[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-asaeda-icnrg-ccninfo) 00 01

ICN Research Group                                             H. Asaeda
Internet-Draft                                                   A. Ooka
Intended status: Experimental                                       NICT
Expires: September 12, 2019                                      X. Shao
                                          Kitami Institute of Technology
                                                          March 11, 2019


CCNinfo: Discovering Content and Network Information in Content-Centric
                                Networks
                      draft-irtf-icnrg-ccninfo-01

Abstract

   This document describes a mechanism named "CCNinfo" that discovers
   information about the network topology and in-network cache in
   Content-Centric Networks (CCN).  CCNinfo investigates: 1) the CCN
   routing path information per name prefix, 2) the Round-Trip Time
   (RTT) between content forwarder and consumer, and 3) the states of
   in-network cache per name prefix.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 12, 2019.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



Asaeda, et al.         Expires September 12, 2019               [Page 1]


Internet-Draft                   CCNinfo                      March 2019


   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.1.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   7
   3.  CCNinfo Message Formats . . . . . . . . . . . . . . . . . . .   8
     3.1.  Request Message . . . . . . . . . . . . . . . . . . . . .   9
       3.1.1.  Request Block . . . . . . . . . . . . . . . . . . . .  11
       3.1.2.  Report Block  . . . . . . . . . . . . . . . . . . . .  13
     3.2.  Reply Message . . . . . . . . . . . . . . . . . . . . . .  14
       3.2.1.  Reply Block . . . . . . . . . . . . . . . . . . . . .  16
         3.2.1.1.  Reply Sub-Block . . . . . . . . . . . . . . . . .  16
   4.  CCNinfo User Behavior . . . . . . . . . . . . . . . . . . . .  19
     4.1.  Sending CCNinfo Request . . . . . . . . . . . . . . . . .  19
       4.1.1.  Routing Path Information  . . . . . . . . . . . . . .  20
       4.1.2.  In-Network Cache Information  . . . . . . . . . . . .  20
     4.2.  Receiving CCNinfo Reply . . . . . . . . . . . . . . . . .  20
   5.  Router Behavior . . . . . . . . . . . . . . . . . . . . . . .  20
     5.1.  User and Neighbor Verification  . . . . . . . . . . . . .  20
     5.2.  Receiving CCNinfo Request . . . . . . . . . . . . . . . .  21
       5.2.1.  Normal Processing . . . . . . . . . . . . . . . . . .  21
     5.3.  Forwarding CCNinfo Request  . . . . . . . . . . . . . . .  22
     5.4.  Sending CCNinfo Reply . . . . . . . . . . . . . . . . . .  23
     5.5.  Forwarding CCNinfo Reply  . . . . . . . . . . . . . . . .  23
   6.  CCNinfo Termination . . . . . . . . . . . . . . . . . . . . .  24
     6.1.  Arriving at First-hop router  . . . . . . . . . . . . . .  24
     6.2.  Arriving at Router Having Cache . . . . . . . . . . . . .  24
     6.3.  Invalid Request . . . . . . . . . . . . . . . . . . . . .  24
     6.4.  No Route  . . . . . . . . . . . . . . . . . . . . . . . .  24
     6.5.  No Information  . . . . . . . . . . . . . . . . . . . . .  24
     6.6.  No Space  . . . . . . . . . . . . . . . . . . . . . . . .  24
     6.7.  Fatal Error . . . . . . . . . . . . . . . . . . . . . . .  25
     6.8.  CCNinfo Reply Timeout . . . . . . . . . . . . . . . . . .  25
     6.9.  Non-Supported Node  . . . . . . . . . . . . . . . . . . .  25
     6.10. Administratively Prohibited . . . . . . . . . . . . . . .  25
   7.  Configurations  . . . . . . . . . . . . . . . . . . . . . . .  25
     7.1.  CCNinfo Reply Timeout . . . . . . . . . . . . . . . . . .  25
     7.2.  HopLimit in Fixed Header  . . . . . . . . . . . . . . . .  25
     7.3.  Access Control  . . . . . . . . . . . . . . . . . . . . .  25
   8.  Diagnosis and Analysis  . . . . . . . . . . . . . . . . . . .  26
     8.1.  Number of Hops  . . . . . . . . . . . . . . . . . . . . .  26
     8.2.  Caching Router Identification . . . . . . . . . . . . . .  26
     8.3.  TTL or Hop Limit  . . . . . . . . . . . . . . . . . . . .  26



Asaeda, et al.         Expires September 12, 2019               [Page 2]


Internet-Draft                   CCNinfo                      March 2019


     8.4.  Time Delay  . . . . . . . . . . . . . . . . . . . . . . .  26
     8.5.  Path Stretch  . . . . . . . . . . . . . . . . . . . . . .  26
     8.6.  Cache Hit Probability . . . . . . . . . . . . . . . . . .  26
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  27
     9.1.  Policy-Based Information Provisioning for Request . . . .  27
     9.2.  Filtering of CCNinfo Users Located in Invalid Networks  .  27
     9.3.  Topology Discovery  . . . . . . . . . . . . . . . . . . .  28
     9.4.  Characteristics of Content  . . . . . . . . . . . . . . .  28
     9.5.  Longer or Shorter CCNinfo Reply Timeout . . . . . . . . .  28
     9.6.  Limiting Request Rates  . . . . . . . . . . . . . . . . .  28
     9.7.  Limiting Reply Rates  . . . . . . . . . . . . . . . . . .  28
     9.8.  Adjacency Verification  . . . . . . . . . . . . . . . . .  29
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  29
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  29
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  29
     11.2.  Informative References . . . . . . . . . . . . . . . . .  29
   Appendix A.  ccninfo Command and Options  . . . . . . . . . . . .  30
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  31

1.  Introduction

   In Content-Centric Networks (CCN), publishers provide content through
   the network, and receivers retrieve content by name.  In this network
   architecture, routers forward content requests by means of their
   Forwarding Information Bases (FIBs), which are populated by name-
   based routing protocols.  CCN also enables receivers to retrieve
   content from an in-network cache.

   In CCN, while consumers do not generally need to know which content
   forwarder is transmitting the content to them, operators and
   developers may want to identify the content forwarder and observe the
   routing path information per name prefix for troubleshooting or
   investigating the network conditions.

   Traceroute [6] is a useful tool for discovering the routing
   conditions in IP networks as it provides intermediate router
   addresses along the path between source and destination and the
   Round-Trip Time (RTT) for the path.  However, this IP-based network
   tool cannot trace the name prefix paths used in CCN.  Moreover, such
   IP-based network tool does not obtain the states of the in-network
   cache to be discovered.

   This document describes the specification of "CCNinfo", an active
   networking tool for discovering the path and content caching
   information in CCN.  CCNinfo is designed based on the work previously
   published in [5].





Asaeda, et al.         Expires September 12, 2019               [Page 3]


Internet-Draft                   CCNinfo                      March 2019


   CCNinfo can be implemented with the ccninfo user command and the
   forwarding function implementation on a content forwarder (e.g.,
   router).  The CCNinfo user (e.g., consumer) invokes the ccninfo
   command (described in Appendix A) with the name prefix of the
   content.  The ccninfo command initiates the "Request" message
   (described in Section 3.1).  The Request message, for example,
   obtains routing path and cache information.  When an appropriate
   adjacent neighbor router receives the Request message, it retrieves
   cache information.  If the router is not the content forwarder for
   the request, it inserts its "Report" block (described in
   Section 3.1.2) into the Request message and forwards the Request
   message to its upstream neighbor router(s) decided by its FIB.  These
   two message types, Request and Reply messages, are encoded in the
   CCNx TLV format [1].

