
Request) + 1, the Reply SHOULD be silently ignored.
After the Contrace user has determined that s/he has traced the whole
path or as much as s/he can expect to, s/he might collect statistics
by waiting a timeout. Useful statistics provided by Contrace can be
seen in Section 9.
5. Router Behavior
5.1. Receiving Contrace Request
Upon receiving a Contrace Request message, a router MUST examine
whether the message comes from a valid adjacent neighbor node. If it
is invalid, the Request SHOULD be silently ignored.
When a router receives a Contrace Request message with a scheme name
(e.g., ndn:/), the router checks whether the Request sets both "%x02"
and "%x08" bits in the Flag or not. If not, the router returns a
Reply with the INVALID_REQUEST return code. The router next checks
whether it has the FIB for the specified scheme name. It the router
has the corresponding FIB, it sends the Reply message back to the
Contrace user. For a Request with a scheme name, the router SHOULD
only inform the supported scheme name. See Section 5.3. If the
router does not have the FIB for the specified scheme name but has
the default neighbor router for another scheme name (e.g., FIB entry
for ccnx:/), it forwards the Request to the default neighbor router.
See Section 5.2. If the router does not have the FIB for the
specified scheme name and does not have the default neighbor router
for another scheme name, the router returns the Reply with the
NO_ROUTE return code.
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When a router receives a Request message requesting cache
information, the router retrieves the cache information from its CS.
If the router is the caching router that caches the requested
content, it sends the Reply message. See Section 5.3. Otherwise,
the router forwards the Request message to its upstream router(s).
See Section 5.2.
If a router cannot continue the Request, it MUST put an appropriate
ReturnCode in the Request message, change the Type field value in the
fixed header from PT_TRACE_REQ to PT_TRACE_REPLY, and forward the
Reply message back toward the Contrace user. See Section 7.
5.2. Forwarding Contrace Request
When a router decides to forward a Request message to its upstream
router(s), it MUST insert a Report block having the Request Arrival
Time and Node Identifier to the hop-by-hop TLV header of the Request
message. The router then forwards the Request message upstream
toward the publisher or caching router based on the FIB entry.
When the router forwards the Request message, it MUST record the
Request ID at the corresponding PIT entry. The router can later
decide the PIT entry to correctly forward back the Reply message even
if it receives multiple Reply messages within the same timeout
period. (See below.)
Contrace supports multipath forwarding. The Request messages can be
forwarded to multiple neighbor routers. When the Request messages
forwarded to multiple routers, the different Reply messages will be
forwarded from different routers or publisher. To support this case,
PIT entries initiated by Contrace remain until the configured
Contrace Reply Timeout (Section 8.1) passes. In other words, unlike
the ordinary Interest-Data communications in CCN, the router SHOULD
NOT remove the PIT entry created by the Contrace Request before the
timeout value expires, even if the router receives the Contrace
Reply.
Routers can configure the Contrace Reply Timeout Section 8.1, which
is the allowable timeout value to keep the PIT entry. In order to
avoid DoS attacks (Section 10.5), routers MAY configure the shorter
timeout value than the user-configured Contrace timeout value. If it
is shorter, the Request may be timed out and the Contrace user may
not receive the Reply as expected.
Contrace Requests SHOULD NOT result in PIT aggregation in routers
during the Request message transmission.
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5.3. Sending Contrace Reply
When a router decides to send a Reply message to its downstream
neighbor router or the Contrace user, it MUST insert a Report block
having the Request Arrival Time and Node Identifier to the hop-by-hop
TLV header of the Request message. And then the router MUST insert
the corresponding Reply block and Reply sub-block(s) to the payload
if there is no error. The router does not insert any Reply block/
sub-block if there is an error. The router finally changes the Type
field in the fixed header from PT_TRACE_REQ to PT_TRACE_REPLY and
forwards the message back as the Reply toward the Contrace user in a
hop-by-hop manner.
