Internet DRAFT - draft-boucadair-rtgwg-sdn-and-semantic-routing

draft-boucadair-rtgwg-sdn-and-semantic-routing







IRTF                                                        M. Boucadair
Internet-Draft                                                    Orange
Intended status: Informational                                D. Trossen
Expires: 6 November 2023                                          Huawei
                                                               A. Farrel
                                                      Old Dog Consulting
                                                              5 May 2023


     Considerations for the use of SDN in Semantic Routing Networks
           draft-boucadair-rtgwg-sdn-and-semantic-routing-00

Abstract

   The forwarding of packets in today's networks has long evolved beyond
   ensuring mere reachability of the receiving endpoint.  Instead, other
   'purposes' of communication, e.g., ensuring quality of service of
   delivery, ensuring protection against path failures through utilizing
   more than one, and others, are realized by many extensions to the
   original reachability purpose of IP routing.

   Semantic Routing defines an approach to realizing such extended
   purposes beyond reachability by instead making routing and forwarding
   decisions based, not only on the destination IP address, but on other
   information carried in an IP packet.  The intent is to facilitate
   enhanced routing decisions based on this information in order to
   provide differentiated forwarding paths for specific packet flows.

   Software Defined Networking (SDN) places control of network elements
   (including all or some of their forwarding decisions) within external
   software components called controllers and orchestrators.  This
   approach differs from conventional approaches that solely rely upon
   distributed routing protocols for the delivery of advanced
   connectivity services.  By doing so, SDN aims to enable network
   elements to be simplified while still performing forwarding function.

   This document examines the applicability of SDN techniques to
   Semantic Routing and provides considerations for the development of
   Semantic Routing solutions in the context of SDN.

Status of This Memo

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







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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Software Defined Networking (SDN): An Overview  . . . . . . .   4
   3.  Semantic Routing: Summary of Required Technical Elements  . .   5
   4.  Programmable Forwarding . . . . . . . . . . . . . . . . . . .   6
     4.1.  Motivation  . . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  SDN for Semantic Routing: The Intended Behavior . . . . .   8
   5.  Policy-Based Semantic Routing . . . . . . . . . . . . . . . .  10
   6.  Network-Wide Coordination . . . . . . . . . . . . . . . . . .  11
   7.  Applying Semantic Information to Packets  . . . . . . . . . .  12
   8.  Benefits and Concerns with the Use of SDN for Semantic
           Routing . . . . . . . . . . . . . . . . . . . . . . . . .  13
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   12. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  14
   13. Informative References  . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17






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1.  Introduction

   Service differentiation in the network can be enforced by
   manipulating a set of parameters that belong to distinct dimensions
   (e.g., forwarding, routing, traffic classification, resource
   partitioning).  Through this, the resulting system may be able to
   realize communication that goes beyond the mere reachability that
   original IP routing (and forwarding) aimed at.  As pointed out in
   [I-D.trossen-rtgwg-routing-beyond-reachability], this differentiation
   and its solutions have long found entry into many existing and
   deployed Internet technologies.

   Among the techniques to achieve such differentiation, this document
   focuses on Semantic Routing, which refers to a process that is meant
   to provide differentiated forwarding paths for specific packet flows
   distinct from simple shortest path first routing and, thus, satisfy
   specific service/application requirements.

   More concretely, Semantic Routing is the process of making routing
   and forwarding decisions based, not only on the destination IP
   address of a packet, but also by taking into account other
   information that is carried in the packet such as (but not limited
   to):

   *  Other fields of the IP header, e.g., DSCP/Traffic Class.

   *  The transport header, e.g., transport port numbers [RFC7597] or
      subflows [RFC8803].

   *  Specific transport encapsulation shims, e.g., [RFC8926].

   *  Specific service headers, e.g., [RFC8300].

   *  Metadata.

   Section 3 provides more details about Semantic Routing.

