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Versions: 00 01                                                         
INTAREA                                                        T. Eckert
Internet-Draft                                Futurewei Technologies USA
Intended status: Informational                             July 12, 2021
Expires: January 13, 2022

   Functional Addressing (FA) for internets with Independent Network
                         Address Spaces (IINAS)


   Recent work has raised interest in exploring network layer addressing
   that is more flexible than fixed-length addressing as used in IPv4
   (32 bit) and IPv6 (128 bit).

   The reasons for the interest include both support for multiple and
   potentially novel address semantics, but also optimizations of
   addressing for existing semantics such as unicast tailored not for
   the global Internet but to better support private networks / limited

   This memo explores in the view of the author yet little explored
   reasons for more flexible addresses namely the problems and
   opportunities for Internetworking with Independent Network Address
   Spaces (IINAS).

   To better enable such internetworks, this memo proposes a framework
   for a Functional Addressing model.  This model also intends to
   support several other addressing goals including programmability and
   multiple semantics.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on January 13, 2022.

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Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Disclaimer  . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Challenges  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  High level observations . . . . . . . . . . . . . . . . .   4
     2.2.  Internetworking limited domain networks with IP
           addressing  . . . . . . . . . . . . . . . . . . . . . . .   5
     2.3.  Shorter addresses . . . . . . . . . . . . . . . . . . . .   8
     2.4.  Additional semantics  . . . . . . . . . . . . . . . . . .   9
     2.5.  Programmability . . . . . . . . . . . . . . . . . . . . .  10
   3.  FA-IINAS: Functional Addressing (FA) for Internetworking with
       Independent Network Address Spaces (IINAS)  . . . . . . . . .  10
     3.1.  Addressing for unicast  . . . . . . . . . . . . . . . . .  11
     3.2.  Forwarding  . . . . . . . . . . . . . . . . . . . . . . .  11
       3.2.1.  Dispose Function  . . . . . . . . . . . . . . . . . .  11
       3.2.2.  Steering Function . . . . . . . . . . . . . . . . . .  12
       3.2.3.  Multiple semantics  . . . . . . . . . . . . . . . . .  12
       3.2.4.  Internetworking Function  . . . . . . . . . . . . . .  13
     3.3.  Control Plane . . . . . . . . . . . . . . . . . . . . . .  16
       3.3.1.  Unicast routing . . . . . . . . . . . . . . . . . . .  16
       3.3.2.  Naming  . . . . . . . . . . . . . . . . . . . . . . .  17
       3.3.3.  Routing . . . . . . . . . . . . . . . . . . . . . . .  18
       3.3.4.  Routing policies  . . . . . . . . . . . . . . . . . .  19
     3.4.  Hardware considerations . . . . . . . . . . . . . . . . .  19
       3.4.1.  Forwarding plane simplicity . . . . . . . . . . . . .  19
       3.4.2.  Optimizing for smaller networks . . . . . . . . . . .  20
       3.4.3.  Maximum address sizes . . . . . . . . . . . . . . . .  21
     3.5.  Example packet header encoding  . . . . . . . . . . . . .  21
   4.  Inspirations  . . . . . . . . . . . . . . . . . . . . . . . .  22
     4.1.  E.164 . . . . . . . . . . . . . . . . . . . . . . . . . .  22
     4.2.  MPLS  . . . . . . . . . . . . . . . . . . . . . . . . . .  25

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     4.3.  Segment Routing SR-MPLS / SRv6  . . . . . . . . . . . . .  25
     4.4.  Research  . . . . . . . . . . . . . . . . . . . . . . . .  26
   5.  Summary and conclusions . . . . . . . . . . . . . . . . . . .  26
   6.  Informative References  . . . . . . . . . . . . . . . . . . .  27
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  30

1.  Introduction

1.1.  Overview

   Recent work has examined the value of more flexible than fixed-length
   addressing used in IPv4 (32 bit) and IPv6 (128 bit), see for example
   [I-D.jia-intarea-scenarios-problems-addressing], and

   The reasons for this interest include both support for multiple and
   potentially novel address semantics, see for example
   [I-D.king-irtf-semantic-routing-survey] and
   [I-D.king-irtf-challenges-in-routing], but also optimizations of
   addressing for existing semantics, such as unicast, that are tailored
   not for the global Internet but to better support private networks
   and limited domains ([RFC8799]).

   This memo describes one, in the view of the author yet little
   explored reason, for more flexible addresses namely the problems and
   opportunities for Internetworking with Independent Network Address
   Spaces (IINAS).

   To better enable such internetworks, this memo proposes a framework
   for a Functional Addressing model.  This model also intends to
   support several other addressing model goals including
   programmability and multiple semantics.

   This memo calls the addressing model functional, because addresses
   are constructed as a structure of

1.2.  Disclaimer

   Any proposals made by this document are explicitly for the purpose of
   presenting example options of realizing concepts introduced in the
   memo.  There is no intent for any proposals in this document to
   directly become anything more than just experimental implementations
   for proof of concept purposes.  Equally so or even more so, readers
   are welcome to pick up any subset of ideas from this memo that they
   are interested in and reuse it in other designs.

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2.  Challenges

   This section discusses challenges that gave rise to the proposal in
   this document.  It explores in more detail the core challenge not
   well explored elsewhere and already detailled elsewhere.

2.1.  High level observations

   There are three core challenges we can observe that limit the ability
   to build more varied internetworking solutions for non-solely
   Internet use-cases with especially IPv6:

   o  Fixed size address space: IPv4/IPv6 address space is fixed length,
      not allowing to adopt address length to shorter or longer demands.
      While it is possible to add more addressing via extension headers,
      there is no option to not send, or shorten the IPv4/IPv6 base
      header addresses, when they are not required.  While the reasons
      for fixed size addressing in IPv4/IPv6 can be understood for the
      feasible high-speed, low-cost forwarders of the 1900th, when IPv6
      was conceived, these reasons are today (in the opinion of the
      author) as obsolete as ATM cells where by the end of the 1990th
      when both hardware forwarding and mathematical models allowed to
      provide all ATM type QoS with variable sized packets.

