A Survey of Semantic Internet Routing Techniques
draft-king-irtf-semantic-routing-survey-02

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IRTF                                                             D. King
Internet-Draft                                      Lancaster University
Intended status: Informational                                 A. Farrel
Expires: December 30, 2021                            Old Dog Consulting
                                                           June 28, 2021

            A Survey of Semantic Internet Routing Techniques
               draft-king-irtf-semantic-routing-survey-02

Abstract

   The Internet Protocol (IP) has become the global standard in any
   computer network, independent of the connectivity to the Internet.
   Generally, an IP address is used to identify an interface on a
   network device.  Routing protocols are also required and developed
   based on the assumption that a destination address has this semantic
   with routing decisions made on addresses and additional fields in the
   packet headers.

   Over time, routing decisions were enhanced to route packets according
   to additional information carried within the packets and dependent on
   policy coded in, configured at, or signaled to the routers.  Many
   proposals have been made to add semantics to IP addresses.  The
   intent is usually to facilitate routing decisions based solely on the
   address and without the need to find and process information carried
   in other fields within the packets.

   This document is presented as a survey to support the study and
   further research into clarifying and understanding the issues.  It
   does not pass comment on the advisability or practicality of any of
   the proposals and does not define any technical solutions

Status of This Memo

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   Internet-Drafts are working documents of the Internet Engineering
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   material or to cite them other than as "work in progress."

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   This Internet-Draft will expire on December 30, 2021.

Copyright Notice

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Network Path Selection  . . . . . . . . . . . . . . . . . . .   4
     2.1.  Path Aware Routing  . . . . . . . . . . . . . . . . . . .   5
   3.  What is Semantic Addressing?  . . . . . . . . . . . . . . . .   5
     3.1.  Architectural Considerations  . . . . . . . . . . . . . .   7
   4.  Existing Approaches for Routing Based on Additional Semantics   9
     4.1.  Non-Address-Based Routing . . . . . . . . . . . . . . . .   9
       4.1.1.  Deep Packet Inspection  . . . . . . . . . . . . . . .   9
       4.1.2.  Differentiated Services . . . . . . . . . . . . . . .  10
       4.1.3.  IPv6 Extension Headers  . . . . . . . . . . . . . . .  10
     4.2.  Semantic Overlays . . . . . . . . . . . . . . . . . . . .  11
       4.2.1.  Application-Layer Traffic Optimization  . . . . . . .  11
       4.2.2.  Multipath TCP . . . . . . . . . . . . . . . . . . . .  11
       4.2.3.  Service Function Chaining . . . . . . . . . . . . . .  11
       4.2.4.  Path Computation Element  . . . . . . . . . . . . . .  12
     4.3.  Semantic Addressing . . . . . . . . . . . . . . . . . . .  12
       4.3.1.  Locator/ID Separation Protocol (LISP) . . . . . . . .  12
       4.3.2.  Identifier-Locator Network Protocol . . . . . . . . .  13
       4.3.3.  Segment Routing . . . . . . . . . . . . . . . . . . .  13
       4.3.4.  Preferred Path Routing  . . . . . . . . . . . . . . .  14
       4.3.5.  Connectionless Network Protocol . . . . . . . . . . .  14
     4.4.  Group Semantics . . . . . . . . . . . . . . . . . . . . .  15
       4.4.1.  Multicast . . . . . . . . . . . . . . . . . . . . . .  15
       4.4.2.  Automatic Multicast Tunneling . . . . . . . . . . . .  16
       4.4.3.  Bit Index Explicit Replication  . . . . . . . . . . .  16
   5.  Overview of Current Routing Research Work . . . . . . . . . .  17
     5.1.  Forwarding  . . . . . . . . . . . . . . . . . . . . . . .  17
       5.1.1.  Path Aware Networking . . . . . . . . . . . . . . . .  17
     5.2.  Trust and Accountability  . . . . . . . . . . . . . . . .  17

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       5.2.1.  Scalability, Control, and Isolation on Next-
               Generation Networks . . . . . . . . . . . . . . . . .  18
     5.3.  Layering  . . . . . . . . . . . . . . . . . . . . . . . .  18
       5.3.1.  Recursive InterNetwork Architecture . . . . . . . . .  18
     5.4.  Naming  . . . . . . . . . . . . . . . . . . . . . . . . .  19
       5.4.1.  Information Naming  . . . . . . . . . . . . . . . . .  19
       5.4.2.  Service Naming  . . . . . . . . . . . . . . . . . . .  19
       5.4.3.  Structured Topological Naming . . . . . . . . . . . .  21
       5.4.4.  Geographical Naming . . . . . . . . . . . . . . . . .  21
       5.4.5.  Path-based Naming . . . . . . . . . . . . . . . . . .  21
     5.5.  Routing . . . . . . . . . . . . . . . . . . . . . . . . .  21
       5.5.1.  Inter-Domain Routing  . . . . . . . . . . . . . . . .  21
       5.5.2.  Intra-Domain Routing  . . . . . . . . . . . . . . . .  22
     5.6.  No Changes Needed . . . . . . . . . . . . . . . . . . . .  22
   6.  Challenges for Internet Routing Research  . . . . . . . . . .  22
     6.1.  Routing Research Questions to be Addressed  . . . . . . .  22
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  22
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  23
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  23
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  23
   11. Informative References  . . . . . . . . . . . . . . . . . . .  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  32

1.  Introduction

   The Internet continues to expand rapidly, and the Internet Protocol
   (IP) has become the global standard in many types of computer network
   independent of whether or what connectivity to the Internet it has.
   At the same time, there are increasingly varied expectations of the
   services and service level objectives that can be required from
   networks.  Packet-delivery quality expectations beyond best effort is
   a growth area: throughput, latency, error recovery, and (absence of)
   packet or connectivity loss, reordering, or jitter.  Requirements
   include relative or absolute guarantees or predictable elastic
   changes under contention on these performance factors.  This places
   significant pressure on Service Providers to be aware of the type of
   services being delivered, and to have access to sufficient
   information about how individual packets should be treated to meet
   the user, application and application instance requirements.

   IP addresses facilitate the identification of how a device is
   attached to the Internet and how it is distinguished from every other
   device.  Addresses are used to direct packets to a destination
   (destination address) and indicate to where receiver and network
   replies and error messages should be sent (source address).  An IP
   address may be assigned to each network interface of a device
   connected to a network that uses IP.  Applications use IP addresses

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   to both identify a host and to indicate the physical or virtual
   location of the host.

   This document presents a brief survey of proposals to extend the
   semantics of IP addresses by assigning additional meanings to some
   parts of the address, or by partitioning the address into a set of
   subfields that give scoped addressing instructions.  Some of these
   proposals are intended to be deployed in limited domains [RFC8799]
   that are IP-based, while other proposals are intended for use across
   the Internet.  Limited domains may present their own challenges in
   terms of ensuring the perimeter of the domains, and connecting
   domains across the Internet.

   The impact that some proposals may have on routing systems could
   require clean-slate solutions, hybrid solutions, extensions to
   existing routing protocols, or potentially no changes at all.  A
   separate document ([I-D.king-irtf-challenges-in-routing]) describes
   the challenges to the routing system presented by changes to IP
   address semantics, and sets out research questions that should be
   investigated by those proposing new semantic address schemes.

2.  Network Path Selection

   Two approaches are typically used for network path selection.
   Firstly, a priori assessment by having the feasible paths and
   constraints computed in advance.  Secondly, real-time computation in
   response to changing network conditions.

   The first approach may be conducted offline and allows for concurrent
   or global optimization based on constraints and policy.  As network
   size and complexity increases, the required computing power may
   increase exponentially for this type of computation.