   Software Defined Networking (SDN) places (partial or full) control of
   network elements and their forwarding decisions within dedicated
   software components called controllers and orchestrators.  This
   approach differs from those that solely rely upon distributed routing
   protocols.  An ambition of SDN is to enable network elements to be
   simplified while the network is optimized to deliver value-added
   connectivity services.  Refer to Section 2 for an overview of SDN.







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   This document examines the applicability of SDN to Semantic Routing
   though programbale forwarding (see Section 4 and provides
   considerations for the development of Semantic Routing solutions in
   the context of SDN.

   This document does not elaborate on specific SDN protocols: some SDN
   protocol solutions may be more or less amenable to use for Semantic
   Routing, but that discussion would need detailed analysis which is
   better suited to a further and separate document.

2.  Software Defined Networking (SDN): An Overview

   SDN refers to an approach for network programmability: the capacity
   to initialize, control, and manage network behavior dynamically via
   open interfaces.  Such programmability can facilitate the delivery of
   services in a deterministic, dynamic, and scalable manner.

   SDN emphasizes the role of software in operational networks by
   supporting the separation between data and control planes.  Even if
   such a separation has been adopted by most routing processes for
   decades (Section 2.1 of [RFC7149]), SDN focuses more on the power of
   "central" controllers to optimize route computation within a network
   before populating the Forwarding Information Base (FIB) of the
   network elements.

   The separation of the control and data planes allows faster
   innovation in both planes, and it enables a dynamic and flexible
   approach to implementing new network behaviors as well as to reacting
   to changes in network state and traffic demands.

   SDN has been discussed in many places during the last decade.  For
   example, within the IRTF, [RFC7426] provides a concise reference for
   the SDN research community to address the questions of what SDN is,
   what the layer structure of an SDN architecture is, and how layers
   interface with each other within that architecture.  [RFC7149]
   (published in the IETF stream) offers a service provider's
   perspective of the SDN landscape by describing requirements, issues,
   and other considerations about SDN.  In particular, [RFC7149]
   classifies SDN techniques into the following functional domains:

   *  Techniques for the dynamic discovery of network topology, devices,
      and capabilities, along with relevant information and data models
      that are meant to precisely document such topology, devices, and
      their capabilities.







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   *  Techniques for exposing network services and their characteristics
      and for dynamically capturing the set of service parameters that
      will be used to measure the level of quality associated with the
      delivery of a given service or a combination thereof.

   *  Techniques used by service-requirement-derived dynamic resource
      allocation and policy enforcement schemes, so that networks can be
      programmed accordingly.

   *  Dynamic feedback mechanisms that are meant to assess how
      efficiently a set of policies are enforced from a service
      fulfillment and assurance perspective.

   SDN can be deployed in a recursive model that involves dedicated
   interfaces for both network and service optimization.  Indeed,
   [RFC8597] differentiates the control functions associated with
   transport (that is, the transfer capabilities offered by a networking
   infrastructure) from those related to services in an approach called
   Cooperating Layered Architecture for Software-Defined Networking
   (CLAS).

   To an SDN context, domain-specific controllers can be deployed with
   specific interactions as discussed in Section 4 of [RFC8309].

3.  Semantic Routing: Summary of Required Technical Elements

   As described in [I-D.farrel-irtf-introduction-to-semantic-routing],
   Semantic Routing (or, more generally, Semantic Networking) is the
   process of achieving enhanced routing and forwarding decisions based
   on semantics added to IP packet headers to provide differentiated
   paths for different packet flows distinct from simple shortest path
   first routing.  The additional information or "semantics" may be
   placed in existing header fields (such as the IPv6 Traffic Class
   field or the destination address) or may be carried by adding fields
   to the header.  Further, the semantics may be encoded in the payload
   or additional headers (such as in the port number fields or in an
   IPv6 Extension Header).

   The application of Semantic Routing allows packets from different
   flows (even those between the same applications on the same devices)
   to be marked for different treatment in the network.  The packets may
   then be routed onto different paths according to the capabilities and
   states of the network links in order to meet the requirements of the
   flows.  For example, one flow may need low latency, while another may
   require ultra low jitter, and a third may demand very high bandwidth.

