Internet DRAFT - draft-irtf-icnrg-ccninfo
draft-irtf-icnrg-ccninfo
ICN Research Group H. Asaeda
Internet-Draft A. Ooka
Intended status: Experimental NICT
Expires: 1 July 2023 X. Shao
Toyohashi University of Technology
28 December 2022
CCNinfo: Discovering Content and Network Information in Content-Centric
Networks
draft-irtf-icnrg-ccninfo-15
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 the content forwarder and consumer, and 3) the states
of in-network cache per name prefix. CCNinfo is useful to understand
and debug the behavior of testbed networks and other experimental
deployments of CCN systems.
This document is a product of the IRTF Information-Centric Networking
Research Group (ICNRG). This document represents the consensus view
of ICNRG and has been reviewed extensively by several members of the
ICN community and the RG. The authors and RG chairs approve of the
contents. The document is sponsored under the IRTF and is not issued
by the IETF and is not an IETF standard. This is an experimental
protocol and the specification may change in the future.
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
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 1 July 2023.
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Copyright Notice
Copyright (c) 2022 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
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. CCNinfo as an Experimental Tool . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 7
3. CCNinfo Message Formats . . . . . . . . . . . . . . . . . . . 9
3.1. Request Message . . . . . . . . . . . . . . . . . . . . . 10
3.1.1. Request Header Block and Request Block . . . . . . . 12
3.1.2. Report Block TLV . . . . . . . . . . . . . . . . . . 16
3.1.3. Content Name Specification . . . . . . . . . . . . . 16
3.2. Reply Message . . . . . . . . . . . . . . . . . . . . . . 17
3.2.1. Reply Block TLV . . . . . . . . . . . . . . . . . . . 18
3.2.1.1. Reply Sub-Block TLV . . . . . . . . . . . . . . . 19
4. CCNinfo User Behavior . . . . . . . . . . . . . . . . . . . . 22
4.1. Sending CCNinfo Request . . . . . . . . . . . . . . . . . 22
4.1.1. Routing Path Information . . . . . . . . . . . . . . 23
4.1.2. In-Network Cache Information . . . . . . . . . . . . 23
4.2. Receiving CCNinfo Reply . . . . . . . . . . . . . . . . . 23
5. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 23
5.1. User and Neighbor Verification . . . . . . . . . . . . . 23
5.2. Receiving CCNinfo Request . . . . . . . . . . . . . . . . 24
5.3. Forwarding CCNinfo Request . . . . . . . . . . . . . . . 25
5.3.1. Regular Request . . . . . . . . . . . . . . . . . . . 25
5.3.2. Full Discovery Request . . . . . . . . . . . . . . . 26
5.4. Sending CCNinfo Reply . . . . . . . . . . . . . . . . . . 27
5.5. Forwarding CCNinfo Reply . . . . . . . . . . . . . . . . 27
5.6. PIT Entry Management for Multipath Support . . . . . . . 28
6. CCNinfo Termination . . . . . . . . . . . . . . . . . . . . . 29
6.1. Arriving at First-hop Router . . . . . . . . . . . . . . 29
6.2. Arriving at Router Having Cache . . . . . . . . . . . . . 29
6.3. Arriving at Last Router . . . . . . . . . . . . . . . . . 29
6.4. Invalid Request . . . . . . . . . . . . . . . . . . . . . 30
6.5. No Route . . . . . . . . . . . . . . . . . . . . . . . . 30
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6.6. No Information . . . . . . . . . . . . . . . . . . . . . 30
6.7. No Space . . . . . . . . . . . . . . . . . . . . . . . . 30
6.8. Fatal Error . . . . . . . . . . . . . . . . . . . . . . . 30
6.9. CCNinfo Reply Timeout . . . . . . . . . . . . . . . . . . 31
6.10. Non-Supported Node . . . . . . . . . . . . . . . . . . . 31
6.11. Administratively Prohibited . . . . . . . . . . . . . . . 31
7. Configurations . . . . . . . . . . . . . . . . . . . . . . . 31
7.1. CCNinfo Reply Timeout . . . . . . . . . . . . . . . . . . 31
7.2. HopLimit in Fixed Header . . . . . . . . . . . . . . . . 31
7.3. Access Control . . . . . . . . . . . . . . . . . . . . . 31
8. Diagnosis and Analysis . . . . . . . . . . . . . . . . . . . 31
8.1. Number of Hops and RTT . . . . . . . . . . . . . . . . . 32
8.2. Caching Router Identification . . . . . . . . . . . . . . 32
8.3. TTL or Hop Limit . . . . . . . . . . . . . . . . . . . . 32
8.4. Time Delay . . . . . . . . . . . . . . . . . . . . . . . 32
8.5. Path Stretch . . . . . . . . . . . . . . . . . . . . . . 32
8.6. Cache Hit Probability . . . . . . . . . . . . . . . . . . 32
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33
9.1. Packet Type Registry . . . . . . . . . . . . . . . . . . 33
9.2. Top-Level Type Registry . . . . . . . . . . . . . . . . . 33
9.3. Hop-by-Hop Type Registry . . . . . . . . . . . . . . . . 33
9.4. Message Type Registry . . . . . . . . . . . . . . . . . . 33
9.5. Reply Type Registry . . . . . . . . . . . . . . . . . . . 33
10. Security Considerations . . . . . . . . . . . . . . . . . . . 33
10.1. Policy-Based Information Provisioning for Request . . . 34
10.2. Filtering CCNinfo Users Located in Invalid Networks . . 34
10.3. Topology Discovery . . . . . . . . . . . . . . . . . . . 35
10.4. Characteristics of Content . . . . . . . . . . . . . . . 35
10.5. Computational Attacks . . . . . . . . . . . . . . . . . 35
10.6. Longer or Shorter CCNinfo Reply Timeout . . . . . . . . 35
10.7. Limiting Request Rates . . . . . . . . . . . . . . . . . 36
10.8. Limiting Reply Rates . . . . . . . . . . . . . . . . . . 36
10.9. Adjacency Verification . . . . . . . . . . . . . . . . . 36
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 36
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 36
12.1. Normative References . . . . . . . . . . . . . . . . . . 36
12.2. Informative References . . . . . . . . . . . . . . . . . 37
Appendix A. ccninfo Command and Options . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 39
1. Introduction
In Content-Centric Networks (CCN), publishers provide the content
through the network, and receivers retrieve it by name. In this
network architecture, routers forward content requests through 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.