   o  The Internet as the primary, if not only use-case driving the
      design: The address space semantics provided especially by IPv6 is
      very much focused on the one use-case that drove the development
      of IPv6: The Internet.  While it was and will continue to be th
      core and sufficient reason for maintaining IPv6, it is not
      sufficient in the opinion of the author for the much broader use
      of IPv6.  As of today, a likely overwhelming number of hosts using
      TCP/IP(v6) protocol stacks are not "on the Internet" and the
      majority likely is not even "connected to the Internet", but
      instead, they are part of limited domains.  This even includes
      many routers in large service providers that are used to service
      Internet traffic.  Routers in these networks are only in networks
      that may be called an "underlay" limited domain networks using
      MPLS, SR-MPLS or SRv6 and Internet traffic is tunneled across
      them.  When the network design is secure, those routers are
      neither "on" the internet nor "connect to" the Internet.

   o  Transparent end-to-end addressing at the core of the IP/IPv6
      protocol design, but an ever more diverse reality breaking that
      design for good reasons: The current core principle of IPv4 and
      IP6 is that forwarders have to be passing network layer (IPv4/
      IPv6) addresses transparently and are not allowed to touch/
      modifying them.  This is the core behavior to support primarily
      the Internet use case.  Yet, the IPv4 Internet today would not

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      work without NAT, and arguably, the same may also happen to the
      IPv6 Internet, especially when networks attaching to inexpensive
      Internet offerings want to avoid complex src/dst forwarding for
      IPv6 multihoming, and/or avoid renumbering upon change of provider
      addresses.  Even more so, interconnecting IPv4 and IPv6 networks
      has resulted in no fewer than 24 IPv4/IPv6 NAT solutions (see
      https://en.wikipedia.org/wiki/IPv6_transition_mechanism), giving
      rise to the question if and how on-path processing of addressing
      can be proactively become part of future addressing designs to
      support more flexible internetworking - translating the best of
      past NAT experience into better future designs.  This is a core
      option of what FA-IINAS can do.

2.2.  Internetworking limited domain networks with IP addressing

   One of the core challenges of the existing IP(v4) and IPv6 addressing
   model are the addressing they provide for private networks with or
   without connectivity to the Internet, which are also called limited
   domain networks [RFC8799].

   One reference example is that of networking inside a particular
   product/solution/installation, and then compositing this product with
   other products, probably even multiple times, hierarchical, as show
   in picture Figure 1.  These type of designs are traditional in
   industrial networks.  Similar issues and solutions can be found in
   networks with multiple layers of NAT such as Home Networks that are
   dorm rooms connected via NAT to a dorm network, connected via another
   NAT to a campus network, connected via yet another NAT to maybe
   finally, the Internet.  Similarly designs can happen with more
   complex topologies in federated private networks.

   In pre-IP industrial networks, individual products were hiding their
   interior elements by some (combination) of elements that controlled
   the interior behavior completely and provided only an abstracted view
   of the machinery to the outside.

   With the introduction of IP networking into these type of solutions,
   the ability for gateways to become IP routers and providing
   connectivity into the machinery throughout the larger internetwork
   opened up many important improvements, but of course also challenges,
   especially for security.

   Benefits of network layer internetwork connectivity includes options
   such as control loops that can more easily be built across multiple
   components/levels of the hierarchy and controllers that can be pulled
   out of machinery and positioned elsewhere in the network, enabling
   virtualization and resource multiplexing.  Multiple independently
   running control systems can be implemented in parallel, including

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   solutions like device vendor preventive maintenance telemetry,
   operator managed firmware update or third-party orchestrated security
   audits or intrusion detection/prevention, just to name a few.

   With IP connectivity, all this can be built without the need of
   understanding how to get through various layers of fixed-
   functionality higher-than-network layer gateways that can not be
   extended by third parties.  Instead, new designs are based on end-to-
   end IP connectivity - plus appropriate set of security mesures at
   gateway routers, of course an appropriate set of security/filtering
   measures, for example MUD, [RFC8520].

   |                               Controller / Gateway->Router        |
   |   ...                                  |                          |
   |                                --+-----+----------++..++---+----  |
   |                                  |                         |      |
   |+---------------------------------+----------------+    +---+-----+|
   ||                                 |                | .. | System 5||
   ||                  Controller / Gateway->Router    |    +---------+|
   ||                                 |                |               |
   ||            -----+---------------+-+..+----+----- |               |
   ||                 |                         |      |               |
   ||+----------------+--------------+    +-----+-----+|               |
   |||                |              | .. | Machine 6 ||               |
   |||             Gateway->Router   |    +-----------+|               |
   |||            controller         |                 |               |
   |||                |              |                 |               |
   ||| --+--------+---+--+------+--- |                 |               |
   |||   |        |      |      |    |                 |               |
   ||| actor1 sensor1 actor2 sensor2 |                 |               |
   |||                               |                 |               |
   |||   Machine 1                   |                 |               |
   ||+-------------------------------+                 |               |
   ||  System1                                         |               |
   |+--------------------------------------------------+               |
   |  Installation 1                                                   |

           Figure 1: Example hierarchical composed internetwork

   In the opinion of the author, the most easily adopted addressing
   architecture in these type of solutions today is also the one widely
   used: IPv4 with [RFC1918] addresses.  These addresses are actually
   owned permanently for each deployment case - as long as the scope of
   addressing is well defined.

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   In result, a common scheme of addressing in machinery such as the one
   shown in Figure 1 is to reuse the same or
   addresses for every instance of a product/machinery manufactured.  In
   the example, actor1 could use, sensor1 and so on.
   But equally, if Machine 3 was the same or similar, its internal
   components would share the same machinery.  And when hundreds of
   these products are produced, hey would all have the same addresses.

   To allow deployment and composing those type of machineries, the
   router/switch connecting to the outside/next-level in a hierarchy
   will need simple NATing function for example statically mapping the
   10.0.0.x on the inside to 10.0.1.x on the outside for Machine 1,
   where the same router/switch for Machine 3 would be configured to NAT
   from 10.0.0.x to 10.0.3.x.  And likewise at the next layer of
   hierarchy, 10.0.y.x could be mapped to 10.z.y.x with a different y
   for every instance.

   In support of solutions like this, many if not most industrial
   ethernet switches deployable as machinery gateways do therefore
   support this type of static NAT mappings.  Likewise, common practices
   in industries rely on this addressing with composition via NAT
   approaches, including machineries as large as production lines or in
   transportation networks train cars and all their included

   The desire to avoid NAT in IPv6 and availability of sufficient
   addressing space lead to replacing the concept of [RFC1918] in IPv4
   with the concept of Unique Local Addresses (ULA) in IPv6,
   standardized in [RFC4193].  Instead of the few scoped prefixes of
   [RFC1918], ULA provide for 2^40 different prefixes, and the design
   guidelines are theoretically simple: pick a random prefix and then
   you can interconnect your networks later on with a very low
   probability of address prefix collision/reuse.

