ICN Ping Protocol Specification
draft-irtf-icnrg-icnping-02

Document Type Active Internet-Draft (icnrg RG)
Authors Spyridon Mastorakis  , Jim Gibson  , Ilya Moiseenko  , Ralph Droms  , David Oran 
Last updated 2021-04-11
Replaces draft-mastorakis-icnrg-icnping
Stream Internet Research Task Force (IRTF)
Intended RFC status Experimental
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ICNRG                                                      S. Mastorakis
Internet-Draft                             University of Nebraska, Omaha
Intended status: Experimental                                  J. Gibson
Expires: 13 October 2021                                   Cisco Systems
                                                            I. Moiseenko
                                                               Apple Inc
                                                                R. Droms
                                                             Google Inc.
                                                                 D. Oran
                                     Network Systems Research and Design
                                                           11 April 2021

                    ICN Ping Protocol Specification
                      draft-irtf-icnrg-icnping-02

Abstract

   This document presents the design of an ICN Ping protocol.  It
   includes the operations of both the client and the forwarder.

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 13 October 2021.

Copyright Notice

   Copyright (c) 2021 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.  Code Components

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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Background on IP-Based Ping Operation . . . . . . . . . . . .   3
   3.  Ping Functionality Challenges and Opportunities in ICN  . . .   4
   4.  ICN Ping Echo CCNx Packet Formats . . . . . . . . . . . . . .   6
     4.1.  ICN Ping Echo Request CCNx Packet Format  . . . . . . . .   6
     4.2.  Ping Echo Reply CCNx Packet Format  . . . . . . . . . . .   8
   5.  ICN Ping Echo NDN Packet Formats  . . . . . . . . . . . . . .  12
     5.1.  ICN Ping Echo Request NDN Packet Format . . . . . . . . .  12
     5.2.  Ping Echo Reply NDN Packet Format . . . . . . . . . . . .  13
   6.  Forwarder Handling  . . . . . . . . . . . . . . . . . . . . .  14
   7.  Protocol Operation For Locally-Scoped Namespaces  . . . . . .  15
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  17
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  17
     10.2.  Informative References . . . . . . . . . . . . . . . . .  17
   Appendix A.  Ping Client Application (Consumer) Operation . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   Ascertaining data plane reachability to a destination and taking
   coarse performance measurements of round trip time are fundamental
   facilities for network administration and troubleshooting.  In IP,
   where routing and forwarding are based on IP addresses, ICMP echo and
   ICMP echo response are the protocol mechanisms used for this purpose,
   generally exercised through the familiar ping utility.  In ICN, where
   routing and forwarding are based on name prefixes, the ability to
   ascertain reachability of names is required.

   This document proposes protocol mechanisms for a ping equivalent in
   ICN (CCNx [RFC8609] and NDN [NDNTLV]) networks.  A non-normative
   appendix suggests useful properties for an ICN ping client
   application, analogous to IP ping, that originates echo requests and
   processes echo replies.

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1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

1.2.  Terminology

   To aid the understanding of readers, we define the following terms:

   *  Content object: A network-level packet that carries payload,
      uniquely identified by a name, and is directly secured [RFC8793].

   *  Producer: An ICN entity that creates Data packets and makes them
      available for retrieval [RFC8793].

   *  Producer's name: The name prefix that a request must carry in
      order to reach a producer over an ICN network.

   *  Named Data: A synonym for a content object.

   *  Round Trip Time (RTT): The time between sending a request for a
      specific piece of named data and receiving the corresponding piece
      of named data.

   *  Sender: An entity that sends a request for named data or a piece
      of named data.

   *  Name of a sender: An alias of producer's name.

   *  Border forwarder: The forwarder that is the border of a network
      region where a producer's name is directly routable (i.e., the
      producer's name is present in the FIB of forwarders within this
      network region).

2.  Background on IP-Based Ping Operation

   In IP-based ping, an IP address is specified by the user either
   directly, or via translation of a domain name through DNS.  The ping
   client application sends a number of ICMP Echo Request packets with
   the specified IP address as the IP destination address and an IP
   address from the client's host as the IP source address.

   Each ICMP Echo Request is forwarded across the network based on its
   destination IP address.  If it eventually reaches the destination,
   the destination responds by sending back an ICMP Echo Reply packet to
   the IP source address from the ICMP Echo Request.