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In CCN, while consumers do not generally need to know the content
forwarder that is transmitting the content to them, the 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.
IP traceroute is a useful tool for discovering the routing conditions
in IP networks because it provides intermediate router addresses
along the path between the 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 tools do not obtain the states of the in-network cache to be
discovered.
Contrace [7] enables end users (i.e., consumers) to investigate path
and in-network cache conditions in CCN. Contrace is implemented as
an external daemon process running over TCP/IP that can interact with
a previous CCNx forwarding daemon (CCNx-0.8.2) to retrieve the
caching information on the forwarding daemon. This solution is
flexible, but it requires defining the common APIs used for global
deployment in TCP/IP networks. ICN ping [8] and traceroute [9] are
lightweight operational tools that enable a user to explore the
path(s) that reach a publisher or a cache storing the named content.
ICN ping and traceroute, however, do not expose detailed information
about the forwarders deployed by a network operator.
This document describes the specifications of "CCNinfo", an active
networking tool for discovering the path and content caching
information in CCN. CCNinfo defines the protocol messages to
investigate path and in-network cache conditions in CCN. It is
embedded in the CCNx forwarding process and can facilitate with non-
IP networks as with the basic CCN concept.
The two message types, Request and Reply messages, are encoded in the
CCNx TLV format [1]. The 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 [10].
CCNinfo facilitates the tracing of a routing path and provides: 1)
the RTT between the content forwarder (i.e., caching router or first-
hop router) and consumer, 2) the states of the 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 cached content objects, 2) number of cached content objects,
3) number of accesses (i.e., received Interests) per content, and 4)
elapsed cache time and remaining cache lifetime of content.
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CCNinfo supports multipath forwarding. The Request messages can be
forwarded to multiple neighbor routers. When the Request messages
are forwarded to multiple routers, the different Reply messages are
forwarded from different routers or publishers.
Furthermore, CCNinfo implements policy-based information provisioning
that enables administrators to "hide" secure or private information
but does not disrupt message forwarding. This policy-based
information provisioning reduces the deployment barrier faced by
operators in installing and running CCNinfo on their routers.
The document represents the consensus of the Information-Centric
Networking Research Group (ICNRG). This document was read and
reviewed by the active research group members. It is not an IETF
product and is not a standard.
1.1. CCNinfo as an Experimental Tool
In order to carry out meaningful experimentation with CCNx protocols,
comprehensive instrumentation and management information is needed to
take measurements and explore both the performance and robustness
characteristics of the protocols and of the applications using them.
CCNinfo's primary goal is to gather and report this information. As
experience is gained with both the CCNx protocols and CCNinfo itself,
we can refine the instrumentation capabilities and discover what
additional capabilities might be needed in CCNinfo and conversely
which features wind up not being of sufficient value to justify the
implementation complexity and execution overhead.
CCNinfo is intended as a comprehensive experimental tool for CCNx-
based networks. It provides a wealth of information from forwarders,
including on-path in-network cache conditions as well as forwarding
path instrumentation of multiple paths toward content forwarders. As
an experimental capability that exposes detailed information about
the forwarders deployed by a network operator, CCNinfo employs more
granular authorization policies than those required of ICN ping or
ICN traceroute.
CCNinfo uses two message types: Request and Reply. A CCNinfo user,
e.g., consumer, initiates a CCNinfo Request message when s/he wants
to obtain routing path and cache information. When an adjacent
neighbor router receives the Request message, it examines its own
cache information. If the router does not cache the specified
content, it inserts its Report block into the hop-by-hop header of
the Request message and forwards the message to its upstream neighbor
router(s) decided by its FIB. In Figure 1, CCNinfo user and routers
(Router A, B, C) insert their own Report blocks into the Request
message and forward the message toward the content forwarder.
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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 message invoked by CCNinfo user and forwarded
by routers.
When the Request message reaches the content forwarder, the content
forwarder forms the Reply message; it inserts its own Reply block TLV
and Reply sub-block TLV(s) to the Request message. The Reply message
is then forwarded back toward the user in a hop-by-hop manner along
the Pending Interest Table (PIT) entries. In Figure 2, each router
(Router C, B, and A) 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 the Publisher. Another Reply
message from the Caching router (i.e., Reply(C)) is discarded at
Router B if the other Reply message (i.e., Reply(P)) was already
forwarded by Router B.
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 |
+---------+
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Figure 2: Reply messages forwarded by routers, and one Reply
message is received by CCNinfo user.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 (RFC2119 [3] and RFC8174 [4]) when, and only when, they appear in
all capitals, as shown here.
2.1. Definitions
This document follows the basic terminologies and definitions
described in [1]. Although CCNinfo requests flow in the opposite
direction to the data flow, we refer to "upstream" and "downstream"
with respect to data, unless explicitly specified.
Scheme name
It indicates a URI and protocol. This document only considers
"ccnx:/" 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 that uniquely
identifies the name of a content object.
Node
A node within a CCN network can fulfill the role of a data
publisher, a data consumer, and/or a forwarder for interest and
content object as given in [6].
Consumer
A node that requests content objects by generating and sending out
interests. It is a same definition of ICN Consumer as given in
[6].
Publisher
A node that creates content objects and makes them available for
retrieval. It is a same definition of ICN Producer as given in
[6].
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Router
A node that implements stateful forwarding in the path between
consumer and publisher.
Caching router
A node that temporarily stores and potentially carries interests
or content objects before forwarding it to next node.
Content forwarder
It is either a caching router or a first-hop router that forwards
content objects to consumers.
CCNinfo user
A node that initiates the CCNinfo Request, which is consumer or
router that invokes the CCNinfo user program with the name prefix
of the content. The CCNinfo user program, such as "ccninfo"
command described in Appendix A or other similar commands,
initiates the Request message to obtain routing path and cache
information.
Incoming face
The face on which data are expected to arrive from the specified
name prefix.
Outgoing face
The face to which data from the publisher or router are expected
to transmit for the specified name prefix. It is also the face on
which the Request messages are received.
Upstream router
The router that connects to an Incoming face of a router.
Downstream router
The router that connects to an Outgoing face of a router.
First-hop router (FHR)
The router that matches a FIB entry with an Outgoing face
referring to a local application or a publisher.