   Unfortunately, low probabilities of address collision is not a good
   design principle for most of these type of environments because there
   is really no good operational solution what do if such collision
   occurs, and rare errors are also very hard to build resilient
   solutions for.  Also the probabilities begin to become much higher
   when not looking at a connection of just two or few of such ULA
   networks, but when there can be thousands of such networks, such as
   in the transportation networks use case.

   In result, ULA is not very persuasive for many such deployments,
   especially when the alternative with IPv4 is address prefix mapping
   as required for NAT, when NAT an an almost free provisioning side
   effect of setting up the required connectivity via permit lists via
   network/transport filters.  The need to automate such in-network

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   filtering to secure such deployments can also be seen in the advent
   of MUD, [RFC8520].

   If one considers that most of these subnet networks will have fewer
   than 253 hosts connected to it, then the IPv6 ULA solution does also
   not provide for any more bits for subnets than the 16 bits of z.y in
   the above example using IPv4 10.z.y.x with x being the host part: The
   lower 64 bits of the IPv6 address is hard to use for anything than
   the host parts with non-router hosts.  The whole ULA prefix is 48
   bits, leaving just 16 bit (128 - 64 -48).  Add to that the non
   insignificant IPv6 packet header overhead plus fewer availability of
   NAT in IPv6 products because it is assumed to be less required, plus
   the insufficiency of "low likelihood of collisions" when attempting
   to utilize only ULA.

   Vendors of equipment that have assigned Provider Independent IPv6
   address space could of course allocate addressing from that space for
   equipment they manufacture or integrate, whether it is globally
   unique or "generic", e.g.: reused across every instance of a product
   and hence requiring NAT.  Unfortunately, and unlike ethernet, where
   one actually does own addresses after buying an OUI, assigned IPv6
   addressing is not permanent, and even though revocation of address
   allocation is not standard practice, standardized solutions for
   global IPv6 address space (like IPv4 global address space) really
   need to allow the ability for those addresses to be returnable
   instead of being handed off in products to customers.

   Even though in hindsight, the hierarchical address allocation from
   the available 16 bits in 10.x.y.z for two layers of interconnections
   in the above example looks obvious and simple, in many cases the
   creation of multiple hierarchies is only an afterthought and the
   fixed address length and prior suboptimal assignment of addressing in
   a deployment will cause the need for a lot of re-addressing.  This is
   a recurring problem in larger enterprise/commercial networks under
   unplanned growth or mergers & acquisitions, especially of course in
   IPv4.  Likewise, once the 16 available bits in the above described
   NAT approach are used up, whether it is IPv4 or IPv6 with ULA, no
   further extensions of the design are possible.

2.3.  Shorter addresses

   As has been noted in prior memos, shorter addresses than IPv6 128 bit
   are highly desirable in private networks / limited domains whenever
   it is clear that the total required addressing space is much smaller
   and connectivity to e.g.: the Internet is not required.  Evidence of
   such requirements can be found for example in header compression for
   IoT networks such as [RFC6282].  Such compression introduces yet
   another layer of complexity - the whole ecosystem of devices and

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   diagnostic options has to support it to be equally acceptable as
   uncompressed packets.

2.4.  Additional semantics

   New semantics can only be introduced into existing IPv4/IPv6 when
   their required address size fits nicely into the 32 or 128 bit
   address space.

   This section does not aim to be complete, see
   [I-D.king-irtf-semantic-routing-survey] for a broader survey.
   Instead it will provide additional levels of details for the benefits
   of fittingly sized addresses for few examples, that the author is
   familiar with.

   When ignorin Anycast, IP Multicast is likely the most widely adopted
   additional semantic added to IPv4.  With IPv6, IP Multicast became
   even more flexible and easy to deploy, because the additional bits of
   IPv6 addresses allowed to encode additional IP multicast parameters
   through additional fields in IPv6 addresses: Scope address field
   [RFC4291], SSM addresses [RFC4607], Unicast prefix multicast
   addresses [RFC3306] and embedded-RP [RFC3956].  Nevertheless,
   especially embedded-RP could have benefitted from even longer
   addresses because with the 128 bits available the solution had to
   take a hit in the complexity of deployment.  It requires to engineer
   that RP address such that its non-0 host port is very short (4 bits).

   In contrast, Bit Indexed Explicit Replication (BIER) which started in
   the IETF in 2014 and resulted in the architecture [RFC8279], did not
   choose the option to integrate into IP/IPv6 because it desired
   addresses sizes of at least per-network configurable from 64 to 4096
   bit plus additional qualifiers of at least 16 bits (so-called SD, SI
   address qualifiers).  This made it necessary for BIER to (re-!)invent
   its own network layer packet header, [RFC8296] which duplicates
   pretty much all packet header fields of MPLS plus IP packets plus
   additional BIER header fields, so that it can be used in both MPLS
   and non-MPLS networks.

   Similar arguments about the limited size of IPv6 address could likely
   be made for ICN/CCN networks because the semantic of their addresses
   is that of data items such as time slices of specific spatial and
   temporal resolutions of some media such as an audio/video recording -
   and those name spaces would ideally have addresses as long as URLs.

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2.5.  Programmability

   Segment Routing via IPv6 (SRv6) introduced with [RFC8986] and
   [RFC8754] (SRH) and architecture in which source routing with an IPv6
   extension header is combined with encoding of additional processing
   semantics into the destination and source routing hops IPv6
   addresses.  SRv6 calls this programmability.

   SRv6 is a very flexible and theoretically extensible concept but
   challenged by the fixed address length design of IPv6.  For most
   steering hop addresses, the bits reserved for this additional packet
   processing are not required, but when they are required there may
   even be too few bits available.  Variable length addresses allowing
   for variable long programming field in the address would in the
   opinion of the author be highly beneficial.

   One evidence for the programmability bits seen as wasteful in many
   cases is a variety of currently proposed drafts to provide more
   compressed source routing options for SRv6 (as of mid 2021).

3.  FA-IINAS: Functional Addressing (FA) for Internetworking with
    Independent Network Address Spaces (IINAS)

   This section outlines an addressing design that attempts to solve the
   above described challenges and calls it tentatively FA-IINAS.
   Functional Addressing refers to the design aspect that addresses in
   this design can be interpreted as functions with parameters.