   The second approach must consider the speed of calculation where
   complex constraints are applied to the path selection.  This
   processing may delay service setup and the responsiveness to changes
   (such as failures) in the network.  Network topology filters may be
   applied to reduce the complexity of the network data and the
   computation algorithm, however, the path computation accuracy and
   optimality may be negatively affected.

   In both approaches, the amount of information that needs to be
   imported and processed can become very large (e.g., in large
   networks, with many possible paths and route metrics), which might
   impede the scalability of either method both in terms of the storage
   and the distribution of the information.

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   In the last decade, significant research has been conducted into the
   architecture of the future Internet (for example, [RESEARCHFIAref]
   and [ITUNET2030ref]).  During this research, several techniques
   emerged, highlighting the benefits of path awareness and path
   selection for end-hosts, and multiple path-aware network
   architectures have been proposed, including SCION [SCIONref] and RINA
   [RINAref], and the work of the Path Aware Networking Research Group
   (PANRG) as discussed later in this document.

   When choosing the best paths or topology structures, the following
   may need to be considered:

   o  The method by which a path, or set of paths, is to be calculated.
      For example, a path may be selected automatically by the routing
      protocol or may imposed (perhaps for traffic engineering reasons)
      by a central controller or management entity.

   o  The criteria used for selecting the best path.  For example,
      classic route preference, or administrative policies such as
      economic costs, resilience, security, and if requested, applying
      geopolitical considerations.

2.1.  Path Aware Routing

   The current architecture for IP networking is built using a best-
   effort philosophy.  There are techniques discussed in this document
   that attempt better-than-best-effort delivery.  The start-point and
   end-point of a path are identified using IP addresses, and traffic is
   steered along the path that does not necessarily follow the "shortest
   path first" route through the network.  Furthermore, the path might
   not run all the way from a packet's source to its destination.  The
   assumption is that a packet reaching the end of a path is forwarded
   to its destination using best-effort techniques.

   Evaluating and building paths that respect requirements that go
   beyond the simple best effort model is particularly challenging and
   computationally heavy since numerous quality-related parameters need
   to be considered.

3.  What is Semantic Addressing?

   Networks are often divided into addressing regions for various
   administrative or technological reasons.  Different routing paradigms
   may be applied in each region, and within a single region specific
   "private" semantics may be applied to the IP addresses.

   These address semantics are established using customer types,
   customer connections, topological constraints, performance groups,

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   and security, etc.  Service Providers or network operators will apply
   local policies to user and application packets as they enter the
   network possibly mapping addresses or possibly encapsulating them
   with an additional IP header.  In some case, the packet has its
   source and destination within a single network and the network
   operator can apply address semantics policies across the whole
   network.  In other cases (such as general IP-based traffic), a packet
   will require a path across multiple networks, and each may apply its
   own set of traffic forwarding policies.  In these cases, there is
   often no consistency or guaranteed performance unless a Service Level
   Agreement (SLA) is applied to traffic traversing multiple networks.

   Semantic Addressing is a term that applies to any of the many
   proposals have been made to add semantics to IPv6 addresses beyond
   the simple identification of the source and destination, for example,
   [I-D.jia-scenarios-flexible-address-structure].  These proposals may
   set the meaning of an address within the scope of a limited domain,
   or suggest an address semantic that is meaningful at specific points
   in the network.  In this context, a "limited domain" means that the
   interpretation of the address is only applicable to a well-defined
   set of network nodes, and if a packet bearing an address with a
   modified semantic were to escape from the domain, the special meaning
   of the address would be lost.  Additionally (or alternatively), the
   meaning of "specific points in the network" may be applied to the
   source and destination nodes of a packet, while all transit nodes are
   unaware of the special semantic, however it could be the case that
   some key transit nodes are able to access the meaning of the address
   and so apply special routing or other functions to the packet.

   Such proposals include the following:

   o  Providing semantics specific to mobile networks so that a user or
      device may move through the network without disruption to their
      service [CONTENT-RTG-MOBILEref].

   o  Enabling optimized multicast traffic distribution by encoding
      multicast tree and replication instructions within addresses
      [MULTICAST-SRref].

   o  Using addresses to identify different device types so that their
      traffic may be handled differently [SEMANTICRTG].

   o  Content-based routing (CBR), forwarding of the packet based on
      message content rather than the destination addresses
      [OPENSRNref].

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   o  Deriving IP addresses from the lower layer identifiers and using
      addresses depending on the underlying connectivity (for example,
      [RFC6282].

   o  Identifying hierarchical connectivity so that routing can be
      simplified [EIBPref].

   o  Providing geographic location information within addresses
      [GEO-IPref].

   o  Indicating the application or network function on a destination
      device or at a specific location; or enable Service Function
      Chaining (SFC).

   o  Expressing how a packet should be handled, prioritized, or
      allocated network resources as it is forwarded through the network
      [TERASTREAMref].

   o  Using cryptographic algorithms to mask the identity of the source
      or destination, masking routing tables within the domain, while
      still enabling packet forwarding across the network
      [BLIND-FORWARDINGref].

   In many cases, it may be argued that existing mechanisms applied on
   top of the common address semantic defined in [RFC4291] can deliver
   the correct functionality for these scenarios.  That is, packets may
   be tunneled over IP using a number of existing encapsulation
   techniques.  Nevertheless, there is pressure to reduce the amount of
   encapsulation (partly to resist reduction in the maximum transmission
   unit (MTU) over the network, and partly to achieve a flatter and more
   transparent network architecture).  This leads to investigations into
   whether the current IP addresses can be "overloaded" (without any
   negative connotations being attached to that word) by adding
   semantics to the addresses.

   Semantic Routing is the process of routing packets that contain IP
   addresses with additional semantics, possibly using that information
   to perform policy-based routing or other enhanced routing functions.
   Several technical challenges exist for semantic routing: these are
   discussed further in [I-D.king-irtf-challenges-in-routing].

3.1.  Architectural Considerations

   Semantics may be applied in a number of ways to integrate with
   existing routing architectures.  The most obvious is to build an
   overlay such that IP is used only to route packets between network
   nodes that utilize the semantics at a higher layer.  There are a
   number of uses of this approach including Service Function Chaining

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   (SFC) (see Section 4.2.3) and Information Centric Networking (ICN)
   (see Section 5.4.1).  An overlay may be achieved in a higher layer,
   or may be performed using tunneling techniques (such as IP-in-IP) to
   traverse the areas of the IP network that cannot parse additional
   semantics and so join together those nodes that use the semantics.

   The application of semantics may also be constrained to within a
   limited domain.  In some cases, such a domain will use IP, but be
   disconnected from Internet.  In those cases, the challenges are
   limited to enabling the desired function within the domain.  In other
   cases, traffic from within the domain is exchanged with other domains
   that are connected together across an IP-based network using tunnels
   or via application gateways.  And in another case traffic from the
   domain is routed across the Internet to other nodes and this requires
   backward-compatible routing approaches, tunnels, or gateway
   functions.

   Limited domains [RFC8799] are a fact of networking life.  They are
   used to safely deploy or test features and functions in a controlled
   environment so that they cannot contaminate other networks or the
   Internet in general.  Examples of limited domain in use today
   include:

   o  Internet of Things (IoT) networks such as factory floors or home
      networks

   o  Deterministic Networks (DetNet) that operate in campus networks or
      private WANs to provide deterministic data paths with bounded
      latency, low loss, predictable jitter, and high reliability.

   o  Content Distribution Networks (CDN) where clusters of servers
      share content provision but may also need to be interconnected.

   o  Physical security may be provided for a site simply by not
      permitting traffic to enter or leave the site.  This may be
      expanded by connecting multiple sites together using tunnels
      across the Internet to form a Virtual Private Network (VPN).