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   If an ICMP Echo Request does not reach the destination or the Echo
   reply is lost, the ping client times out.  Any ICMP error messages,
   such as "no route to destination", generated by the ICMP Echo Request
   message are returned to the client and reported.

3.  Ping Functionality Challenges and Opportunities in ICN

   In ICN, the communication paradigm is based exclusively on named
   objects.  An Interest is forwarded across the network based on the
   name prefix that it carries.  Eventually, a content object is
   retrieved either from a producer application or some forwarder's
   Content Store (CS).

   IP-based ping was built as an add-on measurement and debugging tool
   on top of an already existing network architecture.  In ICN, we have
   the opportunity to incorporate diagnostic mechanisms directly in the
   network layer protocol, and hopefully provide more powerful
   diagnostic capability than can be realized through the layered ICMP
   Echo approach.

   An ICN network differs from an IP network in at least 4 important
   ways:

   *  IP identifies interfaces to an IP network with a fixed-length
      address, and delivers IP packets to one or more of these
      interfaces.  ICN identifies units of data in the network with a
      variable length name consisting of a hierarchical list of name
      components.

   *  An IP-based network depends on the IP packets having source IP
      addresses that are used as the destination address for replies.
      On the other hand, ICN Interests do not have source addresses and
      they are forwarded based on names, which do not refer to a unique
      end-point.  Data packets follow the reverse path of the Interests
      based on hop-by-hop state created during Interest forwarding.

   *  An IP network supports multi-path, single destination, stateless
      packet forwarding and delivery via unicast, a limited form of
      multi-destination selected delivery with anycast, and group-based
      multi-destination delivery via multicast.  In contrast, ICN
      supports multi-path and multi-destination stateful Interest
      forwarding and multi-destination delivery of named data.  This
      single forwarding semantic subsumes the functions of unicast,
      anycast, and multicast.  As a result, consecutive (or
      retransmitted) ICN Interest messages may be forwarded through an
      ICN network along different paths, and may be forwarded to
      different data sources (e.g., end-node applications, in-network
      storage) holding a copy of the requested unit of data.  This can

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      lead to a significant variance in round-trip times, which while
      resulting in a more robust overall forwarding architecture, has
      implications for a network troubleshooting mechanism like ping.

   *  In the case of multiple Interests with the same name arriving at a
      forwarder, a number of Interests may be aggregated in a common
      Pending Interest Table (PIT) entry and only one of them forwarded
      onward.  Depending on the lifetime of a PIT entry, the round-trip
      time an Interest-Data exchange might significantly vary (e.g., it
      might be shorter than the full round-trip time to reach the
      original content producer).  To this end, the round-trip time
      experienced by consumers might also vary.

   These differences introduce new challenges, new opportunities and new
   requirements in the design of an ICN ping protocol.  Following this
   communication model, a ping client should be able to express ping
   echo requests with some name prefix and receive responses.

   Our goals are the following:

   *  Test the reachability and the operational state of an ICN
      forwarder.

   *  Test the reachability of a producer or a data repository (in the
      sense of whether Interests for a prefix that it serves can be
      forwarded to it) and discover the forwarder with local
      connectivity to (an instance of) this producer or repository.

   *  Test whether a specific named object is cached in some on-path CS,
      and, if so, return the administrative name of the corresponding
      forwarder.

   *  Perform some simple network performance measurements.

   To this end, a ping name can represent:

   *  An administrative name that has been assigned to a forwarder.

   *  A name that includes an application's namespace as a prefix.

   *  A named object that might reside in some in-network storage.

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   In order to provide stable and reliable diagnostics, it is desirable
   that the packet encoding of a ping echo request enable the forwarders
   to distinguish a ping from a normal Interest, while also allowing for
   forwarding behavior to be as similar as possible to that of an
   Interest packet.  In the same way, the encoding of a ping echo reply
   should allow for forwarder processing as close as possible to that
   used for data packets.

   The ping protocol should also enable relatively robust round-trip
   time measurements.  To this end, it is important to have a mechanism
   to steer consecutive ping echo requests for the same name towards an
   individual path.  Such a capability was initially published in
   [PATHSTEERING] and has been specified for CCNx in
   [I-D.oran-icnrg-pathsteering].

