path: root/doc/rfc/rfc9344.txt

Internet Research Task Force (IRTF)                            H. Asaeda
Request for Comments: 9344                                       A. Ooka
Category: Experimental                                              NICT
ISSN: 2070-1721                                                  X. Shao
                                      Toyohashi University of Technology
                                                           February 2023


CCNinfo: Discovering Content and Network Information in Content-Centric
                                Networks

Abstract

   This document describes a mechanism named "CCNinfo" that discovers
   information about the network topology and in-network cache in
   Content-Centric Networks (CCNs).  CCNinfo investigates 1) the CCN
   routing path information per name prefix, 2) the Round-Trip Time
   (RTT) between the content forwarder and the 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, 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 document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  This document is a product of the Internet Research Task
   Force (IRTF).  The IRTF publishes the results of Internet-related
   research and development activities.  These results might not be
   suitable for deployment.  This RFC represents the consensus of the
   Information-Centric Networking Research Group of the Internet
   Research Task Force (IRTF).  Documents approved for publication by
   the IRSG are not candidates for any level of Internet Standard; see
   Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9344.

Copyright Notice

   Copyright (c) 2023 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
   to this document.

Table of Contents

   1.  Introduction
     1.1.  CCNinfo as an Experimental Tool
   2.  Terminology
     2.1.  Definitions
   3.  CCNinfo Message Formats
     3.1.  Request Message
       3.1.1.  Request Header Block and Request Block
       3.1.2.  Report Block TLV
       3.1.3.  Content Name Specification
     3.2.  Reply Message
       3.2.1.  Reply Block TLV
         3.2.1.1.  Reply Sub-Block TLV
   4.  CCNinfo User Behavior
     4.1.  Sending CCNinfo Request
       4.1.1.  Routing Path Information
       4.1.2.  In-Network Cache Information
     4.2.  Receiving CCNinfo Reply
   5.  Router Behavior
     5.1.  User and Neighbor Verification
     5.2.  Receiving CCNinfo Request
     5.3.  Forwarding CCNinfo Request
       5.3.1.  Regular Request
       5.3.2.  Full Discovery Request
     5.4.  Sending CCNinfo Reply
     5.5.  Forwarding CCNinfo Reply
     5.6.  PIT Entry Management for Multipath Support
   6.  CCNinfo Termination
     6.1.  Arriving at First-Hop Router
     6.2.  Arriving at Router Having Cache
     6.3.  Arriving at Last Router
     6.4.  Invalid Request
     6.5.  No Route
     6.6.  No Information
     6.7.  No Space
     6.8.  Fatal Error
     6.9.  CCNinfo Reply Timeout
     6.10. Non-Supported Node
     6.11. Administratively Prohibited
   7.  Configurations
     7.1.  CCNinfo Reply Timeout
     7.2.  HopLimit in Fixed Header
     7.3.  Access Control
   8.  Diagnosis and Analysis
     8.1.  Number of Hops and RTT
     8.2.  Caching Router Identification
     8.3.  TTL or Hop Limit
     8.4.  Time Delay
     8.5.  Path Stretch
     8.6.  Cache Hit Probability
   9.  IANA Considerations
     9.1.  Packet Type Registry
     9.2.  Top-Level Type Registry
     9.3.  Hop-by-Hop Type Registry
     9.4.  Message Type Registry
     9.5.  Reply Type Registry
   10. Security Considerations
     10.1.  Policy-Based Information Provisioning for Request
     10.2.  Filtering CCNinfo Users Located in Invalid Networks
     10.3.  Topology Discovery
     10.4.  Characteristics of Content
     10.5.  Computational Attacks
     10.6.  Longer or Shorter CCNinfo Reply Timeout
     10.7.  Limiting Request Rates
     10.8.  Limiting Reply Rates
     10.9.  Adjacency Verification
   11. References
     11.1.  Normative References
     11.2.  Informative References
   Appendix A.  ccninfo Command and Options
   Acknowledgements
   Authors' Addresses

1.  Introduction

   In Content-Centric Networks (CCNs), 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.