Last-hop router (LHR)
The router that is directly connected to a consumer.
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3. CCNinfo Message Formats
CCNinfo Request and Reply 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 12).
The Reply message consists of a fixed header, Request block TLV,
Report block TLV(s), Reply block TLV (Figure 14), and Reply sub-block
TLV(s) (Figure 15).
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 PacketType values in the fixed header shown in Figure 3 are
PT_CCNINFO_REQUEST and PT_CCNINFO_REPLY, respectively (Figure 4).
CCNinfo Request and Reply messages are forwarded in a hop-by-hop
manner. When the Request message reaches the content forwarder, the
content forwarder turns it into a Reply message by changing the Type
field value in the fixed header from PT_CCNINFO_REQUEST to
PT_CCNINFO_REPLY and forwards it back toward the node that initiated
the Request message.
Code Type name
======== =====================
%x00 PT_INTEREST [1]
%x01 PT_CONTENT [1]
%x02 PT_RETURN [1]
%x03 PT_CCNINFO_REQUEST
%x04 PT_CCNINFO_REPLY
Figure 4: Packet Type Namespace
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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, a 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
============= =========================
%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 5: Top-Level Type Namespace
3.1. Request Message
When a CCNinfo user initiates a discovery request (e.g., via the
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 shown in Figure 6. It consists of a
fixed header, Request header block TLV (Figure 7), Report block
TLV(s) (Figure 12), Name TLV, and Request block TLV. Request header
block TLV and Report block TLV(s) are contained in the hop-by-hop
header, as those might change from hop to hop. Request block TLV is
encoded in the PacketPayload TLV by content forwarder as the protocol
message itself. The PacketType value of the Request message is
PT_CCNINFO_REQUEST (Figure 4). The Type value of the Top-Level type
namespace is T_DISCOVERY (Figure 5).
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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 header block TLV /
+---------------+---------------+---------------+---------------+
/ Report block TLV 1 /
+---------------+---------------+---------------+---------------+
/ Report block TLV 2 /
+---------------+---------------+---------------+---------------+
/ . /
/ . /
+---------------+---------------+---------------+---------------+
/ Report block TLV n /
+===============+===============+===============+===============+
| Type (=T_DISCOVERY) | MessageLength |
+---------------+---------------+---------------+---------------+
| T_NAME | Length |
+---------------+---------------+---------------+---------------+
/ Name segment TLVs (name prefix specified by CCNinfo user) /
+---------------+---------------+---------------+---------------+
/ Request block TLV /
+---------------+---------------+---------------+---------------+
/ Optional CCNx ValidationAlgorithm TLV /
+---------------+---------------+---------------+---------------+
/ Optional CCNx ValidationPayload TLV (ValidationAlg required) /
+---------------+---------------+---------------+---------------+
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 whenever a
Request packet is forwarded. It is specified by the CCNinfo user
program. The HopLimit value MUST be decremented by 1 prior to
forwarding the Request packet. The packet is discarded if
HopLimit is decremented to zero. HopLimit limits the distance
that a Request may travel on the network. Only the specified
number of hops from the CCNinfo user traces the Request. The last
router stops the trace and sends the Reply message back to the
CCNinfo user.
ReturnCode: 8 bits
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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.
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 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
owing to 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 In a fatal error, 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 Header Block and Request Block
When a CCNinfo user transmits the Request message, s/he MUST insert
her/his Request header block TLV (Figure 7) into the hop-by-hop
header and Request block TLV (Figure 10) into the message before
sending it through the Incoming face(s).
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Type (=T_DISC_REQHDR) | Length |
+---------------+---------------+-------+-------+-------+-+-+-+-+
| Request ID |SkipHop| Flags |V|F|O|C|
+---------------+---------------+-------+-------+-------+-+-+-+-+
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Figure 7: Request header 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_REQHDR
%x0009 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 type value of the Request
block TLV MUST be T_DISC_REQHDR.
Length: 16 bits
Length of Value field in octets.
Request ID: 16 bits
This field is used as a unique identifier for the CCNinfo Request
so that the duplicate or delayed Reply messages can be detected.
SkipHop (Skip Hop Count): 4 bits
Number of skipped routers for a Request. It is specified by the
CCNinfo user program. The number of routers corresponding to the
value specified in this field are skipped and the CCNinfo Request
messages are forwarded to the next router without the addition of
Report blocks; the next upstream router then starts the trace.
The maximum value of this parameter is 15. This value MUST be
lower than that of HopLimit at the fixed header.
Flags: 12 bits
The Flags field is used to indicate the types of the content or
path discoveries. Currently, as shown in Figure 9, four bits,
"C", "O", "F", and "V" are assigned, and the other 8 bits are
reserved (MBZ) for the future use. Each flag can be mutually
specified with other flags. These flags are set by the CCNinfo
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user program when they initiate Requests (see Appendix A), and the
routers that receive the Requests deal with the flags and change
the behaviors (see Section 5 for details). The Flag values
defined in this Flags field correspond to the Reply sub-blocks.
Flag Value Description
----- ----- -----------------------------------------------------
C 0 Path discovery (i.e., no cache information retrieved)
(default)
C 1 Path and cache information retrieval
O 0 Request to any content forwarder (default)
O 1 Publisher discovery (i.e., only FHR can reply)
F 0 Request based on FIB's forwarding strategy (default)
F 1 Full discovery request. Request to possible multiple
upstream routers specified in FIB simultaneously
V 0 No reply validation (default)
V 1 Reply sender validates Reply message
Figure 9: Codes and types specified in Flags field
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 (=T_DISC_REQ) | Length |
+---------------+---------------+---------------+---------------+
| Request Arrival Time |
+---------------+---------------+---------------+---------------+
/ Node Identifier /
+---------------+---------------+---------------+---------------+
Figure 10: Request block TLV (packet payload)
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-%x000C Reserved [1]
%x000D T_DISC_REQ
%x000E T_DISC_REPLY
%x0FFE T_PAD [1]
%x0FFF T_ORG [1]
%x1000-%x1FFF Reserved [1]
Figure 11: CCNx Message Type Namespace
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Type: 16 bits
Format of the Value field. For the Request block TLV, the type
value(s) MUST be T_DISC_REQ (see Figure 11) 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 message at the router. The
32-bit form of an NTP timestamp consists of the middle 32 bits of
the full 64-bit form; that is, the low 16 bits of the integer part
and the high 16 bits of the fractional part.
