Internet DRAFT - draft-asaeda-icnrg-ccninfo
draft-asaeda-icnrg-ccninfo
ICN Research Group H. Asaeda
Internet-Draft NICT
Intended status: Experimental X. Shao
Expires: January 1, 2019 Kitami Institute of Technology
June 30, 2018
CCNinfo: Discovering Content and Network Information in Content-Centric
Networks
draft-asaeda-icnrg-ccninfo-01
Abstract
This document describes a mechanism named "CCNinfo" that discovers
information about the network topology and in-network cache in
Content-Centric Networks (CCN). CCNinfo investigates: 1) the CCN
routing 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.
In addition, it discovers a gateway that supports different protocols
such as CCN and Named-Data Networks (NDN).
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on January 1, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 6
3. CCNinfo 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. CCNinfo User Behavior . . . . . . . . . . . . . . . . . . . . 19
4.1. Sending CCNinfo Request . . . . . . . . . . . . . . . . . 19
4.1.1. Gateway Discovery . . . . . . . . . . . . . . . . . . 19
4.1.2. Routing Path Information . . . . . . . . . . . . . . 20
4.1.3. In-Network Cache Information . . . . . . . . . . . . 20
4.2. Receiving CCNinfo Reply . . . . . . . . . . . . . . . . . 20
5. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 21
5.1. Receiving CCNinfo Request . . . . . . . . . . . . . . . . 21
5.1.1. Request Packet Verification . . . . . . . . . . . . . 21
5.1.2. Request Normal Processing . . . . . . . . . . . . . . 21
5.2. Forwarding CCNinfo Request . . . . . . . . . . . . . . . 22
5.3. Sending CCNinfo Reply . . . . . . . . . . . . . . . . . . 23
5.4. Forwarding CCNinfo Reply . . . . . . . . . . . . . . . . 24
6. Publisher Behavior . . . . . . . . . . . . . . . . . . . . . 24
7. CCNinfo Termination . . . . . . . . . . . . . . . . . . . . . 25
7.1. Arriving at Publisher or Gateway . . . . . . . . . . . . 25
7.2. Arriving at Router Having Cache . . . . . . . . . . . . . 25
7.3. No Route . . . . . . . . . . . . . . . . . . . . . . . . 25
7.4. No Information . . . . . . . . . . . . . . . . . . . . . 25
7.5. No Space . . . . . . . . . . . . . . . . . . . . . . . . 25
7.6. Fatal Error . . . . . . . . . . . . . . . . . . . . . . . 25
7.7. CCNinfo Reply Timeout . . . . . . . . . . . . . . . . . . 26
7.8. Non-Supported Node . . . . . . . . . . . . . . . . . . . 26
7.9. Administratively Prohibited . . . . . . . . . . . . . . . 26
8. Configurations . . . . . . . . . . . . . . . . . . . . . . . 26
8.1. CCNinfo Reply Timeout . . . . . . . . . . . . . . . . . . 26
8.2. HopLimit in Fixed Header . . . . . . . . . . . . . . . . 26
8.3. Access Control . . . . . . . . . . . . . . . . . . . . . 26
9. Diagnosis and Analysis . . . . . . . . . . . . . . . . . . . 26
9.1. Number of Hops . . . . . . . . . . . . . . . . . . . . . 26
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9.2. Caching Router and Gateway Identification . . . . . . . . 27
9.3. TTL or Hop Limit . . . . . . . . . . . . . . . . . . . . 27
9.4. Time Delay . . . . . . . . . . . . . . . . . . . . . . . 27
9.5. Path Stretch . . . . . . . . . . . . . . . . . . . . . . 27
9.6. Cache Hit Probability . . . . . . . . . . . . . . . . . . 27
10. Security Considerations . . . . . . . . . . . . . . . . . . . 27
10.1. Policy-Based Information Provisioning for Request . . . 27
10.2. Filtering of CCNinfo Users Located in Invalid Networks . 28
10.3. Topology Discovery . . . . . . . . . . . . . . . . . . . 28
10.4. Characteristics of Content . . . . . . . . . . . . . . . 29
10.5. Longer or Shorter CCNinfo Reply Timeout . . . . . . . . 29
10.6. Limiting Request Rates . . . . . . . . . . . . . . . . . 29
10.7. Limiting Reply Rates . . . . . . . . . . . . . . . . . . 29
10.8. Adjacency Verification . . . . . . . . . . . . . . . . . 29
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 30
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 30
12.1. Normative References . . . . . . . . . . . . . . . . . . 30
12.2. Informative References . . . . . . . . . . . . . . . . . 30
Appendix A. ccninfo Command and Options . . . . . . . . . . . . 30
Appendix B. Change History . . . . . . . . . . . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33
1. Introduction
In Content-Centric Networks (CCN), 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 also enables receivers to retrieve
content from an in-network cache.