   In this way, the Request message is forwarded by routers toward the
   content publisher, and the Report record is inserted by each
   intermediate router.  When the Request message reaches the content
   forwarder (i.e., a router who can forward the specified cache or
   content), the content forwarder forms the "Reply" message (described
   in Section 3.2) and sends it to the downstream neighbor router.  The
   Reply message is forwarded back toward the user in a hop-by-hop
   manner.  This request-reply message flow, walking up the tree from a
   consumer toward a publisher, is similar to the behavior of the IP
   multicast traceroute facility [7].

   CCNinfo supports multipath forwarding.  The Request messages can be
   forwarded to multiple neighbor routers.  When the Request messages
   forwarded to multiple routers, the different Reply messages will be
   forwarded from different routers or publisher.





















Asaeda, et al.         Expires September 12, 2019               [Page 4]


Internet-Draft                   CCNinfo                      March 2019


           1. Request    2. Request    3. Request
              (+U)          (U+A)         (U+A+B)
             +----+        +----+        +----+
             |    |        |    |        |    |
             |    v        |    v        |    v
    +--------+    +--------+    +--------+    +--------+    +---------+
    | CCNinfo|----| Router |----| Router |----| Router |----|Publisher|
    |  user  |    |   A    |    |   B    |    |   C    |    |         |
    +--------+    +--------+    +--------+    +--------+    +---------+
                                         \
                                          \          +-------+
                                3. Request \         | Cache |
                                   (U+A+B)  \ +---------+    |
                                             v| Caching |----+
                                              |  router |
                                              +---------+

       Figure 1: Request messages forwarded by consumer and routers.
   CCNinfo user and routers (i.e., Router A,B,C) insert their own Report
    blocks into the Request message and forward the message toward the
          content forwarder (i.e., caching router and publisher)

           3. Reply(P)   2. Reply(P)   1. Reply(P)
             +----+        +----+        +----+
             |    |        |    |        |    |
             v    |        v    |        v    |
    +--------+    +--------+    +--------+    +--------+    +---------+
    | CCNinfo|----| Router |----| Router |----| Router |----|Publisher|
    |  user  |    |   A    |    |   B    |    |   C    |    |         |
    +--------+    +--------+    +--------+    +--------+    +---------+
                                         ^
                                          \          +-------+
                               1. Reply(C) \         | Cache |
                                            \ +---------+    |
                                             \| Caching |----+
                                              |  router |
                                              +---------+

     Figure 2: Default behavior.  Reply messages forwarded by routers.
      Each router forwards the Reply message along its PIT entry, and
     finally the CCNinfo user receives a Reply message from Router C,
    which is the first-hop router for Publisher.  Another Reply message
     from Caching router is discarded at Router B as the corresponding
                   Reply message was already forwarded.







Asaeda, et al.         Expires September 12, 2019               [Page 5]


Internet-Draft                   CCNinfo                      March 2019


           3. Reply(C)   2. Reply(C)
           3. Reply(P)   2. Reply(P)   1. Reply(P)
             +----+        +----+        +----+
             |    |        |    |        |    |
             v    |        v    |        v    |
    +--------+    +--------+    +--------+    +--------+    +---------+
    | CCNinfo|----| Router |----| Router |----| Router |----|Publisher|
    |  user  |    |   A    |    |   B    |    |   C    |    |         |
    +--------+    +--------+    +--------+    +--------+    +---------+
                                         ^
                                          \          +-------+
                               1. Reply(C) \         | Cache |
                                            \ +---------+    |
                                             \| Caching |----+
                                              |  router |
                                              +---------+

      Figure 3: Full discovery request.  Reply messages forwarded by
   publisher and routers.  Each router forwards the Reply message along
      its PIT entry, and finally the CCNinfo user receives two Reply
      messages: one from the first-hop router and the other from the
                              caching router.

   CCNinfo facilitates the tracing of a routing path and provides: 1)
   the RTT between content forwarder (i.e., caching router or first-hop
   router) and consumer, 2) the states of in-network cache per name
   prefix, and 3) the routing path information per name prefix.

   In addition, CCNinfo identifies the states of the cache, such as the
   following metrics for Content Store (CS) in the content forwarder: 1)
   size of the cached content objects, 2) number of the cached content
   objects, 3) number of the accesses (i.e., received Interests) per
   content, and 4) elapsed cache time and remain cache lifetime of
   content.

   Furthermore, CCNinfo implements policy-based information provisioning
   that enables administrators to "hide" secure or private information,
   but does not disrupt the forwarding of messages.  This policy-based
   information provisioning reduces the deployment barrier faced by
   operators in installing and running CCNinfo on their routers.

2.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
   and "OPTIONAL" are to be interpreted as described in RFC 2119 [3],
   and indicate requirement levels for compliant CCNinfo
   implementations.



Asaeda, et al.         Expires September 12, 2019               [Page 6]


Internet-Draft                   CCNinfo                      March 2019


2.1.  Definitions

   Since CCNinfo requests flow in the opposite direction to the data
   flow, we refer to "upstream" and "downstream" with respect to data,
   unless explicitly specified.

   Router
      It is a router facilitating CCN-based content retrieval in the
      path between consumer and publisher.

   Scheme name
      It indicates a URI and protocol.  This document only considers
      "ccn:/" as the scheme name.

   Prefix name
      A prefix name, which is defined in [2], is a name that does not
      uniquely identify a single content object, but rather a namespace
      or prefix of an existing content object name.

   Exact name
      An exact name, which is defined in [2], is one which uniquely
      identifies the name of a content object.

   Node
      It is a router, publisher, or consumer.

   Content forwarder
      It is either a caching router or a first-hop router that forwards
      content objects to consumers.

   CCNinfo user
      It is a node that invokes the ccninfo command and initiates the
      CCNinfo Request.

   Incoming face
      The face on which data is expected to arrive from the specified
      name prefix.

   Outgoing face
      The face to which data from the publisher or router is expected to
      transmit for the specified name prefix.  It is also the face on
      which the Request messages are received.

   Upstream router
      The router, connecting to the Incoming face of a router, which is
      responsible for forwarding data for the specified name prefix to
      the router.




Asaeda, et al.         Expires September 12, 2019               [Page 7]


Internet-Draft                   CCNinfo                      March 2019


   First-hop router (FHR)
      The router that is directly connected to the publisher.

   Last-hop router (LHR)
      The router that is directly connected to the consumers.

3.  CCNinfo Message Formats

   CCNinfo uses two message types: Request and Reply.  Both messages are
   encoded in the CCNx TLV format ([1], Figure 4).  The Request message
   consists of a fixed header, Request block TLV Figure 8, and Report
   block TLV(s) Figure 11.  The Reply message consists of a fixed
   header, Request block TLV, Report block TLV(s), and Reply block/sub-
   block TLV(s) Figure 14.