   It is also important, in the case of ping echo requests for the same
   name from different sources to have a mechanism to avoid those
   requests being aggregated in the PIT.  To this end, we need some
   encoding in the ping echo requests to make each request for a common
   name unique, hence avoiding PIT aggregation and further enabling the
   exact match of a response with a particular ping packet.

   Note that ICN ping is a protocol that estimates the perceived RTT
   based on a single request-reply exchange.  A measurement application
   is needed to make proper use of this protocol to explore multiple
   paths and compute various statistics, such as the variance, average,
   maximum and minimum RTT values as well as loss rates.

4.  ICN Ping Echo CCNx Packet Formats

   In this section, we describe the Echo Packet Format according to the
   CCNx packet format [RFC8569], where messages exist within outermost
   containments (packets).  Specifically, we specify two types of ping
   packets, an echo request and an echo reply packet type.

4.1.  ICN Ping Echo Request CCNx Packet Format

   The format of the ping echo request packet is presented below:

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    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    |  EchoRequest  |         PacketLength          |
    |               |               |                               |
    +---------------+---------------+---------------+---------------+
    |               |               |               |               |
    |    HopLimit   |    Reserved   |     Flags     |  HeaderLength |
    |               |               |               |               |
    +---------------+---------------+---------------+---------------+
    /                                                               /
    /                   PathSteering TLV                            /
    /                                                               /
    +---------------+---------------+---------------+---------------+
    |                                                               |
    |                   Echo Request Message TLVs                   |
    |                                                               |
    +---------------+---------------+---------------+---------------+

      <postamble>:
        

                 Figure 1: Echo Request CCNx Packet Format

   The existing packet header fields have the same definition as the
   header fields of a CCNx Interest packet.  The value of the packet
   type field is _Echo Request_. The exact numeric value of this field
   type is to be assigned in the Packet Type IANA Registry for CCNx (see
   section 4.1 of [RFC8569].

   Compared to the typical format of a CCNx packet header from
   [RFC8569], in order to enable path steering of Echo Requests, there
   is an optional fixed header Pathsteering TLV as specified in
   [I-D.oran-icnrg-pathsteering] added to the packet header:

   The message format of an echo request is presented below:

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    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

    +---------------+---------------+---------------+---------------+
    |                               |                               |
    |        MessageType = 1        |          MessageLength        |
    |                               |                               |
    +---------------+---------------+---------------+---------------+
    |                                                               |
    |                          Name TLV                             |
    |                                                               |
    +---------------+---------------+---------------+---------------+

                   Figure 2: Echo Request Message Format

   The echo request message is of type Interest in order to leverage the
   Interest forwarding behavior provided by the network.  The Name TLV
   has the structure described in [RFC8609].  The name consists of the
   prefix that we would like to ping appended with a nonce typed name
   component as its last component.  The exact numeric value of this
   field type is to be assigned in the Name Component Type IANA Registry
   for CCNx (see section 4.5 of [RFC8609].  The value of this TLV is a
   64-bit nonce.  The purpose of the nonce is to avoid Interest
   aggregation and allow client matching of replies with requests.  As
   described below, the nonce is ignored for CS checking.

    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

    +---------------+---------------+---------------+---------------+
    |                               |                               |
    |           Nonce_Type          |       Nonce_Length = 8        |
    |                               |                               |
    +---------------+---------------+---------------+---------------+
    |                                                               |
    |                                                               |
    |                                                               |
    |                          Nonce_Value                          |
    |                                                               |
    |                                                               |
    +---------------+---------------+---------------+---------------+

        Figure 3: Nonce Name component TLV for Echo Request messages

4.2.  Ping Echo Reply CCNx Packet Format

   The format of a ping echo reply packet is presented below:

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 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    |   EchoReply   |          PacketLength         |
 |               |               |                               |
 +---------------+---------------+---------------+---------------+
 |                               |               |               |
 |            Reserved           |     Flags     | HeaderLength  |
 |                               |               |               |
 +---------------+---------------+---------------+---------------+
 |                                                               |
 |                        PathSteering TLV                               |
 |                                                               |
 +---------------+---------------+---------------+---------------+
 |                                                               |
 |                    Echo Reply Message TLVs                    |
 |                                                               |
 +---------------+---------------+---------------+---------------+

               Figure 4: Echo Reply CCNx Packet Format

   The header of an echo reply consists of the header fields of a CCNx
   Content Object and a hop-by-hop PathSteering TLV.  The value of the
   packet type field is Echo Reply.  The exact numeric value of this
   field type is to be assigned in the Packet Type IANA Registry for
   CCNx (see section 4.1 of [RFC8569].  The PathSteering header TLV from
   [I-D.oran-icnrg-pathsteering] is as defined for the echo request
   packet.