In CCN, 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
routing path information per name prefix for troubleshooting or
investigating the network conditions.
Traceroute [5] is a useful tool for discovering 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. Moreover, such
IP-based network tool does not obtain the states of the in-network
cache to be discovered.
This document describes the specification of "CCNinfo", an active
networking tool for discovering the path and content caching
information in CCN. CCNinfo potentially discovers devices and
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functions/applications in CCN. CCNinfo is designed based on the work
previously published in [4].
CCNinfo can be implemented with the ccninfo user command and the
forwarding function implementation on a content forwarder (e.g.,
router or publisher). The CCNinfo user (e.g., consumer) invokes the
ccninfo command (described in Appendix A) with the name prefix of the
content, the device name, or the function (or application) name. The
ccninfo command initiates the "Request" message (described in
Section 3.1). The Request message, for example, obtains routing 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, Request and Reply
messages, are encoded in the CCNx TLV format [1].
In this way, the Request message is forwarded by routers toward the
content publisher, and the 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 "Reply" message
(described in Section 3.2) and sends it to the downstream neighbor
router. The Reply message is forwarded back toward the 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].
CCNinfo 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 CCNinfo 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
+--------+ +--------+ +--------+ +--------+ +---------+
| CCNinfo|----| 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.
CCNinfo 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 |
+--------+ +--------+ +--------+ +--------+ +---------+
| CCNinfo|----| 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 CCNinfo user
receives two Reply messages: one from the publisher and the other
from the caching router.
CCNinfo 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 routing path information per name prefix.
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In addition, CCNinfo 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, CCNinfo 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 CCNinfo 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 CCNinfo
implementations.
2.1. Definitions
Since CCNinfo 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 "ccn:/" 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 has multiple FIBs for
different protocols and establishes the connections with different
neighbor routers for each protocol.
Node
It is a router, gateway, publisher, or consumer.
Content forwarder
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It is either a caching router or a publisher that holds the cache
(or content) and forwards it to consumers.
CCNinfo user
It is a node that invokes the ccninfo command and initiates the
CCNinfo 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 Request messages are received.
3. CCNinfo Message Formats
CCNinfo 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_REQUEST
and PT_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 value in the fixed header
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from PT_REQUEST to PT_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_REQUEST
5 PT_REPLY
Figure 4: Packet Type Namespace
The CCNinfo Request and Reply messages 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_DISCOVERY (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_DISCOVERY
Figure 5: Top-Level Type Namespace
3.1. Request Message
When a CCNinfo user initiates a discovery request (e.g., by ccninfo
command described in Appendix A), a CCNinfo Request message is
created and forwarded to its upstream router through the Incoming
face(s) determined by its FIB.
The Request message format 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_DISCOVERY (Figure 5). The Type value for the Report
message is PT_REQUEST.
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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 | PacketType | PacketLength |
+---------------+---------------+---------------+---------------+
| HopLimit | ReturnCode |Reserved (MBZ) | HeaderLength |
+===============+===============+===============+===============+
| |
+ Request block TLV +
| |
+---------------+---------------+---------------+---------------+
/ Report block TLV 1 /
+---------------+---------------+---------------+---------------+
/ Report block TLV 2 /
+---------------+---------------+---------------+---------------+
/ . /
/ . /
+---------------+---------------+---------------+---------------+
/ Report block TLV n /
+===============+===============+===============+===============+
| T_DISCOVERY | MessageLength |
+---------------+---------------+---------------+---------------+
| T_NAME | Length |
+---------------+---------------+---------------+---------------+
/ Name segment TLVs (name prefix specified by ccninfo command) /
+---------------+---------------+---------------+---------------+
Figure 6: Request message consists of a fixed header, Request block
TLV, Report block TLV(s), and Name TLV
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 CCNinfo Request arrived on an interface
to which this router would not forward for
the specified name/function toward the
publisher.