When a router decides to send the Reply message for the Request for
the specified scheme name as seen in Section 5.1, it forms the Reply
message including a Reply block and a Reply sub-block with the
T_TRACE_GATEWAY type value (Figure 16) and the scheme name
(Figure 9). After the router puts the NO_ERROR return code in the
fixed header, it sends the Reply back toward the Contrace user.
When a router decides to send the Reply message for the Request for
the cache information, it forms the Reply message including a Reply
block and a Reply sub-block with the T_TRACE_CONTENT type value
(Figure 15) and various cache information. After the router puts the
NO_ERROR return code in the fixed header, it sends the Reply back
toward the Contrace user.
5.4. Forwarding Contrace Reply
When the router receives a Contrace Reply whose Request ID matches
the one in the original Contrace Request block TLV from a valid
adjacent neighbor node, it MUST relay the Contrace Reply back to the
Contrace user. If the router does not receive the corresponding
Reply within the [Contrace Reply Timeout] period, then it removes the
corresponding PIT entry and terminates the trace.
Contrace Replies MUST NOT be cached in routers upon the Reply message
transmission.
6. Publisher Behavior
Upon receiving a Contrace Request message, a publisher MUST examine
whether the message comes from a valid adjacent neighbor node. If it
is invalid, the Request SHOULD be silently ignored.
If a publisher cannot accept the Request, it MUST note an appropriate
ReturnCode in the Request message, change the Type field value in the
fixed header from PT_TRACE_REQ to PT_TRACE_REPLY, and forward the
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message as the Reply back to the Contrace user. See Section 7 for
details.
If a publisher accepts the Request forwarded by a valid adjacent
neighbor node, it retrieves the local content information. The Reply
message having a Reply block and Reply sub-block(s) is transmitted
back to the neighbor node that had forwarded the Request message.
7. Contrace Termination
When performing an expanding hop-by-hop trace, it is necessary to
determine when to stop expanding. There are several cases an
intermediate router might return a Reply before a Request reaches the
caching router or the publisher.
7.1. Arriving at Publisher or Gateway
A Contrace Request can be determined to have arrived at the publisher
or gateway.
7.2. Arriving at Router Having Cache
A Contrace Request can be determined to have arrived at the router
having the specified content cache within the specified HopLimit.
7.3. No Route
If the router cannot determine the forwarding paths or neighbor
routers for the specified named prefix, device name, or function, the
router MUST note a ReturnCode of NO_ROUTE in the fixed header of the
message, and forwards the message as the Reply back to the Contrace
user.
7.4. No Information
If the router does not have any information about the specified named
prefix, device name, or function, the router MUST note a ReturnCode
of NO_INFO in the fixed header of the message, and forwards the
message as the Reply back to the Contrace user.
7.5. No Space
If appending the Report block would make the Contrace Request packet
longer than the MTU of the Incoming face, or longer than 1280 bytes
(especially in the situation supporting IPv6 as the payload [3]), the
router MUST note a ReturnCode of NO_SPACE in the fixed header of the
message, and forwards the message as the Reply back to the Contrace
user.
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7.6. Fatal Error
A Contrace Request has encountered a fatal error if the last
ReturnCode in the trace has the 0x80 bit set (see Section 3.1).
7.7. Contrace Reply Timeout
If a Contrace user or a router encounters the Request or Reply
message whose expires its own [Contrace Reply Timeout] value
(Section 8.1), which is used to time out a Contrace Reply such as the
case of Section 7.8.
7.8. Non-Supported Node
Cases will arise in which a router or a publisher along the path does
not support Contrace. In such cases, a Contrace user and routers
that forward the Contrace Request will time out the Contrace request.
7.9. Administratively Prohibited
If Contrace is administratively prohibited, a router or a publisher
rejects the Request message and its downstream router will reply the
Contrace Reply with the ReturnCode of ADMIN_PROHIB.
8. Configurations
8.1. Contrace Reply Timeout
The [Contrace Reply Timeout] value is used to time out a Contrace
Reply. Both Contrace users and routers can configure their own
Contrace Reply Timeout values. Contrace users, for example, can
configure the timeout value by the contrace command. The default
[Contrace Reply Timeout] value is 4 (seconds). Routers may want to
configure the short timeout values because of some security concern,
e.g., Section 10.5. However, the [Contrace Reply Timeout] value
SHOULD NOT be larger than 6 (seconds) and SHOULD NOT be lower than 3
(seconds).