   A ping echo reply message is of type Content Object, contains a Name
   TLV (name of the corresponding echo request), a PayloadType TLV and
   an ExpiryTime TLV with a value of 0 to indicate that echo replies
   must not be returned from network caches.

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    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

    +---------------+---------------+---------------+---------------+
    |                               |                               |
    |        MessageType = 2        |          MessageLength        |
    |                               |                               |
    +---------------+---------------+---------------+---------------+
    |                                                               |
    |                            Name TLV                           |
    |                                                               |
    +---------------+---------------+---------------+---------------+
    |                                                               |
    |                         PayloadType TLV                       |
    |                                                               |
    +---------------+---------------+---------------+---------------+
    |                                                               |
    |                         ExpiryTime TLV                        |
    |                                                               |
    +---------------+---------------+---------------+---------------+

                    Figure 5: Echo Reply Message Format

   The PayloadType TLV is presented below.  It is of type
   T_PAYLOADTYPE_DATA, and the data schema consists of 3 TLVs: 1) the
   name of the sender of this reply (with the same structure as a CCNx
   Name TLV), 2) the sender's signature of their own name (with the same
   structure as a CCNx ValidationPayload TLV), 3) a TLV with a return
   code to indicate what led to the generation of this reply (i.e.,
   existence of a local application, a CS hit or a match with a
   forwarder's administrative name as specified in Section 6).

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    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_PAYLOADTYPE_DATA      |             Length            |
    |                               |                               |
    +---------------+---------------+---------------+---------------+
    /                                                               /
    /                      Sender's Name TLV                        /
    /                                                               /
    +---------------+---------------+---------------+---------------+
    /                                                               /
    /                    Sender's Signature TLV                     /
    /                                                               /
    +---------------+---------------+---------------+---------------+
    /                                                               /
    /                     Echo Reply Code TLV                       /
    /                                                               /
    +---------------+---------------+---------------+---------------+

                    Figure 6: Echo Reply Message Format

   The goal of including the name of the sender in the echo reply is to
   enable the user to reach this entity directly to ask for further
   management/administrative information using generic Interest-Data
   exchanges or by employing a more comprehensive management tool such
   as CCNInfo [I-D.irtf-icnrg-ccninfo] after a successful verification
   of the sender's name.

   The structure of the Echo Reply Code TLV is presented below (16-bit
   value).  The defined values are the following:

   *  1: Indicates that the target name matched the administrative name
      of a forwarder.

   *  2: Indicates that the target name matched a prefix served by an
      application.

   *  3: Indicates that the target name matched the name of an object in
      a forwarder's CS.

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    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

    +---------------+---------------+---------------+---------------+
    |                               |                               |
    |     Echo_Reply_Code_Type      |  Echo_Reply_Code_Length = 2   |
    |                               |                               |
    +---------------+---------------+---------------+---------------+
    |                                                               |
    |                      Echo_Reply_Code_Value                    |
    +---------------+---------------+---------------+---------------+

                       Figure 7: Echo Reply Code TLV

5.  ICN Ping Echo NDN Packet Formats

   In this section, we present the ICN Ping Echo Request and Reply
   Format according to the NDN packet specification [NDNTLV].

5.1.  ICN Ping Echo Request NDN Packet Format

   An echo request is encoded as an NDN Interest packet.  Its format is
   the following:

           EchoRequest ::= INTEREST-TYPE TLV-LENGTH
                             Name
                             MustBeFresh
                             Nonce
                             Parameters?

                  Figure 8: Echo Request NDN Packet Format

   The name field of an echo request consists of the name prefix to be
   pinged, a nonce value (it can be the value of the Nonce field) and
   the suffix "ping" to denote that this Interest is a ping request.