0x02 INVALID_REQUEST Invalid CCNinfo Request is received.
0x03 NO_ROUTE This router has no route for the name 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 NO_GATAWAY CCNinfo Request arrived on a non-gateway
router.
0x07 INFO_HIDDEN Information is hidden from this discovery
because of some policy.
0x0E ADMIN_PROHIB CCNinfo 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 CCNinfo 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).
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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_DISC_REQ | Length |
+---------------+---------------+-------------------------------+
| SchemeName | SkipHopCount | Reserved (MBZ) |
+---------------+---------------+-------------------------------+
| Request ID | Flags |
+---------------+---------------+-------------------------------+
Figure 7: Request block TLV (hop-by-hop header)
Code Type name
============= =====================
1 T_INTLIFE [1]
2 T_CACHETIME [1]
3 T_MSGHASH [1]
4 - 7 Reserved [1]
8 T_DISC_REQ
9 T_DISC_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_DISC_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 ccn:/
1 ndn:/
%x02-%FF Not assigned
Figure 9: Scheme Names
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SkipHopCount: 8 bits
Number of skipped routers. This value MUST be lower than the
value of HopLimit at the fixed header.
Request ID: 16 bits
This field is used as a unique identifier for this CCNinfo Request
so that duplicate or delayed Reply messages can be detected.
Flags: 16 bits
The discovery conditions specified as the ccninfo command options
(described in Appendix A) are transferred in the Flags field. The
discovery 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 Parallel request. Request to multiple upstream
routers simultaneously (name_prefix, device_name,
and function_name)
%x16 Discovery of gateway supporting specified scheme
name (name_prefix, device_name, and function_name)
%x32 Function's or application's version number retrieval
(function_name)
%x64-%x32768 Not assigned
Figure 10: Codes and types specified in Flags field
3.1.2. Report Block
A CCNinfo 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_DISC_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_DISC_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 CCNinfo 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 CCNinfo does not require all the routers on the path to
have synchronized clocks in order to measure one-way latency.
Node Identifier: variable length
This field specifies the CCNinfo user or the router identifier
(e.g., IPv4 address) of the Incoming face on which packets from
the publisher are expected to arrive, or all-zeros if unknown or
unnumbered. Since we may not always rely on the IP addressing
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architecture, it would be necessary to define the identifier
uniqueness (e.g., by specifying the protocol family) for this
field. However, defining such uniqueness is out of scope of this
document. Potentially, this field may be defined as a new TLV,
which might be defined in the document for the CCNx TLV format[1].
3.2. Reply Message
When a content forwarder receives a CCNinfo 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_REQUEST to PT_REPLY. The
Reply message (see Figure 12) would then be forwarded back toward the
CCNinfo 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 | PacketType | PacketLength |
+---------------+---------------+---------------+---------------+
| HopLimit | ReturnCode |Reserved (MBZ) | HeaderLength |
+===============+===============+===============+===============+
| |
+ Request block TLV +
| |
+---------------+---------------+---------------+---------------+
/ . /
/ . /
/ n Report block TLVs /
/ . /
/ . /
+===============+===============+===============+===============+
| T_DISCOVERY | MessageLength |
+---------------+---------------+---------------+---------------+
| T_NAME | Length |
+---------------+---------------+---------------+---------------+
/ Name segment TLVs (name prefix specified by ccninfo 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]
7 T_DISC_REPLY
8 - 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_DISC_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_DISC_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_DISC_CONTENT
and T_DISC_CONTENT_OWNER (Figure 15) and for T_DISC_GATEWAY
(Figure 16) are defined; other Reply sub-block TLVs will be defined
in separate document(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
+---------------+---------------+---------------+---------------+
| 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_DISC_CONTENT and
T_DISC_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_DISC_GATEWAY (packet payload)
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Code Type name
============= ===========================
0 T_DISC_CONTENT
1 T_DISC_CONTENT_OWNER
2 T_DISC_GATEWAY
3 T_DISC_DEVICE
4 T_DISC_FUNCTION
%x0FFF T_ORG
%x1000-%x1FFF Reserved (Experimental Use)
Figure 17: CCNinfo 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 CCNinfo Reply
Type Namespace (Figure 17). T_DISC_CONTENT is specified when the
cache information is replied from a caching router.