   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 the 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 [Contrace] 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 (Information-Centric
   Networking) ping [ICN-PING] and traceroute [ICN-TRACEROUTE] 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 [RFC8609].  The Request-and-Reply message flow,
   walking up the tree from a consumer toward a publisher, is similar to
   the behavior of the IP multicast traceroute facility [RFC8487].

   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
   metrics for Content Store (CS) in the content forwarder as follows:
   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.

   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 they want 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 (Routers
   A, B, C) insert their own Report blocks into the Request message and
   forward the message toward the content forwarder.

           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 the 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
   (Routers 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 |
                                              +---------+

        Figure 2: Reply Messages Forwarded by Routers, and One Reply
                  Message is Received by the 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] [RFC8174] 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 [RFC8609].  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:
      A scheme name indicates a URI and protocol.  This document only
      considers "ccnx:/" as the scheme name.

   Prefix name:
      A prefix name, which is defined in [RFC8569], 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 [RFC8569], 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 described in [RFC8793].

   Consumer:
      A node that requests Content Objects by generating and sending out
      Interests.  It is the same definition of ICN Consumer, as given in
      [RFC8793].

   Publisher:
      A node that creates Content Objects and makes them available for
      retrieval.  It is the same definition of ICN Producer, as given in
      [RFC8793].

   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 the next node.

   Content forwarder:
      A content forwarder 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 either a
      consumer or a 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 is 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.

3.  CCNinfo Message Formats

   CCNinfo Request and Reply messages are encoded in the CCNx TLV format
   (see [RFC8609] and Figure 3).  The Request message consists of a
   fixed header, Request block TLV (Figure 5), and Report block TLV(s)
   (Figure 7).  The Reply message consists of a fixed header, Request
   block TLV, Report block TLV(s), Reply block TLV (Figure 9), and Reply
   sub-block TLV(s) (Figure 10).

                          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 [RFC8609]

   The PacketType values in the fixed header shown in Figure 3 are
   PT_CCNINFO_REQUEST and PT_CCNINFO_REPLY (see Table 1).  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.

                     +======+=======================+
                     | Type | Name                  |
                     +======+=======================+
                     | 0x00 | PT_INTEREST [RFC8609] |
                     +------+-----------------------+
                     | 0x01 | PT_CONTENT [RFC8609]  |
                     +------+-----------------------+
                     | 0x02 | PT_RETURN [RFC8609]   |
                     +------+-----------------------+
                     | 0x03 | PT_CCNINFO_REQUEST    |
                     +------+-----------------------+
                     | 0x04 | PT_CCNINFO_REPLY      |
                     +------+-----------------------+

                        Table 1: CCNx Packet Types

   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 (Table 2), 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.

                +========+================================+
                | Type   | Name                           |
                +========+================================+
                | 0x0000 | Reserved [RFC8609]             |
                +--------+--------------------------------+
                | 0x0001 | T_INTEREST [RFC8609]           |
                +--------+--------------------------------+
                | 0x0002 | T_OBJECT [RFC8609]             |
                +--------+--------------------------------+
                | 0x0003 | T_VALIDATION_ALG [RFC8609]     |
                +--------+--------------------------------+
                | 0x0004 | T_VALIDATION_PAYLOAD [RFC8609] |
                +--------+--------------------------------+
                | 0x0005 | T_DISCOVERY                    |
                +--------+--------------------------------+

                       Table 2: CCNx Top-Level Types

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 4.  It consists of a
   fixed header, Request header block TLV (Figure 5), Report block
   TLV(s) (Figure 7), 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 (Table 1).  The Type value of the CCNx Top-Level
   type is T_DISCOVERY (Table 2).