                          1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +---------------+---------------+---------------+---------------+
     |    Version    |  PacketType   |         PacketLength          |
     +---------------+---------------+---------------+---------------+
     |           PacketType specific fields          | HeaderLength  |
     +---------------+---------------+---------------+---------------+
     / Optional Hop-by-hop header TLVs                               /
     +---------------+---------------+---------------+---------------+
     / PacketPayload TLVs                                            /
     +---------------+---------------+---------------+---------------+
     / Optional CCNx ValidationAlgorithm TLV                         /
     +---------------+---------------+---------------+---------------+
     / Optional CCNx ValidationPayload TLV (ValidationAlg required)  /
     +---------------+---------------+---------------+---------------+

                        Figure 4: Packet format [1]

   The Request and Reply Type values in the fixed header are PT_REQUEST
   and PT_REPLY, respectively (Figure 5).  These messages are forwarded
   in a hop-by-hop manner.  When the Request message reaches the content
   forwarder, the content forwarder turns the Request message into a
   Reply message by changing the Type field value in the fixed header
   from PT_REQUEST to PT_REPLY and forwards back to the node that has
   initiated the Request message.











Asaeda, et al.         Expires September 12, 2019               [Page 8]


Internet-Draft                   CCNinfo                      March 2019


                      Code         Type name
                    ========      =====================
                      %x00        PT_INTEREST [1]
                      %x01        PT_CONTENT [1]
                      %x02        PT_RETURN [1]
                      %x03        PT_REQUEST
                      %x04        PT_REPLY

                      Figure 5: Packet Type Namespace

   The CCNinfo Request and Reply messages MUST begin with a fixed header
   with either a Request or Reply type value to specify whether it is a
   Request message or Reply message.  Following a fixed header, there
   can be a sequence of optional hop-by-hop header TLV(s) for a Request
   message.  In the case of a Request message, it is followed by a
   sequence of Report blocks, each from a router on the path toward the
   publisher or caching router.

   At the beginning of PacketPayload TLVs, one top-level TLV type,
   T_DISCOVERY (Figure 6), exists at the outermost level of a CCNx
   protocol message.  This TLV indicates that the Name segment TLV(s)
   and Reply block TLV(s) would follow in the Request or Reply message.

                   Code           Type name
               =============      =========================
                  %x0000          Reserved [1]
                  %x0001          T_INTEREST [1]
                  %x0002          T_OBJECT [1]
                  %x0003          T_VALIDATION_ALG [1]
                  %x0004          T_VALIDATION_PAYLOAD [1]
                  %x0005          T_DISCOVERY

                    Figure 6: Top-Level Type Namespace

3.1.  Request Message

   When a CCNinfo user initiates a discovery request (e.g., by ccninfo
   command described in Appendix A), a CCNinfo Request message is
   created and forwarded to its upstream router through the Incoming
   face(s) determined by its FIB.

   The Request message format is as shown in Figure 7.  It consists of a
   fixed header, Request block TLV (Figure 8), Report block TLV(s)
   (Figure 11), and Name TLV.  The Type value of Top-Level type
   namespace is T_DISCOVERY (Figure 6).  The Type value for the Report
   message is PT_REQUEST.





Asaeda, et al.         Expires September 12, 2019               [Page 9]


Internet-Draft                   CCNinfo                      March 2019


                          1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +---------------+---------------+---------------+---------------+
     |    Version    |  PacketType   |         PacketLength          |
     +---------------+---------------+---------------+---------------+
     |    HopLimit   |   ReturnCode  | Reserved(MBZ) | HeaderLength  |
     +===============+===============+===============+===============+
     |                                                               |
     +                       Request block TLV                       +
     |                                                               |
     +---------------+---------------+---------------+---------------+
     /                       Report block TLV 1                      /
     +---------------+---------------+---------------+---------------+
     /                       Report block TLV 2                      /
     +---------------+---------------+---------------+---------------+
     /                               .                               /
     /                               .                               /
     +---------------+---------------+---------------+---------------+
     /                       Report block TLV n                      /
     +===============+===============+===============+===============+
     |          T_DISCOVERY          |         MessageLength         |
     +---------------+---------------+---------------+---------------+
     |            T_NAME             |             Length            |
     +---------------+---------------+---------------+---------------+
     / Name segment TLVs (name prefix specified by ccninfo command) /
     +---------------+---------------+---------------+---------------+

    Figure 7: Request message consists of a fixed header, Request block
                  TLV, Report block TLV(s), and Name TLV

   HopLimit: 8 bits

      HopLimit is a counter that is decremented with each hop whenever a
      Request packet is forwarded.  It limits the distance a Request may
      travel on the network.

   ReturnCode: 8 bits

      ReturnCode is used for the Reply message.  This value is replaced
      by the content forwarder when the Request message is returned as
      the Reply message (see Section 3.2).  Until then, this field MUST
      be transmitted as zeros and ignored on receipt.









Asaeda, et al.         Expires September 12, 2019              [Page 10]


Internet-Draft                   CCNinfo                      March 2019


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

   Reserved (MBZ): 8 bits

      The reserved fields in the Value field MUST be transmitted as
      zeros and ignored on receipt.

3.1.1.  Request Block

   When a CCNinfo user transmits the Request message, it MUST insert the
   Request block TLV (Figure 8) and the Report block TLV (Figure 11) of
   its own to the Request message before sending it through the Incoming
   face(s).
















Asaeda, et al.         Expires September 12, 2019              [Page 11]


Internet-Draft                   CCNinfo                      March 2019


                          1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +---------------+---------------+---------------+---------------+
     |           T_DISC_REQ          |             Length            |
     +---------------+---------------+---------------+---------+-+-+-+
     |           Request ID          | SkipHopCount  |  Flags  |F|O|C|
     +---------------+---------------+---------------+---------+-+-+-+
     |                     Request Arrival Time                      |
     +---------------+---------------+---------------+---------------+
     /                        Node Identifier                        /
     +---------------+---------------+---------------+---------------+


              Figure 8: Request block TLV (hop-by-hop header)

                   Code           Type name
               =============      =========================
                  %x0000          Reserved [1]
                  %x0001          T_INTLIFE [1]
                  %x0002          T_CACHETIME [1]
                  %x0003          T_MSGHASH [1]
               %x0004-%x0007      Reserved [1]
                  %x0008          T_DISC_REQ
                  %x0009          T_DISC_REPORT
                  %x0FFE          T_PAD [1]
                  %x0FFF          T_ORG [1]
               %x1000-%x1FFF      Reserved [1]

                    Figure 9: Hop-by-Hop Type Namespace

   Type: 16 bits

      Format of the Value field.  For the single Request block TLV, the
      type value MUST be T_DISC_REQ.  For all the available types for
      hop-by-hop type namespace, please see Figure 9.

   Length: 16 bits

      Length of Value field in octets.

   Request ID: 16 bits

      This field is used as a unique identifier for this CCNinfo Request
      so that duplicate or delayed Reply messages can be detected.

   SkipHopCount: 8 bits





Asaeda, et al.         Expires September 12, 2019              [Page 12]


Internet-Draft                   CCNinfo                      March 2019


      Number of skipped routers for a Request.  This value MUST be lower
      than the value of HopLimit at the fixed header.

   Flags: 16 bits

      Flags field is used to indicate the types of the content or path
      discoveries.  Currently, as shown in Figure 10, three bits, "C",
      "O", and "F", are assigned, and the other 5 bits are reserved
      (MBZ) for the future use.  These flags are set by CCNinfo users
      when they initiate Requests (see Appendix A), and routers that
      receive the Requests deal with the flags and change the behaviors
      (see Section 5 for details).