   Notwithstanding other granularities or options, this document assumes
   that addresses are textually represented in hexadecimal and that the
   minimum structure element of an address is 4 bit so that the
   different structural elements of an address can simply be shown as
   concatenation of hex digits.  The "." character is inserted
   optionally to show where in an address one semantic part ends and
   another starts.

   Like in IPv6 IoT networks, such as those using RPL ([RFC6550]) as
   their routing protocol, this memo starts by assuming all nodes are
   routers and that addresses are predominantly node addresses as
   opposed to IP/IPv6, which defines unicast addresses to be interface
   addresses.  This is but an academic differentiation, because node
   addresses can also be represented as interface addresses of so-called
   "loopback" interfaces.

   A network in this design is an independent address space, not shared
   with other networks.  A nework has theoretically unlimited long
   addresses whose prefixes are mapped onto the nodes of the network,
   which are expected to form a graph of transitively connected nodes.

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   Practical limits to address length are subject to acceptable

3.1.  Addressing for unicast

   Each node is assigned one or more node prefixes from the networks
   address space and none of these node prefixes can be overlapping.  In
   other words, no assigned nodeprefix can be a prefix of another
   assigned nodeprefix.  This rule ensures that every node "owns" any
   address equal or longer to its assigned nodeprefix.  Allocation of
   node prefixes is currently out of scope for this memo but could rely
   on any well-known methods including manual operator assigned, SDN
   controll managed, or as initially described in this document assigned
   by manufacturer/vendor.

   Routing in a network is assumed to enable forwarding across the graph
   of the network to the node owning the nodeprefix of the address.

   Given variable long addresses, the first observation of this
   addressing scheme is that it allows to combine short addresses with

   In a simple example the first 200 nodes are assigned addresses 01 ...
   c8, at which point in time the network operator gets worried about
   growth exceeding the 256 mark and starts to assign longer addresses:
   c90 ... f000, at which point in time ever increasing success might
   cause assignment of even longer prefixes.

   Addresses longer than the assigned "nodeprefix" are used to
   instantiate a specific function on the node itself.  A generic
   representation of an address could be

3.2.  Forwarding

3.2.1.  Dispose Function

   When using a single digit function field, function = 0 could for
   example be "dispose" to decapsulate the packets payload and deliver
   it to the host stack.  Parameter could for example be the next-
   protocol value, eliminating the need to have a separate packet header
   field for this parameter.

   While not being the same crucial issue as for the node prefixes
   themselves, putting the next-protocol into the address makes it
   extensible too, so one would not run out of a 256 space as IPv4/IPv6
   might do at some point.

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3.2.2.  Steering Function

   Command = 1 could be a "steer" command and the parameter is another
   address.  To act on the command, the node would strip the nodeprefix
   and command part of the address and forward it based on the address
   parameter.  For example node 73 (e.g.: node with nodeprefix 73)
   receives a packet with destination address  It
   forwards the same packet with the stripped destination address to node 55, which likewise forwards the packet with
   stripped destination address 33.0 to node 33, which ultimately
   receives it.

3.2.3.  Multiple semantics

   To introduce additional semantics into a network, such as for example
   multicasting, we need to generalize how to interpret the first part
   of the address, which so far was only interpreted to be a nodeprefix
   for unicast forwarding.

   address = prefix{.nodefunction{.nodefunction-parameters}}
   prefix = semantic{.semantic-parameters}

   semantic / = unicast-forward

   unicast-forward = <set of prefixes>
   unicast-forward-parameters = node-prefix

   semantic /= multicast-forward
   multicast-forward = <set of prefixes>
   multicast-forward-parameters = multicast-group

                                 Figure 2

   In other words, the prefix at the start of the address is composed of
   a semantic and its parameter, and the case discussed so far is simply
   the unicast-forward semantic followed by a node-prefix parameter.

   Again, semantic can be an arbitrarily long or short prefix, but no
   semantic can be a prefix of another semantic.

   In a practical example, this scheme is easily applied to existing
   IPv4 / IPv6 address spaces.  For IPv4:

 unicast-forward = 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D
 multicast-forward = E

                                 Figure 3

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   In other words, because IP multicast uses addresses, its
   non-overlapping semantic prefix is E, and IPv4 unicast addresses use
   the non-overlapping prefixes 0...D.  Assume further that a node in
   the network had assigned prefix, then this would
   translate in our scheme into:


                                 Figure 4

   When a node processes this address, the 4-bit prefix 0 indicates that
   the following prefix has to be looked up in unicast forwarding.  This
   prefix is A0000.  Once the packet is delivered to the node, he
   remaining 8 bit XX can accordingly be interpreted by the node as a
   nodefunction with parameters.

   Likewise, an address would translate into E.F010203, so the
   first 4-bit E value would indicate that multicast forwarding needs to
   be applied to the rest of the address, and with IP Multicast
   forwarding not having further structure (ignoring willfully for
   simplicity of the example that it does, for example with SSM), all
   the remainder of the IPv4 address is the multicast-group

   In summary, the logic does really only generalize what routers today
   already do when they do prefix lookups, except for the following core

   o  In IPv4/IPv6, the address semantic is hard-coded by IETF
      standards.  In FA-IINAS they are definable by every network.

   o  In IPv4/IPv6, there is no notion of nodefunction{.nodefunction-
      parameters}, only SRv6 has this concept.

   In actual IPv4/IPv6 hardware forwarding lookups, one would not do one
   lookup for the semantic, followed by another lookup for the semantic-
   parameters for the case of unicast-forward, instead this would be
   flattened.  The same type of flattening would of course be useable in
   FA-IINAS.  Whether or how flattening or other optimizations are
   feasible for other semantics such as multicast is of course highly
   semantic and node implementation specific.

3.2.4.  Internetworking Function

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   .  Network1                    .
   .                R1            .
   .        R2      21      R3    .
   .        23              23    .
   .    R4              R5        .
   .    24              25        .
   .    ||2.2       2.2//\\2.3    .
        ||           //    \\
   .....||..........//.  ...\\........
   .    ||2.1   2.1// .  .2.2\\2.1   .
   .    R4        R5==========R5     .
   .    14        15  .  .    15     .
   . R6       R7      .  .       R10 .
   . 26       27      .  .       21  .
   .                 .  .            .
   . Network2       .  .  Network3   .
   .               .  .              .
   .    R9        .  .     R8        .
   .    21       .  .      23        .
   . 2.4||      .   .  2.4//\\2.5    .
   .....||.......   .....//..\\.......
        ||              //    \\
        ||             //      \\
   .....||............//. ......\\....
   .    ||2.1     2.3// . .   2.3\\  .
   .    R11        R8============R8  .
   .    11        12 2.5. .   2.4 11 .
   .          R12       . .          .
   .          12        . .  R13     .
   .                    . .  13      .
   .                    . .          .
   . Network4           . . Network5 .
   ...................... ............