                          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 4: Request Message

   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

      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                    |
         +=======+=================+================================+
         | 0x00  | NO_ERROR        | No error                       |
         +-------+-----------------+--------------------------------+
         | 0x01  | WRONG_IF        | CCNinfo Request arrived on an  |
         |       |                 | interface to which this router |
         |       |                 | would not forward for the      |
         |       |                 | specified name and/or function |
         |       |                 | toward the publisher.          |
         +-------+-----------------+--------------------------------+
         | 0x02  | INVALID_REQUEST | Invalid CCNinfo Request is     |
         |       |                 | received.                      |
         +-------+-----------------+--------------------------------+
         | 0x03  | NO_ROUTE        | This router has no route for   |
         |       |                 | the name prefix and no way to  |
         |       |                 | determine a route.             |
         +-------+-----------------+--------------------------------+
         | 0x04  | NO_INFO         | This router has no cache       |
         |       |                 | information for the specified  |
         |       |                 | name prefix.                   |
         +-------+-----------------+--------------------------------+
         | 0x05  | NO_SPACE        | There was not enough room to   |
         |       |                 | insert another Report block in |
         |       |                 | the packet.                    |
         +-------+-----------------+--------------------------------+
         | 0x06  | INFO_HIDDEN     | Information is hidden from     |
         |       |                 | this discovery owing to some   |
         |       |                 | policy.                        |
         +-------+-----------------+--------------------------------+
         | 0x0E  | ADMIN_PROHIB    | CCNinfo Request is             |
         |       |                 | administratively prohibited.   |
         +-------+-----------------+--------------------------------+
         | 0x0F  | UNKNOWN_REQUEST | This router does not support   |
         |       |                 | or recognize the Request       |
         |       |                 | message.                       |
         +-------+-----------------+--------------------------------+
         | 0x80  | FATAL_ERROR     | In a fatal error, the router   |
         |       |                 | may know the upstream router   |
         |       |                 | but cannot forward the message |
         |       |                 | to it.                         |
         +-------+-----------------+--------------------------------+

                Table 3: ReturnCode Used for the Reply Message

   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, they MUST insert
   their Request header block TLV (Figure 5) into the hop-by-hop header
   and Request block TLV (Figure 6) 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|
     +---------------+---------------+-------+-------+-------+-+-+-+-+

           Figure 5: Request Header Block TLV (Hop-by-Hop Header)

                 +===============+=======================+
                 | Type          | Name                  |
                 +===============+=======================+
                 | 0x0000        | Reserved [RFC8609]    |
                 +---------------+-----------------------+
                 | 0x0001        | T_INTLIFE [RFC8609]   |
                 +---------------+-----------------------+
                 | 0x0002        | T_CACHETIME [RFC8609] |
                 +---------------+-----------------------+
                 | 0x0003        | T_MSGHASH [RFC8609]   |
                 +---------------+-----------------------+
                 | 0x0004-0x0007 | Reserved [RFC8609]    |
                 +---------------+-----------------------+
                 | 0x0008        | T_DISC_REQHDR         |
                 +---------------+-----------------------+
                 | 0x0009        | T_DISC_REPORT         |
                 +---------------+-----------------------+
                 | 0x0FFE        | T_PAD [RFC8609]       |
                 +---------------+-----------------------+
                 | 0x0FFF        | T_ORG [RFC8609]       |
                 +---------------+-----------------------+
                 | 0x1000-0x1FFF | Reserved [RFC8609]    |
                 +---------------+-----------------------+

                       Table 4: CCNx Hop-by-Hop Types

   Type:  16 bits

      Format of the Value field.  The type value of the Request header
      block TLV MUST be T_DISC_REQHDR.