   Three elements are needed to achieve Semantic Routing:




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   *  The capabilities and state of the network must be discovered.

   *  The packets must be marked (with semantic information) according
      to their required delivery characteristics.

   *  The routers must be programmed to forward the traffic according to
      how the packets are marked.

   All these elements can be matched to the SDN functional domains
   listed in Section 2.  From that standpoint, this document provides
   more details on how SDN can be used to satisfy specific Semantic
   Routing needs.

4.  Programmable Forwarding

   Programmable Forwarding is the term applied to the use of control
   techniques to instruct network devices how to forward packets in a
   programmatic way.

4.1.  Motivation

   Modern networks are designed to carry traffic that belongs to a
   variety of services/applications that have distinct traffic
   performance requirements, reliability and robustness expectations,
   and service-specific needs [RFC7665][RFC8517].  Such expectations,
   and other forwarding requirements that can be captured in a Service
   Level Agreement (SLA) [RFC7297], can be considered by providers when
   designing their networks in order to be able to deliver
   differentiated forwarding behaviors.  However, conventional routing
   and forwarding procedures do not always offer the required
   functionalities for such differentiated service delivery.  Thus,
   additional means have to be enabled in these networks for the sake of
   innovative service delivery while minimizing the induced complexity
   to operate such networks.  Also, these means should be tweaked to
   ensure consistent forwarding behaviors network-wide.

   The aforementioned means are not only extensions to routing
   protocols, but include other mechanisms that affect the forwarding
   behaviors within a network.  A non-exhaustive list of sample
   capabilities that can be offered by appropriate control of forwarding
   elements is provided below:

   Resource Pooling:  A network may host dedicated functions that
      implement resource pooling among many available paths or that
      control which path is used to steer traffic as a function of the
      observed round-trip time (RTT) (e.g., enable Mutlipath TCP (MPTCP)
      converters [RFC8803] in specific network segments, including data
      centers as detailed in Section 2.1 of [RFC8041]).



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      There is a need to interact with the underlying forwarding
      elements to communicate a set forwarding policies that will ensure
      that such service differentiation is provided to the specific
      flows.  These forwarding policies include, for example, a set of
      rules that characterize the flows that are eligible to the
      resource pooling service or the scheduling policies (maximize link
      utilization, grab extra resources only when needed, etc.).

      These polices are then enforced by programmable forwarders.

   Performance-based Route Selection:  Some applications may have strict
      traffic performance requirements (e.g., a low one-way delay
      [RFC7679]), however, the underlying network elements might not
      support a mechanism to disseminate performance metrics associated
      with specific paths and/or perform performance-based route
      selection (e.g., [I-D.ietf-idr-performance-routing]).

      As an alternative, an off-line Semantic Routing approach could be
      used to collect measurement data to reach a given content (e.g.,
      one-way delay to reach specific data centers), perform route
      selection based on this data, and then program the appropriate
      forwarding elements accordingly.

   Energy-efficient Forwarding:  An important effort was made in the
      past to optimize the energy consumption of network elements.
      However, such optimization is node-specific and no standard means
      to optimize the energy consumption at the scale of the network
      have been defined.  For example, many nodes (also, service cards)
      are deployed as backups.

      A controller-based approach can be implemented so that the route
      selection process optimizes the overall energy consumption of a
      path.  Such a process takes into account the current load, avoids
      waking nodes/cards for handling "sparse" traffic (i.e., a minor
      portion of the total traffic), considers node-specific data (e.g.,
      [RFC7460]), etc.  This off-line Semantic Routing approach will
      transition specific cards/nodes to "idle" and wake them as
      appropriate, etc., without breaking service objectives.  Moreover,
      such an approach will have to maintain an up-to-date topology even
      if a node is in an "idle" state (such nodes may be removed from
      adjacency tables if they don't participate in routing
      advertisements).

