CCNinfo: Discovering Content and Network Information in Content-Centric Networks
draft-irtf-icnrg-ccninfo-01
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 9344.
|
|
|---|---|---|---|
| Authors | Hitoshi Asaeda , Atsushi Ooka , Xun Shao | ||
| Last updated | 2019-03-11 (Latest revision 2018-10-08) | ||
| Replaces | draft-asaeda-icnrg-ccninfo | ||
| RFC stream | Internet Research Task Force (IRTF) | ||
| Formats | |||
| IETF conflict review | conflict-review-irtf-icnrg-ccninfo, conflict-review-irtf-icnrg-ccninfo, conflict-review-irtf-icnrg-ccninfo, conflict-review-irtf-icnrg-ccninfo, conflict-review-irtf-icnrg-ccninfo, conflict-review-irtf-icnrg-ccninfo | ||
| Additional resources | Mailing list discussion | ||
| Stream | IRTF state | Active RG Document | |
| Consensus boilerplate | Unknown | ||
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 9344 (Experimental) | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-irtf-icnrg-ccninfo-01
ICN Research Group H. Asaeda
Internet-Draft A. Ooka
Intended status: Experimental NICT
Expires: September 12, 2019 X. Shao
Kitami Institute of Technology
March 11, 2019
CCNinfo: Discovering Content and Network Information in Content-Centric
Networks
draft-irtf-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, 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
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 12, 2019.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 7
3. CCNinfo Message Formats . . . . . . . . . . . . . . . . . . . 8
3.1. Request Message . . . . . . . . . . . . . . . . . . . . . 9
3.1.1. Request Block . . . . . . . . . . . . . . . . . . . . 11
3.1.2. Report Block . . . . . . . . . . . . . . . . . . . . 13
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. Routing Path Information . . . . . . . . . . . . . . 20
4.1.2. In-Network Cache Information . . . . . . . . . . . . 20
4.2. Receiving CCNinfo Reply . . . . . . . . . . . . . . . . . 20
5. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 20
5.1. User and Neighbor Verification . . . . . . . . . . . . . 20
5.2. Receiving CCNinfo Request . . . . . . . . . . . . . . . . 21
5.2.1. Normal Processing . . . . . . . . . . . . . . . . . . 21
5.3. Forwarding CCNinfo Request . . . . . . . . . . . . . . . 22
5.4. Sending CCNinfo Reply . . . . . . . . . . . . . . . . . . 23
5.5. Forwarding CCNinfo Reply . . . . . . . . . . . . . . . . 23
6. CCNinfo Termination . . . . . . . . . . . . . . . . . . . . . 24
6.1. Arriving at First-hop router . . . . . . . . . . . . . . 24
6.2. Arriving at Router Having Cache . . . . . . . . . . . . . 24
6.3. Invalid Request . . . . . . . . . . . . . . . . . . . . . 24
6.4. No Route . . . . . . . . . . . . . . . . . . . . . . . . 24
6.5. No Information . . . . . . . . . . . . . . . . . . . . . 24
6.6. No Space . . . . . . . . . . . . . . . . . . . . . . . . 24
6.7. Fatal Error . . . . . . . . . . . . . . . . . . . . . . . 25
6.8. CCNinfo Reply Timeout . . . . . . . . . . . . . . . . . . 25
6.9. Non-Supported Node . . . . . . . . . . . . . . . . . . . 25
6.10. Administratively Prohibited . . . . . . . . . . . . . . . 25
7. Configurations . . . . . . . . . . . . . . . . . . . . . . . 25
7.1. CCNinfo Reply Timeout . . . . . . . . . . . . . . . . . . 25
7.2. HopLimit in Fixed Header . . . . . . . . . . . . . . . . 25
7.3. Access Control . . . . . . . . . . . . . . . . . . . . . 25
8. Diagnosis and Analysis . . . . . . . . . . . . . . . . . . . 26
8.1. Number of Hops . . . . . . . . . . . . . . . . . . . . . 26
8.2. Caching Router Identification . . . . . . . . . . . . . . 26
8.3. TTL or Hop Limit . . . . . . . . . . . . . . . . . . . . 26
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8.4. Time Delay . . . . . . . . . . . . . . . . . . . . . . . 26
8.5. Path Stretch . . . . . . . . . . . . . . . . . . . . . . 26
8.6. Cache Hit Probability . . . . . . . . . . . . . . . . . . 26
9. Security Considerations . . . . . . . . . . . . . . . . . . . 27
9.1. Policy-Based Information Provisioning for Request . . . . 27
9.2. Filtering of CCNinfo Users Located in Invalid Networks . 27
