



Internet Research Task Force (IRTF)                              J. Hong
Request for Comments: 9236                                        T. You
Category: Informational                                             ETRI
ISSN: 2070-1721                                                 V. Kafle
                                                                    NICT
                                                              April 2022


  Architectural Considerations of Information-Centric Networking (ICN)
                    Using a Name Resolution Service

Abstract

   This document describes architectural considerations and implications
   related to the use of a Name Resolution Service (NRS) in Information-
   Centric Networking (ICN).  It explains how the ICN architecture can
   change when an NRS is utilized and how its use influences the ICN
   routing system.  This document is a product of the Information-
   Centric Networking Research Group (ICNRG).

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

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

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9236.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents

   1.  Introduction
   2.  Terminology
   3.  Background
   4.  Implications of an NRS in ICN
   5.  ICN Architectural Considerations for NRS
     5.1.  Name Mapping Records Registration, Resolution, and Update
     5.2.  Protocols and Semantics
     5.3.  Routing System
   6.  Conclusion
   7.  IANA Considerations
   8.  Security Considerations
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   Information-Centric Networking (ICN) is an approach to evolving the
   Internet infrastructure to provide direct access to Named Data
   Objects (NDOs) by names.  In two common ICN architectures, Named Data
   Networking (NDN) [NDN] and Content-Centric Networking (CCNx) [CCNx],
   the name of an NDO is used directly to route a request to retrieve
   the data object.  Such direct name-based routing has inherent
   challenges in enabling a globally scalable routing system,
   accommodating producer mobility, and supporting off-path caching.
   These specific issues are discussed in detail in Section 3.  In order
   to address these challenges, a Name Resolution Service (NRS) has been
   utilized in the literature as well as the proposals of several ICN
   projects [Afanasyev] [Zhang2] [Ravindran] [SAIL] [MF] [Bayhan].

   This document describes the potential changes in the ICN architecture
   caused by the introduction of an NRS and the corresponding
   implication to the ICN routing system.  It also describes ICN
   architectural considerations for the integration of an NRS.  The
   scope of this document includes considerations from the perspective
   of an ICN architecture and routing system when using an NRS in ICN.
   A description of the NRS itself is provided in the companion NRS
   design considerations document [RFC9138], which provides the NRS
   approaches, functions, and design considerations.

   This document represents the consensus of the Information-Centric
   Networking Research Group (ICNRG).  It has been reviewed extensively
   by the Research Group (RG) members who are actively involved in the
   research and development of the technology covered by this document.
   It is not an IETF product and is not a standard.

2.  Terminology

   Name Resolution Service (NRS):  An NRS in ICN is defined as a service
      that provides the function of translating a content name or a data
      object name into some other information such as a routable prefix,
      a locator, an off-path-cache pointer, or an alias name that is
      more amenable than the input name to forwarding the object request
      toward the target destination storing the NDO [RFC9138].  An NRS
      is most likely implemented through the use of a distributed
      mapping database system.  The Domain Name System (DNS) may be used
      as an NRS.  However, in this case, the requirements of frequent
      updates of NRS records due to the creations of a lot of new NDOs
      and changes in their locations in the network need to be
      considered.

   NRS server:  An NRS comprises the distributed NRS servers storing the
      mapping records in their databases.  NRS servers store and
      maintain the mapping records that keep the mappings of content or
      object name to some other information that is used for forwarding
      the content request or the content itself.

   NRS resolver:  The client-side function of an NRS is called an NRS
      resolver.  The NRS resolver is responsible for initiating name
      resolution request queries that ultimately lead to a name
      resolution of the target data objects.  NRS resolvers can be
      located in the consumer (or client) nodes and/or ICN routers.  An
      NRS resolver may also cache the mapping records obtained through
      the name resolution for later usage.