   Limited domains are also used as a driver for innovation.  They
   provide a safe space to run experiments and deploy new functions such
   as advances in traffic steering, improvements in security, and new
   routing protocols.  A limited domains is a way to achieve incremental
   deployability on an isolated island, and this enables innovation that
   may (or may not) percolate to the whole Internet at a later stage.
   For example, experiments to increase the programmability of network
   forwarding functions need to be carried out in networks of similarly
   capable nodes (so as to avoid the risks of broken interoperability or

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   forwarding loops), yet these experiments need to use real user data
   that is flowing between hosts and servers.

   Because limited domains don't always operate in isolation they may
   need to be connected to other domains over the Internet, or to other
   nodes within the wider Internet.

4.  Existing Approaches for Routing Based on Additional Semantics

   Several IETF-based approaches are available to allow service
   providers to perform policy-based routing, including identifying and
   marking IP traffic either by changing the semantic of IP addresses or
   by adding such a semantic in other fields/namespaces, enabling
   differentiated handling by transit routers (queuing, dropping,
   forwarding, etc.).  The sections below distinguish between those
   schemes that perform routing based on information other than IP
   addresses, those that establish an overlay network in which to apply
   semantics, and those that add semantics to the addresses.  A further
   separate group of approaches is presented here to cover the concept
   of group semantics where a single address identifies more than one
   end point.

4.1.  Non-Address-Based Routing

   Many routing schemes examine not just the destination address field,
   but other field in the packet header to make routing decisions.
   These approaches (sometimes referred to as "policy-based routing")
   allow packets to follow different paths through the network depending
   on semantics assigned to these other fields or simply based on
   hashing algorithms operating on the values of those fields.

4.1.1.  Deep Packet Inspection

   Deep Packet Inspection (DPI) may be used by a router to learn the
   characteristics of packets in order to forward them differently.
   This involves looking into the packet beyond the top-level network-
   layer header to identify the payload.  Once identified, the traffic
   type can be used as an input for marking the packets for network
   handling, or for performing specific policies on the packets.

   However, DPI may be expensive both in processing costs and latency.
   The processing costs means that dedicated infrastructure is necessary
   to carry out the function and this may have an associated financial
   cost.  The latency incurred may be too much for use with any delay/
   jitter sensitive applications.  As a result, DPI is difficult for
   large-scale deployment and its usage is often limited to specific
   functions at the edge of the network.

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   Despite this, "shallow DPI" is commonplace in routers today as they
   examine the five-tuple of source address, destination address,
   payload protocol, source port, and destination port to perform a hash
   function for ECMP purposes (a form of policy-based routing).

4.1.2.  Differentiated Services

   Quality of Service (QoS) based on Differentiated Services [RFC2474]
   is a widely deployed framework specifying a simple and scalable
   coarse-grained mechanism for classifying and managing network
   traffic.  However, in a service providers network, DiffServ codepoint
   (DSCP) values cannot be trusted when they are set by the customer,
   and may have different meanings as packets are passed between
   networks.

   In real-world scenarios, Service Providers deploy "remarking" points
   at the edges of their network, re-classifying received packets by
   rewriting the DSCP field according to local policy using information
   such as the source/destination address, IP protocol number, transport
   layer source/destination ports, and possibly applying DPI as
   described in Section 4.1.1.

   The traffic classification process and node-by-node processing leads
   to increased packet processing overhead and complexity at the edge of
   the Service Providers network.

4.1.3.  IPv6 Extension Headers

   [RFC8200] defines the IPv6 header and also a number of extension
   headers.  These extension headers can be used to carry additional
   information that may be used by transit routers (the hop-by-hop
   options header) or by the destination identified by the destination
   address field (the destination options header).  These extension
   headers could be used to encode additional semantics that might then
   enable routing decisions and determine what functions and operations
   should be performed on a packet.

   [RFC7872] and [I-D.ietf-v6ops-ipv6-ehs-packet-drops] provide some
   discussions about the operational problems of using IPv6 extension
   headers especially in multi-domain environments, while
   [I-D.bonica-6man-ext-hdr-update] proposes to update RFC 8200 with
   guidance regarding the processing, insertion and deletion of IPv6
   extension headers.

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4.2.  Semantic Overlays

   An overlay network is built on top of an underlay or transport
   network.  Packets are encapsulated with the header for the overlay
   network to carry the additional information needed to provide the
   desired function, and then the packets are encapsulated for transport
   through the underlay network.  In this case, no changes are made to
   the meaning of the IP addresses in the underlay, but the destination
   address identifies the next hop in the overlay network rather than
   the ultimate destination of the packet.  In this way, packets can be
   steered through different overlay nodes where routing decisions can
   be made.

4.2.1.  Application-Layer Traffic Optimization

   Application-Layer Traffic Optimization (ALTO) [RFC7285] is an
   architecture and protocol.  ALTO defines abstractions and services to
   provide simplified network views and network services to guide the
   application usage of network resources, including cost.

   An ALTO server gathers information about the network and answers
   queries from an ALTO client that wants to find a suitable path for
   traffic.  ALTO responses are typically used to route whole flows (not
   individual packets) either to suitable destinations (such as network
   functions) or onto paths that have specific qualities.

4.2.2.  Multipath TCP

   Multipath TCP (MPTCP) [RFC8684] enables the use of TCP in a multipath
   network using multiple host addresses.  A Multipath TCP connection
   provides a bidirectional bytestream between two hosts communicating
   like normal TCP and thus does not require any change to the
   applications.  However, Multipath TCP enables the hosts to use
   different paths with different IP addresses to exchange packets
   belonging to the MPTCP connection.

   MPTCP increases the available bandwidth, and so provides shorter
   delays; it increases fault tolerance, by allowing the use of other
   routes when one or more routes become unavailable; and it enables
   traffic engineering and load balancing.

4.2.3.  Service Function Chaining

   Service Function Chaining (SFC) [RFC7665] is the process of sending
   traffic through an ordered set (a sequence) of abstract service
   functions.  This may be achieved using an overlay encapsulation such
   as the Network Service Header (NSH) [RFC8300] or MPLS [RFC8596] that

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   rely on tunneling through an underlay without any additional
   semantics applied to the IP addresses.

   Alternatively, SFC can be performed by adding semantics to the
   addresses, for example, as in Section 4.3.3.

4.2.4.  Path Computation Element

   The Path Computation Element (PCE) [RFC4655] is an architecture and
   protocol [RFC5440] that can be used to assist with network path
   selection.  A PCE is an entity capable of computing paths for a
   single or set of services.  A PCE might be a network node, network
   management station, or dedicated computational platform that is
   resource-aware and has the ability to consider multiple constraints
   for sophisticated path computation.  PCE applications compute label
   switched paths for MPLS and GMPLS traffic engineering, but the PCE
   has been extended for a variety of additional traffic engineering
   problems.

4.3.  Semantic Addressing

   In semantic addressing, additional information or meaning is placed
   into the IP address, and this is used to route packets within the
   network.

4.3.1.  Locator/ID Separation Protocol (LISP)

   The Locator/ID Separation Protocol (LISP) [RFC6830] was published by
   the IETF as an Experimental RFC in 2013 and is now being moved to the
   Standards Track [I-D.ietf-lisp-rfc6830bis] and
   [I-D.ietf-lisp-rfc6833bis].  LISP separates IP addresses into two
   numbering spaces: Endpoint Identifiers (EIDs) and Routing Locators
   (RLOCs).  The former, the EIDs, are used to identify communication
   end-points (as the name states) as well as local routing and
   forwarding in the edge network.  The latter, RLOCs, are used to
   locate the EIDs in the Internet topology end are usually the address
   of ASBRs (Autonomous System Border Routers).  IP packets addressed
   with EIDs are encapsulated with RLOCs for routing and forwarding over
   the Internet.