9.3. Topology Discovery . . . . . . . . . . . . . . . . . . . 28
9.4. Characteristics of Content . . . . . . . . . . . . . . . 28
9.5. Longer or Shorter CCNinfo Reply Timeout . . . . . . . . . 28
9.6. Limiting Request Rates . . . . . . . . . . . . . . . . . 28
9.7. Limiting Reply Rates . . . . . . . . . . . . . . . . . . 28
9.8. Adjacency Verification . . . . . . . . . . . . . . . . . 29
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 29
11.1. Normative References . . . . . . . . . . . . . . . . . . 29
11.2. Informative References . . . . . . . . . . . . . . . . . 29
Appendix A. ccninfo Command and Options . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
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 [6] 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 is designed based on the work previously
published in [5].
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CCNinfo can be implemented with the ccninfo user command and the
forwarding function implementation on a content forwarder (e.g.,
router). The CCNinfo user (e.g., consumer) invokes the ccninfo
command (described in Appendix A) with the name prefix of the
content. 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 who can forward 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 similar to the behavior of the IP
multicast traceroute facility [7].
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.
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1. Request 2. Request 3. Request
(+U) (U+A) (U+A+B)
+----+ +----+ +----+
| | | | | |
| 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(P) 2. Reply(P) 1. Reply(P)
+----+ +----+ +----+
| | | | | |
v | v | v |
+--------+ +--------+ +--------+ +--------+ +---------+
| CCNinfo|----| Router |----| Router |----| Router |----|Publisher|
| user | | A | | B | | C | | |
+--------+ +--------+ +--------+ +--------+ +---------+
^
\ +-------+
1. Reply(C) \ | Cache |
\ +---------+ |
\| Caching |----+
| router |
+---------+
Figure 2: Default behavior. Reply messages forwarded by routers.
Each router forwards the Reply message along its PIT entry, and
finally the CCNinfo user receives a Reply message from Router C,
which is the first-hop router for Publisher. Another Reply message
from Caching router is discarded at Router B as the corresponding
Reply message was already forwarded.
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3. Reply(C) 2. Reply(C)
3. Reply(P) 2. Reply(P) 1. Reply(P)
+----+ +----+ +----+
| | | | | |
v | v | v |
+--------+ +--------+ +--------+ +--------+ +---------+
| CCNinfo|----| Router |----| Router |----| Router |----|Publisher|
| user | | A | | B | | C | | |
+--------+ +--------+ +--------+ +--------+ +---------+
^
\ +-------+
1. Reply(C) \ | Cache |
\ +---------+ |
\| Caching |----+
| router |
+---------+
Figure 3: Full discovery request. Reply messages forwarded by
publisher and routers. Each router forwards the Reply message along
its PIT entry, and finally the CCNinfo user receives two Reply
messages: one from the first-hop router 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 first-hop
router) and consumer, 2) the states of in-network cache per name
prefix, and 3) the routing path information per name prefix.
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 objects, 2) number of the cached content
objects, 3) number of the accesses (i.e., received Interests) per
content, and 4) elapsed cache time and remain cache lifetime of
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 [3],
and indicate requirement levels for compliant CCNinfo
implementations.
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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 CCN-based content retrieval in the
path between consumer and publisher.
Scheme name
It indicates a URI and protocol. This document only considers
"ccn:/" as the scheme name.
Prefix name
A prefix name, which is defined in [2], is a name that does not
uniquely identify a single content object, but rather a namespace
or prefix of an existing content object name.