   Name registration:  In order to populate the NRS, the content names
      and their mapping records must be registered in the NRS system by
      a publisher who has access rights to at least one authoritative
      NRS server or by a producer who generates named data objects.  The
      records contain the mapping of an object name to some information
      such as other alias names, routable prefixes, and locators, which
      are used for forwarding the content request.  Thus, a publisher or
      producer of content creates an NRS registration request and sends
      it to an NRS server.  On registration, the NRS server stores (or
      updates) the name mapping record in the database and sends an
      acknowledgement back to the producer or publisher that made the
      registration request.

   Name resolution:  Name resolution is the main function of the NRS
      system.  It is performed by an NRS resolver, which can be deployed
      on a consumer node or an ICN router.  Resolvers are responsible
      for either returning a cached mapping record (whose lifetime has
      not expired) or alternatively sending a name resolution request
      toward an NRS server.  The NRS server searches for the content
      name in its mapping record database and, if found, retrieves the
      mapping record and returns it in a name resolution response
      message to the NRS resolver.

   NRS node:  NRS servers are also referred to as NRS nodes that
      maintain the name records.  The terms are used interchangeably.

   NRS client:  A node that uses the NRS is called an NRS client.  Any
      node that initiates a name registration, resolution, or update
      procedure is an NRS client; that is, NRS resolvers, ICN client
      nodes, ICN routers, or producers can be NRS clients.

3.  Background

   A pure name-based routing approach in ICN has inherent challenges in
   enabling a globally scalable routing system, accommodating producer
   mobility, and supporting off-path caching.  In order to address these
   challenges, an NRS has been utilized in proposals and literature of
   several ICN projects as follows:

   Routing scalability:  In ICN, application names identifying content
      are intended to be used directly for packet delivery, so ICN
      routers run a name-based routing protocol to build name-based
      routing and forwarding tables.  Similar to the scalability
      challenge of IP routing, if non-aggregatable name prefixes are
      injected into the Default Route Free Zone (DFZ) of ICN routers,
      they would be driving the uncontrolled growth of the DFZ routing
      table size.  Thus, providing the level of indirection enabled by
      an NRS in ICN can be an approach to keeping the routing table size
      under control.  The NRS system resolves name prefixes that do not
      exist in the DFZ forwarding table into globally routable prefixes
      such as the one proposed in NDN [Afanasyev].  Another approach
      dealing with routing scalability is the Multi-level Distributed
      Hash Table (MDHT) used in NetInf [Dannewitz].  It provides name-
      based anycast routing that can support a non-hierarchical
      namespace and can be adopted on a global scale [Dannewitz2].

   Producer mobility:  In ICN, if a producer moves into a different name
      domain that uses a different name prefix, the request for a
      content produced by the moving producer with the origin content
      name must be forwarded to the moving producer's new location.
      Especially in a hierarchical naming scheme, producer mobility
      support is much harder than in a flat naming scheme since the
      routing tables in a broader area need to be updated to track the
      producer movement.  Therefore, various ICN architectures such as
      NetInf [Dannewitz] and MobilityFirst [MF] have adopted NRS systems
      to tackle the issues of producers whose location changes.

   Off-path caching:  In-network caching is a common feature of an ICN
      architecture.  Caching approaches can be categorized into on-path
      caching and off-path caching, according to the location of caches
      in relation to the forwarding path from the original content store
      to a consumer.  Off-path caching, sometimes also referred to as
      content replication or content storing, aims to replicate a Named
      Data Object in various locations within a network in order to
      increase the availability of content, reduce access latency, or
      both.  These caching locations may not be lying along the content
      forwarding path.  Thus, finding off-path cached content requires
      more complex forwarding procedures if a pure name-based routing is
      employed.  In order to support access to off-path caches, the
      locations of replicas are usually advertised into a name-based
      routing system or into an NRS as described in [Bayhan].

   This document discusses architectural considerations and implications
   of ICN when an NRS is utilized to solve such challenges facing a
   name-based routing in ICN.