   Length:  16 bits

      Length of the 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 Table 5, 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 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                             |
            +------+-------+-------------------------------------+

              Table 5: 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 6: Request Block TLV (Packet Payload)

               +===============+==========================+
               | Type          | Name                     |
               +===============+==========================+
               | 0x0000        | T_NAME [RFC8609]         |
               +---------------+--------------------------+
               | 0x0001        | T_PAYLOAD [RFC8609]      |
               +---------------+--------------------------+
               | 0x0002        | T_KEYIDRESTR [RFC8609]   |
               +---------------+--------------------------+
               | 0x0003        | T_OBJHASHRESTR [RFC8609] |
               +---------------+--------------------------+
               | 0x0005        | T_PAYLDTYPE [RFC8609]    |
               +---------------+--------------------------+
               | 0x0006        | T_EXPIRY [RFC8609]       |
               +---------------+--------------------------+
               | 0x0007-0x000C | Reserved [RFC8609]       |
               +---------------+--------------------------+
               | 0x000D        | T_DISC_REQ               |
               +---------------+--------------------------+
               | 0x000E        | T_DISC_REPLY             |
               +---------------+--------------------------+
               | 0x0FFE        | T_PAD [RFC8609]          |
               +---------------+--------------------------+
               | 0x0FFF        | T_ORG [RFC8609]          |
               +---------------+--------------------------+
               | 0x1000-0x1FFF | Reserved [RFC8609]       |
               +---------------+--------------------------+

                       Table 6: CCNx Message Types

   Type:  16 bits

      Format of the Value field.  For the Request block TLV, the type
      value(s) MUST be T_DISC_REQ (see Table 6) in the current
      specification.

   Length:  16 bits

      Length of the 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 the consumer.

   Node Identifier:  variable length

      This field specifies the node identifier (e.g., node name or hash-
      based self-certifying name [DCAuth]) or all-zeros if unknown.
      This document assumes that the Name TLV defined in the CCNx TLV
      format [RFC8609] can be used for this field and the node
      identifier is specified in it.

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 7), the
   Request Arrival Time and Node Identifier values 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 7: 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 of the CCNx hop-by-hop types, please see
      Table 4.

   Length:  16 bits

      Length of the 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 [RFC8609], which is followed by
   CCNinfo.  CCNinfo enables the specification of the content name with
   either 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, they will obtain the summary
   information of the matched Content Objects in the content forwarder.
   In contrast, when a CCNinfo user specifies an exact name, they will
   obtain information 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 8) is then 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 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 8: Reply Message

3.2.1.  Reply Block TLV

   The Reply block TLV is an envelope for the Reply sub-block TLV(s)
   (explained in the next section).

                          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 9: 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 Table 6 in the current
      specification.

   Length:  16 bits

      Length of the Value field in octets.  This length is the total
      length of the 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 10.  (Other Reply sub-block TLVs will be discussed in separate
   document(s).)

   Note that some routers may not be capable of reporting the following
   values: Object Size, Object Count, # Received Interest, First Seqnum,
   Last Seqnum, Elapsed Cache Time, and Remain Cache Lifetime (shown in
   Figure 10).  Or, some routers do not report these values due to their
   policy.  In that case, the routers MUST set these fields to a value
   of all ones (i.e., 0xFFFFFFFF).  The value of each field MUST 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 10: Reply Sub-Block TLV for T_DISC_CONTENT and
                 T_DISC_CONTENT_PUBLISHER (Packet Payload)

             +===============+===============================+
             | Type          | Name                          |
             +===============+===============================+
             | 0x0000        | T_DISC_CONTENT                |
             +---------------+-------------------------------+
             | 0x0001        | T_DISC_CONTENT_PUBLISHER      |
             +---------------+-------------------------------+
             | 0x0FFF        | T_ORG                         |
             +---------------+-------------------------------+
             | 0x1000-0x1FFF | Reserved for Experimental Use |
             +---------------+-------------------------------+

                         Table 7: CCNx Reply Types

   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 CCNx Reply Types (Table 7).  T_DISC_CONTENT is
      specified when a content forwarder replies with the cache
      information.  T_DISC_CONTENT_PUBLISHER is specified when a FHR
      attached to a publisher replies with the original content
      information.

   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

      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 [CONSEC-CACHING].

   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 they receive 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 and Flags
   (specified in the Request header block), and Node Identifier and
   Request Arrival Time (specified in the Request block).