Exact name
An exact name, which is defined in [2], is one which uniquely
identifies the name of a content object.
Node
It is a router, publisher, or consumer.
Content forwarder
It is either a caching router or a first-hop router that forwards
content objects 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.
Upstream router
The router, connecting to the Incoming face of a router, which is
responsible for forwarding data for the specified name prefix to
the router.
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First-hop router (FHR)
The router that is directly connected to the publisher.
Last-hop router (LHR)
The router that is directly connected to the consumers.
3. CCNinfo Message Formats
CCNinfo uses two message types: Request and Reply. Both messages are
encoded in the CCNx TLV format ([1], Figure 4). The Request message
consists of a fixed header, Request block TLV Figure 8, 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 4: Packet format [1]
The Request and Reply Type values in the fixed header are PT_REQUEST
and PT_REPLY, respectively (Figure 5). 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
from PT_REQUEST to PT_REPLY and forwards back to the node that has
initiated the Request message.
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Code Type name
======== =====================
%x00 PT_INTEREST [1]
%x01 PT_CONTENT [1]
%x02 PT_RETURN [1]
%x03 PT_REQUEST
%x04 PT_REPLY
Figure 5: 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 6), 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
============= =========================
%x0000 Reserved [1]
%x0001 T_INTEREST [1]
%x0002 T_OBJECT [1]
%x0003 T_VALIDATION_ALG [1]
%x0004 T_VALIDATION_PAYLOAD [1]
%x0005 T_DISCOVERY
Figure 6: 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 7. It consists of a
fixed header, Request block TLV (Figure 8), Report block TLV(s)
(Figure 11), and Name TLV. The Type value of Top-Level type
namespace is T_DISCOVERY (Figure 6). 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 7: 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 whenever a
Request packet is forwarded. 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
----- --------------- ----------------------------------------------
%x00 NO_ERROR No error
%x01 WRONG_IF CCNinfo Request arrived on an interface
to which this router would not forward for
the specified name/function toward the
publisher.
%x02 INVALID_REQUEST Invalid CCNinfo Request is received.
%x03 NO_ROUTE This router has no route for the name prefix
and no way to determine a potential route.
%x04 NO_INFO This router has no cache information for the
specified name prefix.
%x05 NO_SPACE There was not enough room to insert another
Report block in the packet.
%x06 INFO_HIDDEN Information is hidden from this discovery
because of some policy.
%x0E ADMIN_PROHIB CCNinfo Request is administratively
prohibited.
%x0F UNKNOWN_REQUEST This router does not support/recognize the
Request message.
%x80 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 8) 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 |
+---------------+---------------+---------------+---------+-+-+-+
| Request ID | SkipHopCount | Flags |F|O|C|
+---------------+---------------+---------------+---------+-+-+-+
| Request Arrival Time |
+---------------+---------------+---------------+---------------+
/ Node Identifier /
+---------------+---------------+---------------+---------------+
Figure 8: Request block TLV (hop-by-hop header)
Code Type name
============= =========================
%x0000 Reserved [1]
%x0001 T_INTLIFE [1]
%x0002 T_CACHETIME [1]
%x0003 T_MSGHASH [1]
%x0004-%x0007 Reserved [1]
%x0008 T_DISC_REQ
%x0009 T_DISC_REPORT
%x0FFE T_PAD [1]
%x0FFF T_ORG [1]
%x1000-%x1FFF Reserved [1]
Figure 9: 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 9.
Length: 16 bits
Length of Value field in octets.
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.
SkipHopCount: 8 bits
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Number of skipped routers for a Request. This value MUST be lower
than the value of HopLimit at the fixed header.
Flags: 16 bits
Flags field is used to indicate the types of the content or path
discoveries. Currently, as shown in Figure 10, three bits, "C",
"O", and "F", are assigned, and the other 5 bits are reserved
(MBZ) for the future use. These flags are set by CCNinfo users
when they initiate Requests (see Appendix A), and routers that
receive the Requests deal with the flags and change the behaviors
(see Section 5 for details).