                     Figure 5: Internetworking example

   Figure 5 shows an example internetworking topology of 5 networks,
   each with its own independent address space.  Globally unique Rxx
   numbers are used to refer to routers.

   An edge node is a router that has prefixes from two or more networks
   into which it connects.  In the example, R4 connects into Network1
   with prefix 24 and into Network2 with Prefix 14.  Likewise, R8
   connects into Network3 with prefix 23, into Network4 with prefix 12
   and into Network5 with prefix 11.  An edge node can be a router
   simply with different interfaces into different networks, or it can

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   be decomposed into multiple devices, each in a separate network.  In
   this section we describe behavior as if it was a single device.

   For an edge node to pass a network into a separate network, the
   internetworking function on the node has to be called.  In the
   example, this function is codepoint 2 on all edge nodes, and the
   first parameter is an identifier of local relevance for the network
   into which to pass the packet.  In actual deployment, this function
   number can of course be locally significant to the Network and/or
   even each edge router, assuming appropriate control plane to assign
   the number to this function.

   Assume R12 (12) in Network4 wants to send a packet to R1 (21) in
   Network1.  To send it R12->R8->R5->R1, R12 would have to use a
   destination address of, or numerically without
   separators 0x12231521210.

   12 will route the packet in Network4 towards R8 because of the
   destination address 12/8 prefix. .2 indicates to R8 that it should
   invoke the interworking function and pass the packet into Network 3.
   As part of the interworking function, R8 then strips all the address
   prefix it has processed so far from the destination address, leaving  R8 then forwards the packet with this destination
   address into Network 3, where it will be received by R5, which again
   invokes the interworking function due to .2, forwarding the packet
   into Network1, stripping from the destination address and
   forwarding the packet with destination address 21.0 into Network1,
   where it will finally be received by R1 which passes the packet to
   its host stack because of dispose function 0.

   To (optionally) allow for a return path, each edge node could equally
   but inversely process the source address: When R12 sends the packet,
   it would indicate a source address of 12.0.  When R8 passes the
   packet via its interworking function into Network3, it would prepend
   its return path interworking function address, making the source
   address, where 23 is R8 address prefix in Network3 and
   2.4 internetworking function to return the packet into Network4.
   Likewise, when R5 processes the packet by its interworking function,
   it would prepend its return path address element to the source
   address, before sending the packet into Network1, making the source
   address  This is then the address to which R1
   could send return packets, and likewise, on its way towards R1, the
   address, for example when travelling via Network3 always has a
   returnable source address.

   With this behavior of the interworking function, it is obvious, that
   address management of networks would want to keep a sufficiently
   large number of very short prefixes, such as those in this example or

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   even shorter to address the interworking function in a sufficiently
   larger number of edge routers so that a complete internetwork path
   address will not become too long to exceed the maximum address

3.3.  Control Plane

   This section reviews a range of control plane considerations
   necessary to build a working solution out of the functional
   addressing.  In short, what is required for functions to be flexibly
   configurable and extensible in the network, it requires a control
   plane that in its principles is very much based on what was learned
   in MPLS.

3.3.1.  Unicast routing

   FA-IINAS expects a control plane that supports routing for unicast-
   forward parameters (address prefixes) in the same way as it is done
   today for IPv4/IP6.  Except that it would be for address prefixes
   (multicast-forward-parameter) of different length and not limited to
   just 32/128 bits as in IPv4/IPv6.

   In addition, FA-IINAS needs control-plane functions that allow
   defining the semantics and their prefixes, like the above example of
   0...D for IPv4 style unicast-forwarding semantic and D for IPv4 style
   multicast-forwarding semantic.

   One of the core challenges for this control plane function is that
   inconsistency between nodes can have significant different negative
   impacts than the today accepted "eventual consistency" in IPv4/IPv6
   unicast routing that is achieved by the most widely deployed unicast
   forwarding control planes: distributed routing protocols (IGP/BGP).

   The degree of concerns will highly depend on the actual new issues
   that could happen in the face of inconsistencies, and this can only
   be vetted with a given set of semantics.

   In a most simple example, semantics may simple be configurable via a
   management plane, and such an approach can be pre-staged, pre-
   configured, validated network devices, such as in industrial or
   embedded environments.

   In the case of a most flexible, agile type of network, control plane
   mechanisms would have to be extended to support strong consistency
   models, for example through node-to-node security associations
   coupled with a strong consistency network-wide-core-config mechanism.
   Such mechanisms could in the opinion of the author easily be built on
   the framework provided by [RFC8994] which provides these hop-by-hop

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   security associations and inband control plane infrastructure,
   coupled with [RFC8990] as the protocol to negotiate the configuration
   with strong consistency.

3.3.2.  Naming  Intra network naming

   In FA-IINAS, nodes are acting as routers, and the addresses described
   are assigned to them persistently.  This eliminates in many cases,
   especially when the network is primarily for m2m communications the
   need for DNS names, because effectively the address of a node is its
   persistent name.

   In networks small enough, e.g.: maybe <= 20,000 nodes, the very same
   argument can also apply to nodes that are hosts, e.g. without the
   need to support full routing/FA-IINAS operations, but still having a
   persistent address assigned that is routed in the networks routing

   If indeed there is a need to use DNS or other naming schemes, then
   this is no different than applying naming with DNS to today's
   [RFC1918] addresses.  Simple inter network naming

   The need to support (DNS) names is equally lower in interconnected
   FA-IINAS networks assuming the intra network naming arguments
   outlined before apply to the interconnected networks.

   Because an address in a different FA-IINAS network is dependent on
   the path from/to its corresponding peer, it is of course not
   sufficient to simply have a global internetwork name to address

   One of the likely oldest solutions is to align name resolution with
   packet forwarding so that the very same edge nodes between two
   networks that do translate addresses can accordingly also translate
   their name resolution.  This was productized and fairly widely
   deployed as early as the late 1990th for IPv4 with rfc1918 addresses,
   see for example [CiscoNAT].

   This type of solutions relies on well-known routing policies such as
   simple hierarchical routing though and are not generic for arbitrary

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3.3.3.  Routing  With internetwork topology knowledge

   When FA-IINAS networks are connected in an arbitrary topology instead
   of a simple hierarchy, the fundamental problem is that of
   constructing the address of a target peer as a path through a set of
   appropriate network edge nodes in the address, followed by the nodes
   address within its network.