   The "Parameters" field of the Request contains the following
   PathSteering TLV:

           PathSteering TLV ::= PATHSTEERING-TLV-TYPE TLV-LENGTH BYTE{8}

                         Figure 9: PathSteering TLV

   Since the NDN packet format does not provide a mechanism to prevent
   the network from caching specific data packets, we use the
   MustBeFresh selector for echo requests (in combination with a
   Freshness Period TLV of value 0 for echo replies) to avoid fetching
   cached echo replies with an expired freshness period [REALTIME].

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5.2.  Ping Echo Reply NDN Packet Format

   An echo reply is encoded as an NDN Data packet.  Its format is the
   following:

           EchoReply ::= DATA-TLV TLV-LENGTH
                           PathSteering TLV
                           Name
                           MetaInfo
                           Content
                           Signature

                  Figure 10: Echo Reply NDN Packet Format

   Compared to the format of a regular NDN Data packet, an echo reply
   contains a PathSteering TLV field, which is not included in the
   security envelope, since it might be modified in a hop-by-hop fashion
   by the forwarders along the reverse path.

   The name of an echo reply is the name of the corresponding echo
   request, while the format of the MetaInfo field is the following:

         MetaInfo ::= META-INFO-TYPE TLV-LENGTH
                        ContentType
                        FreshnessPeriod

                          Figure 11: MetaInfo TLV

   The value of the ContentType TLV is 0.  The same applies to the value
   of the FreshnessPeriod TLV, so that the replies are treated as stale
   data as soon as they are received by a forwarder.

   The content of an echo reply consists of the following 2 TLVs:
   Sender's name (with a structure similar as an NDN Name TLV) and Echo
   Reply Code.  There is no need to have a separate TLV for the sender's
   signature in the content of the reply, since every NDN data packet
   carries the signature of the data producer.

   The Echo Reply Code TLV format is the following (with the values
   specified in Section 4.2):

           EchoReplyCode ::= ECHOREPLYCODE-TLV-TYPE TLV-LENGTH BYTE{2}

                       Figure 12: Echo Reply Code TLV

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6.  Forwarder Handling

   We present the workflow of the forwarder's operation in Figure 13.
   When a forwarder receives an echo request, it first extracts the
   message's base name (i.e., the request name with the Nonce name
   component excluded and the suffix "ping" in the case of an echo
   request with the NDN packet format).

   In some cases, the forwarder originates an echo reply, sending the
   reply downstream through the face on which the echo request was
   received.  This echo reply includes the forwarder's own name and
   signature and the appropriate echo reply code based on the condition
   that triggered the reply generation.  It also includes a pathSteering
   TLV, initially containing a null value (since the echo reply
   originator did not forward the request and, thus, does not make a
   path choice).

   The forwarder generates and returns an echo reply in the following
   cases:

   *  Assuming that a forwarder has been given one or more
      administrative names, the echo request base name exactly matches
      any of the forwarder's administrative name(s).

   *  The echo request's base name exactly matches the name of a
      content-object residing in the forwarder's CS (unless the ping
      client application has chosen not to receive replies due to CS
      hits as specified in Appendix A).

   *  The echo request base name matches (in a Longest Prefix Match
      manner) a FIB entry with an outgoing face referring to a local
      application.

   If none of the conditions to reply to the echo request are met, the
   forwarder will attempt to forward the echo request upstream based on
   the path steering value (if present), the results of the FIB LPM
   lookup and PIT creation (based on the name including the nonce typed
   name component and the suffix "ping" in the case of an echo request
   with the NDN packet format).  If no valid next-hop is found, an
   InterestReturn is sent downstream indicating "no route" (as with a
   failed attempt to forward an ordinary Interest).

   A received echo reply will be matched to an existing PIT entry as
   usual.  On the reverse path, the path steering TLV of an echo reply
   will be updated by each forwarder to encode its next-hop choice.
   When included in subsequent echo requests, this pathSteering TLV
   allows the forwarders to steer the echo requests along the same path.