   Flag    Value   Description
   -----   -----   ----------------------------------------------------
     C       0     Path discovery (i.e., no cache information retried)
     C       1     Cache information retrieval (default)
     O       0     Request to any content forwarder (default)
     O       1     Publisher reachability (i.e., only FHR can reply)
     F       0     Request based on FIB's strategy (default)
     F       1     Full discovery request. Request to multiple upstream
                   routers simultaneously

            Figure 10: Codes and types specified in Flags field

3.1.2.  Report Block

   A CCNinfo user and each upstream router along the path would insert
   its own Report block TLV without changing the Type field of the fixed
   header of the Request message until one of these routers is ready to
   send a Reply.  In the Report block TLV (Figure 11), the Request
   Arrival Time and the Node Identifier MUST be inserted.

                          1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +---------------+---------------+---------------+---------------+
     |         T_DISC_REPORT         |             Length            |
     +---------------+---------------+---------------+---------------+
     |                     Request Arrival Time                      |
     +---------------+---------------+---------------+---------------+
     /                        Node Identifier                        /
     +---------------+---------------+---------------+---------------+

              Figure 11: Report block TLV (hop-by-hop header)

   Type: 16 bits





Asaeda, et al.         Expires September 12, 2019              [Page 13]


Internet-Draft                   CCNinfo                      March 2019


      Format of the Value field.  For the Report block TLV, the type
      value(s) MUST be T_DISC_REPORT in the current specification.

   Length: 16 bits

      Length of Value field in octets.

   Request Arrival Time: 32 bits

      The Request Arrival Time is a 32-bit NTP timestamp specifying the
      arrival time of the CCNinfo Request packet at this router.  The
      32-bit form of an NTP timestamp consists of the middle 32 bits of
      the full 64-bit form; that is, the low 16 bits of the integer part
      and the high 16 bits of the fractional part.

      The following formula converts from a UNIX timeval to a 32-bit NTP
      timestamp:

         request_arrival_time
         = ((tv.tv_sec + 32384) << 16) + ((tv.tv_nsec << 7) / 1953125)

      The constant 32384 is the number of seconds from Jan 1, 1900 to
      Jan 1, 1970 truncated to 16 bits.  ((tv.tv_nsec << 7) / 1953125)
      is a reduction of ((tv.tv_nsec / 1000000000) << 16).

      Note that it is RECOMMENDED that all the routers on the path to
      have synchronized clocks; however, if they do not have
      synchronized clocks, CCNinfo measures one-way latency.

   Node Identifier: variable length

      This field specifies the CCNinfo user or the router identifier
      (e.g., IPv4 address) of the Incoming face on which packets from
      the publisher are expected to arrive, or all-zeros if unknown or
      unnumbered.  Since we may not always rely on the IP addressing
      architecture, it would be necessary to define the identifier
      uniqueness (e.g., by specifying the protocol family) for this
      field.  However, defining such uniqueness is out of scope of this
      document.  Potentially, this field may be defined as a new TLV
      based on the CCNx TLV format [1].

3.2.  Reply Message

   When a content forwarder receives a CCNinfo Request message from the
   appropriate adjacent neighbor router, it would insert a Reply block
   TLV and Reply sub-block TLV(s) of its own to the Request message and
   turn the Request into the Reply by changing the Type field of the
   fixed header of the Request message from PT_REQUEST to PT_REPLY.  The



Asaeda, et al.         Expires September 12, 2019              [Page 14]


Internet-Draft                   CCNinfo                      March 2019


   Reply message (see Figure 12) would then be forwarded back toward the
   CCNinfo user in a hop-by-hop manner.

                          1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +---------------+---------------+---------------+---------------+
     |    Version    |  PacketType   |         PacketLength          |
     +---------------+---------------+-------------+-+---------------+
     |    HopLimit   |   ReturnCode  | Reserved(MBZ) | HeaderLength  |
     +===============+===============+=============+=+===============+
     |                                                               |
     +                       Request block TLV                       +
     |                                                               |
     +---------------+---------------+---------------+---------------+
     /                               .                               /
     /                               .                               /
     /                      n Report block TLVs                      /
     /                               .                               /
     /                               .                               /
     +===============+===============+===============+===============+
     |          T_DISCOVERY          |         MessageLength         |
     +---------------+---------------+---------------+---------------+
     |            T_NAME             |             Length            |
     +---------------+---------------+---------------+---------------+
     / Name segment TLVs (name prefix specified by ccninfo command) /
     +---------------+---------------+---------------+---------------+
     /                        Reply block TLV                        /
     +---------------+---------------+---------------+---------------+
     /                     Reply sub-block TLV 1                     /
     +---------------+---------------+---------------+---------------+
     /                     Reply sub-block TLV 2                     /
     +---------------+---------------+---------------+---------------+
     /                               .                               /
     /                               .                               /
     +---------------+---------------+---------------+---------------+
     /                     Reply sub-block TLV k                     /
     +---------------+---------------+---------------+---------------+

    Figure 12: Reply message consists of a fixed header, Request block
   TLV, Report block TLV(s), Name TLV, and Reply block/sub-block TLV(s)











Asaeda, et al.         Expires September 12, 2019              [Page 15]


Internet-Draft                   CCNinfo                      March 2019


                       Code          Type name
                  ==============     ===================
                      %x0000         T_NAME [1]
                      %x0001         T_PAYLOAD [1]
                      %x0002         T_KEYIDRESTR [1]
                      %x0003         T_OBJHASHRESTR [1]
                      %x0005         T_PAYLDTYPE [1]
                      %x0006         T_EXPIRY [1]
                      %x0007         T_DISC_REPLY
                  %x0008-%x0012      Reserved [1]
                      %x0FFE         T_PAD [1]
                      %x0FFF         T_ORG [1]
                  %x1000-%x1FFF      Reserved [1]

                  Figure 13: CCNx Message Type Namespace

3.2.1.  Reply Block

   The Reply block TLV is an envelope for Reply sub-block TLV(s)
   (explained in Section 3.2.1.1).

                          1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +---------------+---------------+---------------+---------------+
     |         T_DISC_REPLY          |             Length            |
     +---------------+---------------+---------------+---------------+

                Figure 14: Reply block TLV (packet payload)

   Type: 16 bits

      Format of the Value field.  For the Reply block TLV, the type
      value MUST be T_DISC_REPLY in the current specification.

   Length: 16 bits

      Length of Value field in octets.  This length is a total length of
      Reply sub-block(s).

3.2.1.1.  Reply Sub-Block

   In addition to the Reply block, a router on the traced path will add
   one or multiple Reply sub-blocks followed by the Reply block before
   sending the Reply to its neighbor router.

   The Reply sub-block is flexible for various purposes.  For instance,
   operators and developers may want to obtain various characteristics
   of content such as content's ownership and copyright, or other cache



Asaeda, et al.         Expires September 12, 2019              [Page 16]


Internet-Draft                   CCNinfo                      March 2019


   states and conditions.  In this document, Reply sub-block TLVs for
   T_DISC_CONTENT and T_DISC_CONTENT_OWNER (Figure 15) are defined;
   other Reply sub-block TLVs will be defined in separate document(s).