   In many interconnected FA-IINAS networks, one can assume to have
   systems that can do this, such as in an industrial setting where a
   global view of the topology of networks exists and a PCE/SDN-
   controller will choose the path and can accordingly calculate also
   the addresses from the path.  With internetwork naming knowledge

   A decentralized solution can be built by relying on a combination of
   naming and internetwork routing.

   Every network (name space) is assigned a globally unique identifier.
   This identifier is only used in the control-plane, so it should be
   reasonably easy to have a set of construction mechanisms allowing
   everyone to easily create its own namespace, such as for example from
   some owned location (street address) and/or other owned names/

   When a global naming system like DNS then exists, an FA-IINAS address
   is the combination of FA-IINAS network identifier and address within
   that network.

   Across the interconnected FA-IINAS networks, the edge-routers would
   operate extended versions of a protocol like BGP through which any
   party can calculate desired paths.  The extensions would include the
   FA-IINAS network identifiers and address prefix mapping rules of the
   edge-nodes, thereby allowing to also calculate addresses from FA-
   IINAS network identifiers and address.

   When large number of small networks (such as users homes) connect to
   larger networks (such as an ISP), those ISP would be concerned of
   having to propagate millions of small FA-IINAS network mappings into
   BGP.  This is not done today with IPv4/IPv6, and it would not scale
   any better with FA-IINAS.  Instead, the fact that the home network
   would be reachable with one or more ISP could be done by also
   creating naming system mappings from the home networks identifier to
   the identifier and address prefix mappings of the ISP to which the
   home network is connected.

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   When a peer looks up a name and retrieves an FA-IINAS address but
   cannot find the FA-IINAS network identifier in its internetwork
   routing information, it can instead resolve it to the "next higher
   up" ISP FA-IINAS network-identifier/prefix - and recurse this until
   it has routing information.

   Likewise, when a peer does not have any routing information (because
   it does not participate in internet routing information), it has to
   forward the appropriate resolution request hierarchically upward.

   In summary, it would be architecturally "easy" to extend DNS and BGP
   with the necessary extensions to resolve names to FA-IINAS addresses
   and construct relative FA-IINAS addresses from this information.

3.3.4.  Routing policies

   Note that this "easy" part does not include the possible desire to be
   more or less flexible in path selection.  Whereas today, packets,
   once they enter "the Internet" are not under steering control of the
   sender but under "hop by hop hot-potato steering" control of the ISP,
   with FA-IINAS this may be different - or the same.  If a sender then
   constructed an FA-IINAS address implying an internetwork path that
   was not desirable for this traffic by the indicated transit networks,
   this would cause an error.  Therefore, the above outlined procedures
   hinted at relying on the internetwork routing information whenever
   available and only resort to using naming system to fill in the
   additional (edge) information.

   Today it is becoming more common to use alternative than "native
   Internet" paths by steering traffic across virtual/container routers
   in cloud DC, many of which have ample and underutilized international
   connectivity.  However, additional charges for compute and forwarding
   will apply.  These type of high-overhead solutions could be replaced
   by FA-IINAS to steer traffic across such additional networks and
   without the need to instantiate VM/containers.  It would require
   appropriate and lightweight identity and accounting forwarding plane
   packet header information so that those additional charges could be

3.4.  Hardware considerations

3.4.1.  Forwarding plane simplicity

   Forwarding of FA-IINAS packets based on destination address is the
   same type of prefix lookup on the destination address as it is today
   in IPv4/IPv6, except that the maximum lookup prefix can be shorter or
   longer, this is detailed in the next section.

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   The steering function should have a lookup complexity whose
   complexity is in the order of SR-MPLS or even simpler.  It can
   constitute of a prefix lookup in the same forwarding table as non-
   steered forwarding, but the adjacency would then have to strip the
   looked up prefix from the destination address (comparable to MPLS
   label pop) and forward the packet again based on the remainder of the
   destination address - unless additional on-node service functions
   have to be invoked.

   The interworking function is very much like the steering function,
   but it also prepends a return prefix to the source address field,
   making it the most expensive forwarding plane operation.

   In general, the author assumes that packet processing that strips a
   prefix from the destination address and optionally adds a prefix to
   the source address is well feasible in next generation, highest-
   speed, lowest-cost forwarding engines.

   Optimizations beyond this are possible but would break the
   independent address allocation across networks.  For example, if it
   is possible for an edge node to have the same prefix length across
   the networks it connects to, and source address follows destination
   address in the packet encoding, then stripping the destination
   address could be achieved by shifting the destination address in a
   contiguous packet buffer, making head for the source address prefix
   to be prepended to the following source address field.

3.4.2.  Optimizing for smaller networks

   One of the benefits of FI-IINAS is that it allows to adopt the
   address space size based on the requirements of networks and
   therefore also allows to optimize hardware known to be built/sold
   only into limited size networks, such as many industrial and almost
   all embedded networks.

   For example, low-cost, high-speed hardware forwarding might be
   possible to design less expensive with just 16 bit lookups instead of
   for up to 128 bit lookups, as may be required for IPv6.  Equipment
   could be sold with that profile parameters "for networks with up to
   2^16 nodes".

   Because of the way FA-IINAS is designed, a limit to 2^16 nodes does
   not mean that FA-IINAS addresses are only 16 bits.  Instead they can
   still be "arbitrary" long (where arbitrary is subject to a discussion
   point further below in this section).  Just the length of the
   unicast-forward part of the address is limited to 16 bits.

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3.4.3.  Maximum address sizes

   The permissible maximum size of source and destination address are
   primarily subject to the header size that inexpensive hardware
   forwarding can examine and modify.  For future generations, this
   might likely be as much as 512 bytes, so to optimize hardware lookup
   it might be interesting to consider the option of carrying the
   addresses not consecutively, but carry them as

3.5.  Example packet header encoding

   The following encodings propose a couple of ideas that could be
   interesting in addressing.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
|Version|VE |ECN| DestAddrLen   | SrcAddrLen    | Hop Limit     |
| Destination Address ...
| Source Address ...                                                            |

                 Figure 6: Example packet header encoding

   Version: A version number for this packet header from the same
   registry as the IPv4/IPv6 version number field.

   VE: Version Extension. 00.  Reserved for future variations of the
   header, such as new extension header formats if desired, so as to not
   use up any more than one Version code point.