   Network Partitioning:  A network may need to be partitioned in order
      to rationalize the delivery of advanced connectivity services, and
      to address specific forwarding requirements of groups of services/
      applications.  Network slicing [I-D.ietf-teas-ietf-network-slices]
      can be considered to deliver these services.  However, an



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      intelligence is needed to decide the criteria to be used to
      partition the available resources, filter them, decide whether
      network extensions are needed, ensure whether/how resource
      preemption is adequately implemented, etc.

      These tasks are better achieved using a central intelligence that
      has direct visibility into the intents of applications, underlying
      network capabilities, local policies and guidelines, etc.  As an
      output of processing these various inputs, a set of node-specific
      policies is generated, and then pushed using available SDN
      interface.

   Alternative Forwarding:  The programmability of SDN in the form of
      forwarding actions defined on packet header fields allows for
      realizing forwarding techniques beyond the typical longest-prefix
      match used for IP-based reachability.  Solutions, like those in
      [ICC2016], use a binary representation of links in a network to
      realize a path-based forwarding action that acts purely on node-
      local state, independent of the nature of the path or the
      communications traversing it.  As discussed in Section 7, the
      limitation of forwarding actions to apply only to defined (IP)
      packet header fields results in issues that need special
      consideration when realizing such solutions in real-world
      deployments.

   The next subsection further details which elements are needed when
   interacting with programmable forwarders in an SDN context.

4.2.  SDN for Semantic Routing: The Intended Behavior

   SDN minimizes the required changes to legacy (interior) routing
   protocols.  More concretely, SDN can be used to provide the intended
   Semantic Routing behavior, especially:

   *  Identify the forwarding elements that can be safely involved in
      providing the intended Semantic Routing features.

   *  Maintain abstract topologies that involve these elements and their
      capabilities.

   *  Capture application-specific intents and derive the corresponding
      forwarding requirements and, then, forwarding policies.

   *  Map these abstract topologies to (groups of) applications with
      specific Semantic Routing needs.






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   *  Program a subset of nodes (called boundary nodes) with the
      required classification and marking policies to bind flows to
      their intended Semantic Routing behaviors.

      In order to adequately process the application flows that require
      specific differentiated forwarding, SDN controllers maintain a
      table that allows to unambiguously identify such flows.  The
      content of that table is used to derive the appropriate
      classification/match rules that are then communicated by an SDN
      controller to a set of forwarding elements.

      When volatile data (e.g., dynamic IP addresses) are used to build
      such rules, it is the responsibility of the SDN controllers to
      update the rules whenever a new identifier is used.  Failure to
      maintain "fresh" classification rules will lead to service
      failure/degradation.

   *  Supply intermediate nodes (that is, nodes that are not boundary
      nodes) with the appropriate rules to locate and interpret the bits
      within the packet to determine and execute forwarding actions as
      established by Semantic Routing.

   *  Automatically adjust, if possible, the network MTU to accommodate
      any overhead that is introcuced by any extra bits used to signal
      Semantic Routing behavior.

   *  Instruct egress boundary nodes about the required actions such as
      stripping or setting any Semantic Routing bits.

   *  Interact with the underlying nodes to maintain, retrieve, and
      disseminate the data that are used for assuring that Semantic
      Routing policies are appropriately fulfilled.

   *  Configure OAM policies to measure the network behavior and adjust
      the forwarding processes.

   *  Monitor the network and detect parts of the network where policies
      are broken or suboptimal.

   *  Automate the overall procedure [RFC8969].

   At least three approaches can be considered by an SDN controller to
   accomplish the above tasks:








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   *  Compute (centrally) the differentiated paths and install the
      required forwarding rules in involved nodes.  Strict or loose
      paths may be installed.  This approach has the merit of
      implementing new path selection algorithms without requiring them
      to be supported by every involved node.

   *  Assign (centrally) differentiated link information and install the
      required forwarding rules in the involved nodes.  End-to-end paths
      are constructed without involvement of the SDN controller,
      utilizing the link information to establish path identifiers on
      which installed forwarding rules can act upon without additional
      path-specific knowledge being required.  See [ICC2016] for an
      example of such an approach.