                          1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +---------------+---------------+---------------+---------------+
     |             Type              |             Length            |
     +---------------+---------------+---------------+---------------+
     |                          Object Size                          |
     +---------------+---------------+---------------+---------------+
     |                         Object Count                          |
     +---------------+---------------+---------------+---------------+
     |                      # Received Interest                      |
     +---------------+---------------+---------------+---------------+
     |                         First Seqnum                          |
     +---------------+---------------+---------------+---------------+
     |                          Last Seqnum                          |
     +---------------+---------------+---------------+---------------+
     |                       Elapsed Cache Time                      |
     +---------------+---------------+---------------+---------------+
     |                      Remain Cache Lifetime                    |
     +---------------+---------------+---------------+---------------+
     |            T_NAME             |             Length            |
     +---------------+---------------+---------------+---------------+
     /                       Name Segment TLVs                       /
     +---------------+---------------+---------------+---------------+

           Figure 15: Reply sub-block TLV for T_DISC_CONTENT and
                   T_DISC_CONTENT_OWNER (packet payload)

                   Code          Type name
               =============     ===========================
                  %x0000         T_DISC_CONTENT
                  %x0001         T_DISC_CONTENT_OWNER
                  %x0FFF         T_ORG
               %x1000-%x1FFF     Reserved (Experimental Use)

                  Figure 16: CCNinfo Reply Type Namespace

   Type: 16 bits

      Format of the Value field.  For the Reply sub-block TLV, the type
      value MUST be one of the type value defined in the CCNinfo Reply
      Type Namespace (Figure 16).  T_DISC_CONTENT is specified when the
      cache information is replied from a caching router.
      T_DISC_CONTENT_OWNER is specified when the content information is
      replied from a FHR attached to a publisher.



Asaeda, et al.         Expires September 12, 2019              [Page 17]


Internet-Draft                   CCNinfo                      March 2019


   Length: 16 bits

      Length of Value field in octets.

   Object Size: 32 bits

      The total size (byte) of the (cached) content objects.  Note that
      the maximum size expressed by 32 bit field is about 4.29 GB.  This
      value MAY be null when FHR sends the Reply message.

   Object Count: 32 bits

      The number of the (cached) content objects.  Note that the maximum
      count expressed by 32 bit field is about 4.29 billion.  This value
      MAY be null when FHR sends the Reply message.

   # Received Interest: 32 bits

      The total number of the received Interest messages to retrieve the
      cached content objects.

   First Seqnum: 32 bits

      The first sequential number of the (cached) content objects.  This
      value MAY be null if the router does not know or cannot report.

   Last Seqnum: 32 bits

      The last sequential number of the (cached) content objects.  Above
      First Seqnum and this Last Seqnum do not guarantee the
      consecutiveness of the cached content objects.  This value MAY be
      null if the router does not know or cannot report.

   Elapsed Cache Time: 32 bits

      The elapsed time (seconds) after the oldest content object of the
      content is cached.  This value MAY be null if the router does not
      know or cannot report.

   Remain Cache Lifetime: 32 bits

      The lifetime (seconds) of a content object, which is removed first
      among the cached content objects.  This value MAY be null if the
      router does not know or cannot report.

   Specification of the Name TLV (whose type value is T_NAME) and the
   Name Segment TLVs are described in [1], and CCNinfo follows that
   specification.  CCNinfo also allows to specify the content name



Asaeda, et al.         Expires September 12, 2019              [Page 18]


Internet-Draft                   CCNinfo                      March 2019


   either with a prefix name (such as "ccn:/news/today") or an exact
   name (such as "ccn:/news/today/Chunk=10").  When a CCNinfo user
   specifies a prefix name, s/he will obtain the information of the
   matched content objects in the content forwarder.  On the other hand,
   when a CCNinfo user specifies an exact name, s/he will obtain only
   about the specified content object in the content forwarder.

4.  CCNinfo User Behavior

4.1.  Sending CCNinfo Request

   The CCNinfo user's program (e.g., ccninfo command) enables user to
   obtain both the routing path information and in-network cache
   information in a same time.

   A CCNinfo user initiates a CCNinfo Request by sending the Request
   message to the adjacent neighbor router(s) of interest.  As a typical
   example, a CCNinfo user invokes the ccninfo command (detailed in
   Appendix A) that forms a Request message and sends it to the user's
   adjacent neighbor router(s).

   When the CCNinfo user's program initiates a Request message, it MUST
   insert the necessary values, the "Request ID" (in the Request block)
   and the "Node Identifier" (in the Report block), in the Request and
   Report blocks.  The Request ID MUST be unique for the CCNinfo user
   until s/he receives the corresponding Reply message(s) or times out
   the Request.

   Because of some policy, a router needs to validate CCNinfo Requests
   (whether it accepts the Request or not) especially when the router
   receives the "full discovery request" (see Section 5.3).  To support
   this requirement, the CCNinfo user's program MAY require appending
   the user's signature into the CCNx ValidationPayload TLV.  The router
   then forwards the Request message or reply the Reply message whenever
   it approves the Request.

   After the CCNinfo user's program sends the Request message, until the
   Reply times out or the expected numbers of Replies or a Reply message
   having a non-zero ReturnCode in the fixed header is received, the
   CCNinfo user's program MUST keep the following information; Request
   ID and Flags specified in the Request block, Node Identifier and
   Request Arrival Time specified in the Report block, and HopLimit
   specified in the fixed header.








Asaeda, et al.         Expires September 12, 2019              [Page 19]


Internet-Draft                   CCNinfo                      March 2019


4.1.1.  Routing Path Information

   A CCNinfo user can send a CCNinfo Request for investigating routing
   path information for the specified named content.  By the Request,
   the legitimate user can obtain; 1) identifiers (e.g., IP addresses)
   of intermediate routers, 2) identifier of content forwarder, 3)
   number of hops between content forwarder and consumer, and 4) RTT
   between content forwarder and consumer, per name prefix.  This
   CCNinfo Request is terminated when it reaches the content forwarder.

4.1.2.  In-Network Cache Information

   A CCNinfo user can send a CCNinfo Request for investigating in-
   network cache information.  By the Request, the legitimate user can
   obtain; 1) size of the cached content objects, 2) number of the
   cached content objects, 3) number of the accesses (i.e., received
   Interests) per content, and 4) lifetime and expiration time of the
   cached content object, for Content Store (CS) in the content
   forwarder.  This CCNinfo Request is terminated when it reaches the
   content forwarder.

4.2.  Receiving CCNinfo Reply

   A CCNinfo user's program will receive one or multiple CCNinfo Reply
   messages from the adjacent neighbor router that has previously
   received and forwarded the Request message(s).  When the program
   receives the Reply, it MUST compare the kept Request ID and Node
   Identifier and the ones noted in the Request block TLV in the Reply.
   If they do not match, the Reply message MUST be silently discarded.

   If the number of the Report blocks in the received Reply is more than
   the initial HopLimit value (which was inserted in the original
   Request), the Reply MUST be silently ignored.

   After the CCNinfo user has determined that s/he has traced the whole
   path or as much as s/he can expect to, s/he might collect statistics
   by waiting a timeout.  Useful statistics provided by CCNinfo can be
   seen in Section 8.

5.  Router Behavior

5.1.  User and Neighbor Verification

   Upon receiving a CCNinfo Request message, a router MAY examine
   whether the message comes from a valid CCNinfo user.  If the router
   recognizes that the Request sender's signature specified in the
   Request is invalid, it terminates the Request as defined in
   Section 6.3.



Asaeda, et al.         Expires September 12, 2019              [Page 20]


Internet-Draft                   CCNinfo                      March 2019


   Upon receiving a CCNinfo Request/Reply message, a router MAY examine
   whether the message comes from a valid adjacent neighbor node.  If
   the router recognizes that the Request/Reply sender is invalid, the
   Request/Reply message MUST be silently ignored.  See Section 9.8.

5.2.  Receiving CCNinfo Request

5.2.1.  Normal Processing

   After the CCNinfo Request message verification, the router performs
   the following steps.