   As end-to-end packet forwarding includes both EIDs and RLOCs an
   additional control-plane is needed.  This control plane provides a
   mapping system and basic traffic engineering capabilities.
   Multihoming becomes easier because one EID can be associated to more
   than one RLOC or even to a local network address prefix.

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4.3.2.  Identifier-Locator Network Protocol

   The Identifier-Locator Network Protocol (ILNP) [RFC6740] is an
   experimental network protocol designed to separate the two functions
   of network addresses: identification of network endpoints, topology
   or location information.  Differently from LISP, ILNP encodes both
   locator and identifier in the IPv6 address format (128 bits).  More
   specifically, the most significant 64 bits of the 128 bits IPv6
   address is the locator, while the less significant 64 bits form the
   identifier.  Upon reaching the destination network, a cache is used
   to find the corresponding node.  Furthermore, DNS can be dynamically
   updated, which is essential for mobility and also for provider-
   independent addresses.  Similar to LISP, multihoming can be set by
   assigning multiple locators to the same identifier.  In addition,
   identifiers can also be encrypted for privacy reasons.  It was
   intended that ILNP should be backwards-compatible with existing IP,
   and that it should be incrementally-deployable.

4.3.3.  Segment Routing

   Segment Routing (SR) [RFC8402] leverages the source routing paradigm.
   A node steers a packet through an ordered list of instructions,
   called "segments".  A segment can represent any instruction,
   topological or service based.  A segment can have a semantic local to
   an SR node or global within an SR domain.  SR provides a mechanism
   that allows a flow to be restricted to a specific topological path,
   while maintaining per-flow state only at the ingress node(s) to the
   SR domain.

   In SR for IPv6 networks (SRv6) segment routing functions are used to
   achieve a networking objective that goes beyond packet routing, in
   order to provide "network programming" [RFC8986].  The network
   program is expressed as a list of instructions, which are represented
   as 128-bit segments, called Segment Identifiers (SID) - encoded and
   presented in the form of an IPv6 address.  The first instruction of
   the network program is placed in the Destination Address field of the
   packet.  If the network program requires more than one instruction,
   the remaining list of instructions is placed in the Segment Routing
   Extension Header (SRH)[RFC8754].

   An SRv6 instruction can represent any topological or service-based
   instruction.  The SRv6 domain is the service provider domain where
   SRv6 services are built to transport any kind of customer traffic
   including IPv4, IPv6, or frames.  SRv6 is the instantiation of
   Segment Routing deployed on the IPv6 data plane.  Therefore, in order
   to support SRv6, the network must first be enabled for IPv6.

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   For nodes forwarding traffic, the SRH in the IPv6 header is only
   processed if the destination address identifies the local node.  In
   this case, the node must take several actions, including reading the
   SRH, performing any node-specific actions identified by the
   destination address or the next SIDs in the SRH, and re-writing the
   IPv6 destination address field using information from the SRH before
   forwarding the packet.

4.3.4.  Preferred Path Routing

   Preferred Path Routing (PPR)
   [I-D.chunduri-lsr-isis-preferred-path-routing] is a proposed routing
   protocol mechanism where alternate forwarding state is installed for
   a set of different preferred paths.  Each preferred path is described
   as an ordered linear list of nodes, links, and network functions, and
   the path is identified by a network-global preferred path identifier.
   If a packet is marked with preferred path identifier, it is forwarded
   according to the preferred path that has been installed on the
   router.  If a packet is not marked or if the preferred path is not
   installed on the router, the packet is forwarded using the normal
   shortest path first algorithm.

   In PPR, the preferred path identifier is encoded in an IP address,
   but the address is only used in an encapsulation of the end-to-end
   packet.  This approach is a hybrid in that it is applying a different
   meaning to the IP addresses, using that meaning in an encapsulation,
   but routing the packets through an existing IP network.

4.3.5.  Connectionless Network Protocol

   The Connectionless Network Protocol (CLNP) [CLNPref] is a network
   layer encoding that supports variable length, hierarchical
   addressing.  It is widely deployed in many communications networks
   and is the ITU-T's standardized encoding for packets in the
   management plane for Synchronous Digital Hierarchy (SDH) networks.
   For a while, CLNP was considered in competition with IP as the
   network layer encoding for the Internet, but IP (in conjunction with
   TCP) won out.

   Many of the considerations for semantic addressing can be handled
   using CLNP, and it is particularly well suited to applications that
   demand variable length addresses or that structure addresses
   hierarchically for routing or geo-political reasons.

   Routing for CLNP can be achieved using the IS-IS routing protocol in
   its full form as documented in [ISISref] rather than its IP-only form
   [RFC1195].  While this may make it possible to use CLNP alongside IP
   in some routed networks, it does not integrate the use of IP

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   addresses with additional semantics with the historic use of IP
   addresses except in "ships that pass in the night" fashion.
   Alternatively, [RFC1069] explains how to carry regular IP addresses
   in CLNP.

4.4.  Group Semantics

   A mayor enhanced addressing semantic in IP is called "group
   semantics".  Here, an IP address identifies more than one individual
   interface or node.  This facilitates the delivery of a packet to any
   one of a group of destinations, or to all members of a group.

4.4.1.  Multicast

   Multicast address semantics support delivery to all members of a
   group of destinations.  This is a controlled variant of broadcasting
   where packets are delivered to all possible receivers in a particular
   (static) scope such as a multi-access link.  Membership of a
   multicast link is dynamically signalled by the group members, and a
   group is identified by a specific address.

   IP multicast [RFC1112], based on the protocol and service definition
   aspects of Steve Deering's PhD, is widely deployed for IPv4.  It is
   equally adopted and used in IPv6 using the addressing architecture
   specified in [RFC4291].  In IP multicast (Any Source Multicast - ASM)
   any node can send to the multicast group and have its packets
   delivered to all members of the group.

   Research deployments in the 1990s (the so called 'MBone' [MBONEref])
   indicated that IP multicast gave rise to a number of issues related
   to address assignment, implementation, scale, and security.  The
   problem of allocation and management of IP multicast (group)
   addresses led to several proposals including Multicast Address
   Dynamic Client Allocation Protocol (MADCAP) [RFC2730], the Multicast
   Address Allocation Architecture (MALLOC) [RFC6308], the Multicast
   Address-Set Claim Protocol (MASC) [RFC2909], and the Multicast-Scope
   Zone Announcement Protocol (MZAP) [RFC2776], but none was widely
   adopted.  Attempts to create a complete routing protocol suite for IP
   multicast service model within the IETF resulted in the Multicast
   Source Discovery Protocol (MSDP) being published as an experimental
   RFC [RFC3618].

   The popularity of multicast as a concept and the widespread
   deployment of commercial IPv4 multicast led to the development of
   "Source Specific Multicast" service (SSM) [RFC4607].  In SSM, the
   combination of the Source and Group addresses (S,G) of an IP
   multicast packet form a so-called SSM channel address, which

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   identifies group of receivers and implies a single permitted sender.
   Receivers subscribe to every SSM channel.

   From the perspective of a service user, SSM solves the security issue
   (only valid sources can send traffic) and the address assignment
   issue (all group addresses are relative to the source address).  For
   the operator, SSM also eliminates the complex operational
   requirements of ASM.

4.4.2.  Automatic Multicast Tunneling

   Automatic Multicast Tunneling (AMT) [RFC7450] is a protocol for
   delivering multicast traffic from sources in a multicast-enabled
   network to receivers that lack multicast connectivity to the source
   network.  The protocol uses UDP encapsulation and unicast replication
   to provide this functionality as a hybrid solution using both
   multicast routing and an overlay approach.