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) the node identifier of the content
   forwarder, 3) the number of hops between the content forwarder and
   the consumer, and 4) the RTT between the content forwarder and the
   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) the number of cached
   Content Objects, 3) the number of accesses (i.e., received Interests)
   per content, and 4) the 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 values 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 they have traced the whole
   path or the maximum path that they can be expected to, they 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.

   Upon receiving a CCNinfo Request or Reply message, a router MAY
   examine whether the message comes from a valid adjacent neighbor
   node.  If the router recognizes that the Request or Reply sender is
   invalid, it SHOULD silently ignore the 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 the value 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 Table 5) 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, 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
       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, 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
       [Cefore-site], 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 values 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.

   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 Table 5) 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 11, 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 11: Full Discovery Request: Reply Messages Forwarded by
                         the Publisher and Routers

   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 a NO_ERROR return code, it
   inserts a Report block with the Request Arrival Time and Node
   Identifier values to the Request message.  Then, the router inserts
   the corresponding Reply sub-block(s) (Figure 10) 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 values match those in the PIT entry, which is 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.

   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 a multipath condition, there is a case
   (Figure 12) 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 values, including different Report blocks, are
   received by the router (Router D).

                               +--------+
                               | Router |
                               |   B    |
                               +--------+
                              /          \
                             /            \
     +--------+    +--------+              +--------+     +---------+
     | CCNinfo|----| Router |              | Router | ... |Publisher|
     |  user  |    |   A    |              |   D    |     |         |
     +--------+    +--------+              +--------+     +---------+
                             \            /
                              \          /
                               +--------+
                               | Router |
                               |   C    |
                               +--------+

            Figure 12: An Example of Multipath Network Topology

   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 12
   receives a CCNinfo Request from Router B, its PIT includes the
   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 to 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 a NO_INFO return code without appending any Reply
   block or sub-block TLVs.

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, the Reply block, or 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., 0x85) in the fixed header and forward the message
   back to the CCNinfo user.

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 and/or 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

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 and/or cache), thereby
   enabling the investigation of the routing/caching strategy in
   networks.

9.  IANA Considerations

   This section details each kind of CCNx protocol value that has been
   registered.  As per [RFC8126], four assignments have been made in
   existing registries, and a new Reply Type registry has been created
   in the "Content-Centric Networking (CCNx)" registry group.

9.1.  Packet Type Registry

   As shown in Table 1, CCNinfo defines two packet types,
   PT_CCNINFO_REQUEST and PT_CCNINFO_REPLY, whose values are 0x03 and
   0x04, respectively.

9.2.  Top-Level Type Registry

   As shown in Table 2, CCNinfo defines one top-level type, T_DISCOVERY,
   whose value is 0x0005.

9.3.  Hop-by-Hop Type Registry

   As shown in Table 4, CCNinfo defines two hop-by-hop types,
   T_DISC_REQHDR and T_DISC_REPORT, whose values are 0x0008 and 0x0009,
   respectively.

9.4.  Message Type Registry

   As shown in Table 6, CCNinfo defines two message types, T_DISC_REQ
   and T_DISC_REPLY, whose values are 0x000D and 0x000E, respectively.

9.5.  Reply Type Registry

   IANA has created the "CCNx Reply Types" registry and allocated the
   reply types.  The registration procedure is "RFC Required" [RFC8126].
   The Type value is 2 octets.  The range is 0x0000-0xFFFF.  As shown in
   Table 7, CCNinfo defines three reply types, T_DISC_CONTENT,
   T_DISC_CONTENT_PUBLISHER, and T_ORG, whose values are 0x0000, 0x0001,
   and 0x0FFF, respectively.

10.  Security Considerations

   This section addresses some of the security considerations.

10.1.  Policy-Based Information Provisioning for Request

   Although CCNinfo gives excellent troubleshooting cues, some network
   administrators or operators may not want to disclose everything about
   their network to the public or may wish to securely transmit private
   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 block or 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 or 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.

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 cannot only hide
   these values owing to privacy and 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; they only retrieve 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.

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 to 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
   and/or router adjacency, while a hop-by-hop authentication such as
   [DCAuth] 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.  References

11.1.  Normative References

   [RFC2119]  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>.