   1.  The value of the "HopLimit" in the fixed header and the value of
       the "SkipHopCount" in the Request block are counters that are
       decremented with each hop.  If the HopLimit value is zero, the
       router terminates the Request as defined in Section 6.4.  If the
       SkipHopCount value is equal or more than the HopLimit value, the
       router terminates the Request as defined in Section 6.3.
       Otherwise, until the SkipHopCount value becomes zero, the router
       forwards the Request message to the upstream router(s) without
       adding its own Report block and without replying the Request.  If
       the router does not know the upstream router(s) for the specified
       name prefix, it terminates the Request as defined in Section 6.4.

   2.  The router examines the Flags field (specified in Figure 10) in
       the Request block of received CCNinfo Request.  If the "C" flag
       is set but the "O" flag is not set, that is categorized as the
       "cache information discovery".  If both the "C" and "O" flags are
       not set, that is categorized as the "routing path information
       discovery".  If "O" flag is set, that is categorized as the
       "publisher discovery".

   3.  If the Request is either the "cache information discovery" or the
       "routing path information discovery", the router examines its FIB
       and CS.  If the router caches the specified content, it inserts
       own Report block in the hop-by-hop header, and sends the Reply
       message with own Reply block and sub-block(s) (in case of cache
       information discovery) or sends the Reply message with own Reply
       block without adding any Reply sub-block (in case of routing path
       information discovery).  If the router does not cache the
       specified content but knows the upstream neighbor router(s) for
       the specified name prefix, it inserts own Report block and
       forwards the Request to the upstream neighbor(s).  If the router
       does not cache the specified content and does not know the
       upstream neighbor router(s) for the specified name prefix, it
       terminates the Request as defined in Section 6.4.





Asaeda, et al.         Expires September 12, 2019              [Page 21]


Internet-Draft                   CCNinfo                      March 2019


   4.  If the Request is the "publisher discovery", the router examines
       whether it is the FHR for the requested content.  If it is the
       FHR, it sends the Reply message with own Report block and sub-
       block.  If the router is not the FHR but knows the upstream
       neighbor router(s) for the specified name prefix, it adds the own
       Report block and forwards the Request to the neighbor(s).  If the
       node is not the FHR and does not know the upstream neighbor
       router(s) for the specified name prefix, it terminates the
       Request as defined in Section 6.4.

5.3.  Forwarding CCNinfo Request

   When a router decides to forward a Request message with its Report
   block to its upstream router(s), it specifies the Request Arrival
   Time and Node Identifier in the Report block of the Request message.
   The router then forwards the Request message upstream toward the
   publisher or caching router based on the FIB entry.

   When the router forwards the Request message, it MUST record the
   Request ID, the F flag, and the Node Identifier specified in the
   Request block at the corresponding PIT entry.  The router can later
   check the PIT entry to correctly forward back the Reply message(s).
   (See below.)

   CCNinfo supports multipath forwarding.  The Request messages can be
   forwarded to multiple neighbor routers.  Some router may have
   strategy for multipath forwarding; when it sends Interest messages to
   multiple neighbor routers, it may delay or prioritize to send the
   message to the upstream routers.  The CCNinfo Request, as the
   default, complies with such strategy; a CCNinfo user could trace the
   actual forwarding path based on the forwarding strategy.

   On the other hand, there may be the case that a CCNinfo user wants to
   discover all potential forwarding paths based on routers' FIBs.  The
   "full discovery request" enables this function.  If a CCNinfo user
   sets the F flag in the Request block of the Request message (as seen
   in Figure 10) to request the full discovery, the upstream routers
   forward the Requests to the all multiple upstream routers based on
   the FIBs simultaneously.  Then the CCNinfo user could trace the all
   potential forwarding paths.  Note that some routers MAY ignore the
   full discovery request according to their policy.  In that case, the
   router terminates the Request as defined in Section 6.10.

   When the Request messages forwarded to multiple routers, the
   different Reply messages will be forwarded from different routers or
   publisher.  To support this case, PIT entries initiated by CCNinfo
   remain until the configured CCNinfo Reply Timeout (Section 7.1)
   passes.  In other words, unlike the ordinary Interest-Data



Asaeda, et al.         Expires September 12, 2019              [Page 22]


Internet-Draft                   CCNinfo                      March 2019


   communications in CCN, the router SHOULD NOT remove the PIT entry
   created by the CCNinfo Request until the timeout value expires.

   CCNinfo Requests SHOULD NOT result in PIT aggregation in routers
   during the Request message transmission.

5.4.  Sending CCNinfo Reply

   When a router decides to send a Reply message to its downstream
   neighbor router or the CCNinfo user with NO_ERROR return code, it
   inserts a Report block having the Request Arrival Time and Node
   Identifier to the hop-by-hop TLV header of the Request message.  And
   then the router inserts the corresponding Reply block with an
   appropriate type value (Figure 15) and Reply sub-block(s) to the
   payload.  The router does not insert any Reply block/sub-block if
   there is an error.  The router finally changes the Type field in the
   fixed header from PT_REQUEST to PT_REPLY and forwards the message
   back as the Reply toward the CCNinfo user in a hop-by-hop manner.

   If a router cannot continue the Request, it MUST put an appropriate
   ReturnCode in the Request message, change the Type field value in the
   fixed header from PT_REQUEST to PT_REPLY, and forward the Reply
   message back toward the CCNinfo user, to terminate the request.  See
   Section 6.

5.5.  Forwarding CCNinfo Reply

   When a router receives a CCNinfo Reply whose Request ID and Node
   Identifier match the ones in the PIT entry and sent from a valid
   adjacent neighbor router, it forwards the CCNinfo Reply back toward
   the CCNinfo user.  If the router does not receive the corresponding
   Reply within the [CCNinfo Reply Timeout] period, then it removes the
   corresponding PIT entry and terminates the trace.

   Flags field in the Request block TLV is used to indicate whether the
   router keeps the PIT entry during the CCNinfo Reply Timeout even
   after one or more corresponding Reply messages are forwarded.  When
   the CCNinfo user does not set the F flag (i.e., "0"), the
   intermediate routers immediately remove the PIT entry whenever they
   forward the corresponding Reply message.  When the CCNinfo user sets
   the F flag (i.e., "1"), which means the CCNinfo user chooses the
   "full discovery request", the intermediate routers keep the PIT entry
   within the [CCNinfo Reply Timeout] period.  After this timeout, the
   PIT entry is removed.

   CCNinfo Replies MUST NOT be cached in routers upon the Reply message
   transmission.




Asaeda, et al.         Expires September 12, 2019              [Page 23]


Internet-Draft                   CCNinfo                      March 2019


6.  CCNinfo Termination

   When performing an expanding hop-by-hop trace, it is necessary to
   determine when to stop expanding.  There are several cases an
   intermediate router might return a Reply before a Request reaches the
   caching router or the publisher.

6.1.  Arriving at First-hop router

   A CCNinfo Request can be determined to have arrived at the first-hop
   router.

6.2.  Arriving at Router Having Cache

   A CCNinfo Request can be determined to have arrived at the router
   having the specified content cache within the specified HopLimit.

6.3.  Invalid Request

   If the router does not accept the Request, the router MUST note a
   ReturnCode of INVALID_REQUEST in the fixed header of the message and
   forward the message without appending any Reply (sub-)block TLV as
   the Reply back to the CCNinfo user.  The router MAY, however,
   randomly ignore the received invalid messages.  (See Section 9.6.)