T_DISC_CONTENT_OWNER is specified when the content information is
replied from a publisher. T_DISC_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. CCNinfo User Behavior
4.1. Sending CCNinfo Request
A CCNinfo user initiates a CCNinfo Request by sending the Request
message to the adjacent neighbor router(s) of interest. As a typical
example, a CCNinfo user invokes the ccninfo command (detailed in
Appendix A) that forms a Request message and sends it to the user's
adjacent neighbor router(s).
When the CCNinfo 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. CCNinfo user's program MUST also record the Request
ID at the corresponding PIT entry. The Request ID is a unique
identifier for the CCNinfo Request.
After the CCNinfo user's program sends the Request message, until the
Reply times out, the CCNinfo 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.
4.1.1. Gateway Discovery
A CCNinfo Request can be used for gateway discovery; if a CCNinfo
user invokes a CCNinfo Request with a scheme name (e.g., ccn:/ or
ndn:/) and the "gateway discovery" flag value (i.e., "%x16" bit as
seen in Figure 10), s/he could potentially discover a gateway that
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supports different protocols such as CCN and NDN. The CCNinfo
Request for gateway discovery only indicates the routing path
information (see Section 4.1.2) and the scheme name whether the
router is a gateway or not; it does not provide other information,
e.g., cache information.
4.1.2. Routing Path Information
A CCNinfo user can send a CCNinfo Request for investigating routing
path information for the specified named content. By the Request,
the legitimate user can obtain; 1) identifiers (e.g., IP addresses)
of intermediate routers, 2) identifier of content forwarder, 3)
number of hops between content forwarder and consumer, and 4) RTT
between content forwarder and consumer, per name prefix. This
CCNinfo Request is terminated when it reaches the content forwarder.
The ccninfo command enables user to obtain both the routing path
information and in-network cache information (see below) in a same
time.
4.1.3. In-Network Cache Information
A CCNinfo user can send a CCNinfo Request for investigating in-
network cache information. By this Request, the legitimate user can
obtain; 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, for Content Store (CS) in the content forwarder. This CCNinfo
Request is terminated when it reaches the content forwarder.
4.2. Receiving CCNinfo Reply
A CCNinfo user's program will receive one or multiple CCNinfo 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 CCNinfo 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 CCNinfo can be
seen in Section 9.
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5. Router Behavior
5.1. Receiving CCNinfo Request
5.1.1. Request Packet Verification
Upon receiving a CCNinfo Request message, a router MUST examine
whether the message comes from a valid adjacent neighbor node. If it
is invalid, the Request MUST be silently ignored. The router next
examines the value of the "HopLimit" in the fixed header and the
value of the "SkipHopCount" in the Request block (Figure 7). If
SkipHopCount value is equal or more than the HopLimit value, the
Request MUST be silently ignored.
5.1.2. Request Normal Processing
When a router receives a CCNinfo Request message, it performs the
following steps.
1. HopLimit and SkipHopCount are counters that are decremented with
each hop. The router terminates the CCNinfo Request when the
HopLimit value becomes zero. Until the SkipHopCount value
becomes zero, the router forwards the CCNinfo Request messages to
the upstream router(s) (if it knows) without adding its own
Report block and without replying the Request. If the router
does not know the upstream router(s), without depending on the
SkipHopCount value, it replies the CCNinfo Reply message with
NO_ROUTE return code.
2. The router examines the Flags field of the Request block of
received CCNinfo Request. If the flag value indicates "%x00" or
"%x01" bit (as seen in Figure 10) for "cache information
discovery", the router examines its FIB and CS. If the router
caches the specified content, it inserts own Report block to the
message and sends the Reply message with own Reply block and sub-
block. If the router does not cache the specified content but
knows the neighbor router(s) for the specified name prefix, it
inserts own Report block and forwards the Request to the upstream
neighbor(s). If the router does not cache the specified content
and does not know the upstream neighbor router(s) for the
specified name prefix, it replies the CCNinfo Reply message with
NO_ROUTE return code.