   [RFC8126]  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>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8569]  Mosko, M., Solis, I., and C. Wood, "Content-Centric
              Networking (CCNx) Semantics", RFC 8569,
              DOI 10.17487/RFC8569, July 2019,
              <https://www.rfc-editor.org/info/rfc8569>.

   [RFC8609]  Mosko, M., Solis, I., and C. Wood, "Content-Centric
              Networking (CCNx) Messages in TLV Format", RFC 8609,
              DOI 10.17487/RFC8609, July 2019,
              <https://www.rfc-editor.org/info/rfc8609>.

11.2.  Informative References

   [Cefore]   Asaeda, H., Ooka, A., Matsuzono, K., and R. Li, "Cefore:
              Software Platform Enabling Content-Centric Networking and
              Beyond", IEICE Transaction on Communications, Volume
              E102-B, Issue 9, pp. 1792-1803,
              DOI 10.1587/transcom.2018EII0001, September 2019,
              <https://doi.org/10.1587/transcom.2018EII0001>.

   [Cefore-site]
              "Cefore", <https://cefore.net/>.

   [CONSEC-CACHING]
              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, MO, USA,
              DOI 10.1109/ICC.2018.8422233, May 2018,
              <https://doi.org/10.1109/ICC.2018.8422233>.

   [Contrace] 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,
              DOI 10.1109/MCOM.2015.7060502, March 2015,
              <https://doi.org/10.1109/MCOM.2015.7060502>.

   [DCAuth]   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, Vol.
              7, No. 1, pp. 15-27, DOI 10.1109/TNSE.2018.2872049,
              October 2018, <https://doi.org/10.1109/TNSE.2018.2872049>.

   [ICN-PING] Mastorakis, S., Oran, D., Gibson, J., Moiseenko, I., and
              R. Droms, "ICN Ping Protocol Specification", Work in
              Progress, Internet-Draft, draft-irtf-icnrg-icnping-07, 16
              October 2022, <https://datatracker.ietf.org/doc/html/
              draft-irtf-icnrg-icnping-07>.

   [ICN-TRACEROUTE]
              Mastorakis, S., Oran, D., Moiseenko, I., Gibson, J., and
              R. Droms, "ICN Traceroute Protocol Specification", Work in
              Progress, Internet-Draft, draft-irtf-icnrg-icntraceroute-
              07, 16 October 2022,
              <https://datatracker.ietf.org/doc/html/draft-irtf-icnrg-
              icntraceroute-07>.

   [RFC8487]  Asaeda, H., Meyer, K., and W. Lee, Ed., "Mtrace Version 2:
              Traceroute Facility for IP Multicast", RFC 8487,
              DOI 10.17487/RFC8487, October 2018,
              <https://www.rfc-editor.org/info/rfc8487>.

   [RFC8793]  Wissingh, B., 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,
              DOI 10.17487/RFC8793, June 2020,
              <https://www.rfc-editor.org/info/rfc8793>.

Appendix A.  ccninfo Command and Options

   CCNinfo is implemented in Cefore [Cefore] [Cefore-site].  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 the ccninfo command is as follows:

   ccninfo [-c] [-f] [-o] [-V] [-r hop_count] [-s hop_count]
      [-v algorithm] name_prefix

   name_prefix:
      The 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 the tracing of 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.

   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:
      The 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:
      The 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 their signature.  The Request message will include
      the CCNx ValidationPayload TLV.  The validation algorithm is
      specified by the CCNinfo user.

Acknowledgements

   The authors would like to thank Jérôme François, Erik Kline, Spyridon
   Mastorakis, Paulo Mendes, Ilya Moiseenko, David Oran, and Thierry
   Turletti for their valuable comments and suggestions on this
   document.

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


   Xun Shao
   Toyohashi University of Technology
   1-1 Hibarigaoka Tempaku-cho, Toyohashi, Aichi
   441-8580
   Japan
   Email: shao.xun.ls@tut.jp