6.4.  No Route

   If the router cannot determine the routing paths or neighbor routers
   for the specified name prefix within the specified HopLimit, the
   router MUST note a ReturnCode of NO_ROUTE in the fixed header of the
   message and forward the message as the Reply back to the CCNinfo
   user.

6.5.  No Information

   If the router does not have any information about the specified name
   prefix within the specified HopLimit, the router MUST note a
   ReturnCode of NO_INFO in the fixed header of the message and forward
   the message as the Reply back to the CCNinfo user.

6.6.  No Space

   If appending the Report block would exceed the maximum (i.e., 255
   byte) header length or make the CCNinfo Request message longer than
   the MTU of the Incoming face or longer than 1280 bytes (especially in
   the situation supporting IPv6 as the payload [4]), the router MUST
   note a ReturnCode of NO_SPACE in the fixed header of the message and
   forward the message as the Reply back to the CCNinfo user.



Asaeda, et al.         Expires September 12, 2019              [Page 24]


Internet-Draft                   CCNinfo                      March 2019


6.7.  Fatal Error

   A CCNinfo Request has encountered a fatal error if the last
   ReturnCode in the trace has the 0x80 bit set (see Section 3.1).

6.8.  CCNinfo Reply Timeout

   If a router receives the Request or Reply message that expires its
   own [CCNinfo Reply Timeout] value (Section 7.1), the router will
   silently discard the Request or Reply message.

6.9.  Non-Supported Node

   Cases will arise in which a router or a publisher along the path does
   not support CCNinfo.  In such cases, a CCNinfo user and routers that
   forward the CCNinfo Request will time out the CCNinfo request.

6.10.  Administratively Prohibited

   If CCNinfo is administratively prohibited, the router rejects the
   Request message and MUST reply the CCNinfo Reply with the ReturnCode
   of ADMIN_PROHIB.  The router MAY, however, randomly ignore the
   rejected messages.  (See Section 9.6.)

7.  Configurations

7.1.  CCNinfo Reply Timeout

   The [CCNinfo Reply Timeout] value is used to time out a CCNinfo
   Reply.  The value for a router can be statically configured by the
   router's administrators/operators.  The default value is 4 (seconds).
   The [CCNinfo Reply Timeout] value SHOULD NOT be larger than 5
   (seconds) and SHOULD NOT be lower than 2 (seconds).

7.2.  HopLimit in Fixed Header

   If a CCNinfo user does not specify the HopLimit value in a fixed
   header for a Request message as the HopLimit, the HopLimit is set to
   32.  Note that 0 HopLimit is an invalid Request; hence the router in
   this case follows the way defined in Section 6.3.

7.3.  Access Control

   A router MAY configure the valid or invalid networks to enable an
   access control.  The access control can be defined per name prefix,
   such as "who can retrieve which name prefix".  See Section 9.2.





Asaeda, et al.         Expires September 12, 2019              [Page 25]


Internet-Draft                   CCNinfo                      March 2019


8.  Diagnosis and Analysis

8.1.  Number of Hops

   A CCNinfo Request message is forwarded in a hop-by-hop manner and
   each forwarding router appended its own Report block.  We can then
   verify the number of hops to reach the content forwarder or the
   publisher.

8.2.  Caching Router Identification

   It is possible to identify the routers in the path from the CCNinfo
   user to the content forwarder, while some routers may hide their
   identifier (e.g., IP address) with all-zeros in the Report blocks
   (Section 9.1).

8.3.  TTL or Hop Limit

   By taking the HopLimit from the content forwarder and forwarding TTL
   threshold over all hops, it is possible to discover the TTL or hop
   limit required for the content forwarder to reach the CCNinfo user.

8.4.  Time Delay

   If the routers have synchronized clocks, it is possible to estimate
   propagation and queuing delay from the differences between the
   timestamps at successive hops.  However, this delay includes control
   processing overhead, so is not necessarily indicative of the delay
   that data traffic would experience.

8.5.  Path Stretch

   By getting the path stretch "d / P", where "d" is the hop count of
   the data and "P" is the hop count from the consumer to the publisher,
   we can measure the improvement in path stretch in various cases, such
   as different caching and routing algorithms.  We can then facilitate
   investigation of the performance of the protocol.

8.6.  Cache Hit Probability

   CCNinfo can show the number of received interests per cache or chunk
   on a router.  By this, CCNinfo measures the content popularity (i.e.,
   the number of accesses for each content/cache), and you can
   investigate the routing/caching strategy in networks.







Asaeda, et al.         Expires September 12, 2019              [Page 26]


Internet-Draft                   CCNinfo                      March 2019


9.  Security Considerations

   This section addresses some of the security considerations.

9.1.  Policy-Based Information Provisioning for Request

   Although CCNinfo gives excellent troubleshooting cues, some network
   administrators or operators may not want to disclose everything about
   their network to the public, or may wish to securely transmit private
   information to specific members of their networks.  CCNinfo provides
   policy-based information provisioning allowing network administrators
   to specify their response policy for each router.

   The access policy regarding "who is allowed to retrieve" and/or "what
   kind of information" can be defined for each router.  For the former
   access policy, routers having the specified content MAY examine the
   signature enclosed in the Request message and decide whether they
   should notify the content information in the Reply or not.  If the
   routers decide to not notify the content information, they MUST reply
   the CCNinfo Reply with the ReturnCode of ADMIN_PROHIB without
   appending any Reply (sub-)block TLV.  For the latter policy, the
   permission, whether (1) All (all cache information is disclosed), (2)
   Partial (cache information with the particular name prefix can (or
   cannot) be disclosed), or (3) Deny (no cache information is
   disclosed), is defined at routers.

   On the other hand, we entail that each router does not disrupt
   forwarding CCNinfo Request and Reply messages.  When a Request
   message is received, the router SHOULD insert Report block if the
   ReturnCode is NO_ERROR.  Here, according to the policy configuration,
   the Node Identifier field in the Report block MAY be null (i.e., all-
   zeros), but the Request Arrival Time field SHOULD NOT be null.  At
   last, the router SHOULD forward the Request message to the upstream
   router toward the content forwarder if the ReturnCode is kept with
   NO_ERROR.

9.2.  Filtering of CCNinfo Users Located in Invalid Networks

   A router MAY support an access control mechanism to filter out
   Requests from invalid CCNinfo users.  For it, invalid networks (or
   domains) could, for example, be configured via a list of allowed/
   disallowed networks (as seen in Section 7.3).  If a Request is
   received from the disallowed network (according to the Node
   Identifier in the Request block), the Request MUST NOT be processed
   and the Reply with the ReturnCode of INFO_HIDDEN may be used to note
   that.  The router MAY, however, perform rate-limited logging of such
   events.




Asaeda, et al.         Expires September 12, 2019              [Page 27]


Internet-Draft                   CCNinfo                      March 2019


9.3.  Topology Discovery

   CCNinfo can be used to discover actively-used topologies.  If a
   network topology is a secret, CCNinfo Requests SHOULD be restricted
   at the border of the domain, using the ADMIN_PROHIB return code.

9.4.  Characteristics of Content

   CCNinfo can be used to discover what publishers are sending to what
   kinds of contents.  If this information is a secret, CCNinfo Requests
   SHOULD be restricted at the border of the domain, using the
   ADMIN_PROHIB return code.