The following formula converts from a timespec (fractional part in
nanoseconds) to a 32-bit NTP timestamp:
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), where "<<"
denotes a logical left shift.
Note that it is RECOMMENDED for all the routers on the path to
have synchronized clocks to measure one-way latency per hop;
however, even if they do not have synchronized clocks, CCNinfo
measures the RTT between the content forwarder and consumer.
Node Identifier: variable length
This field specifies the node identifier (e.g., node name or hash-
based self-certifying name [11]) or all-zeros if unknown. This
document assumes that the Name TLV defined in the CCNx TLV format
[1] can be used for this field and the node identifier is
specified in it.
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3.1.2. Report Block TLV
A CCNinfo user and each upstream router along the path would insert
their 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 12), the
Request Arrival Time and 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
+---------------+---------------+---------------+---------------+
| Type (=T_DISC_REPORT) | Length |
+---------------+---------------+---------------+---------------+
| Request Arrival Time |
+---------------+---------------+---------------+---------------+
/ Node Identifier /
+---------------+---------------+---------------+---------------+
Figure 12: Report block TLV (hop-by-hop header)
Type: 16 bits
Format of the Value field. For the Report block TLV, the type
value(s) MUST be T_DISC_REPORT in the current specification. For
all the available types for hop-by-hop type namespace, please see
Figure 8.
Length: 16 bits
Length of Value field in octets.
Request Arrival Time: 32 bits
Same definition as given in Section 3.1.1.
Node Identifier: variable length
Same definition as given in Section 3.1.1.
3.1.3. Content Name Specification
Specifications of the Name TLV (whose type value is T_NAME) and the
Name Segment TLVs are described in [1], which are followed by
CCNinfo. CCNinfo enables to specification of the content name either
with a prefix name without chunk number (such as "ccnx:/news/today")
or an exact name (such as "ccnx:/news/today/Chunk=10"). When a
CCNinfo user specifies a prefix name, s/he will obtain the summary
information of the matched content objects in the content forwarder.
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In contrast, when a CCNinfo user specifies an exact name, s/he will
obtain only about the specified content object in the content
forwarder. A CCNinfo Request message MUST NOT be sent only with a
scheme name, ccnx:/. It will be rejected and discarded by routers.
3.2. Reply Message
When a content forwarder receives a CCNinfo Request message from an
appropriate adjacent neighbor router, it inserts its own Reply block
TLV and Reply sub-block TLV(s) to the Request message and turns the
Request into the Reply by changing the Type field of the fixed header
of the Request message from PT_CCNINFO_REQUEST to PT_CCNINFO_REPLY.
The Reply message (see Figure 13) is then 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 header block TLV /
+---------------+---------------+---------------+---------------+
/ . /
/ . /
/ n Report block TLVs /
/ . /
/ . /
+===============+===============+===============+===============+
| Type (=T_DISCOVERY) | MessageLength |
+---------------+---------------+---------------+---------------+
| T_NAME | Length |
+---------------+---------------+---------------+---------------+
/ Name segment TLVs (name prefix specified by CCNinfo user) /
+---------------+---------------+---------------+---------------+
/ Request block TLV /
+---------------+---------------+---------------+---------------+
/ Reply block TLV /
+---------------+---------------+---------------+---------------+
/ Reply sub-block TLV 1 /
+---------------+---------------+---------------+---------------+
/ . /
/ . /
+---------------+---------------+---------------+---------------+
/ Reply sub-block TLV k /
+---------------+---------------+---------------+---------------+
/ Optional CCNx ValidationAlgorithm TLV /
+---------------+---------------+---------------+---------------+
/ Optional CCNx ValidationPayload TLV (ValidationAlg required) /
+---------------+---------------+---------------+---------------+
Figure 13: Reply message consists of a fixed header, Request
block TLV, Report block TLV(s), Name TLV, and Reply block/sub-
block TLV(s)
3.2.1. Reply Block TLV
The Reply block TLV is an envelope for the Reply sub-block TLV(s)
(explained from the next section).
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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
+---------------+---------------+---------------+---------------+
| Type (=T_DISC_REPLY) | Length |
+---------------+---------------+---------------+---------------+
| Request Arrival Time |
+---------------+---------------+---------------+---------------+
/ Node Identifier /
+---------------+---------------+---------------+---------------+
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 shown in Figure 11 in the current
specification.
Length: 16 bits
Length of the Value field in octets. This length is the total
length of Reply sub-block(s).
Request Arrival Time: 32 bits
Same definition as given in Section 3.1.1.
Node Identifier: variable length
Same definition as given in Section 3.1.1.
3.2.1.1. Reply Sub-Block TLV
The router on the traced path will add one or multiple Reply sub-
blocks followed by the Reply block TLV before sending the Reply to
its neighbor router. This section describes the Reply sub-block TLV
for informing various cache states and conditions as shown in
Figure 15. (Other Reply sub-block TLVs will be discussed in separate
document(s).)
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Note that some routers may not be capable of reporting the following
values, such as Object Size, Object Count, # Received Interest, First
Seqnum, Last Seqnum, Elapsed Cache Time, and Remain Cache Lifetime,
shown in Figure 15, or do not report these values due to their
policy. In that case, the routers set these fields to a value of all
ones (i.e., %xFFFFFFFF). The value of each field will be also all-
one when the value is equal to or bigger than the maximum size
expressed by the 32-bit field. The CCNinfo user program MUST inform
that these values are not valid if the fields received are set to the
value of all ones.
If the cache is refreshed after reboot, the value in each field MUST
be refreshed (i.e., MUST be set to 0). If the cache remains after
reboot, the value MUST NOT be refreshed (i.e., MUST be reflected as
it is).
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_PUBLISHER (packet payload)
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Code Type name
============= ===========================
%x0000 T_DISC_CONTENT
%x0001 T_DISC_CONTENT_PUBLISHER
%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 either T_DISC_CONTENT or T_DISC_CONTENT_PUBLISHER
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_PUBLISHER is specified when
the content information is replied from a FHR attached to a
publisher.
Length: 16 bits
Length of the Value field in octets.
Object Size: 32 bits
The total size (KB) of the unexpired content objects. Values less
than 1 KB are truncated. Note that the maximum size expressed by
the 32-bit field is approximately 4.29 TB.