   *  Rely upon a distributed routing protocol to customize the route
      selection process ([RFC9350], for example).  In such cases, the
      SDN controller is responsible for communicating the parameters to
      be used for the route selection process, selecting the nodes that
      will participate in a given topology, and configuring any tunnels
      to interconnect these nodes.

   A hierarchical SDN design can also be considered, where specific
   controllers are enabled in each domain with dedicated interfaces to
   share data (e.g., radio bottlenecks, expectations).  These domains do
   not need to support the same technological implementations.  The
   interaction between the SDN controllers eases the delivery of
   consistent Semantic Routing behaviors without requiring common domain
   configuration.

5.  Policy-Based Semantic Routing

   Policy is a term applied to the application of local or network-wide
   operational choices made by the network manager.  These may range
   from decisions about what traffic to admit to the network, how
   network resources should be used to support different traffic flows,
   how errors or security violations are handled, and how packets are
   routed through the network.

   Policies are usually made available to network operators as
   configuration elements on network nodes.  However, these
   configuration actions need to be coordinated across the whole network
   if the policies are to be effective.  Thus, a mechanism is desired
   that allows an operator to set a network-wide policy in one place and
   that results in that policy being pushed out to the network nodes
   that need to act on the policy.






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   Semantic Routing is particularly amenable to a policy-based approach.
   That is, an operator (or their software tools) can make decisions
   about how different traffic flows should be handeled in the network.
   Those decisions can then be installed on network nodes so that
   different traffic is handled differently and according to the
   policies.

   SDN is a powerly approach to implement a policy-based network
   management framework.  The operator need only select or configure the
   desired policies at the controller: the controller will realize the
   policies and install the necessary instructions and behaviors on the
   network nodes.

6.  Network-Wide Coordination

   Critical to the correct functioning of any routing system is proper
   network-wide coordination.  In many cases, the coordination starts
   with the collection and dissemination of network connectivity
   information (known as the network topology), the capabilities of the
   network nodes and links, and the current state (up, down, degraded,
   busy, etc.) of those nodes and links.  But an even mode fundamental
   element of network-wide coordination is the decision about which
   routing algorithms and procedures will be used because, if different
   nodes or even different parts of the network) apply different routing
   approaches, it is very possible that traffic will loop or be dropped.
   Thus, th first elements of coordination are finding out what the
   network looks like and agreeing how to route traffic.

   These essentials are no less relevant in Semantic Routing.  All nodes
   that participate in a Semantic Routing network need to have the same
   understanding of the additional information carried in packets, and
   must make coordinated forwarding decisions based on a coordinated
   routing algorithm.

   A centralized approach, such as that achieved in an SDN system, is
   particularly useful in this context because it allows the
   coordination to be applied through a central point of control which
   may remove the complexity and "fragility" from the routing system.
   This coordination may be considered in parallel with the aspects of
   policy-based routing described in Section 5.











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7.  Applying Semantic Information to Packets

   Given the focus of Semantic Routing is the use within IP networks,
   semantic information that can be used in SDN-based Semantic Routing
   is limited to those fields specifically defined for use with Semantic
   Routing (see Section 2 for more information).  This document
   deliberately makes no comment on the specifications that may be
   produced to define such fields, their meaning, and their encoding.

   SDN aligns with the concept of Semantic Routing in that it allows the
   network devices to be programmed for forwarding actions indicated by
   a wide range of packet header fields beyond simply the IP destination
   addresses.

   However, Semantic Routing solutions have also been proposed that
   "overwrite" existing protocol fields in order for them to carry
   semantic information that can be used to drive a forwarding action
   outside their original semantics.  [POINT2015] and [POINT2016]
   outline an example of such approaches in which semantic information
   is used for a path-based forwarding decision; while the absence of
   "path" information is foreseen as an actionable packet header field
   in IPv6.