9.5.  Longer or Shorter CCNinfo Reply Timeout

   Routers can configure the CCNinfo Reply Timeout (Section 7.1), which
   is the allowable timeout value to keep the PIT entry.  If routers
   configure the longer timeout value, there may be an attractive attack
   vector against PIT memory.  Moreover, especially when the full
   discovery request option (Section 5.3) is specified for the CCNinfo
   Request, a number of Reply messages may come back and cause a
   response storm.  (See Section 9.7 for rate limiting to avoid the
   storm).  In order to avoid DoS attacks, routers may configure the
   timeout value, which is shorter than the user-configured CCNinfo
   timeout value.  However, if it is too short, the Request may be timed
   out and the CCNinfo user does not receive the all Replies and only
   retrieves the partial path information (i.e., information about part
   of the tree).

   There may be the way to allow for incremental exploration (i.e., to
   explore the part of the tree the previous operation did not explore),
   whereas discussing such mechanism is out of scope of this document.

9.6.  Limiting Request Rates

   A router may limit CCNinfo Requests by ignoring some of the
   consecutive messages.  The router MAY randomly ignore the received
   messages to minimize the processing overhead, i.e., to keep fairness
   in processing requests, or prevent traffic amplification.  No error
   is returned.  The rate limit is left to the router's implementation.

9.7.  Limiting Reply Rates

   CCNinfo supporting multipath forwarding may result in one Request
   returning multiple Reply messages.  In order to prevent abuse, the
   routers in the traced path MAY need to rate-limit the Replies.  No
   error is returned.  The rate limit function is left to the router's
   implementation.



Asaeda, et al.         Expires September 12, 2019              [Page 28]


Internet-Draft                   CCNinfo                      March 2019


9.8.  Adjacency Verification

   It is assumed that CCNinfo Request and Reply messages are forwarded
   by adjacent neighbor nodes or routers.  Defining the secure way to
   verify the adjacency cannot rely on the way specified in CCNx message
   format or semantics, yet specifying the mechanism to validate
   adjacent neighbor routers is out of scope of this document.  An
   adjacency verification mechanism and the corresponding TLV for
   adjacency verification using hop-by-hop TLV header such as [8] is the
   potential way and will be defined in a separate document.

10.  Acknowledgements

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

11.  References

11.1.  Normative References

   [1]        Mosko, M., Solis, I., and C. Wood, "CCNx Messages in TLV
              Format", draft-irtf-icnrg-ccnxmessages-09 (work in
              progress), January 2019.

   [2]        Mosko, M., Solis, I., and C. Wood, "CCNx Semantics",
              draft-irtf-icnrg-ccnxsemantics-10 (work in progress),
              January 2019.

   [3]        Bradner, S., "Key words for use in RFCs to indicate
              requirement levels", RFC 2119, March 1997.

   [4]        Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 8200, July 2017.

11.2.  Informative References

   [5]        Asaeda, H., Matsuzono, K., and T. Turletti, "Contrace: A
              Tool for Measuring and Tracing Content-Centric Networks",
              IEEE Communications Magazine, Vol.53, No.3, pp.182-188,
              March 2015.

   [6]        Malkin, G., "Traceroute Using an IP Option", RFC 1393,
              January 1993.

   [7]        Asaeda, H., Mayer, K., and W. Lee, "Mtrace Version 2:
              Traceroute Facility for IP Multicast", RFC 8487, October
              2018.



Asaeda, et al.         Expires September 12, 2019              [Page 29]


Internet-Draft                   CCNinfo                      March 2019


   [8]        Li, R., Asaeda, H., and J. Wu, "DCAuth: Data-Centric
              Authentication for Secure In-Network Big-Data Retrieval",
              IEEE Transactions on Network Science and Engineering
              (TNSE) , October 2018.

Appendix A.  ccninfo Command and Options

   The ccninfo command enables the CCNinfo user to investigate the
   routing path based on the name prefix of the content (e.g.,
   ccn:/news/today).  The name prefix is mandatory but exclusive
   options; that is, only one of them should be used with the ccninfo
   command at once.

   The usage of ccninfo command is as follows:

   Usage: ccninfo [-f] [-n] [-o] [-r hop_count] [-s hop_count]
          name_prefix

   name_prefix
      Prefix name of content (e.g., ccn:/news/today) or exact name of
      content (e.g., ccn:/news/today/Chunk=10) the CCNinfo user wants to
      trace.

   f option
      This option enables "full discovery request"; routers ignore the
      forwarding strategy and send CCNinfo Requests to multiple upstream
      routers simultaneously.  The CCNinfo user could then trace the all
      potential forwarding paths.

   n option
      This option can be specified if a CCNinfo user only needs the
      routing path information to the specified content/cache and RTT
      between CCNinfo user and content forwarder; therefore, cache
      information is not given.

   o option
      This option enables to trace the path to the content publisher.
      Each router along the path to the publisher inserts each Report
      block and forwards the Request message.  It does not send Reply
      even if it caches the specified content.  FHR that attaches the
      publisher (who has the complete set of content and is not a
      caching router) replies the Reply message.

   r option
      Number of traced routers.  If the CCNinfo user specifies this
      option, only the specified number of hops from the CCNinfo user
      trace the Request; each router inserts its own Report block and
      forwards the Request message to the upstream router(s), and the



Asaeda, et al.         Expires September 12, 2019              [Page 30]


Internet-Draft                   CCNinfo                      March 2019


      last router stops the trace and sends the Reply message back to
      the CCNinfo user.  This value is set in the "HopLimit" field
      located in the fixed header of the Request.  For example, when the
      CCNinfo user invokes the CCNinfo command with this option such as
      "-r 3", only three routers along the path examine their path and
      cache information.  If there is a caching router or FHR within the
      hop count along the path, the caching router or FHR sends back the
      Reply message and terminates the trace request.  If the last
      router does not have the corresponding cache, it replies the Reply
      message with NO_INFO return code (described in Section 3.1) with
      no Reply block TLV inserted.  The Request messages are terminated
      at FHR; therefore, although the maximum value for this option a
      CCNinfo user can specify is 255, the Request messages should be in
      general reached at FHR within significantly lower than 255 hops.

   s option
      Number of skipped routers.  If the CCNinfo user specifies this
      option, the number of hops from the CCNinfo user simply forward
      the CCNinfo Request messages without adding its own Report block
      and without replying the Request, and the next upstream router
      starts the trace.  This value is set in the "SkipHopCount" field
      located in the Request block TLV.  For example, when the CCNinfo
      user invokes the CCNinfo command with this option such as "-s 3",
      the three upstream routers along the path only forwards the
      Request message, but does not append their Report blocks in the
      hop-by-hop headers and does not send the Reply messages even
      though they have the corresponding cache.  The Request messages
      are terminated at FHR; therefore, although the maximum value for
      this option a CCNinfo user can specify is 255, if the Request
      messages reaches FHR, the FHR silently discards the Request
      message and the request will be timed out.

Authors' Addresses

   Hitoshi Asaeda
   National Institute of Information and Communications Technology
   4-2-1 Nukui-Kitamachi
   Koganei, Tokyo  184-8795
   Japan

   Email: asaeda@nict.go.jp










Asaeda, et al.         Expires September 12, 2019              [Page 31]


Internet-Draft                   CCNinfo                      March 2019


   Atsushi Ooka
   National Institute of Information and Communications Technology
   4-2-1 Nukui-Kitamachi
   Koganei, Tokyo  184-8795
   Japan

   Email: a-ooka@nict.go.jp


   Xun Shao
   Kitami Institute of Technology
   165 Koen-cho
   Kitami, Hokkaido  090-8507
   Japan

   Email: x-shao@mail.kitami-it.ac.jp



































Asaeda, et al.         Expires September 12, 2019              [Page 32]


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/