Object Count: 32 bits
The number of the unexpired content objects. Note that the
maximum count expressed by the 32-bit field is approximately 4.29
billion.
# 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 unexpired content objects.
Last Seqnum: 32 bits
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The last sequential number of the unexpired content objects. The
First Seqnum and Last Seqnum do not guarantee the consecutiveness
of the cached content objects; however, knowing these values may
help in the analysis of consecutive or discontinuous chunks such
as [12].
Elapsed Cache Time: 32 bits
The elapsed time (seconds) after the oldest content object of the
content is cached.
Remain Cache Lifetime: 32 bits
The lifetime (seconds) of a content object, which is lastly
cached.
4. CCNinfo User Behavior
4.1. Sending CCNinfo Request
A CCNinfo user invokes a CCNinfo user program (e.g., ccninfo command)
that initiates a CCNinfo Request message and sends it to the user's
adjacent neighbor router(s) of interest. The user later obtains both
the routing path information and in-network cache information in the
single Reply.
When the CCNinfo user program initiates a Request message, it MUST
insert the necessary values, i.e., the "Request ID" and the "Node
Identifier", in the Request block. The Request ID MUST be unique for
the CCNinfo user until s/he receives the corresponding Reply
message(s) or the Request is timed out.
Owing to some policies, a router may want to validate the CCNinfo
Requests using the CCNx ValidationPayload TLV (whether it accepts the
Request or not) especially when the router receives the "full
discovery request" (see Section 5.3.2). Accordingly, the CCNinfo
user program MAY require validating the Request message and appending
the user's signature into the CCNx ValidationPayload TLV. The router
then forwards the Request message. If the router does not approve
the Request, it rejects the Request message as described in
Section 6.11.
After the CCNinfo user program sends the Request message, until the
Reply is timed out or the expected numbers of Replies or a Reply
message with a non-zero ReturnCode in the fixed header is received,
the CCNinfo user program MUST keep the following information:
HopLimit, specified in the fixed header, Request ID, Flags, Node
Identifier, and Request Arrival Time, specified in the Request block.
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4.1.1. Routing Path Information
A CCNinfo user can send a CCNinfo Request for investigating the
routing path information for the specified named content. Using the
Request, a legitimate user can obtain 1) the node identifiers of the
intermediate routers, 2) node identifier of the content forwarder, 3)
number of hops between the content forwarder and consumer, and 4) RTT
between the 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. Using the Request, a legitimate user can
obtain 1) the size of cached content objects, 2) number of cached
content objects, 3) number of accesses (i.e., received Interests) per
content, and 4) lifetime and expiration time of the cached content
objects, for Content Store (CS) in the content forwarder, unless the
content forwarder is capable of reporting them (see Section 3.2.1.1).
This CCNinfo Request is terminated when it reaches the content
forwarder.
4.2. Receiving CCNinfo Reply
A CCNinfo user program will receive one or multiple CCNinfo Reply
messages from the adjacent neighbor router(s). When the program
receives the Reply, it MUST compare the kept Request ID and Node
Identifier to identify the Request and Reply pair. If they do not
match, the Reply message MUST be silently discarded.
If the number of 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 the maximum path that s/he can be expected to, s/he might
collect statistics by waiting for a timeout. Useful statistics
provided by CCNinfo are stated in Section 8.
5. Router Behavior
5.1. User and Neighbor Verification
Upon receiving a CCNinfo Request message, a router MAY examine
whether a valid CCNinfo user has sent the message. If the router
recognizes that the Request sender's signature specified in the
Request is invalid, it SHOULD terminate the Request, as defined in
Section 6.4.
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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, it
SHOULD silently ignore the Request/Reply message, as specified in
Section 10.9.
5.2. Receiving CCNinfo Request
After a router accepts the CCNinfo Request message, it performs the
following steps.
1. The value of "HopLimit" in the fixed header and that of "SkipHop
(Skip Hop Count)" 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 6.5. If the
SkipHop value is equal to or more than the HopLimit value, the
router terminates the Request, as defined in Section 6.4.
Otherwise, until the SkipHop value becomes zero, the router
forwards the Request message to the upstream router(s) without
adding its own Report block and without replying to the Request.
If the router does not know the upstream router(s) regarding the
specified name prefix, it terminates the Request, as defined in
Section 6.5. It should be noted that the Request messages are
terminated at the FHR; therefore, although the maximum value for
the HopLimit is 255 and that for SkipHop is 15, if the Request
messages reach the FHR before the HopLimit or SkipHop value
becomes 0, the FHR silently discards the Request message and the
Request is timed out.
2. The router examines the Flags field (specified in Figure 9) in
the Request block of the received CCNinfo Request. If the "C"
flag is not set, it is categorized as the "routing path
information discovery". If the "C" flag is set, it is the "cache
information discovery". If the "O" flag is set, it is the
"publisher discovery".
3. If the Request is either "cache information discovery" or
"routing path information discovery", the router examines its FIB
and CS. If the router caches the specified content, it sends the
Reply message with its own Reply block and sub-block(s). If the
router cannot insert its own Reply block or sub-block(s) because
of no space, it terminates the Request, as specified in
Section 6.7. If the router does not cache the specified content
but knows the upstream neighbor router(s) for the specified name
prefix, it creates the PIT entry, and inserts its own Report
block in the hop-by-hop header and forwards the Request to the
upstream neighbor(s). If the router cannot insert its own Report
block because of no space, or if the router does not cache the
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specified content and does not know the upstream neighbor
router(s) for the specified name prefix, it terminates the
Request, as defined in Section 6.5.
4. If the Request is the "publisher discovery", the router examines
whether it is the FHR for the requested content. If the router
is the FHR, it sends the Reply message with its own Report block
and sub-blocks (in the case of cache information discovery) or
the Reply message with its own Report block without adding any
Reply sub-blocks (in the case of routing path information
discovery). If the router is not the FHR but knows the upstream
neighbor router(s) for the specified name prefix, it creates the
PIT entry, and inserts its own Report block and forwards the
Request to the upstream neighbor(s). If the router cannot insert
its own Report block in the hop-by-hop header because of no
space, it terminates the Request, as specified in Section 6.7.
If the router 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 6.5. Note that in Cefore
[14], there is an API by which a publisher informs the
application prefix to the FHR and the FHR registers it into the
FIB. The prefix entry then can be statically configured on other
routers or announced by a routing protocol.