3. If the flag value indicates "%x02" bit for "routing path
information discovery", the router examines its FIB and CS. If
the router caches the specified content, it inserts own Report
block to the message and sends the Reply message with own Reply
block. The router does not insert any Reply sub-block here. If
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the router does not cache the specified content but knows the
neighbor router(s) for the specified name prefix, it inserts own
Report block and forwards the Request to the upstream
neighbor(s). If the router does not cache the specified content
and does not know the upstream neighbor router(s) for the
specified name prefix, it replies the CCNinfo Reply message with
NO_ROUTE return code.
4. If the flag value indicates "%x04" bit for "publisher discovery",
the node receiving the Request message examines whether it owns
the requested content as the publisher. If it is the publisher,
it sends the Reply message with own Report block and sub-block.
If the node is not the publisher but know the upstream neighbor
router(s) for the specified name prefix, it adds the own Report
block and forwards the Request to the neighbor(s). If the node
is not the publisher and does not know the upstream neighbor
router(s) for the specified name prefix, it replies the CCNinfo
Reply message with NO_ROUTE return code.
5. When a router receives a CCNinfo Request in which the "gateway
discovery" flag (i.e., "%x16") is set in the Flags field and a
scheme name is specified, the router examines whether it has the
FIB for the specified scheme name and the connections with the
neighbor router(s) for the scheme protocol. If the router is the
gateway, it sends the Reply message back toward the CCNinfo user.
If the router does not have the FIB for the specified scheme name
or does not connect to any neighbor router for the specified
scheme name, the router returns the Reply with NO_GATEWAY return
code.
5.2. Forwarding CCNinfo Request
When a router decides to forward a Request message with its Report
block to its upstream router(s), it specifies the Request Arrival
Time and Node Identifier in the Report block 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.)
CCNinfo supports multipath forwarding. The Request messages can be
forwarded to multiple neighbor routers. Some router may have
strategy for multipath forwarding; when it sends Interest messages to
multiple neighbor routers, it may delay or prioritize to send the
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message to the upstream routers. The CCNinfo Request, as the
default, complies with such strategy; a CCNinfo user could trace the
actual forwarding path based on the strategy. On the other hand,
there may be the case that a CCNinfo user wants to discover all
potential forwarding paths based on routers' FIBs. If a CCNinfo user
invokes a CCNinfo Request with the parallel request flag (i.e.,
"%x08" bit as seen in Figure 10), the forwarding strategy will be
ignored and the router sends Requests to multiple upstream routers
simultaneously, and the CCNinfo user could trace the all potential
forwarding paths. Note that this flag may be ignored according to
the router's policy.
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 CCNinfo
remain until the configured CCNinfo 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 CCNinfo Request until the timeout value expires.
CCNinfo Requests SHOULD NOT result in PIT aggregation in routers
during the Request message transmission.
5.3. Sending CCNinfo Reply
When a router decides to send a Reply message to its downstream
neighbor router or the CCNinfo user with NO_ERROR return code, it
inserts 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 inserts the corresponding Reply block and Reply sub-
block to the payload. 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_REQUEST to PT_REPLY and forwards
the message back as the Reply toward the CCNinfo user in a hop-by-hop
manner.
When a router decides to send the Reply message for the Request for
the cache or routing path information discovery, it forms the Reply
message including a Reply block and a Reply sub-block with the
T_DISC_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 CCNinfo user.
When a router decides to send the Reply message for the Request for
the publisher discovery, it forms the Reply message including a Reply
block and a Reply sub-block with the T_DISC_CONTENT_OWNER type value
(Figure 15) and various cache information. After the router puts the
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NO_ERROR return code in the fixed header, it sends the Reply back
toward the CCNinfo user.
When a router decides to send the Reply message for the Request for
the gateway discovery, it forms the Reply message including a Reply
block and a Reply sub-block with the T_DISC_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 CCNinfo user.
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_REQUEST to PT_REPLY, and forward the Reply
message back toward the CCNinfo user, to terminate the request. See
Section 7.
5.4. Forwarding CCNinfo Reply
When a router receives a CCNinfo Reply whose Request ID matches the
one in the original CCNinfo Request block TLV from a valid adjacent
neighbor node, it MUST relay the CCNinfo Reply back to the CCNinfo
user. If the router does not receive the corresponding Reply within
the [CCNinfo Reply Timeout] period, then it removes the corresponding
PIT entry and terminates the trace.
CCNinfo Replies MUST NOT be cached in routers upon the Reply message
transmission.