8.2. HopLimit in Fixed Header
If a Contrace user does not specify the HopLimit value in a fixed
header for a Request message as the HopLimit, the HopLimit is set to
32. Note that a Contrace user specifies 0 as the HopLimit, it is an
invalid Request and discarded.
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8.3. Access Control
A router MAY configure the valid or invalid networks to enable an
access control. The access control can be defined per named prefix,
such as "who can retrieve which named prefix". See Section 10.2.
9. Diagnosis and Analysis
9.1. Number of Hops
A Contrace Request message is forwarded in a hop-by-hop manner and
each forwarding router appended its own Report block. We can then
verify the number of hops to reach the content forwarder or the
publisher.
9.2. Caching Router and Gateway Identification
It is possible to identify the caching routers or a gateway in the
path from the Contrace user to the content forwarder, while some
routers may hide their identifier (with all-zeros) in the Report
blocks (Section 10.1).
9.3. TTL or Hop Limit
By taking the HopLimit from the content forwarder and forwarding TTL
threshold over all hops, it is possible to discover the TTL or hop
limit required for the content forwarder to reach the Contrace user.
9.4. Time Delay
If the routers have synchronized clocks, it is possible to estimate
the RTT between Contrace user and successive hops. If all the
routers on the path do not have synchronized clocks, the Contrace
user can estimate the RTT between Contrace user and content
forwarder. Note that this delay includes control processing
overhead, so is not necessarily indicative of the delay that data
traffic would experience.
9.5. Path Stretch
By getting the path stretch "d / P", where "d" is the hop count of
the data and "P" is the hop count from the consumer to the publisher,
we can measure the improvement in path stretch in various cases, such
as different caching and routing algorithms. We can then facilitate
investigation of the performance of the protocol.
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9.6. Cache Hit Probability
Contrace can show the number of received interests per cache or chunk
on a router. By this, Contrace measures the content popularity
(i.e., the number of accesses for each content/cache), and you can
investigate the routing/caching strategy in networks.
10. Security Considerations
This section addresses some of the security considerations.
10.1. Policy-Based Information Provisioning for Request
Although Contrace gives excellent troubleshooting cues, some network
administrators or operators may not want to disclose everything about
their network to the public, or may wish to securely transmit private
information to specific members of their networks. Contrace provides
policy-based information provisioning allowing network administrators
to specify their response policy for each router.
The access policy regarding "who is allowed to retrieve what kind of
information" can be defined for each router. The permission, whether
(1) All (all cache information is disclosed), (2) Partial (cache
information with the particular name prefix can (or cannot) be
disclosed), or (3) Deny (no cache information is disclosed), is
defined at routers.
On the other hand, we entail that each router does not disrupt
forwarding Contrace Request and Reply messages. When a Request
message is received, the router SHOULD insert Report block. Here,
according to the policy configuration, the Node Identifier field in
the Report block MAY be null (i.e., all-zeros), but the Request
Arrival Time field SHOULD NOT be null. At last, the router SHOULD
forward the Request message to the upstream router toward the content
forwarder if no fatal error occurs.
10.2. Filtering of Contrace Users Located in Invalid Networks
A router MAY support an access control mechanism to filter out
Requests from invalid Contrace users. For it, invalid networks (or
domains) could, for example, be configured via a list of allowed/
disallowed networks (as seen in Section 8.3). If a Request is
received from the disallowed network (according to the Node
Identifier in the Request block), the Request SHOULD NOT be processed
and the Reply with the ReturnCode of INFO_HIDDEN may be used to note
that. The router MAY, however, perform rate limited logging of such
events.
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10.3. Topology Discovery
Contrace can be used to discover actively-used topologies. If a
network topology is a secret, Contrace Requests may be restricted at
the border of the domain, using the ADMIN_PROHIB return code.