   DestAddrLen: The length of the Destination Address field in bytes.
   Valid values are 1...255 bytes.  One byte minimum length is mandatory
   because of the need to indicate some semantic for processing the

   SrcAddrLen: The length of the Source Address field in bytes.  Valid
   values are 0...255 bytes.  The Source Address field is therefore

   ECN: See [RFC3168] and the documents updating it.

   Rsv: Reserved.

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   Hop Limit: As in IPv6

   Beside the variable length of the Source and Destination address
   fields and hence their length indications, the difference to the IPv6
   header are as follows:

   Only the two ECN bits are maintained from the IPv4/IPv6 Traffic Class
   field.  This is because in the majority of networks, the other 6 bits
   of Traffic Class, DSCP are not being used, and where QoS
   differentiation would be used, often additional or different QoS
   parameters may be required that are not supported by IPv4/IPv6.  Such
   a new network header would thus be a great opportunity to improve on
   QoS header parameters through a better QoS extension header, where it
   is needed (outside scope of this document), and not proliferate not
   ubiquitously used elements in the base header.  The same reason
   applies to removing the Flow Label field.

   ECN on the other hand is very fundamental for the majority of all
   traffic in Internet and limited domain networks.

4.  Inspirations

   This section reviews prior addressing and networking technologies
   that did inspire this memo and compares it with them.

4.1.  E.164

   E.164 telephone numbers traditionally worked (and may still work)
   similar to this mechanisms handling of addresses by adding and
   removing prefixes and allowing to grow networks hierarchically.

   In Germany for example a town/city might have had a subscriber
   numbering plan starting with 3 digit numbers and expanding over time
   into 5 digits. 0 was excluded as the first digit of any assigned
   number.  Let our example subscriber have number 1234

   When the phone systems of towns/cities where connected, dialing a
   different town/city would use a concatenation of the inter-city
   traffic discrimination code "0" followed by the dial code for the
   town/city, followed by the subscriber number.  Let our example town
   dial code be 4111, the subscriber number dialed from a different city
   would be 04111 1234.  Again, "0" was excluded as the first digit of a
   trunk prefix.

   When finally the phone systems of countries where connected, dialing
   a different country would use a concatenation of the international
   traffic discrimination code "00" followed by the country dial code,
   which in our example is 49 for Germany followed by the dial code for

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   the city, followed by the subscriber number - 0049 4111 1234 for our
   example subscriber.  Note that this number would of course only work
   when calling from countries that also do use "00" as the
   international traffic discrimination code.  When calling the number
   from the USA, one would have to dial 011 4111 1234, because the USA
   uses 011 as the internal traffic discrimination code.

   Of course, understanding foreign countries traffic discrimination
   code rules to reverse engineer a foreign telephone number so as to
   translate it to the according rules of the calling-from country is
   one of the problems that is leading more and more subscribers to
   prefer the absolute E.164 telephone numbers like +49 4111 1234.

   On the other hand, when the interplanetary telephone network will
   "soon" [I-D.draft-farrel-soon] arrive and there are not enough
   country codes available in Earth's existing numbering plan, one would
   have to find a way to attach prefixes in front of existing E.164
   numbers, something that E.164 likely cannot afford, but which would
   be possible with UPVLA.

   In our example the UPVLA address could be 0003 49 4111 1234 and a new
   solar system "absolute" address could be ++3 49 4111 1234.

   Obviously, Mercury has to get 1, Venus 2 and Earth 3 and so on, so
   that it would be easier to remember how to dial other planets than it
   is now to remember how to dial other countries.

   If one was to use the solution proposed in this memo to build the
   phone network addressing system with the example numbering plan, one
   could set up a multi-tiered internetwork as shown in Figure 7.

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    .                         .
    . Solar System network    .
    .                         .
    .  prefix "3"             .  |
    .  .....................  .  v strip 3 from dst, prepend 0 to dst
    ...| Planet Edge Node  ....    forward into global network
    .  .....................  .  ^ strip 0 from dst, prepend 3 to src
    .         prefix "0"      .  | forward into solar system network
    .                         .
    .                         .
    .  "global" network       .
    .                         .
    .   prefix "49"           .  |
    .  +-------------------+  .  v strip 49 from dst, prepend 0 to dst
    ...| Country Edge Node |...    forward into country network
    .  +-------------------+  .  ^ strip 0 from dst, prepend 49 to src
    .         prefix "0"      .  | forward into global network
    .                         .
    .  "country" network      .
    .                         .
    .   prefix "4111"         .  |
    .  +-------------------+  .  v strip 4111 from dst, prepend 0 to dst
    ...| City Edge Node    |...    forward into city network
    .  +-------------------+  .  ^ strip 0 from dst, prepend 4111 to src
    .         prefix "0"      .    forward into country network
    .                         .
    .  city network           .
    .                         .
    .     subscriber 1234     .

   Figure 7: Example internetwork for E.164 style address structure with

   Packets destined to an address starting with "0" would be routed to
   an edge node of the city network, which "owns" the "0" prefix, there
   that "0" prefix is stripped, but the cities own prefix of in the
   example "4111" is prepended to the source address, and then the
   packet is forwarded into the country network.

   When a packet is received from the country network on a city edge
   node, the opposite happens, the cities own prefix, e.g.: 4111 is
   stripped from the destination address and 0 is prepended to the
   source address, then the packet is forwarded into the city network
   and routed to the destination.  Which can generate return packets by
   just swapping source and destination addresses.

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   The same process will happen across 2 network tiers when a 00 prefix
   is used or even 3 network tiers, once we have (soon ;-) a Solar
   System Network.

   Of course, each tier and each instance of each tier can choose its
   own addressing scheme and prefixes for the edge routers.  It is left
   as an exercise to the reader for example to amend the example with
   its own home countries traffic discrimination codes.

4.2.  MPLS

   Adding/Removing or swapping prefixes is the core forwarding process
   step in Multiprotocol Label Switching [RFC3031].  Due to the time
   MPLS was designed, it had to have a very fixed size and functionality
   stack architecture, but as claimed in before, the author thinks that
   today an MPLS stack could easily be built just with the proposed
   addressing scheme address.

   Compared to MPLS, the proposed scheme does not mandate that that
   every steering address needs to contain QoS (EXP) and TTL fields as
   are present in MPLS Label Stack entries, but of course they would be
   equally possible as parameters of appropriate functions.