Flag Value Description
----- ----- ----------------------------------------------------
C 0 Path discovery (i.e., no cache information retried)
C 1 Cache information retrieval (default)
O 0 Request to any content forwarder (default)
O 1 Publisher reachability (i.e., only FHR can reply)
F 0 Request based on FIB's strategy (default)
F 1 Full discovery request. Request to multiple upstream
routers simultaneously
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.
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
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Format of the Value field. For the Report block TLV, the type
value(s) MUST be T_DISC_REPORT in the current specification.
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 it is RECOMMENDED that all the routers on the path to
have synchronized clocks; however, if they do not have
synchronized clocks, CCNinfo measures 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
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
based on 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
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Reply message (see Figure 12) would then be forwarded back toward the
CCNinfo user in a hop-by-hop manner.
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
============== ===================
%x0000 T_NAME [1]
%x0001 T_PAYLOAD [1]
%x0002 T_KEYIDRESTR [1]
%x0003 T_OBJHASHRESTR [1]
%x0005 T_PAYLDTYPE [1]
%x0006 T_EXPIRY [1]
%x0007 T_DISC_REPLY
%x0008-%x0012 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 Reply block TLV, the type
value MUST be T_DISC_REPLY in the current specification.
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. In this document, Reply sub-block TLVs for
T_DISC_CONTENT and T_DISC_CONTENT_OWNER (Figure 15) 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 |
+---------------+---------------+---------------+---------------+
| Object Size |
+---------------+---------------+---------------+---------------+
| Object Count |
+---------------+---------------+---------------+---------------+
| # Received Interest |
+---------------+---------------+---------------+---------------+
| First Seqnum |
+---------------+---------------+---------------+---------------+
| Last Seqnum |
+---------------+---------------+---------------+---------------+
| Elapsed Cache Time |
+---------------+---------------+---------------+---------------+
| Remain Cache Lifetime |
+---------------+---------------+---------------+---------------+
| T_NAME | Length |
+---------------+---------------+---------------+---------------+
/ Name Segment TLVs /
+---------------+---------------+---------------+---------------+
Figure 15: Reply sub-block TLV for T_DISC_CONTENT and
T_DISC_CONTENT_OWNER (packet payload)
Code Type name
============= ===========================
%x0000 T_DISC_CONTENT
%x0001 T_DISC_CONTENT_OWNER
%x0FFF T_ORG
%x1000-%x1FFF Reserved (Experimental Use)
Figure 16: 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 16). 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 FHR attached to a publisher.
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Length: 16 bits
Length of Value field in octets.
Object Size: 32 bits
The total size (byte) of the (cached) content objects. Note that
the maximum size expressed by 32 bit field is about 4.29 GB. This
value MAY be null when FHR sends the Reply message.
Object Count: 32 bits
The number of the (cached) content objects. Note that the maximum
count expressed by 32 bit field is about 4.29 billion. This value
MAY be null when FHR sends the Reply message.
# Received Interest: 32 bits
The total number of the received Interest messages to retrieve the
cached content objects.
First Seqnum: 32 bits
The first sequential number of the (cached) content objects. This
value MAY be null if the router does not know or cannot report.
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. This value MAY be
null if the router does not know or cannot report.
Elapsed Cache Time: 32 bits
The elapsed time (seconds) after the oldest content object of the
content is cached. This value MAY be null if the router does not
know or cannot report.
Remain Cache Lifetime: 32 bits
The lifetime (seconds) of a content object, which is removed first
among the cached content objects. This value MAY be null if the
router does not know or cannot report.
Specification of the Name TLV (whose type value is T_NAME) and the
Name Segment TLVs are described in [1], and CCNinfo follows that
specification. CCNinfo also allows to specify the content name
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either with a prefix name (such as "ccn:/news/today") or an exact
name (such as "ccn:/news/today/Chunk=10"). When a CCNinfo user
specifies a prefix name, s/he will obtain the information of the
matched content objects in the content forwarder. On the other hand,
when a CCNinfo user specifies an exact name, s/he will obtain only
about the specified content object in the content forwarder.