10.4. Characteristics of Content
Contrace can be used to discover what publishers are sending to what
kinds of contents. If this information is a secret, Contrace
Requests may be restricted at the border of the domain, using the
ADMIN_PROHIB return code.
10.5. Shortening Contrace Reply Timeout
Routers can configure the Contrace Reply Timeout Section 8.1, which
is the allowable timeout value to keep the PIT entry. In order to
avoid DoS attacks, routers MAY configure the shorter timeout value
than the user-configured Contrace timeout value. If it is shorter,
the Request may be timed out and the Contrace user may not receive
the Reply as expected.
10.6. Limiting Request Rates
A router may limit Contrace Requests by ignoring some of the
consecutive messages. The router MAY randomly ignore the received
messages to minimize the processing overhead, i.e., to keep fairness
in processing requests, or prevent traffic amplification. No error
is returned. The rate limit is left to the router's implementation.
10.7. Limiting Reply Rates
Contrace supporting multipath forwarding may result in one Request
returning multiple Reply messages. In order to prevent abuse, the
routers in the traced path MAY need to rate-limit the Replies. No
error is returned. The rate limit function is left to the router's
implementation.
10.8. Adjacency Verification
Contrace Request and Reply messages MUST be forwarded by adjacent
neighbor nodes or routers. Forwarding Contrace messages given from
non-adjacent neighbor nodes/routers MUST be prohibited. Such invalid
messages SHOULD be silently discarded. Note that defining the secure
way to verify the adjacency cannot rely on the way specified in CCNx
message format or semantics, and hence an new TLV for adjacency
verification using hop-by-hop TLV header will be [TBD].
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11. References
11.1. Normative References
[1] Mosko, M., Solis, I., and C. Wood, "CCNx Messages in TLV
Format", draft-irtf-icnrg-ccnxmessages-03 (work in
progress), June 2016.
[2] Bradner, S., "Key words for use in RFCs to indicate
requirement levels", RFC 2119, March 1997.
[3] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
11.2. Informative References
[4] Asaeda, H., Matsuzono, K., and T. Turletti, "Contrace: A
Tool for Measuring and Tracing Content-Centric Networks",
IEEE Communications Magazine, Vol.53, No.3, pp.182-188,
March 2015.
[5] Malkin, G., "Traceroute Using an IP Option", RFC 1393,
January 1993.
[6] Asaeda, H., Mayer, K., and W. Lee, "Mtrace Version 2:
Traceroute Facility for IP Multicast", draft-ietf-mboned-
mtrace-v2-16 (work in progress), October 2016.
[7] Gill, V., Heasley, J., Meyer, D., Savola, P., and C.
Pignataro, "The Generalized TTL Security Mechanism
(GTSM)", RFC 5082, October 2007.
Appendix A. Contrace Command and Options
The contrace command enables the Contrace user to investigate the
forwarding path based on the name prefix of the content (e.g.,
ccnx:/news/today), device name, and function (or application) name.
The name prefix, device name, and function name (or application name)
are mandatory but exclusive options; that is, only one of them should
be used with the contrace command at once.
The usage of contrace command is as follows:
Usage: contrace [-p] [-g] [-n] [-o] [-r hop_count] [-s hop_count] [-w
wait_time] name_prefix; or,
Usage: contrace [-r hop_count] [-s hop_count] [-w wait_time]
device_name | function_name (or application_name)
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name_prefix
Name prefix of the content (e.g., ccnx:/news/today) the Contrace
user wants to trace. If the Contrace user specifies only a scheme
name, e.g., "ccnx:/", s/he must specify "-g" option (i.e.,
contrace -g ccnx:/). In that case, the Contrace user discovers
the router having the FIB of the specified scheme name and the RTT
between Contrace user and the router. The -p option allows a
partial match for the name prefix; otherwise, an exact match is
required.
device_name
Device name (e.g., ccnx:/%device/server-A, ccnx:/%device/sensor-
123) the Contrace user wants to trace. Here, we assume the
contrace command with the "%device" prefix indicates the trace
request for specified device/server/node, but defining the syntax
of device name specification is [TBD].