4.  Implications of an NRS in ICN

   An NRS is not a mandatory part of an ICN architecture, as the
   majority of ICN architectures uses name-based routing that avoids the
   need for a name resolution procedure.  Therefore, the utilization of
   an NRS in an ICN architecture changes some architectural aspects at
   least with respect to forwarding procedures, latency, and security,
   as discussed below:

   Forwarding procedure:  When an NRS is included in an ICN
      architecture, the name resolution procedure has to be included in
      the ICN overall routing and forwarding architectural procedures.
      To integrate an NRS into an ICN architecture, there are certain
      things that have to be decided and specified such as where, when,
      and how the name resolution task is performed.

   Latency:  When an NRS is included in an ICN architecture, additional
      latency introduced by the name resolution process is incurred by
      the routing and forwarding system.  Although the latency due to
      the name resolution is added, the total latency of individual
      requests being served could be lower if the nearest copies or off-
      path caches can be located by the NRS lookup procedure.
      Additionally, there might be a favorable trade-off between the
      name resolution latency and inter-domain traffic reduction by
      finding the nearest off-path cached copy of the content.  Finding
      the nearest cache holding the content might significantly reduce
      the content discovery as well as delivery latency.

   Security:  When any new component such as an NRS is introduced in the
      ICN architecture, the attack surface may increase.  Protection of
      the NRS system itself against attacks such as Distributed Denial
      of Service (DDoS) and spoofing or alteration of name mapping
      records and related signaling messages may be challenging.

5.  ICN Architectural Considerations for NRS

   This section discusses the various items that can be considered from
   the perspective of ICN architecture when employing an NRS system.
   These items are related to the registration, resolution, and update
   of name mapping records, protocols and messages, and integration with
   the routing system.

5.1.  Name Mapping Records Registration, Resolution, and Update

   When an NRS is integrated in ICN architecture, the functions related
   to the registration, resolution, and update of name mapping records
   have to be considered.  The NRS nodes maintain the name mapping
   records and may exist as an overlay network over the ICN routers,
   that is, they communicate to each other through ICN routers.
   Figure 1 shows the NRS nodes and NRS clients connected through an
   underlying network.  The NRS nodes should be deployed in such a
   manner that an NRS node is always available at a short distance from
   an NRS client so that communication latency for the name registration
   and resolution requested by the NRS client remains very low.  The
   name registration, name resolution, and name record update procedures
   are briefly discussed below.

                  +------------+             +------------+
                  |  NRS Node  |             |  NRS Node  |
                  +------------+             +------------+
                        |                          |
                        |                          |
     +------------+     |                          |     +------------+
     | NRS Client |--------------------------------------| NRS Client |
     +------------+         underlying network           +------------+

          Figure 1: NRS Nodes and NRS Clients Connected through an
                             Underlying Network


   Name registration:  Name registration is performed by the producer
      (as an NRS client) when it creates a new content.  When a producer
      creates content and assigns a name from its name prefix space to
      the content, the producer performs the name registration in an NRS
      node.  Name registration may be performed by an ICN router when
      the ICN architecture supports off-path caching or cooperative
      caching since involving an NRS may be a good idea for off-path
      caching.  The ICN routers with forwarder caches do not require
      name registration for their cached content because they lie on the
      path toward an upstream content store or producer.  They will be
      hit when a future request is forwarded to the content producer by
      an ICN router lying downstream toward the ICN client node.
      However, ICN routers performing off-path caching of content must
      invoke the name registration procedure so that other ICN routers
      can depend on name resolutions to know about the off-path cache
      locations.  If a content gets cached in many off-path ICN routers,
      all of them may register the same content names in the same NRS
      node, resulting in multiple registration actions.  In this case,
      the NRS node adds the new location of the content to the name
      record together with the previous locations.  In this way, each of
      the name records stored in the NRS node may contain multiple
      locations of the content.  Assigning validity time or a lifetime
      of each mapping record may be considered especially for the off-
      path caching content and managing mobility.