   Here, the path is constructed by a Path Computation Element (PCE)
   [RFC4655] that matches a given service name against previously
   announced locations where said service name is located.  The path is
   represented as a concatenation of individual link information, which
   in pushed by the SDN controller to the network nodes so that they can
   perform local forwarding actions on packets that arrive.  Given the
   binary structure of the end-to-end path information, the forwarding
   operation can be implemented in a standard-compliant manner with its
   realization described in [ICC2016] as an arbitrary wildcard matching
   operation.

   However, the constraint of acting only on limited packet fields
   requires that the path information be carried in one of those
   standard-defined packet header fields: thereby overwriting (or
   overloading) any existing packet header field.  [POINT2016] uses the
   IPv6 address fields for this purpose, representing the longest
   continuous binary field in the IPv6 header (two addresses make up 256
   bits in total) allows the support of topologies with up to 256 links.

   Given the approach chosen in [POINT2016], any IPv6 address
   information, if needed, cannot be present in the packet header and so
   is provided in the encapsulated payload.  This leads to repeated
   encapsulation with the overhead of carrying two IP headers in a
   single packet: one used for path-based forwarding and one for the
   operations in arriving endpoint.  Only newer SDN-based forwarding



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   plane programming tools, such as P4, would allow for such overhead to
   be removed by placing the path information into another packet header
   field (or even the payload as an extended header of sort) to act
   upon.

8.  Benefits and Concerns with the Use of SDN for Semantic Routing

   The programmability of SDN provides a fertile ground for forwarding
   decision that go beyond the reachability information provided through
   IPv4/v6 addresses, e.g., by using other packet header fields.  This
   not only allows for extending the simple reachability-driven
   forwarding decision with richer, e.g., policy-based, decisions (as
   discussed in Section 5), it may also enable new forwarding paradigms
   per se, such as those in [POINT2016], which in turn may realize
   forwarding behaviours like multicast at much lower cost points and
   higher efficiency (see [ICC2016]).

   However, SDN specifications have limited capabilities when it comes
   to the additional (i.e., new) packet header fields that may be used
   for forwarding actions.  As a consequence, "true" Semantic Routing on
   any semantic enhancement, which is included in the packet, is only
   possible in a manner limited to those existing fields.

   Solutions such as those in [POINT2016], using methods outlined in
   [ICC2016], attempt to break this limitation albeit by overwriting
   standard-defined packet header fields, thereby changing the semantics
   of those fields within the scope (i.e., network domain) where the
   "re-defined" semantics are known and understood.

   This limits any solution to a limited domain [RFC8799].  More
   importantly, the redefinition of packet fields poses the danger of
   exposing this (non-standard compliant) semantic to elements outside
   the limited domain: semantic leakage may occur, or nodes outside the
   domain may misinterpret overwritten fields, requiring methods, such
   as dedicated gateways, to preventi such leakage.  This can be seen in
   [POINT2016], where the boundaries to IP-compliant end devices and
   other domains alike are delimited by dedicated gateway elements.
   Those gateways usually act at higher layers than the forwarding
   layer, thereby incurring complexity and often delay.

   See also [I-D.king-irtf-challenges-in-routing] for a discussion of
   issues and concerns that need to be examined when applying a new
   routing or forwarding paradigm to a self-contained network or
   Internet.







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9.  Security Considerations

   SDN-related considerations are discussed in Section 5 of [RFC7149].

10.  IANA Considerations

   This document makes no requests for IANA action.

11.  Acknowledgements

   Thanks to George Polyzos for helpful comments on this work.

   This work is partially supported by the European Commission under
   Horizon 2020 grant agreement number 101015857 Secured autonomic
   traffic management for a Tera of SDN flows (Teraflow).

12.  Contributors

   George Xylomenos
   Email: xgeorge@aueb.gr

13.  Informative References

   [I-D.farrel-irtf-introduction-to-semantic-routing]
              Farrel, A. and D. King, "An Introduction to Semantic
              Routing", Work in Progress, Internet-Draft, draft-farrel-
              irtf-introduction-to-semantic-routing-04, 25 April 2022,
              <https://datatracker.ietf.org/doc/html/draft-farrel-irtf-
              introduction-to-semantic-routing-04>.