6. Publisher Behavior
Upon receiving a CCNinfo 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 will note an appropriate
ReturnCode in the Request message, change the Type field value in the
fixed header from PT_REQUEST to PT_REPLY, and forward the message as
the Reply back to the CCNinfo 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 is transmitted back
to the neighbor node that had forwarded the Request message.
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7. CCNinfo 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 CCNinfo Request can be determined to have arrived at the publisher
or gateway.
7.2. Arriving at Router Having Cache
A CCNinfo 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 routing paths or neighbor routers
for the specified name prefix, device name, or function within the
specified HopLimit, 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 CCNinfo user.
7.4. No Information
If the router does not have any information about the specified name
prefix, device name, or function within the specified HopLimit, 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 CCNinfo
user.
7.5. No Space
If appending the Report block would make the CCNinfo 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 CCNinfo
user.
7.6. Fatal Error
A CCNinfo Request has encountered a fatal error if the last
ReturnCode in the trace has the 0x80 bit set (see Section 3.1).
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7.7. CCNinfo Reply Timeout
If a router receives the Request or Reply message that expires its
own [CCNinfo Reply Timeout] value (Section 8.1), the router will
discard the Request or Reply message.
7.8. Non-Supported Node
Cases will arise in which a router or a publisher along the path does
not support CCNinfo. In such cases, a CCNinfo user and routers that
forward the CCNinfo Request will time out the CCNinfo request.
7.9. Administratively Prohibited
If CCNinfo is administratively prohibited, a router or a publisher
rejects the Request message, and the router or the publisher, or its
downstream router will reply the CCNinfo Reply with the ReturnCode of
ADMIN_PROHIB.
8. Configurations
8.1. CCNinfo Reply Timeout
The [CCNinfo Reply Timeout] value is used to time out a CCNinfo
Reply. The value for a router can be statically configured by the
router's administrators/operators. The default value is 4 (seconds).
The [CCNinfo Reply Timeout] value SHOULD NOT be larger than 5
(seconds) and SHOULD NOT be lower than 2 (seconds).
8.2. HopLimit in Fixed Header
If a CCNinfo 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 0 HopLimit is an invalid Request and hence discarded.
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 name prefix,
such as "who can retrieve which name prefix". See Section 10.2.
9. Diagnosis and Analysis
9.1. Number of Hops
A CCNinfo Request message is forwarded in a hop-by-hop manner and
each forwarding router appended its own Report block. We can then
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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 CCNinfo 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 CCNinfo user.
9.4. Time Delay
If the routers have synchronized clocks, it is possible to estimate
propagation and queuing delay from the differences between the
timestamps at successive hops. However, this delay includes control
processing overhead, so is not necessarily indicative of the delay
that data traffic would experience.
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.
9.6. Cache Hit Probability
CCNinfo can show the number of received interests per cache or chunk
on a router. By this, CCNinfo 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 CCNinfo 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
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information to specific members of their networks. CCNinfo 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" and/or "what
kind of information" can be defined for each router. For the former
access policy, routers having the specified content can examine the
signature enclosed in the Request message and decide whether they
should notify the content information in the Reply or not. If the
routers decide to not notify the content information, they reply the
CCNinfo Reply with the ReturnCode of ADMIN_PROHIB without appending
any Reply (sub-)block TLV. For the latter policy, 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 CCNinfo 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 CCNinfo Users Located in Invalid Networks
A router MAY support an access control mechanism to filter out
Requests from invalid CCNinfo 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.
10.3. Topology Discovery
CCNinfo can be used to discover actively-used topologies. If a
network topology is a secret, CCNinfo Requests may be restricted at
the border of the domain, using the ADMIN_PROHIB return code.
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10.4. Characteristics of Content
CCNinfo can be used to discover what publishers are sending to what
kinds of contents. If this information is a secret, CCNinfo Requests
may be restricted at the border of the domain, using the ADMIN_PROHIB
return code.
10.5. Longer or Shorter CCNinfo Reply Timeout
Routers can configure the CCNinfo Reply Timeout (Section 8.1), which
is the allowable timeout value to keep the PIT entry. If routers
configure the longer timeout value, there may be an attractive attack
vector against PIT memory. Moreover, especially when the parallel
request option (Section 5.2) is specified for the CCNinfo Request, a
number of Reply messages may come back and cause a response storm.