4.4.3.  Bit Index Explicit Replication

   The IETF standardized or otherwise deployed protocol solutions in
   support of ASM and SSM in about 2015 relied all on per-hop, per ASM-
   group/per-SSM-channel stateful hop-by-hop forwarding/replication.
   Service Provider at that time were starting to removing or reduce
   heavy-weight control and per-hop forwarding processing in unicast
   caused by MPLS LDP/RSVP-TE driven designs, replacing it with more
   lightweight MPLS-SR and later SRv6 forwarding and associated control
   planes.  But to reduce the cost for multicast service, the only
   transit-hop stateless solution available was ingress-replication,
   tunnel multicast across unicast, hence trading hop-by-hop state (and
   its control and management plane cost) in the network against traffic
   overhead and (under congestion) higher latency.

   Bit Index Explicit Replication (BIER) [RFC8279] addresses these
   problems.  BIER does not contain the notion of ASM or SSM groups.
   Instead, a sender enumerates the set of receivers to which the packet
   is to be delivered.  The network routers forward packets and
   replicate them onto the shortest paths to the destinations.  As the
   packets are replicated, so the enumeration of the receivers is pruned
   on each copy of the packet.

   BIER is able to use existing routing protocols without modification,
   but requires enhancements in the forwarding plane to encode, parse,
   and act on the set of receivers.  The BIER information is carried in
   new encapsulations [RFC8296] that is carried hop-by-hop in IP.  Thus,
   the additional semantic is in an overlay.

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5.  Overview of Current Routing Research Work

   This section presents a limited survey of techniques and projects
   that provide mechanisms to facilitate path and forwarding decisions
   based on contextual information.

   More recently, the proceedings of the June 2021 Semantic Addressing
   and Routing for Future Networks (SARNET-21) Workshop was compiled and
   published as [I-D.galis-irtf-sarnet21-report].  It captures the views
   and positions of the participants as expressed during the workshop.

5.1.  Forwarding

   Some research work is engaged in examining the emerging set of new
   requirements that exceed the network and transport services of the
   current Internet, which only delivers "best effort" service.  This
   work aims to determine what features can be built on top of existing
   solutions by adding additional new components or features.  A
   starting point for this discussion can be found in
   [I-D.bryant-arch-fwd-layer-ps].

   Several aditional techniques for improving IP-based routing have been
   proposed, some of these are highlighted below.

5.1.1.  Path Aware Networking

   The IRTF's Path Aware Networking Research Group [PANRGref] aims to
   support research in bringing path aware techniques into use in the
   Internet.  This research overlaps with many past and existing IETF
   and IRTF efforts including multipath transport protocols, congestion
   control in multiply-connected environments, traffic engineering, and
   alternate routing architectures.

   [I-D.irtf-panrg-path-properties] offers a vocabulary of path
   properties.  By doing so it gives some clarity of the distinction
   between path aware routing and semantic routing as considered in this
   document.

   [I-D.irtf-panrg-what-not-to-do] provides a catalog and analysis of
   past efforts to develop and deploy Path Aware techniques.  Most, but
   not all, of these mechanisms were considered at higher levels,
   although some apply at the IP routing and forwarding layer.

5.2.  Trust and Accountability

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5.2.1.  Scalability, Control, and Isolation on Next-Generation Networks

   The SCION (Scalability, Control, and Isolation on Next-Generation
   Networks) [SCIONref] inter-domain network architecture has been
   designed to address security and scalability issues and provides an
   alternative to current Border Gateway Protocol (BGP) solutions.  The
   SCION proposal combines a globally distributed public key
   infrastructure, a way to efficiently derive symmetric keys between
   any network entities, and the forwarding approach of packet-carried
   forwarding state.

   SCION End-hosts fetch viable path segments from the path server
   infrastructure, and construct the exact forwarding route themselves
   by combining those path segments.  The architecture ensures that a
   variety of combinations among the path segments are feasible, while
   cryptographic protections prevent unauthorized combinations or path-
   segment alteration.  The architecture further enables path
   validation, providing per-packet verifiable guarantees on the path
   traversed.

5.3.  Layering

5.3.1.  Recursive InterNetwork Architecture

   Recursive Inter Network Architecture (RINA) [RINAref] builds upon the
   principle that applications communicate through Inter-process
   Communication (IPC) facilities.  For an application to communicate
   through the distributed IPC facility, it only needs to know the name
   of the destination application and to use the IPC interface to
   request communication.

   By leveraging IPC concepts RINA allows two processes to communicate,
   IPC requires certain functions such as locating processes,
   determining permission, passing information, scheduling, and managing
   memory.  Similarly, two applications on different end-hosts should
   communicate by utilizing the services of a distributed IPC facility
   (DIF).  A DIF is an organizing structure, generally referred to as a
   "layer".

   The scope and functions provided by the different IPC facilities may
   vary given the different type of network and performance goals.
   Moreover, an IPC layer may recursively request services from other
   IPC layers.  The idea of recursively using multiple inter-process
   communication services creates a multilayer structure repeated until
   an IPC facility can fit well for physical technologies, e.g., wired
   or wireless networks.

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5.4.  Naming

5.4.1.  Information Naming

   Information-Centric Networking (ICN) [ICNref] is an approach to
   evolve the Internet infrastructure away from a host-centric paradigm,
   based on perpetual connectivity and the end-to-end principle, to a
   network architecture in which the focal point is information (or
   content or data) that is assigned specific identifiers.

   Several scenarios exist for semantic-based networking, providing
   reachability based on Content Routing [CONTENTref] and Name Data
   Networking [NDNref].  The technology area of ICN is now reaching
   maturity, after many years of research and commercial investigation.
   A technical discussion into the deployment and operation of ICNs
   continues in the IETF: [RFC8763] provides several important
   deployment considerations for facilitating ICN and practical
   deployments.

   Although ICN is primarily an overlay technology, a more recently
   concept, Hybrid-Information-Centric Networking (hICN), has been
   introduced [HICNref].  In an hICN environment the ICN aspect is
   integrated into the IPv6 architecture, reusing existing IPv6 packet
   formats with the intention of maintaining compatibility with existing
   and deployed IP network technology without creating overlays that
   might require a new packet format or additional encapsulations.  The
   work is described in [I-D.muscariello-intarea-hicn].

5.4.2.  Service Naming

5.4.2.1.  Dynamic Anycast

   Dyncast (Dynamic anycast) addresses the problem of directing traffic
   from a client to one service instance among several available, while
   considering decision metrics beyond shortest path when doing so.
   Those service instances are therefore possible destinations for a
   specific service demand.  [I-D.liu-dyncast-ps-usecases] outlines
   several use cases where such traffic steering requirement is
   desirable and may occur, such as in edge computing scenarios but also
   in distribution of video content in scenarios like autonomous
   driving.  The draft also outlines problems with existing solutions,
   most notably latency in changing relations from one service instance
   to another due to a change in metric, which defines that decision
   (e.g., load in servers, latency, or a combination of several such
   metrics).

   Key to the proposed dyncast [I-D.li-dyncast-architecture]
   architecture is to build on the notion of (IP) anycast, while

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   changing the addressing semantic from a locator-based addressing to a
   service-oriented one.  Here, the initial "service demand" packet is
   being identified through a service identifier as destination address.
   This identifier is then mapped onto a binding IP (locator-based)
   address at the ingress of the network, allowing for locator-based
   routing to be used throughout the network.  The ingress-based
   architecture is designed in such a way that ingress nodes upon
   arrival of a new service demand can determine which instance (i.e.,
   which binding IP address) to use considering both network- and
   service-related metrics.  These metrics can be distributed among
   ingress nodes in various ways, including over a routing protocol
   solution.