   Likewise the proposal does not think it is appropriate to require
   complicated scanning ahead into the address in search of Special
   Label Stack entries.  Therefore, FA-IINAS would require that any per-
   hop accessible information that is not included in the hops function/
   parameters would have to be carried would have to be carried in a
   separated extensions header.

4.3.  Segment Routing SR-MPLS / SRv6

   FA-IINAS can support more compact packet steering than SR-MPLS when
   the prefixes are accordingly chosen to be shorter than the 32 bits
   for an LSE.

   While it would be possible to emulate MPLS LSE by using prefixes of
   20 bit and following them with 12 bit of functional parameters
   indicating EXP and TTL, the proposal in this memo does not assume
   that transit routers would be able to act on those EXP or TTL bits.
   While it would be easily possible to define such additional transit
   hop semantic through extensions to the control plane, the author
   believes that the per-path parameters of TTL in a base header and
   more flexible QoS in an extension header is the more likely most
   useful option for these two functions.

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   In comparison to SRv6, FA-IINAS allows of course more compact
   representation of steering hops and also more easily few or many per-
   hop bits for programmability, as desired.

   What FA-IINAS does not provide for is to keep the sequence of
   steering addresses in the header up to the final receiver.  This
   might be useful for diagnostics, but it is seemingly not so important
   that it did stop the adoption of SR-MPLS, where the steering hops are
   likewise removed from the packet header when steering happens.

   Other functions than steering and per-steering hop programmability
   provided by SRv6 via SRH (such as its TLV for the receiver) are
   unaffected by this proposal and could equally be provided for by an
   SRH style extension header without the source routing part.

4.4.  Research

   [Haoyu] proposes a hierarchical addressing scheme and provides
   reviews in a lot more detail a set of other reasons for such
   addressing scheme.  That paper does not allow for arbitrary
   composition of networks without a clear hierarchy or root thereof, as
   FA-IINAS does.

5.  Summary and conclusions

   This memo introduces a simple but hopefully very attractive
   addressing scheme that leverages variable length address sizes with
   the potential for simple address prefix processing (push/pop/swap) on
   steering hops, service-function hops and especially network edge

   Push/pop/swap of network prefixes on network edge nodes allows to
   introduce a non-global internetworking address architecture that
   should make it a lot easier to build and manage many embedded,
   private or otherwise limited domain internetworks and optimize
   forwarding engines for a variety of different of these type of
   networks such as through known maximum network prefix lengths.

   When network addresses as in FA-IINAS become effectively internetwork
   path addresses, they also allow for a much wider range of possible
   routing policies.  In a time where the classical Internet with its
   "sender just gets one path", this can be a highly beneficial
   enhancement to explore (not that this was already proposed, maybe way
   ahead of its time and with vastly different mechanisms in solutions
   as early as [RFC1621], [RFC1622]).

   In this version of the memo, these are only limited considerations
   about how to refine details of the proposal to find incremental,

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   near-term deployment options, for example by using existing IPv6
   headers and using an unassigned prefix to define FA-IINAS addressing
   semantic into it (limited of course to 128 bit then).  These type of
   considerations can be subject for future revisions of this memo.

6.  Informative References

              Akkiraju, P., Delgadillo, K., and Y. Rekhter, "Enabling
              Enterprise Multihoming with Cisco IOS Network Address
              Translation (NAT)", 2000,

   [Haoyu]    Song, H., Zhang, Z., Qu, Y., and J. Guichard, "Adaptive
              Addresses for Next Generation IP Protocol in Hierarchical
              Networks", IEEE 2020 IEEE 28th International Conference on
              Network Protocols (ICNP), n.d..

              Farrel, A., "A Definition of the Term "Soon" for Use in
              Discussions with Working Group Chairs and Area Directors",
              draft-farrel-soon-07 (work in progress), March 2021.

              Jia, Y., Chen, Z., and S. Jiang, "Flexible IP: An
              Adaptable IP Address Structure", draft-jia-flex-ip-
              address-structure-00 (work in progress), October 2020.

              Jia, Y., Trossen, D., Iannone, L., Shenoy, N., Mendes, P.,
              3rd, D. E. E., and P. Liu, "Challenging Scenarios and
              Problems in Internet Addressing", draft-jia-intarea-
              scenarios-problems-addressing-01 (work in progress), July

              King, D. and A. Farrel, "Challenges for the Internet
              Routing Infrastructure Introduced by Changes in Address
              Semantics", draft-king-irtf-challenges-in-routing-03 (work
              in progress), June 2021.

              King, D. and A. Farrel, "A Survey of Semantic Internet
              Routing Techniques", draft-king-irtf-semantic-routing-
              survey-02 (work in progress), June 2021.

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   [RFC1621]  Francis, P., "Pip Near-term Architecture", RFC 1621,
              DOI 10.17487/RFC1621, May 1994,

   [RFC1622]  Francis, P., "Pip Header Processing", RFC 1622,
              DOI 10.17487/RFC1622, May 1994,

   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
              and E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP",
              RFC 3168, DOI 10.17487/RFC3168, September 2001,

   [RFC3306]  Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6
              Multicast Addresses", RFC 3306, DOI 10.17487/RFC3306,
              August 2002, <https://www.rfc-editor.org/info/rfc3306>.

   [RFC3956]  Savola, P. and B. Haberman, "Embedding the Rendezvous
              Point (RP) Address in an IPv6 Multicast Address",
              RFC 3956, DOI 10.17487/RFC3956, November 2004,

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,

   [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,

   [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,

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   [RFC6550]  Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
              Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
              JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
              Low-Power and Lossy Networks", RFC 6550,
              DOI 10.17487/RFC6550, March 2012,

   [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,

   [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>.

   [RFC8520]  Lear, E., Droms, R., and D. Romascanu, "Manufacturer Usage
              Description Specification", RFC 8520,
              DOI 10.17487/RFC8520, March 2019,

   [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,

   [RFC8799]  Carpenter, B. and B. Liu, "Limited Domains and Internet
              Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,

   [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,

   [RFC8990]  Bormann, C., Carpenter, B., Ed., and B. Liu, Ed., "GeneRic
              Autonomic Signaling Protocol (GRASP)", RFC 8990,
              DOI 10.17487/RFC8990, May 2021,

   [RFC8994]  Eckert, T., Ed., Behringer, M., Ed., and S. Bjarnason, "An
              Autonomic Control Plane (ACP)", RFC 8994,
              DOI 10.17487/RFC8994, May 2021,

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Author's Address

   Toerless Eckert
   Futurewei Technologies USA

   Email: tte@cs.fau.de

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