4. CCNinfo User Behavior
4.1. Sending CCNinfo Request
The CCNinfo user's program (e.g., ccninfo command) enables user to
obtain both the routing path information and in-network cache
information in a same time.
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. The Request ID MUST be unique for the CCNinfo user
until s/he receives the corresponding Reply message(s) or times out
the Request.
Because of some policy, a router needs to validate CCNinfo Requests
(whether it accepts the Request or not) especially when the router
receives the "full discovery request" (see Section 5.3). To support
this requirement, the CCNinfo user's program MAY require appending
the user's signature into the CCNx ValidationPayload TLV. The router
then forwards the Request message or reply the Reply message whenever
it approves the Request.
After the CCNinfo user's program sends the Request message, until the
Reply times out or the expected numbers of Replies or a Reply message
having a non-zero ReturnCode in the fixed header is received, 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.
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4.1.1. 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.
4.1.2. In-Network Cache Information
A CCNinfo user can send a CCNinfo Request for investigating in-
network cache information. By the Request, the legitimate user can
obtain; 1) size of the cached content objects, 2) number of the
cached content objects, 3) number of the accesses (i.e., received
Interests) per content, and 4) lifetime and expiration time of the
cached content object, 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 Node
Identifier and the ones noted in the Request block TLV in the Reply.
If they do not match, the Reply message MUST 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), the Reply MUST 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 8.
5. Router Behavior
5.1. User and Neighbor Verification
Upon receiving a CCNinfo Request message, a router MAY examine
whether the message comes from a valid CCNinfo user. If the router
recognizes that the Request sender's signature specified in the
Request is invalid, it terminates the Request as defined in
Section 6.3.
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Upon receiving a CCNinfo Request/Reply message, a router MAY examine
whether the message comes from a valid adjacent neighbor node. If
the router recognizes that the Request/Reply sender is invalid, the
Request/Reply message MUST be silently ignored. See Section 9.8.
5.2. Receiving CCNinfo Request
5.2.1. Normal Processing
After the CCNinfo Request message verification, the router performs
the following steps.
1. The value of the "HopLimit" in the fixed header and the value of
the "SkipHopCount" in the Request block are counters that are
decremented with each hop. If the HopLimit value is zero, the
router terminates the Request as defined in Section 6.4. If the
SkipHopCount value is equal or more than the HopLimit value, the
router terminates the Request as defined in Section 6.3.
Otherwise, until the SkipHopCount value becomes zero, the router
forwards the Request message to the upstream router(s) without
adding its own Report block and without replying the Request. If
the router does not know the upstream router(s) for the specified
name prefix, it terminates the Request as defined in Section 6.4.
2. The router examines the Flags field (specified in Figure 10) in
the Request block of received CCNinfo Request. If the "C" flag
is set but the "O" flag is not set, that is categorized as the
"cache information discovery". If both the "C" and "O" flags are
not set, that is categorized as the "routing path information
discovery". If "O" flag is set, that is categorized as the
"publisher discovery".
3. If the Request is either the "cache information discovery" or the
"routing path information discovery", the router examines its FIB
and CS. If the router caches the specified content, it inserts
own Report block in the hop-by-hop header, and sends the Reply
message with own Reply block and sub-block(s) (in case of cache
information discovery) or sends the Reply message with own Reply
block without adding any Reply sub-block (in case of routing path
information discovery). If the router does not cache the
specified content but knows the upstream 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
terminates the Request as defined in Section 6.4.
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4. If the Request is the "publisher discovery", the router examines
whether it is the FHR for the requested content. If it is the
FHR, it sends the Reply message with own Report block and sub-
block. If the router is not the FHR but knows 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 FHR and does not know the upstream neighbor
router(s) for the specified name prefix, it terminates the
Request as defined in Section 6.4.
5.3. 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, the F flag, and the Node Identifier specified in the
Request block at the corresponding PIT entry. The router can later
check the PIT entry to correctly forward back the Reply message(s).