   The overall forwarding decision is based on the adherence to what is
   termed "instance affinity", i.e., the need to adhere to a previous
   routing decision for more than one packet, unlike IP forwarding on
   locator addresses.  This affinity is created, by means of a binding
   table on the ingress nodes, since often more than one packet is
   needed for the overall service-level transaction with a specific
   service instance.  For instance, HTTP requests may span more than one
   routed packet.  Also, a service instance may also create ephemeral
   state, which requires the client to continue communicating with this
   instance for the duration of this state.  While the affinity is
   entirely defined by the application layer protocol, the network layer
   takes the affinity marking as input into the decision to renew its
   routing decision.

5.4.2.2.  Prioritycast

   A modification to anycast that can be instantiated by additional
   engineering in the routing system is called "prioritycast".  Instead
   of relying on the shortest path forwarding semantic, prioritycast
   directs all traffic to the anycast address instance that is reachable
   and has the highest priority.  This approach only requires small
   modifications to routing protocols so that priorities are advertised
   along side the addresses.

   Prioritycast was originally introduced as a recommended operational
   practice for deployments of Bidirectional PIM (Bidir-PIM) [RFC8736]
   which requires a single active instance of its Rendezvous Point (RP)
   service.  The RP is the root of a bidirectional tree and prioritycast
   addresses for RP allow fast failover without additional redundancy
   protocols beside the routing protocol, which would otherwise be
   necessary for such a redundancy service.

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5.4.3.  Structured Topological Naming

   TBD

5.4.4.  Geographical Naming

   TBD

5.4.5.  Path-based Naming

   TBD

5.4.5.1.  ICNP

   TBD

5.4.5.2.  Reed

   TBD

5.5.  Routing

5.5.1.  Inter-Domain Routing

5.5.1.1.  Expedited Internet Bypass Protocol

   The Expedited Internet Bypass Protocol (EIBP) [EIBPref] is a clean
   slate approach to routing and forwarding in the Internet using the
   Internet infrastructure, but bypassing the Internet Protocol (IP).
   The EIBP method may be deployed in current routers and when invoked
   for a specific end to end IP hosts or networks, EIBP bypasses the
   heavy traffic and security challenges faced at Layer-3.  EIBP does
   not require routing protocols, instead it abstracts network
   structural (physical or logical) information into intelligent
   forwarding addresses that are acquired by EIBP routers automatically.

   The Forwarding tables used by EIBP are proportional to the
   connectivity (degree) at a routing device making the protocol
   scalable.  The EIBP routing system does not require network-wide
   dissemination.  Topology change impacts are local and thus
   instabilities on topology changes are minimal.  EIBP is a low
   configuration protocol, which can be deployed in an AS and extended
   to multiple ASes independently.  EIBP evaluations were conducted
   using GENI testbeds and compared to IP using Open Shortest Path First
   and Border Gateway Protocol.  Significant performance improvements in
   terms of convergence and churn rates highlight the capabilities of
   EIBP.

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5.5.2.  Intra-Domain Routing

5.6.  No Changes Needed

   It is entirely possible that some forms of modified address semantic
   will work perfectly well with existing routing protocols and
   mechanisms either across the whole Internet or within limited and
   carefully controlled domains.  Claims for this sort of functionality
   need to be the subject of careful research and analysis as the
   existing protocols were developed with a different view of the
   meaning of IP addresses, and because routing systems are notoriously
   fragile.

6.  Challenges for Internet Routing Research

   Improving IP-based semantic network routing capabilities and capacity
   so that they scale and address a set of growing requirements presents
   significant research challenges, and will require contributions from
   the networking research community.

6.1.  Routing Research Questions to be Addressed

   As research into the scenarios and possible uses of semantic
   addressing progresses, a number of questions need to be addressed in
   the scope of routing.  These questions go beyond "Why do we need this
   function?" and "What could we achieve by carrying this additional
   semantic in an IP address?"  The questions are also distinct from
   issues of how the additional semantics can be encoded within an IP
   address.  All of those issues are, of course, important
   considerations in the debate about semantic addressing, but they form
   part of the essential groundwork of research into semantic addressing
   itself.

   The document "Challenges for the Internet Routing Infrastructure
   Introduced by Changes in Address Semantics"
   [I-D.king-irtf-challenges-in-routing] sets out the challenges for the
   routing system, and how it might be impacted by the use of semantic
   addressing.

7.  Security Considerations

   This document is a survey of existing work and so introduces no
   security considerations of itself.  However, many of the proposals
   referenced either are intended to improve security or have their own
   security implications.  For example:

   o  In network path selection, the criteria used for selecting the
      best path may include security considerations.

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   o  Semantic addresses may be established using security criteria.

   o  Physical security may be provided for a site or limited domain
      simply by not permitting traffic to enter or leave the site.  This
      may be expanded by connecting multiple sites together using
      tunnels across the Internet to form a Virtual Private Network
      (VPN) such that the same level of security is shared by all nodes
      that participate in the VPN provided that the tunnels are
      themselves secure.

   o  There are also additional complexities for security when any form
      of multicast or anycast is used because of issues of address
      assignment and the formation of security associations.

8.  IANA Considerations

   This document makes no requests for IANA action.

9.  Acknowledgements

   Thanks to Stewart Bryant for useful conversations.  Luigi Iannone,
   Robert Raszuk, Ron Bonica, Marie-Jose; Montpetit, Yizhou Li, Toerless
   Eckert, Tony Li, Joel Halpern, and Carsten Bormann made helpful
   suggestions.  The text on Dyncast is based on suggestions from Dirk
   Trossen, Luigi Iannone, and Yizhou Li.  Toerless Eckert suggested
   text for the multicast sections.

   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).

10.  Contributors

               Joanna Dang
               Email: dangjuanna@huawei.com

               Dirk Trossen
               Email: dirk.trossen@huawei.com

11.  Informative References

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   [BLIND-FORWARDINGref]
              Simsek, I., "On-Demand Blind Packet Forwarding",
              Paper 30th International Telecommunication Networks and
              Applications Conference (ITNAC), 2020, 2020,
              <https://www.computer.org/csdl/proceedings-article/
              itnac/2020/09315187/1qmfFPPggrC>.

   [CLEANSLATEref]
              Feldmann, A., "Internet Clean-Slate Design: What and
              Why?", Paper Annals of telecommunications-annales des
              telecommunications;64(5):271-6, 2009, 2009,
              <http://ccr.sigcomm.org/online/files/p59-feldmannA.pdf>.

   [CLNPref]  "Protocol for providing the connectionless-mode network
              service: Protocol specification - Part 1",
              standard ISO/IEC 8473-1:1998, 1998,
              <https://www.iso.org/standard/30931.html>.

   [CONTENT-RTG-MOBILEref]
              Liu, H. and W. He, "Rich Semantic Content-oriented Routing
              for mobile Ad Hoc Networks", Paper The International
              Conference on Information Networking (ICOIN2014), 2014,
              2014, <https://ieeexplore.ieee.org/document/6799682>.

   [CONTENTref]
              Choi, J., Han, J., and E. Cho, "A survey on content-
              oriented networking for efficient content delivery",
              Paper IEEE Communications Magazine, 49(3): 121-127, May
              2011., 2011, <https://ieeexplore.ieee.org/
              iel5/35/5723785/05723809.pdf>.

   [EIBPref]  Shenoy, N., "Can We Improve Internet Performance? An
              Expedited Internet Bypass Protocol", Presentation 28th
              IEEE International Conference on Network Protocols, 2020,
              <https://icnp20.cs.ucr.edu/Slides/NIPAA/D-3_invited.pptx>.