function_name (or application_name)
Function name (e.g., ccnx:/%function/firewall,
ccnx:/%function/transcoding/mpeg2-h.264) or application name
(e.g., ccnx:/%application/mplayer) the Contrace user wants to
trace. Here, we assume the contrace command with the "%function"
or "%application" prefix indicates the trace request for specified
function or application, but defining the syntax of function or
application name specification is [TBD].
g option
This option can be specified if a Contrace user wants to discover
a gateway that supports specified scheme name and may have
multiple FIBs. When a Contrace user specifies only a scheme name,
e.g., "ccnx:/", this option must be specified and other content
name prefix is ignored.
n option
This option can be specified if a Contrace user only needs the
routing path information to the specified content/cache and RTT
between Contrace user and content forwarder (i.e., cache
information is not given).
o option
This option can be specified if a Contrace user needs to trace the
path to the content publisher. If this option is specified, each
router along the path to the publisher only forwards the Request
message; it does not insert each Report block and does not send
Reply even if it caches the specified content. The publisher (who
has the complete set of content and is not a caching router)
replies the Reply message. Specifying only a scheme name is not
allowed with this option.
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r option
Number of traced routers. If the Contrace user specifies this
option, only the specified number of hops from the Contrace user
trace the Request; each router inserts its own Report block and
forwards the Request message to the upstream router(s), and the
last router stops the trace and sends the Reply message back to
the Contrace user. This value is set in the "HopLimit" field
located in the fixed header of the Request. For example, when the
Contrace user invokes the Contrace command with this option such
as "-r 3", the two upstream routers along the path append their
Report blocks in the Request message, and the next (and last)
router sends back the Reply message. If there is a caching router
within the hop count along the path, the caching router sends back
the Reply message and terminates the trace request. If the last
router does not have the corresponding cache, it replies the Reply
message with NO_INFO return code (described in Section 3.1) with
no Reply block TLV inserted. The Request messages are terminated
at publishers; therefore, although the maximum value for this
option a Contrace user can specify is 255, the Request messages
should be in general reached at the publisher within significantly
lower than 255 hops.
s option
Number of skipped routers. If the Contrace user specifies this
option, the number of hops from the Contrace user simply forward
the Contrace Request messages without adding its own Report block
and without replying the Request, and the next upstream router
starts the trace. This value is set in the "SkipHopCount" field
located in the Request block TLV. For example, when the Contrace
user invokes the Contrace command with this option such as "-s 3",
the three upstream routers along the path only forwards the
Request message, but does not append their Report blocks in the
hop-by-hop headers and does not send the Reply messages even
though they have the corresponding cache. The Request messages
are terminated at publishers; therefore, although the maximum
value for this option a Contrace user can specify is 255, if the
Request messages reaches the publisher, the publisher silently
discards the Request message and the request will be timed out.
w option
This option defines the Contrace timeout value (in seconds) that
the Contrace user will wait for the Reply. After the timeout, the
Contrace user terminates the Request and silently discards the
Reply message even if s/he receives the Reply. Note that routers
along the path can configure the Contrace Reply Timeout
Section 8.1, which is the allowable timeout value to keep the PIT
entry. In order to avoid DoS attacks Section 10, routers MAY
configure the shorter timeout value than the user-configured
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Internet-Draft Contrace November 2016
Contrace timeout value. If it is shorter, the Request may be
timed out and the Contrace user may not receive the Reply as
expected.
Authors' Addresses
Hitoshi Asaeda
National Institute of Information and Communications Technology
4-2-1 Nukui-Kitamachi
Koganei, Tokyo 184-8795
Japan
Email: asaeda@nict.go.jp
Xun Shao
National Institute of Information and Communications Technology
4-2-1 Nukui-Kitamachi
Koganei, Tokyo 184-8795
Japan
Email: x-shao@nict.go.jp
Thierry Turletti
Inria
2004 Route des Lucioles
Sophia Antipolis 06902
France
Email: thierry.turletti@inria.fr
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