(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
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 forwarding 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. The
"full discovery request" enables this function. If a CCNinfo user
sets the F flag in the Request block of the Request message (as seen
in Figure 10) to request the full discovery, the upstream routers
forward the Requests to the all multiple upstream routers based on
the FIBs simultaneously. Then the CCNinfo user could trace the all
potential forwarding paths. Note that some routers MAY ignore the
full discovery request according to their policy. In that case, the
router terminates the Request as defined in Section 6.10.
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 7.1)
passes. In other words, unlike the ordinary Interest-Data
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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.
5.4. 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 with an
appropriate type value (Figure 15) and Reply sub-block(s) 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.
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 6.
5.5. Forwarding CCNinfo Reply
When a router receives a CCNinfo Reply whose Request ID and Node
Identifier match the ones in the PIT entry and sent from a valid
adjacent neighbor router, it forwards the CCNinfo Reply back toward
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.
Flags field in the Request block TLV is used to indicate whether the
router keeps the PIT entry during the CCNinfo Reply Timeout even
after one or more corresponding Reply messages are forwarded. When
the CCNinfo user does not set the F flag (i.e., "0"), the
intermediate routers immediately remove the PIT entry whenever they
forward the corresponding Reply message. When the CCNinfo user sets
the F flag (i.e., "1"), which means the CCNinfo user chooses the
"full discovery request", the intermediate routers keep the PIT entry
within the [CCNinfo Reply Timeout] period. After this timeout, the
PIT entry is removed.
CCNinfo Replies MUST NOT be cached in routers upon the Reply message
transmission.
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6. 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.
6.1. Arriving at First-hop router
A CCNinfo Request can be determined to have arrived at the first-hop
router.
6.2. 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.
6.3. Invalid Request
If the router does not accept the Request, the router MUST note a
ReturnCode of INVALID_REQUEST in the fixed header of the message and
forward the message without appending any Reply (sub-)block TLV as
the Reply back to the CCNinfo user. The router MAY, however,
randomly ignore the received invalid messages. (See Section 9.6.)
6.4. No Route
If the router cannot determine the routing paths or neighbor routers
for the specified name prefix within the specified HopLimit, the
router MUST note a ReturnCode of NO_ROUTE in the fixed header of the
message and forward the message as the Reply back to the CCNinfo
user.
6.5. No Information
If the router does not have any information about the specified name
prefix within the specified HopLimit, the router MUST note a
ReturnCode of NO_INFO in the fixed header of the message and forward
the message as the Reply back to the CCNinfo user.
6.6. No Space
If appending the Report block would exceed the maximum (i.e., 255
byte) header length or make the CCNinfo Request message longer than
the MTU of the Incoming face or longer than 1280 bytes (especially in
the situation supporting IPv6 as the payload [4]), the router MUST
note a ReturnCode of NO_SPACE in the fixed header of the message and
forward the message as the Reply back to the CCNinfo user.
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6.7. 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).
6.8. CCNinfo Reply Timeout
If a router receives the Request or Reply message that expires its
own [CCNinfo Reply Timeout] value (Section 7.1), the router will
silently discard the Request or Reply message.
6.9. 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.
6.10. Administratively Prohibited
If CCNinfo is administratively prohibited, the router rejects the
Request message and MUST reply the CCNinfo Reply with the ReturnCode
of ADMIN_PROHIB. The router MAY, however, randomly ignore the
rejected messages. (See Section 9.6.)
7. Configurations
7.1. 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).
7.2. 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; hence the router in
this case follows the way defined in Section 6.3.
7.3. 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 9.2.
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8. Diagnosis and Analysis
8.1. 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
verify the number of hops to reach the content forwarder or the
publisher.
8.2. Caching Router Identification
It is possible to identify the routers in the path from the CCNinfo
user to the content forwarder, while some routers may hide their
identifier (e.g., IP address) with all-zeros in the Report blocks
(Section 9.1).
8.3. 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.
8.4. 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.
8.5. 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.
8.6. 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.
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9. Security Considerations
This section addresses some of the security considerations.
9.1. 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
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 MAY 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 MUST 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 if the
ReturnCode is NO_ERROR. 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 the ReturnCode is kept with
NO_ERROR.