5.3. Forwarding CCNinfo Request
5.3.1. Regular 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 like the ordinary
Interest-Data exchanges in CCN.
When the router forwards the Request message, it MUST record the F
flag and Request ID in the Request block of the Request message and
exploiting path labels (specified in Section 1) at the corresponding
PIT entry. The router can later check the PIT entry to correctly
forward the Reply message(s) back.
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CCNinfo supports multipath forwarding. The Request messages can be
forwarded to multiple neighbor routers. Some routers may have a
strategy for multipath forwarding; when a router 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 strategies; a CCNinfo user could
trace the actual forwarding path based on the forwarding strategy and
will receive a single Reply message such as a content object.
5.3.2. Full Discovery Request
There may be a case wherein a CCNinfo user wants to discover all
possible forwarding paths and content forwarders based on the
routers' FIBs. The "full discovery request" enables this
functionality. If a CCNinfo user sets the F flag in the Request
block of the Request message (as seen in Figure 9) to request the
full discovery, the upstream routers simultaneously forward the
Requests to all multiple upstream routers based on the FIBs. Then,
the CCNinfo user can trace all possible forwarding paths. As seen in
Figure 17, each router forwards the Reply message along its PIT entry
and finally, the CCNinfo user receives two Reply messages: one from
the FHR (Router C) and the other from the Caching router.
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 17: Full discovery request. Reply messages forwarded by
publisher and routers.
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To receive different Reply messages forwarded from different routers,
the PIT entries initiated by CCNinfo remain until the configured
CCNinfo Reply Timeout (Section 7.1) is expired. In other words,
unlike the ordinary Interest-Data exchanges in CCN, if routers that
accept the full discovery request receive the full discovery request,
the routers SHOULD NOT remove the PIT entry created by the full
discovery request until the CCNinfo Reply Timeout value expires.
Note that the full discovery request is an OPTIONAL implementation of
CCNinfo; it may not be implemented on routers. Even if it is
implemented on a router, it may not accept the full discovery request
from non-validated CCNinfo users or routers or because of its policy.
If a router does not accept the full discovery request, it rejects
the full discovery request as described in Section 6.11. Routers
that enable the full discovery request MAY rate-limit Replies, as
described in Section 10.8 as well.
5.4. Sending CCNinfo Reply
If there is a caching router or FHR for the specified content within
the specified hop count along the path, the caching router or FHR
sends back the Reply message toward the CCNinfo user and terminates
the Request.
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 with the Request Arrival Time and Node
Identifier to the Request message. Then, the router inserts the
corresponding Reply sub-block(s) (Figure 15) to the payload. The
router finally changes the Type field in the fixed header from
PT_CCNINFO_REQUEST to PT_CCNINFO_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, the router MUST put an
appropriate ReturnCode in the Request message, change the Type field
value in the fixed header from PT_CCNINFO_REQUEST to
PT_CCNINFO_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 those in the PIT entry, 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.
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The 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" (see Section 5.3.2), 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 transmission
of Reply messages.
5.6. PIT Entry Management for Multipath Support
Within a network with multipath condition, there is a case
(Figure 18) wherein a single CCNinfo Request is split into multiple
Requests (e.g., at Router A), which are injected into a single router
(Router D). In this case, multiple Replies with the same Request ID
and Node Identifier including different Report blocks are received by
the router (Router D).
+--------+
| Router |
| B |
+--------+
/ \
/ \
+--------+ +--------+ +--------+ +---------+
| CCNinfo|----| Router | | Router | ... |Publisher|
| user | | A | | D | | |
+--------+ +--------+ +--------+ +---------+
\ /
\ /
+--------+
| Router |
| C |
+--------+
Figure 18
To recognize different CCNinfo Reply messages, the routers MUST
distinguish the PIT entries by the Request ID and exploiting path
labels, which could be a hash value of the concatenation information
of the cumulate Node Identifiers in the hop-by-hop header and the
specified content name. For example, when Router D in Figure 18
receives a CCNinfo Request from Router B, its PIT includes the
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Request ID and value such as H((Router_A|Router_B)|content_name),
where "H" indicates some hash function and "|" indicates
concatenation. When Router D receives a CCNinfo Request from Router
C, its PIT includes the same Request ID and value of
H((Router_A|Router_C)|content_name). Two different Replies are later
received on Router D and each Reply is appropriately forwarded to
Router B and Router C, respectively. Note that two Reply messages
coming from Router B and Router C are reached at Router A, but the
CCNinfo user can only receive the first Reply message either from
Router B or Router C as Router A removes the corresponding PIT entry
after it forwards the first Reply.
To avoid routing loops, when a router seeks the cumulate Node
Identifiers of the Report blocks in the hop-by-hop header, it MUST
examine whether its own Node Identifier is not previously inserted.
If a router detects its own Node Identifier in the hop-by-hop header,
the router inserts its Report block and terminates the Request as
will be described in Section 6.8.
6. CCNinfo Termination
When performing a hop-by-hop trace, it is necessary to determine when
to stop the trace. There are several cases when an intermediate
router might return a Reply before a Request reaches the caching
router or the FHR.
6.1. Arriving at First-hop Router
A CCNinfo Request can be determined to have arrived at the FHR. To
ensure that a router recognizes that it is the FHR for the specified
content, it needs to have a FIB entry (or attach) to the
corresponding publisher or the content.
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. Arriving at Last Router
A CCNinfo Request can be determined to have arrived at the last
router of the specified HopLimit. If the last router does not have
the corresponding cache, it MUST insert its Report block and send the
Reply message with NO_INFO return code without appending any Reply
(sub-)block TLVs.
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6.4. Invalid Request
If the router does not validate the Request or the Reply even it is
required, the router MUST note a ReturnCode of INVALID_REQUEST in the
fixed header of the message, insert its Report block, and forward the
message as the Reply back to the CCNinfo user. The router MAY,
however, randomly ignore the received invalid messages. (See
Section 10.7.)
6.5. No Route
If the router cannot determine the routing paths or neighbor routers
for the specified name prefix within the specified HopLimit, it MUST
note a ReturnCode of NO_ROUTE in the fixed header of the message,
insert its Report block, and forward the message as the Reply back to
the CCNinfo user.