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      ------------------------------------------------------------------------
                                    FORWARD PATH
      ------------------------------------------------------------------------

    Request +------+  +-----+  +-----+(path label)  +--------+ (match) Request
    ------> |Admin |->| CS  |->| PIT | ------------>| Label  |---------------->
            | Name |  +-----+  +-----+              | Lookup |
            |Lookup|     |       | \ (no path label)+--------+
            +------+     |       |  \                |\ (path label mismatch)
       Reply    |        |       |   \               | \
      <---------+        |       v    \              |  \
      (base matches      |   aggregate \             |   \
       admin name)       |              \            |    \
                         | (base         \           |     +------+ Request
                 Reply   |  matches       +----------|---->| FIB  | -------->
               <---------+  cached object)           |     +------+
                                                     |  (no   |  | (base matches
      Interest-Return (NACK)                         v  route)|  | local app
      <----------------------------------------------+<-------+  | face)
      <----------------------------------------------------------+
      Reply
      ------------------------------------------------------------------------
                                    REVERSE PATH
      ------------------------------------------------------------------------

      Interest-return(NACK) +-----+ (update path label) Interest-Return(NACK)
      <---------------------|     |<-----------------------------------------
                            |     |
      Reply  +------+       | PIT |  (update path label)                Reply
      <------|  CS  |<------|     |<-----------------------------------------
             +------+       |     |
                            +-----+
                               |
                               | (no match)
                               v

                    Figure 13: Forwarder Operation

7.  Protocol Operation For Locally-Scoped Namespaces

   In this section, we elaborate on 2 alternative design approaches in
   cases that the pinged prefix corresponds to a locally-scoped
   namespace not directly routable from the client's local network.

   The first approach leverages the NDN Link Object [SNAMP].
   Specifically, the ping client attaches to the expressed request a
   LINK Object that contains a number of routable name prefixes, based
   on which the request can be forwarded until it reaches a network

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   region where the request name itself is routable.  A LINK Object is
   created and signed by a data producer allowed to publish data under a
   locally-scoped namespace.  The way that a client retrieves a LINK
   Object depends on various network design factors and is out of the
   scope of the current draft.

   Based on the current usage of the LINK Object by the NDN team, a
   forwarder at the border of the region where an Interest name becomes
   routable must remove the LINK Object from incoming Interests.  The
   Interest state maintained along the entire forwarding path is based
   on the Interest name regardless of whether it was forwarded based on
   its name or a routable prefix in the LINK Object.

   The second approach is based on prepending a routable prefix to the
   locally-scoped name.  The resulting prefix will be the name of the
   echo requests expressed by the client.  In this way, a request will
   be forwarded based on the routable part of its name.  When it reaches
   the network region where the original locally-scoped name is
   routable, the border forwarder rewrites the request name and deletes
   its routable part.  There are two conditions for a forwarder to
   perform this rewriting operation on a request: 1) the routable part
   of the request name matches a routable name of the network region
   adjacent to the forwarder (assuming that a forwarder is aware of
   those names) and 2) the remaining part of the request name is
   routable across the network region of this forwarder.

   The state maintained along the path, where the locally-scoped name is
   not routable, is based on the routable prefix along with the locally-
   scoped prefix.  Within the network region that the locally-scoped
   prefix is routable, the state is based only on it.  To ensure that
   the generated replies reach the ping client, the border forwarder has
   also to rewrite the name of a reply and prepend the routable prefix
   of the corresponding echo request.

8.  Security Considerations

   A reflection attack could be mounted by a compromised forwarder in
   the case of an echo reply with the CCNx packet format if that
   forwarder includes in the reply the name of a victim forwarder.  This
   could convince a client to direct the future administrative traffic
   towards the victim.  To foil such reflection attacks, the forwarder
   that generates a reply must sign the name included in the payload.
   In this way, the client is able to verify that the included name is
   legitimate and refers to the forwarder that generated the reply.
   Alternatively, the forwarder could include in the reply payload their
   routable prefix(es) encoded as a signed NDN Link Object [SNAMP].

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   Interest flooding attack amplification is possible in the case of the
   second approach to deal with locally-scoped namespaces described in
   Section 7.  To eliminate such amplification, a border forwarder will
   have to maintain extra state in order to prepend the correct routable
   prefix to the name of an outgoing reply, since the forwarder might be
   attached to multiple network regions (reachable under different
   prefixes) or a network region attached to this forwarder might be
   reachable under multiple routable prefixes.