9.2. 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 7.3). If a Request is
received from the disallowed network (according to the Node
Identifier in the Request block), the Request MUST 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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9.3. Topology Discovery
CCNinfo can be used to discover actively-used topologies. If a
network topology is a secret, CCNinfo Requests SHOULD be restricted
at the border of the domain, using the ADMIN_PROHIB return code.
9.4. 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
SHOULD be restricted at the border of the domain, using the
ADMIN_PROHIB return code.
9.5. Longer or Shorter CCNinfo Reply Timeout
Routers can configure the CCNinfo Reply Timeout (Section 7.1), 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 full
discovery request option (Section 5.3) is specified for the CCNinfo
Request, a number of Reply messages may come back and cause a
response storm. (See Section 9.7 for rate limiting to avoid the
storm). In order to avoid DoS attacks, routers may configure the
timeout value, which is shorter 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.
9.6. 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.
9.7. 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.
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9.8. Adjacency Verification
It is assumed that CCNinfo Request and Reply messages are forwarded
by adjacent neighbor nodes or routers. Defining the secure way to
verify the adjacency cannot rely on the way specified in CCNx message
format or semantics, yet specifying the mechanism to validate
adjacent neighbor routers is out of scope of this document. An
adjacency verification mechanism and the corresponding TLV for
adjacency verification using hop-by-hop TLV header such as [8] is the
potential way and will be defined in a separate document.
10. Acknowledgements
The authors would like to thank Spyridon Mastorakis, Ilya Moiseenko,
David Oran, and Thierry Turletti for their valuable comments and
suggestions on this document.
11. References
11.1. Normative References
[1] Mosko, M., Solis, I., and C. Wood, "CCNx Messages in TLV
Format", draft-irtf-icnrg-ccnxmessages-09 (work in
progress), January 2019.
[2] Mosko, M., Solis, I., and C. Wood, "CCNx Semantics",
draft-irtf-icnrg-ccnxsemantics-10 (work in progress),
January 2019.
[3] Bradner, S., "Key words for use in RFCs to indicate
requirement levels", RFC 2119, March 1997.
[4] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 8200, July 2017.
11.2. Informative References
[5] 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.
[6] Malkin, G., "Traceroute Using an IP Option", RFC 1393,
January 1993.
[7] Asaeda, H., Mayer, K., and W. Lee, "Mtrace Version 2:
Traceroute Facility for IP Multicast", RFC 8487, October
2018.
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[8] Li, R., Asaeda, H., and J. Wu, "DCAuth: Data-Centric
Authentication for Secure In-Network Big-Data Retrieval",
IEEE Transactions on Network Science and Engineering
(TNSE) , October 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). The name prefix is mandatory but exclusive
options; that is, only one of them should be used with the ccninfo
command at once.
The usage of ccninfo command is as follows:
Usage: ccninfo [-f] [-n] [-o] [-r hop_count] [-s hop_count]
name_prefix
name_prefix
Prefix name of content (e.g., ccn:/news/today) or exact name of
content (e.g., ccn:/news/today/Chunk=10) the CCNinfo user wants to
trace.
f option
This option enables "full discovery request"; routers 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
between CCNinfo user and content forwarder; therefore, cache
information is not given.
o option
This option enables to trace the path to the content publisher.
Each router along the path to the publisher inserts each Report
block and forwards the Request message. It does not send Reply
even if it caches the specified content. FHR that attaches the
publisher (who has the complete set of content and is not a
caching router) replies the Reply message.
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
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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 or FHR within the
hop count along the path, the caching router or FHR 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 FHR; therefore, although the maximum value for this option a
CCNinfo user can specify is 255, the Request messages should be in
general reached at FHR 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 FHR; therefore, although the maximum value for
this option a CCNinfo user can specify is 255, if the Request
messages reaches FHR, the FHR silently discards the Request
message and the request will be timed out.
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
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Atsushi Ooka
National Institute of Information and Communications Technology
4-2-1 Nukui-Kitamachi
Koganei, Tokyo 184-8795
Japan
Email: a-ooka@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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