6.6. No Information
If the router does not have any information about the specified name
prefix within the specified HopLimit, it MUST note a ReturnCode of
NO_INFO in the fixed header of the message, insert its Report block,
and forward the message as the Reply back to the CCNinfo user.
6.7. No Space
If appending the Report block or the Reply (sub-)block would make the
hop-by-hop header longer than 247 bytes or the Request packet longer
than the MTU of the Incoming face, 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.
6.8. Fatal Error
If a CCNinfo Request has encountered a fatal error, the router MUST
note a ReturnCode of FATAL_ERROR in the fixed header of the message
and forward the message as the Reply back to the CCNinfo user. This
may happen, for example, when the router detects some routing loop in
the Request blocks (see Section 1). The fatal error can be encoded
with another error: if a router detects routing loop but cannot
insert its Report block, it MUST note NO_SPACE and FATAL_ERROR
ReturnCodes (i.e., %x85) in the fixed header and forward the message
back to the CCNinfo user.
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6.9. 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.
6.10. Non-Supported Node
Cases will arise in which a router or a FHR 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.
6.11. Administratively Prohibited
If CCNinfo is administratively prohibited, the router rejects the
Request message and MUST send the CCNinfo Reply with the ReturnCode
of ADMIN_PROHIB. The router MAY, however, randomly ignore the
Request messages to be rejected (see Section 10.7).
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 3 (seconds).
The [CCNinfo Reply Timeout] value SHOULD NOT be larger than 4
(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 the 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 6.4.
7.3. Access Control
A router MAY configure the valid or invalid networks to enable an
access control. The access control MAY be defined per name prefix,
such as "who can retrieve which name prefix" (see Section 10.2).
8. Diagnosis and Analysis
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8.1. Number of Hops and RTT
A CCNinfo Request message is forwarded in a hop-by-hop manner and
each forwarding router appends its own Report block. We can then
verify the number of hops to reach the content forwarder or publisher
and the RTT between the content forwarder or publisher.
8.2. Caching Router Identification
While some routers may hide their node identifiers with all-zeros in
the Report blocks (as seen in Section 10.1), the routers in the path
from the CCNinfo user to the content forwarder can be identified.
8.3. TTL or Hop Limit
By taking the HopLimit from the content forwarder and forwarding the
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
the propagation and queuing delays from the differences between the
timestamps at the successive hops. However, this delay includes the
control processing overhead; therefore, it is not necessarily
indicative of the delay that would be experienced by the data
traffic.
8.5. Path Stretch
By obtaining 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 improvements in path stretch in various cases,
such as in different caching and routing algorithms. We can then
facilitate the 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. Accordingly, CCNinfo measures the content popularity
(i.e., the number of accesses for each content/cache), thereby
enabling the investigation of the routing/caching strategy in
networks.
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9. IANA Considerations
This section details each kind of CCNx protocol value that can be
registered. As per [5], this section makes assignments in four
existing registries and creates a new Reply Type registry in the
"Content-Centric Networking (CCNx)" registry group. The registration
procedure is "RFC Required", which requires only that this document
be published as an RFC.
9.1. Packet Type Registry
As shown in Figure 4, CCNinfo defines two packet types,
PT_CCNINFO_REQUEST and PT_CCNINFO_REPLY, whose suggested values are
%x03 and %x04, respectively.
9.2. Top-Level Type Registry
As shown in Figure 5, CCNinfo defines one top-level type,
T_DISCOVERY, whose suggested value is %x0005.
9.3. Hop-by-Hop Type Registry
As shown in Figure 8, CCNinfo defines two hop-by-hop types,
T_DISC_REQHDR and T_DISC_REPORT, whose suggested values are %x0008
and %x0009, respectively.
9.4. Message Type Registry
As shown in Figure 11, CCNinfo defines two message types, T_DISC_REQ
and T_DISC_REPLY, whose suggested values are %x000D and %x000E,
respectively.
9.5. Reply Type Registry
IANA has created the "CCNx Reply Types" registry and allocated the
reply types. The Type value is 2 octets. The range is
%x0000-%xFFFF. As shown in Figure 16, CCNinfo defines three reply
types, T_DISC_CONTENT, T_DISC_CONTENT_PUBLISHER, and T_ORG, whose
suggested values are %x0000, %x0001, and %x0FFF, respectively.
10. Security Considerations
This section addresses some of the security considerations.
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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
information to specific members of their networks. CCNinfo provides
policy-based information provisioning, thereby 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 cache information" can be defined for each router. For the
former type of access policy, routers with the specified content MAY
examine the signature enclosed in the Request message and decide
whether they should notify the content information in the Reply. If
the routers decide to not notify the content information, they MUST
send the CCNinfo Reply with the ReturnCode of ADMIN_PROHIB without
appending any Reply (sub-)block TLVs. For the latter type of policy,
the permission, whether (1) All (all cache information is disclosed),
(2) Partial (cache information with a particular name prefix can (or
cannot) be disclosed), or (3) Deny (no cache information is
disclosed), is defined at the routers.
In contrast, we entail that each router does not disrupt the
forwarding of CCNinfo Request and Reply messages. When a Request
message is received, the router SHOULD insert the 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.
Finally, the router SHOULD forward the Request message to the
upstream router toward the content forwarder if the ReturnCode is
kept with NO_ERROR.
10.2. Filtering CCNinfo Users Located in Invalid Networks
A router MAY support an access control mechanism to filter out
Requests from invalid CCNinfo users. To accomplish this, invalid
networks (or domains) could, for example, be configured via a list of
allowed/disallowed networks (as observed in Section 7.3). If a
Request is received from a 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 SHOULD be used to
note that. The router MAY, however, perform rate limited logging of
such events.
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10.3. Topology Discovery
CCNinfo can be used to discover actively used topologies. If a
network topology is not disclosed, CCNinfo Requests SHOULD be
restricted at the border of the domain using the ADMIN_PROHIB return
code.
10.4. Characteristics of Content
CCNinfo can be used to discover the type of content being sent by
publishers. If this information is a secret, CCNinfo Requests SHOULD
be restricted at the border of the domain, using the ADMIN_PROHIB
return code.