   [GEO-IPref]
              Dasu, T., Kanza, Y., and D. Srivastava, "Geotagging IP
              Packets for Location-Aware Software-Defined Networking in
              the Presence of Virtual Network Functions", Paper 25th ACM
              SIGSPATIAL International Conference on Advances in
              Geographic Information Systems (ACM SIGSPATIAL 2017),
              2017, <https://about.att.com/ecms/dam/sites/labs_research/
              content/publications/
              AI_Geotagging_IP_Packets_for_Location.pdf>.

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   [HICNref]  Carofiglio, G., Muscariello, L., Auge, J., Papalini, M.,
              Sardara, M., and A. Compagno, "Enabling ICN in the
              Internet Protocol: Analysis and Evaluation of the Hybrid-
              ICN Architecture", Paper Proceedings of the 6th ACM
              Conference on Information-Centric Networking, 2019., 2019,
              <https://www.researchgate.net/publication/336344520_Enabli
              ng_ICN_in_the_Internet_Protocol_Analysis_and_Evaluation_of
              _the_Hybrid-ICN_Architecture>.

   [I-D.bonica-6man-ext-hdr-update]
              Bonica, R. and T. Jinmei, "Inserting, Processing And
              Deleting IPv6 Extension Headers", draft-bonica-6man-ext-
              hdr-update-05 (work in progress), March 2021.

   [I-D.bryant-arch-fwd-layer-ps]
              Bryant, S., Chunduri, U., Eckert, T., and A. Clemm,
              "Forwarding Layer Problem Statement", draft-bryant-arch-
              fwd-layer-ps-02 (work in progress), January 2021.

   [I-D.chunduri-lsr-isis-preferred-path-routing]
              Chunduri, U., Li, R., White, R., Tantsura, J., Contreras,
              L. M., and Y. Qu, "Preferred Path Routing (PPR) in IS-IS",
              draft-chunduri-lsr-isis-preferred-path-routing-06 (work in
              progress), September 2020.

   [I-D.galis-irtf-sarnet21-report]
              Galis, A. and D. Lou, "Semantic Addressing and Routing for
              Future Networks (SARNET-21) Workshop Report", draft-galis-
              irtf-sarnet21-report-00 (work in progress), June 2021.

   [I-D.ietf-lisp-rfc6830bis]
              Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
              Cabellos, "The Locator/ID Separation Protocol (LISP)",
              draft-ietf-lisp-rfc6830bis-36 (work in progress), November
              2020.

   [I-D.ietf-lisp-rfc6833bis]
              Farinacci, D., Maino, F., Fuller, V., and A. Cabellos,
              "Locator/ID Separation Protocol (LISP) Control-Plane",
              draft-ietf-lisp-rfc6833bis-30 (work in progress), November
              2020.

   [I-D.ietf-v6ops-ipv6-ehs-packet-drops]
              Gont, F., Hilliard, N., Doering, G., Kumari, W., Huston,
              G., and W. (. Liu, "Operational Implications of IPv6
              Packets with Extension Headers", draft-ietf-v6ops-ipv6-
              ehs-packet-drops-06 (work in progress), April 2021.

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   [I-D.irtf-panrg-path-properties]
              Enghardt, T. and C. Kraehenbuehl, "A Vocabulary of Path
              Properties", draft-irtf-panrg-path-properties-02 (work in
              progress), February 2021.

   [I-D.irtf-panrg-what-not-to-do]
              Dawkins, S., "Path Aware Networking: Obstacles to
              Deployment (A Bestiary of Roads Not Taken)", draft-irtf-
              panrg-what-not-to-do-19 (work in progress), March 2021.

   [I-D.jia-scenarios-flexible-address-structure]
              Jia, Y., Li, G., and S. Jiang, "Scenarios for Flexible
              Address Structure", draft-jia-scenarios-flexible-address-
              structure-00 (work in progress), October 2020.

   [I-D.king-irtf-challenges-in-routing]
              King, D., Dang, J., and A. Farrel, "Challenges for the
              Internet Routing Infrastructure Introduced by Changes in
              Address Semantics", draft-king-irtf-challenges-in-
              routing-02 (work in progress), May 2021.

   [I-D.li-dyncast-architecture]
              Li, Y., Iannone, L., Trossen, D., and P. Liu, "Dynamic-
              Anycast Architecture", draft-li-dyncast-architecture-00
              (work in progress), February 2021.

   [I-D.liu-dyncast-ps-usecases]
              Liu, P., Willis, P., and D. Trossen, "Dynamic-Anycast
              (Dyncast) Use Cases & Problem Statement", draft-liu-
              dyncast-ps-usecases-01 (work in progress), February 2021.

   [I-D.muscariello-intarea-hicn]
              Muscariello, L., Carofiglio, G., Auge, J., Papalini, M.,
              and M. Sardara, "Hybrid Information-Centric Networking",
              draft-muscariello-intarea-hicn-04 (work in progress), May
              2020.

   [I-D.sarathchandra-coin-appcentres]
              Trossen, D., Sarathchandra, C., and M. Boniface, "In-
              Network Computing for App-Centric Micro-Services", draft-
              sarathchandra-coin-appcentres-04 (work in progress),
              January 2021.

King & Farrel           Expires December 30, 2021              [Page 26]
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   [ICNref]   Barbera, D., Xylomenos, G., Ververidis, C., Siris, V., and
              N. Fotiou, "A Survey of information-centric networking
              research", Paper IEEE Communications Surveys and
              Tutorials, vol. 16, Iss. 2, Q2 2014, 2014,
              <https://www.scopus.com/record/
              display.uri?eid=2-s2.0-84901242669>.

   [ISISref]  "Intermediate System to Intermediate System intra-domain
              routeing information exchange protocol for use in
              conjunction with the protocol for providing the
              connectionless-mode network service", standard ISO/IEC
              10589, 2002, <https://standards.iso.org/ittf/
              PubliclyAvailableStandards/
              c030932_ISO_IEC_10589_2002(E).zip>.

   [ITUNET2030ref]
              "Network 2030 Architecture Framework", Technical
              Specification ITU-T Focus Group on Technologies for
              Network 2030, 2020, <https://www.itu.int/en/ITU-
              T/focusgroups/net2030/Documents/Network_2030_Architecture-
              framework.pdf>.

   [MBONEref]
              Savetz, K., Randall, N., and Y. Lepage, "MBONE:
              Multicasting Tomorrow's Internet", Book IDG, 1996,
              <https://www.savetz.com/mbone/>.

   [MULTICAST-SRref]
              Jia, W. and W. He, "A Scalable Multicast Source Routing
              Architecture for Data Center Networks", Paper  IEEE
              Journal on Selected Areas in Communications, vol. 32, no.
              1, pp. 116-123, January 2014, 2014,
              <https://ieeexplore.ieee.org/document/6799682>.

   [NDNref]   Zhang, L., Afanasyev, A., and J. Burke, "Named Data
              Networking", Paper ACM SIGCOMM Computer Communication,
              Review 44(3): 66-73, 2014, 2014.

   [OPENSRNref]
              Ren, P., Wang, X., Zhao, B., Wu, C., and H. Sun, "OpenSRN:
              A Software-defined Semantic Routing Network Architecture",
              Paper IEEE Conference on Computer Communications Workshops
              (INFOCOM WKSHPS), Hong Kong, 2015, 2015,
              <https://www.researchgate.net/
              publication/308827498_OpenSRN_A_software-
              defined_semantic_routing_network_architecture>.

King & Farrel           Expires December 30, 2021              [Page 27]
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   [PANRGref]
              "Path Aware Networking Research Group", RG Path Aware
              Networking Research Group,
              <https://datatracker.ietf.org/rg/panrg/about>.

   [RESEARCHFIAref]
              Pan, J., Paul, S., and R. Jain, "A Survey of the Research
              on Future Internet Architectures", Paper IEEE
              Communications Magazine, vol. 49, no. 7, July 2011, 2014,
              <https://ieeexplore.ieee.org/document/5936152>.