(See Section 10.7 for rate limiting to avoid the storm). In order to
avoid DoS attacks, routers may configure the shorter timeout value
than the user-configured CCNinfo timeout value. However, if it is
too short, the Request may be timed out and the CCNinfo user does not
receive the all Replies and only retrieves the partial path
information (i.e., information about part of the tree).
There may be the way to allow for incremental exploration (i.e., to
explore the part of the tree the previous operation did not explore),
whereas discussing such mechanism is out of scope of this document.
10.6. Limiting Request Rates
A router may limit CCNinfo 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
CCNinfo 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
CCNinfo Request and Reply messages MUST be forwarded by adjacent
neighbor nodes or routers. Forwarding CCNinfo messages given from
non-adjacent neighbor nodes/routers MUST be prohibited. Such invalid
messages SHOULD be silently discarded. Note that defining the secure
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way to verify the adjacency cannot rely on the way specified in CCNx
message format or semantics. An adjacency verification mechanism and
the corresponding TLV for adjacency verification using hop-by-hop TLV
header will be defined in a separate document.
11. Acknowledgements
The authors would like to thank Spyridon Mastorakis, Ilya Moiseenko,
and David Oran for their valuable comments and suggestions on this
document.
12. References
12.1. Normative References
[1] Mosko, M., Solis, I., and C. Wood, "CCNx Messages in TLV
Format", draft-irtf-icnrg-ccnxmessages-07 (work in
progress), March 2018.
[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 8200, July 2017.
12.2. 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-v2-24 (work in progress), June 2018.
Appendix A. ccninfo Command and Options
The ccninfo command enables the CCNinfo user to investigate the
routing path based on the name prefix of the content (e.g.,
ccn:/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 ccninfo command at once.
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The usage of ccninfo command is as follows:
Usage: ccninfo [-P] [-g] [-f] [-n] [-o] [-r hop_count] [-s hop_count]
name_prefix; or,
Usage: ccninfo [-r hop_count] [-s hop_count] device_name |
function_name (or application_name)
name_prefix
Name prefix of the content (e.g., ccn:/news/today) the CCNinfo
user wants to trace. If the CCNinfo user specifies only a scheme
name, e.g., "ccn:/", s/he must specify "-g" option (i.e., ccninfo
-g ccn:/). In that case, the CCNinfo user discovers the router
having the FIB of the specified scheme name and the RTT between
CCNinfo 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., ccn:/%device/server-A, ccn:/%device/sensor-123)
the CCNinfo user wants to trace. Here, we assume the ccninfo
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., ccn:/%function/firewall,
ccn:/%function/transcoding/mpeg2-h.264) or application name (e.g.,
ccn:/%application/mplayer) the CCNinfo user wants to trace. Here,
we assume the ccninfo 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 enables to discover a gateway that supports specified
scheme name and has multiple FIBs. When a CCNinfo user specifies
only a scheme name, e.g., "ccn:/", this option must be specified
and other content name prefix is ignored.
f option
This option enables to ignore the forwarding strategy and send
CCNinfo Requests to multiple upstream routers simultaneously. The
CCNinfo user could then trace the all potential forwarding paths.
n option
This option can be specified if a CCNinfo user only needs the
routing path information to the specified content/cache and RTT
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between CCNinfo user and content forwarder (i.e., cache
information is not given).
o option
This option enables 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 inserts each
Report block but 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.
r option
Number of traced routers. If the CCNinfo user specifies this
option, only the specified number of hops from the CCNinfo 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 CCNinfo user. This value is set in the "HopLimit" field
located in the fixed header of the Request. For example, when the
CCNinfo user invokes the CCNinfo command with this option such as
"-r 3", only three routers along the path examine their path and
cache information. 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 CCNinfo 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 CCNinfo user specifies this
option, the number of hops from the CCNinfo user simply forward
the CCNinfo 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 CCNinfo
user invokes the CCNinfo 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 CCNinfo user can specify is 255, if the
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Request messages reaches the publisher, the publisher silently
discards the Request message and the request will be timed out.
Appendix B. Change History
This document was created based on the previous "Contrace" document
whose initial version had been published on October 31, 2016.
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
Kitami Institute of Technology
165 Koen-cho
Kitami, Hokkaido 090-8507
Japan
Email: x-shao@mail.kitami-it.ac.jp
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