10.5. Computational Attacks
CCNinfo may impose heavy tasks at content forwarders because it makes
content forwarders seek their internal cache states reported in the
Reply messages whenever they form the Reply messages. The current
CCNinfo specification allows to return null values for several
fields, such as First/Last Seqnum or Elapsed Cache Time fields in the
Reply sub-block. As mentioned in Section 3.2.1.1, these values MAY
be null. This means that the content forwarder can not only hide
these values owing to privacy/security policies, but also skip the
implementations of the complex functions to report these values.
10.6. Longer or Shorter CCNinfo Reply Timeout
Routers can configure CCNinfo Reply Timeout (Section 7.1), which is
the allowable timeout value to keep the PIT entry. If routers
configure a longer timeout value, there may be an attractive attack
vector against the PIT memory. Moreover, especially when the full
discovery request option (Section 5.3) is specified for the CCNinfo
Request, several Reply messages may be returned and cause a response
storm. (See Section 10.8 for rate-limiting to avoid the storm). 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 all Replies; s/he only retrieves the partial path
information (i.e., information about a part of the tree).
There may be a way to enable incremental exploration (i.e., to
explore the part of the tree that was not explored by the previous
operation); however, discussing such mechanisms is out of scope of
this document.
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10.7. Limiting Request Rates
A router MAY rate-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. In such a
case, no error message is returned. The rate limit function is left
to the router's implementation.
10.8. Limiting Reply Rates
CCNinfo supporting multipath forwarding may result in one Request
returning multiple Reply messages. To prevent abuse, the routers in
the traced path MAY need to rate-limit the Replies. In such a case,
no error message is returned. The rate limit function is left to the
router's implementation.
10.9. Adjacency Verification
It is assumed that the CCNinfo Request and Reply messages are
forwarded by adjacent neighbor nodes or routers. The CCNx message
format or semantics do not define a secure way to verify the node/
router adjacency, while HopAuth [11] provides a possible method for
an adjacency verification and defines the corresponding message
format for adjacency verification as well as the router behaviors.
CCNinfo MAY use a similar method for node adjacency verification.
11. Acknowledgements
The authors would like to thank Jerome Francois, Erik Kline, Spyridon
Mastorakis, Paulo Mendes, Ilya Moiseenko, David Oran, and Thierry
Turletti 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", RFC 8609, July 2019,
<https://www.rfc-editor.org/rfc/rfc8609>.
[2] Mosko, M., Solis, I., and C. Wood, "CCNx Semantics",
RFC 8569, July 2019,
<https://www.rfc-editor.org/rfc/rfc8569>.
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[3] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[4] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", May 2017,
<https://www.rfc-editor.org/info/rfc8174>.
[5] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
12.2. Informative References
[6] Wood, C., Afanasyev, A., Zhang, L., Oran, D., and C.
Tschudin, "Information-Centric Networking (ICN): Content-
Centric Networking (CCNx) and Named Data Networking (NDN)
Terminology", RFC 8793, June 2020,
<https://www.rfc-editor.org/rfc/rfc8793>.
[7] 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.
[8] Mastorakis, S., Gibson, J., Moiseenko, I., Droms, R., and
D. Oran, "ICN Ping Protocol Specification", draft-irtf-
icnrg-icnping-06 (work in progress), May 2022.
[9] Mastorakis, S., Gibson, J., Moiseenko, I., Droms, R., and
D. Oran, "ICN Traceroute Protocol Specification", draft-
irtf-icnrg-icntraceroute-06 (work in progress), May 2022.
[10] Asaeda, H., Mayer, K., and W. Lee, "Mtrace Version 2:
Traceroute Facility for IP Multicast", RFC 8487, October
2018, <https://www.rfc-editor.org/rfc/rfc8487>.
[11] Li, R. and H. Asaeda, "Hop-by-Hop Authentication in
Content-Centric Networking/Named Data Networking", draft-
li-icnrg-hopauth-02 (work in progress), February 2020.
[12] Li, R., Matsuzono, K., Asaeda, H., and X. Fu, "Consecutive
Caching and Adaptive Retrieval for In-Network Big Data
Sharing", Proc. IEEE ICC, Kansas City, USA, May 2018.
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[13] Asaeda, H., Ooka, A., Matsuzono, K., and R. Li, "Cefore:
Software Platform Enabling Content-Centric Networking and
Beyond", IEICE Transaction on Communications, Vol.E102-B,
No.9, pp.1792-1803, September 2019.
[14] "Cefore Home Page", <https://cefore.net/>.
Appendix A. ccninfo Command and Options
CCNinfo is implemented in Cefore [13][14]. The command invoked by
the CCNinfo user (e.g., consumer) is named "ccninfo". The ccninfo
command sends the Request message and receives the Reply message(s).
There are several options that can be specified with ccninfo, while
the content name prefix (e.g., ccnx:/news/today) is the mandatory
parameter.
The usage of ccninfo command is as follows:
Usage: ccninfo [-c] [-f] [-o] [-V] [-r hop_count] [-s hop_count] [-v
algo] name_prefix
name_prefix
Prefix name of content (e.g., ccnx:/news/today) or exact name of
content (e.g., ccnx:/news/today/Chunk=10) the CCNinfo user wants
to trace.
c option
This option can be specified if a CCNinfo user needs the cache
information as well as the routing path information for the
specified content/cache and RTT between the CCNinfo user and
content forwarder.
f option
This option enables the "full discovery request"; routers send
CCNinfo Requests to multiple upstream faces based on their FIBs
simultaneously. The CCNinfo user can then trace all possible
forwarding paths.
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) sends the Reply message.
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V option
This option requests the Reply sender to validate the Reply
message with the Reply sender's signature. The Reply message will
then include the CCNx ValidationPayload TLV. The validation
algorithm is selected by the Reply sender.
r option
Number of traced routers. 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.
s option
Number of skipped routers. This value is set in the "SkipHop"
field located in the Request block TLV. For example, when the
CCNinfo user invokes the CCNinfo command with this option, such as
"-s 3", three upstream routers along the path only forward the
Request message but do not append their Report blocks in the hop-
by-hop header and do not send Reply messages despite having the
corresponding cache.
v option
This option enables the CCNinfo user to validate the Request
message with his/her signature. The Request message will include
the CCNx ValidationPayload TLV. The validation algorithm is
specified by the CCNinfo user.
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
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
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Xun Shao
Toyohashi University of Technology
1-1 Hibarigaoka Tempaku-cho, Toyohashi,
Aichi 441-8580
Japan
Email: shao.xun.ls@tut.jp
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