   [I-D.ietf-idr-performance-routing]
              Xu, X., Hegde, S., Talaulikar, K., Boucadair, M., and C.
              Jacquenet, "Performance-based BGP Routing Mechanism", Work
              in Progress, Internet-Draft, draft-ietf-idr-performance-
              routing-03, 22 December 2020,
              <https://datatracker.ietf.org/doc/html/draft-ietf-idr-
              performance-routing-03>.

   [I-D.ietf-teas-ietf-network-slices]
              Farrel, A., Drake, J., Rokui, R., Homma, S., Makhijani,
              K., Contreras, L. M., and J. Tantsura, "A Framework for
              IETF Network Slices", Work in Progress, Internet-Draft,
              draft-ietf-teas-ietf-network-slices-19, 21 January 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-teas-
              ietf-network-slices-19>.






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   [I-D.king-irtf-challenges-in-routing]
              King, D., Farrel, A., and C. Jacquenet, "Challenges for
              the Internet Routing Systems Introduced by Semantic
              Routing", Work in Progress, Internet-Draft, draft-king-
              irtf-challenges-in-routing-08, 25 April 2022,
              <https://datatracker.ietf.org/doc/html/draft-king-irtf-
              challenges-in-routing-08>.

   [I-D.trossen-rtgwg-routing-beyond-reachability]
              Trossen, D., Lou, Z., and S. Jiang, "Continuing to Evolve
              Internet Routing Beyond 'Mere' Reachability", Work in
              Progress, Internet-Draft, draft-trossen-rtgwg-routing-
              beyond-reachability-01, 30 June 2022,
              <https://datatracker.ietf.org/doc/html/draft-trossen-
              rtgwg-routing-beyond-reachability-01>.

   [ICC2016]  Reed, M., Al-Naday, M., Thomos, N., Trossen, D.,
              Petropoulos, G., and S. Spirou, "Stateless multicast
              switching in software defined networks", Paper IEEE ICC
              2016, 2016.

   [POINT2015]
              Trossen, D., Reed, M., Riihijarvi, J., Georgiades, M.,
              Xylomenos, G., and S. Fotiou, "IP Over ICN: The Better
              IP?", Paper EuCNC (European Conference on Networks and
              Communications), Paris, France, 2015.

   [POINT2016]
              Kim, S.-Y.., Robitzsch, S., Trossen, D., Reed, M., Al-
              Naday, M., and J. Riihijarvi, "Realizing IP-based Services
              over an Information-Centric Networking Transport Network",
              Paper Proceedings of the 3rd ACM Conference on
              Information-Centric Networking, Pages 215-216, 2016.

   [RFC4655]  Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
              Computation Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <https://www.rfc-editor.org/info/rfc4655>.

   [RFC7149]  Boucadair, M. and C. Jacquenet, "Software-Defined
              Networking: A Perspective from within a Service Provider
              Environment", RFC 7149, DOI 10.17487/RFC7149, March 2014,
              <https://www.rfc-editor.org/info/rfc7149>.

   [RFC7297]  Boucadair, M., Jacquenet, C., and N. Wang, "IP
              Connectivity Provisioning Profile (CPP)", RFC 7297,
              DOI 10.17487/RFC7297, July 2014,
              <https://www.rfc-editor.org/info/rfc7297>.



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   [RFC7426]  Haleplidis, E., Ed., Pentikousis, K., Ed., Denazis, S.,
              Hadi Salim, J., Meyer, D., and O. Koufopavlou, "Software-
              Defined Networking (SDN): Layers and Architecture
              Terminology", RFC 7426, DOI 10.17487/RFC7426, January
              2015, <https://www.rfc-editor.org/info/rfc7426>.