   Name resolution:  Name resolution is performed by an NRS client to
      obtain the name record from an NRS node by sending a name
      resolution request message and getting a response containing the
      record.  In the name-based ICN routing context, the name
      resolution is needed by any ICN router whose forwarding
      information base (FIB) does not contain the requested name prefix.
      Name resolution may also be performed by the consumer (especially
      in the case where the consumer is multihomed) to forward the
      content request in a better direction so that it obtains the
      content from the nearest cache.  If the consumer is single homed,
      it may not bother to perform name resolution, instead depending on
      either straightforward name-based routing or name resolution by an
      upstream ICN router.  In this case, the consumer creates the
      content request packet containing the content name and forwards to
      the nearest ICN router.  The ICN router checks its FIB table to
      see where to forward the content request.  If the ICN router fails
      to identify whether the requested content is reachable, it
      performs name resolution to obtain the name mapping record and
      adds this information to its FIB.  The ICN router may also perform
      name resolution even before the arrival of a content request to
      use the name mapping record to configure its FIB.

   Name record update:  Name record update is carried out when a content
      name mapping record changes, e.g., the content is not available in
      one or more of the previous locations.  The name record update
      includes the substitution and deletion of the name mapping
      records.  The name record update may take place explicitly by the
      exchange of name record update messages or implicitly when a
      timeout occurs and a name record is deemed to be invalid.  The
      implicit update is possible when each record is accompanied by a
      lifetime value.  The lifetime can be renewed only by the
      authoritative producer or node.  The cached mapping records get
      erased after the lifetime expires unless a lifetime extension
      indication is obtained from the authoritative producer.

5.2.  Protocols and Semantics

   In order to develop an NRS system within a local ICN network domain
   or global ICN network domain, new protocols and semantics must be
   designed and implemented to manage and resolve names among different
   namespaces.

   One way of implementing an NRS for CCNx is by extending the basic TLV
   format and semantics [RFC8569] [RFC8609].  For instance, name
   resolution and response messages can be implemented by defining new
   type fields in the Interest and Content Object messages [CCNxNRS].
   By leveraging the existing CCNx Interest and Content Object packets
   for name resolution and registration, the NRS system can be deployed
   with a few ICN protocol changes.  However, because of confining the
   changes to the basic ICN protocol and semantics, the NRS system may
   not be able to exploit more flexible and scalable designs.

   On the other hand, an NRS system can be designed independently with
   its own protocol and semantics like the NRS system described in
   [Hong].  For instance, the NRS protocol and messages can be
   implemented by using a RESTful API, and the NRS can be operated as an
   application protocol independent of the rest of the ICN protocol.

5.3.  Routing System

   An NRS reduces the routing complexity of ICN architecture compared to
   pure name-based routing.  It does so by permitting the routing system
   to update the routing table on demand with the help of name records
   obtained from NRS.  The routing system therefore needs to make name
   resolution requests and process the information returned, such as a
   prefix, a locator, an off-path-cache pointer, or an alias name,
   obtained from the name resolution.

   No matter what kind of information is obtained from the name
   resolution, as long as it is in the form of a name, the content
   request message in the routing system may be reformatted with the
   obtained information.  In this case, the content name requested
   originally by a consumer needs to be involved in the reformatted
   content request to check the integrity of the binding between the
   name and the requested content.  In other words, the information
   obtained from the name resolution is used to forward the content
   request, and the original content name requested by a consumer is
   used to identify the content.  Alternatively, the resolved
   information may be used to build the routing table.

   The information obtained from name resolution may not be in the form
   of a name.  For example, it may identify tunnel endpoints by IP
   address and instead be used to construct an IP protocol tunnel
   through which to forward the content request.

6.  Conclusion

   A Name Resolution Service (NRS) is not a mandatory part in an ICN
   architecture, as the majority of ICN architectures use name-based
   routing that does not employ a name resolution procedure.  However,
   such name-based routing in ICN has inherent challenges in enabling a
   globally scalable routing system, accommodating producer mobility,
   and supporting off-path caching.  In order to address these
   challenges, an NRS system has been introduced in several ICN
   projects.  Therefore, this document describes how the ICN
   architecture changes when an NRS is utilized and how this affects the
   ICN routing system.