   [RFC1069]  Callon, R. and H. Braun, "Guidelines for the use of
              Internet-IP addresses in the ISO Connectionless-Mode
              Network Protocol", RFC 1069, DOI 10.17487/RFC1069,
              February 1989, <https://www.rfc-editor.org/info/rfc1069>.

   [RFC1112]  Deering, S., "Host extensions for IP multicasting", STD 5,
              RFC 1112, DOI 10.17487/RFC1112, August 1989,
              <https://www.rfc-editor.org/info/rfc1112>.

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, DOI 10.17487/RFC1195,
              December 1990, <https://www.rfc-editor.org/info/rfc1195>.

   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              DOI 10.17487/RFC2474, December 1998,
              <https://www.rfc-editor.org/info/rfc2474>.

   [RFC2730]  Hanna, S., Patel, B., and M. Shah, "Multicast Address
              Dynamic Client Allocation Protocol (MADCAP)", RFC 2730,
              DOI 10.17487/RFC2730, December 1999,
              <https://www.rfc-editor.org/info/rfc2730>.

   [RFC2776]  Handley, M., Thaler, D., and R. Kermode, "Multicast-Scope
              Zone Announcement Protocol (MZAP)", RFC 2776,
              DOI 10.17487/RFC2776, February 2000,
              <https://www.rfc-editor.org/info/rfc2776>.

   [RFC2909]  Radoslavov, P., Estrin, D., Govindan, R., Handley, M.,
              Kumar, S., and D. Thaler, "The Multicast Address-Set Claim
              (MASC) Protocol", RFC 2909, DOI 10.17487/RFC2909,
              September 2000, <https://www.rfc-editor.org/info/rfc2909>.

King & Farrel           Expires December 30, 2021              [Page 28]
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   [RFC3618]  Fenner, B., Ed. and D. Meyer, Ed., "Multicast Source
              Discovery Protocol (MSDP)", RFC 3618,
              DOI 10.17487/RFC3618, October 2003,
              <https://www.rfc-editor.org/info/rfc3618>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [RFC4607]  Holbrook, H. and B. Cain, "Source-Specific Multicast for
              IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
              <https://www.rfc-editor.org/info/rfc4607>.

   [RFC4655]  Farrel, A., Vasseur, J., 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>.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

   [RFC6282]  Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
              Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
              DOI 10.17487/RFC6282, September 2011,
              <https://www.rfc-editor.org/info/rfc6282>.

   [RFC6308]  Savola, P., "Overview of the Internet Multicast Addressing
              Architecture", RFC 6308, DOI 10.17487/RFC6308, June 2011,
              <https://www.rfc-editor.org/info/rfc6308>.

   [RFC6740]  Atkinson, RJ. and SN. Bhatti, "Identifier-Locator Network
              Protocol (ILNP) Architectural Description", RFC 6740,
              DOI 10.17487/RFC6740, November 2012,
              <https://www.rfc-editor.org/info/rfc6740>.

   [RFC6830]  Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
              Locator/ID Separation Protocol (LISP)", RFC 6830,
              DOI 10.17487/RFC6830, January 2013,
              <https://www.rfc-editor.org/info/rfc6830>.

   [RFC7094]  McPherson, D., Oran, D., Thaler, D., and E. Osterweil,
              "Architectural Considerations of IP Anycast", RFC 7094,
              DOI 10.17487/RFC7094, January 2014,
              <https://www.rfc-editor.org/info/rfc7094>.

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   [RFC7285]  Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S.,
              Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
              "Application-Layer Traffic Optimization (ALTO) Protocol",
              RFC 7285, DOI 10.17487/RFC7285, September 2014,
              <https://www.rfc-editor.org/info/rfc7285>.

   [RFC7450]  Bumgardner, G., "Automatic Multicast Tunneling", RFC 7450,
              DOI 10.17487/RFC7450, February 2015,
              <https://www.rfc-editor.org/info/rfc7450>.

   [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>.

   [RFC7872]  Gont, F., Linkova, J., Chown, T., and W. Liu,
              "Observations on the Dropping of Packets with IPv6
              Extension Headers in the Real World", RFC 7872,
              DOI 10.17487/RFC7872, June 2016,
              <https://www.rfc-editor.org/info/rfc7872>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

   [RFC8279]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
              Explicit Replication (BIER)", RFC 8279,
              DOI 10.17487/RFC8279, November 2017,
              <https://www.rfc-editor.org/info/rfc8279>.

   [RFC8296]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
              for Bit Index Explicit Replication (BIER) in MPLS and Non-
              MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
              2018, <https://www.rfc-editor.org/info/rfc8296>.

   [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>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

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   [RFC8596]  Malis, A., Bryant, S., Halpern, J., and W. Henderickx,
              "MPLS Transport Encapsulation for the Service Function
              Chaining (SFC) Network Service Header (NSH)", RFC 8596,
              DOI 10.17487/RFC8596, June 2019,
              <https://www.rfc-editor.org/info/rfc8596>.

   [RFC8684]  Ford, A., Raiciu, C., Handley, M., Bonaventure, O., and C.
              Paasch, "TCP Extensions for Multipath Operation with
              Multiple Addresses", RFC 8684, DOI 10.17487/RFC8684, March
              2020, <https://www.rfc-editor.org/info/rfc8684>.

   [RFC8736]  Venaas, S. and A. Retana, "PIM Message Type Space
              Extension and Reserved Bits", RFC 8736,
              DOI 10.17487/RFC8736, February 2020,
              <https://www.rfc-editor.org/info/rfc8736>.

   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
              <https://www.rfc-editor.org/info/rfc8754>.

   [RFC8763]  Rahman, A., Trossen, D., Kutscher, D., and R. Ravindran,
              "Deployment Considerations for Information-Centric
              Networking (ICN)", RFC 8763, DOI 10.17487/RFC8763, April
              2020, <https://www.rfc-editor.org/info/rfc8763>.

   [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>.

   [RFC8986]  Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
              D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
              (SRv6) Network Programming", RFC 8986,
              DOI 10.17487/RFC8986, February 2021,
              <https://www.rfc-editor.org/info/rfc8986>.

   [RINAref]  Day, J., "Patterns in Network Architecture: A Return to
              Fundamentals", Book Prentice Hall, 2008.

   [SCIONref]
              Barbera, D., Chaut, L., Perrig, A., Reischuk, R., and P.
              Szalachowski, "Patterns in Network Architecture: A Return
              to Fundamentals", Paper The ACM, vol. 60, no. 6, June
              2017, 2017,
              <https://icnp20.cs.ucr.edu/Slides/NIPAA/D-3_invited.pptx>.

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   [SEMANTICRTG]
              Strassner, J., Sung-Su, K., and J. Won-Ki, "Semantic
              Routing for Improved Network Management in the Future
              Internet", Book Chapter Springer, Recent Trends in
              Wireless and Mobile Networks, 2010, 2010,
              <https://link.springer.com/
              chapter/10.1007/978-3-642-14171-3_14>.

   [TERASTREAMref]
              Zaluski, B., Rajtar, B., Habjani, H., Baranek, M., Slibar,
              N., Petracic, R., and T. Sukser, "Terastream
              implementation of all IP new architecture", Paper 36th
              International Convention on Information and Communication
              Technology, Electronics and Microelectronics (MIPRO),
              2013, 2013,
              <https://ieeexplore.ieee.org/document/6596297>.

Authors' Addresses

   Daniel King
   Lancaster University
   UK

   Email: d.king@lancaster.ac.uk

   Adrian Farrel
   Old Dog Consulting
   UK

   Email: adrian@olddog.co.uk

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