   [RFC7460]  Chandramouli, M., Claise, B., Schoening, B., Quittek, J.,
              and T. Dietz, "Monitoring and Control MIB for Power and
              Energy", RFC 7460, DOI 10.17487/RFC7460, March 2015,
              <https://www.rfc-editor.org/info/rfc7460>.

   [RFC7597]  Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S.,
              Murakami, T., and T. Taylor, Ed., "Mapping of Address and
              Port with Encapsulation (MAP-E)", RFC 7597,
              DOI 10.17487/RFC7597, July 2015,
              <https://www.rfc-editor.org/info/rfc7597>.

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,
              <https://www.rfc-editor.org/info/rfc7665>.

   [RFC7679]  Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
              Ed., "A One-Way Delay Metric for IP Performance Metrics
              (IPPM)", STD 81, RFC 7679, DOI 10.17487/RFC7679, January
              2016, <https://www.rfc-editor.org/info/rfc7679>.

   [RFC8041]  Bonaventure, O., Paasch, C., and G. Detal, "Use Cases and
              Operational Experience with Multipath TCP", RFC 8041,
              DOI 10.17487/RFC8041, January 2017,
              <https://www.rfc-editor.org/info/rfc8041>.

   [RFC8300]  Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
              "Network Service Header (NSH)", RFC 8300,
              DOI 10.17487/RFC8300, January 2018,
              <https://www.rfc-editor.org/info/rfc8300>.

   [RFC8309]  Wu, Q., Liu, W., and A. Farrel, "Service Models
              Explained", RFC 8309, DOI 10.17487/RFC8309, January 2018,
              <https://www.rfc-editor.org/info/rfc8309>.

   [RFC8517]  Dolson, D., Ed., Snellman, J., Boucadair, M., Ed., and C.
              Jacquenet, "An Inventory of Transport-Centric Functions
              Provided by Middleboxes: An Operator Perspective",
              RFC 8517, DOI 10.17487/RFC8517, February 2019,
              <https://www.rfc-editor.org/info/rfc8517>.





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   [RFC8597]  Contreras, LM., Bernardos, CJ., Lopez, D., Boucadair, M.,
              and P. Iovanna, "Cooperating Layered Architecture for
              Software-Defined Networking (CLAS)", RFC 8597,
              DOI 10.17487/RFC8597, May 2019,
              <https://www.rfc-editor.org/info/rfc8597>.

   [RFC8799]  Carpenter, B. and B. Liu, "Limited Domains and Internet
              Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,
              <https://www.rfc-editor.org/info/rfc8799>.

   [RFC8803]  Bonaventure, O., Ed., Boucadair, M., Ed., Gundavelli, S.,
              Seo, S., and B. Hesmans, "0-RTT TCP Convert Protocol",
              RFC 8803, DOI 10.17487/RFC8803, July 2020,
              <https://www.rfc-editor.org/info/rfc8803>.

   [RFC8926]  Gross, J., Ed., Ganga, I., Ed., and T. Sridhar, Ed.,
              "Geneve: Generic Network Virtualization Encapsulation",
              RFC 8926, DOI 10.17487/RFC8926, November 2020,
              <https://www.rfc-editor.org/info/rfc8926>.

   [RFC8969]  Wu, Q., Ed., Boucadair, M., Ed., Lopez, D., Xie, C., and
              L. Geng, "A Framework for Automating Service and Network
              Management with YANG", RFC 8969, DOI 10.17487/RFC8969,
              January 2021, <https://www.rfc-editor.org/info/rfc8969>.

   [RFC9350]  Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K.,
              and A. Gulko, "IGP Flexible Algorithm", RFC 9350,
              DOI 10.17487/RFC9350, February 2023,
              <https://www.rfc-editor.org/info/rfc9350>.

Authors' Addresses

   Mohamed Boucadair
   Orange
   Rennes
   France
   Email: mohamed.boucadair@orange.com


   Dirk Trossen
   Huawei
   Munich
   Germany
   Email: dirk.trossen@huawei.com







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   Adrian Farrel
   Old Dog Consulting
   United Kingdom
   Email: adrian@olddog.co.uk















































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