   The document defines a few terminologies related to an NRS and
   explains some inherent challenges of pure name-based routing in ICN
   such as routing scalability, producer mobility, and off-path caching.
   This document describes how the ICN architecture would change with
   respect to procedures, latency, and security when an NRS is utilized.
   According to the ICN architectural changes, this document describes
   ICN architectural considerations for NRS such as the functions
   related to the registration, resolution and update of name mapping
   records, protocols and semantics to implement an NRS system, and the
   routing system involving the name resolution.

7.  IANA Considerations

   This document has no IANA actions.

8.  Security Considerations

   When any new component such as an NRS is introduced in the ICN
   architecture, the attack surface increases.  The related security
   vulnerability issues are discussed below:

   Namespace security:  In order to deploy an NRS system in ICN
      architecture, ICN namespaces, which may be assigned by
      authoritative entities, must be securely mapped to the content
      publishers and securely managed by them.  According to the ICN
      research challenges [RFC7927], a new namespace can also provide an
      integrity verification function to authenticate its publisher.
      The issues of namespace authentication and the mapping among
      different namespaces require further investigation.

   NRS system security:  An NRS requires the deployment of new entities
      (e.g., NRS servers) to build distributed and scalable NRS systems.
      Thus, the entities, e.g., an NRS server maintaining a mapping
      database, could be the focus of attacks by receiving malicious
      requests from innumerable adversaries comprising of Denial-of-
      Service or Distributed-Denial-of-Service attacks.  In addition,
      NRS clients in general must trust the NRS nodes in other network
      domains to some degree, and communication among them must also be
      protected securely to prevent malicious entities from
      participating in this communication.  The history of name
      resolution data requires to be stored and analyzed as in passive
      DNS to uncover potential security incidents or discover malicious
      infrastructures.

   NRS protocol and message security:  In an NRS system, the protocols
      to generate, transmit, and receive NRS messages related to the
      name registration, resolution, and record update should be
      protected by proper security mechanisms.  Proper security measures
      must be provided so that only legitimate nodes can initiate and
      read NRS messages.  These messages must be secured by integrity
      protection and authentication mechanisms so that unauthorized
      parties cannot manipulate them when being forwarded through the
      network.  Security measures to encrypt these messages should also
      be developed to thwart all threats to both security and privacy.
      Numerous problems similar to the security issues of an IP network
      and DNS can affect the overall ICN architecture.  The DNS QNAME
      minimization type of approach would be suitable for preserving
      privacy in the name resolution process.  Therefore, security
      mechanisms such as accessibility, authentication, etc., for the
      NRS system [RFC9138] should be considered to protect not only the
      NRS system but also the ICN architecture overall.

9.  References

9.1.  Normative References

   [RFC7927]  Kutscher, D., Ed., Eum, S., Pentikousis, K., Psaras, I.,
              Corujo, D., Saucez, D., Schmidt, T., and M. Waehlisch,
              "Information-Centric Networking (ICN) Research
              Challenges", RFC 7927, DOI 10.17487/RFC7927, July 2016,
              <https://www.rfc-editor.org/info/rfc7927>.

   [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>.

   [RFC9138]  Hong, J., You, T., Dong, L., Westphal, C., and B. Ohlman,
              "Design Considerations for Name Resolution Service in
              Information-Centric Networking (ICN)", RFC 9138,
              DOI 10.17487/RFC9138, December 2021,
              <https://www.rfc-editor.org/info/rfc9138>.