9.  Acknowledgements

   The authors would like to thank Mark Stapp for the fruitful
   discussion on the objectives of the ICN ping protocol.

10.  References

10.1.  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>.

   [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>.

   [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>.

10.2.  Informative References

   [I-D.irtf-icnrg-ccninfo]
              Asaeda, H., Ooka, A., and X. Shao, "CCNinfo: Discovering
              Content and Network Information in Content-Centric
              Networks", Work in Progress, Internet-Draft, draft-irtf-
              icnrg-ccninfo-05, 21 September 2020,
              <https://tools.ietf.org/html/draft-irtf-icnrg-ccninfo-05>.

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   [I-D.oran-icnrg-pathsteering]
              Moiseenko, I. and D. Oran, "Path Steering in CCNx and
              NDN", Work in Progress, Internet-Draft, draft-oran-icnrg-
              pathsteering-01, 23 April 2020,
              <https://tools.ietf.org/html/draft-oran-icnrg-
              pathsteering-01>.

   [NDNTLV]   "NDN Packet Format Specification.", in Proceedings of the
              IEEE Conference on Computer Communications Workshops
              (INFOCOM WKSHPS), 2016,
              <http://named-data.net/doc/ndn-tlv/>.

   [PATHSTEERING]
              Moiseenko, I. and D. Oran, "Path switching in content
              centric and named data networks", in Proceedings of the
              4th ACM Conference on Information-Centric Networking,
              2017.

   [REALTIME] Mastorakis, S., Gusev, P., Afanasyev, A., and L. Zhang,
              "Real-Time Data Retrieval in Named Data Networking", in
              Proceedings of the 1st IEEE International Conference on
              Hot Topics in Information-Centric Networking, 2017.

   [SNAMP]    Afanasyev, A. and , "SNAMP: Secure namespace mapping to
              scale NDN forwarding", 2015.

Appendix A.  Ping Client Application (Consumer) Operation

   This section is an informative appendix regarding the proposed ping
   client operation.

   The ping client application is responsible for generating echo
   requests for prefixes provided by users.

   When generating a series of echo requests for a specific name, the
   first echo request will typically not include a PathSteering TLV,
   since no TLV value is known.  After an echo reply containing a
   PathSteering TLV is received, each subsequent echo request can
   include the received path steering value in the PathSteering header
   TLV to drive the requests towards a common path as part of checking
   network performance.  To discover more paths, a client can omit the
   path steering TLV in future requests.  Moreover, for each new ping
   echo request, the client has to generate a new nonce and record the
   time that the request was expressed.  It will also set the lifetime
   of an echo request, which will have identical semantics to the
   lifetime of an Interest.

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   Further, the client application might not wish to receive echo
   replies due to CS hits.  A mechanism to achieve that in CCNx would be
   to use a Content Object Hash Restriction TLV with a value of 0 in the
   payload of an echo request message.  In NDN, the exclude filter
   selector can be used.

   When it receives an echo reply, the client would typically match the
   reply to a sent request and compute the round-trip time of the
   request.  It should parse the PathSteering value and decode the
   reply's payload to parse the the sender's name and signature.  The
   client should verify that both the received message and the
   forwarder's name have been signed by the key of the forwarder, whose
   name is included in the payload of the reply (by fetching this
   forwarder's public key and verifying the contained signature).  The
   client can also decode the Echo Reply Code TLV to understand the
   condition that triggered the generation of the reply.

   In the case that an echo reply is not received for a request within a
   certain time interval (lifetime of the request), the client should
   time-out and send a new request with a new nonce value up to some
   maximum number of requests to be sent specified by the user.

Authors' Addresses

   Spyridon Mastorakis
   University of Nebraska, Omaha
   Omaha, NE
   United States of America

   Email: smastorakis@unomaha.edu

   Jim Gibson
   Cisco Systems
   Cambridge, MA
   United States of America

   Email: gibson@cisco.com

   Ilya Moiseenko
   Apple Inc
   Cupertino, CA
   United States of America

   Email: iliamo@mailbox.org

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   Ralph Droms
   Google Inc.
   Cambridge, MA
   United States of America

   Email: rdroms.ietf@gmail.com

   Dave Oran
   Network Systems Research and Design
   Cambridge, MA
   United States of America

   Email: daveoran@orandom.net

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