9.2.  Informative References

   [Afanasyev]
              Afanasyev, A., Yi, C., Wang, L., Zhang, B., and L. Zhang,
              "SNAMP: Secure namespace mapping to scale NDN forwarding",
              2015 IEEE Conference on Computer Communications Workshops
              (INFOCOM WKSHPS), DOI 10.1109/INFCOMW.2015.7179398, April
              2015, <https://doi.org/10.1109/INFCOMW.2015.7179398>.

   [Bayhan]   Bayhan, S., Ott, J., Kangasharju, J., Sathiaseelan, A.,
              and J. Crowcroft, "On Content Indexing for Off-Path
              Caching in Information-Centric Networks", ACM ICN,
              DOI 10.1145/2984356.2984372, September 2016,
              <https://doi.org/10.1145/2984356.2984372>.

   [CCNx]     "Cicn", <https://wiki.fd.io/view/Cicn>.

   [CCNxNRS]  Hong, J., You, T., and Y. Hong, "CCNx Extension for Name
              Resolution Service", Work in Progress, Internet-Draft,
              draft-hong-icnrg-ccnx-nrs-02, 2 July 2018,
              <https://datatracker.ietf.org/doc/html/draft-hong-icnrg-
              ccnx-nrs-02>.

   [Dannewitz]
              Dannewitz, C., Kutscher, D., Ohlman, B., Farrell, S.,
              Ahlgren, B., and H. Karl, "Network of Information (NetInf)
              - An information-centric networking architecture",
              Computer Communications vol. 36, issue 7,
              DOI 10.1016/j.comcom.2013.01.009, April 2013,
              <https://doi.org/10.1016/j.comcom.2013.01.009>.

   [Dannewitz2]
              Dannewitz, C., D'Ambrosio, M., and V. Vercellone,
              "Hierarchical DHT-based name resolution for information-
              centric networks", Computer Communications vol. 36, issue
              7, DOI 10.1016/j.comcom.2013.01.014, April 2013,
              <https://doi.org/10.1016/j.comcom.2013.01.014>.

   [Hong]     Hong, J., Chun, W., and H. Jung, "Demonstrating a Scalable
              Name Resolution System for Information-Centric
              Networking", ACM ICN, DOI 10.1145/2810156.2812617,
              September 2015, <https://doi.org/10.1145/2810156.2812617>.

   [MF]       Future Internet Architecture (FIA), "MobilityFirst",
              <http://mobilityfirst.cs.umass.edu/>.

   [NDN]      NDN, "Named Data Networking", September 2010,
              <https://www.named-data.net>.

   [Ravindran]
              Ravindran, R., Chakraborti, A., and A. Azgin, "Forwarding
              Label support in CCN Protocol", Work in Progress,
              Internet-Draft, draft-ravi-icnrg-ccn-forwarding-label-02,
              5 March 2018, <https://datatracker.ietf.org/doc/html/
              draft-ravi-icnrg-ccn-forwarding-label-02>.

   [SAIL]     "Scalable and Adaptive Internet Solutions (SAIL)",
              <https://www.sail-project.eu/>.

   [Zhang2]   Zhang, Y., Afanasyev, A., Burke, J., and L. Zhang, "A
              Survey of Mobility Support in Named Data Networking",
              Named Data Networking, Workshop on Name-Oriented Mobility:
              Architecture, Algorithms and Applications (NOM), April
              2016.

Acknowledgements

   The authors would like to thank Dave Oran (ICNRG Co-chair) for very
   useful reviews and comments, which helped to immeasurably improve
   this document.

Authors' Addresses

   Jungha Hong
   ETRI
   Yuseung-Gu
   218 Gajeong-ro
   Daejeon
   34129
   Republic of Korea
   Email: jhong@etri.re.kr


   Tae-Wan You
   ETRI
   Yuseung-Gu
   218 Gajeong-ro
   Daejeon
   34129
   Republic of Korea
   Email: twyou@etri.re.kr


   Ved Kafle
   NICT
   Koganei
   4-2-1 Nukui-Kitamachi, Tokyo
   184-8795
   Japan
   Email: kafle@nict.go.jp
