Network Working Group                                       Z. Kahn, Ed.
Internet-Draft                                                  LinkedIn
Intended status: Informational                        J. Brzozowski, Ed.
Expires: November 27, 2018                                       Comcast
                                                           R. White, Ed.
                                                            May 26, 2018

                     Requirements for IPv6 Routers


   The Internet is not one network, but rather a collection of networks.
   The interconnected nature of these networks, and the nature of the
   interconnected systems that make up these networks, is often more
   fragile than it appears.  Perhaps "robust but fragile" is an
   overstatement, but the actions of each vendor, implementor, and
   operator in such an interconnected environment can have a major
   impact on the stability of the overall Internet (as a system).  The
   widespread adoption of IPv6 could, particularly, disrupt network
   operations, in a way that impacts the entire system.

   This time of transition is an opportune time to take stock of lessons
   learned through the operation of large-scale networks on IPv4, and
   consider how to apply these lessons to IPv6.  This document provides
   an overview of the design and architectural decisions that attend
   IPv6 deployment, and a set of IPv6 requirements for routers,
   switches, and middleboxes deployed in IPv6 networks.  The hope of the
   editors and contributors is to provide the necessary background to
   guide equipment manufacturers, protocol implementors, and network
   operators in effective IPv6 deployment.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

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   This Internet-Draft will expire on November 27, 2018.

Copyright Notice

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Contributors  . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Acknowledgments . . . . . . . . . . . . . . . . . . . . .   4
     1.3.  Use and Applicability . . . . . . . . . . . . . . . . . .   4
   2.  Review of the Internet Architecture . . . . . . . . . . . . .   5
     2.1.  Robustness Principle  . . . . . . . . . . . . . . . . . .   5
     2.2.  Complexity  . . . . . . . . . . . . . . . . . . . . . . .   7
       2.2.1.  Elegance  . . . . . . . . . . . . . . . . . . . . . .   7
       2.2.2.  Trade-offs  . . . . . . . . . . . . . . . . . . . . .   8
     2.3.  Layered Structure . . . . . . . . . . . . . . . . . . . .   9
     2.4.  Routers . . . . . . . . . . . . . . . . . . . . . . . . .  10
   3.  Requirements Related to Device Management and Security  . . .  12
     3.1.  Programmable Device Access  . . . . . . . . . . . . . . .  12
     3.2.  Human Readable Device Access  . . . . . . . . . . . . . .  13
     3.3.  Supporting Zero Touch Provisioning for Connected Devices   13
     3.4.  Device Protection against Denial of Service Attacks . . .  15
   4.  Requirements Related to Telemetry . . . . . . . . . . . . . .  15
     4.1.  Device State and Traceablity  . . . . . . . . . . . . . .  16
     4.2.  Topology State and Traceability . . . . . . . . . . . . .  16
     4.3.  Flow State and Traceability . . . . . . . . . . . . . . .  17
   5.  Requirements Related to IPv6 Forwarding and Addressing  . . .  17
     5.1.  The IPv6 Address is not a Host Identifier . . . . . . . .  17
     5.2.  Router IPv6 Addresses . . . . . . . . . . . . . . . . . .  18
     5.3.  The Maximum Transmission Unit . . . . . . . . . . . . . .  19
     5.4.  ICMP Considerations . . . . . . . . . . . . . . . . . . .  20
     5.5.  Machine Access to the Forwarding Table  . . . . . . . . .  21
     5.6.  Processing IPv6 Extension Headers . . . . . . . . . . . .  22
     5.7.  IPv6 Operation by Default . . . . . . . . . . . . . . . .  22
     5.8.  IPv6 Only Operation . . . . . . . . . . . . . . . . . . .  22

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     5.9.  Prefix Length Handling in IPv6 Packet Forwarding  . . . .  23
     5.10. IPv6 Mobility Support . . . . . . . . . . . . . . . . . .  23
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  23
     6.1.  Robustness and Security . . . . . . . . . . . . . . . . .  23
     6.2.  Programmable Device Access and Security . . . . . . . . .  24
     6.3.  Zero Touch Provisioning and Security  . . . . . . . . . .  24
     6.4.  Defaulting to IPv6 Forwarding and Security  . . . . . . .  24
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  25
   8.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . .  25
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  25
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  32

1.  Introduction

   This memo defines and discusses requirements for devices that perform
   forwarding for Internet Protocol version 6 (IPv6).  The "use and
   applicability" section below contains more information on the
   specific target of this draft, and the envisioned use of the draft.

   Readers should recognize that while this memo applies to IPv6,
   routers and middleboxes IPv6 packets will often also process IPv4
   packets, forward based on MPLS labels, and potentially process many
   other protocols.  This memo will only discuss IPv4, MPLS, and other
   protocols as they impact the behavior of an IPv6 forwarding device;
   no attempt is made to specify requirements for protocols other than
   IPv6.  The reader should, therefore, not count on this document as a
   "sole source of truth," but rather use this document as a guide.

   For IPv4 router requirements, readers are referred to [RFC1812].  For
   simplicity, the term "devices" is used interchangeably with the
   phrase "routers and middleboxes" and the term "routers" throughout
   this document.  These three terms represent stylistic differences,
   rather than substantive differences.

   This document is broken into the following sections: a review of
   Internet architecture and principles, requirements relating to device
   management, requirements related to telemetry, requirements related
   to IPv6 forwarding and addressing, and future considerations.
   Following these sections, a short conclusion is provided for review.

1.1.  Contributors

   Shawn Zandi, Pete Lumbis, Fred Baker, James Woodyatt, Erik Muller,
   Lee Howard, and Joe Clarke contributed significant text and ideas to
   this draft.

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1.2.  Acknowledgments

   The editors and contributors would like to thank Ron Bonica, Lorenzo
   Coitti, Brian E.  Carpenter, Tim Chown, Peter Lothberg, and Mikael
   Abrahamsson for their comments, edits, and ideas on the text of this

1.3.  Use and Applicability

   The conceived use of this draft is as a reference point.  The first
   part of the draft is designed to help IPv6 implementors and network
   operators to understand Internet and Internetworking technologies, so
   they can better understand the context of IPv6.  The second part of
   this draft outlines a common set of requirements for devices which
   are designed to forward IPv6 traffic.  This can include (but is not
   limited to) the devices described below.

   o  Devices which are primarily designed to forward traffic between
      more than two interfaces.  These are normally referred to by the
      Internet community as routers or, in some cases, intermediate

   o  Devices which are designed to modify packets rather than "just"
      forwarding them.  These are often referred to by the Internet
      community as middleboxes.  See [RFC7663] for a fuller definition
      of middleboxes.

   This draft is not designed to apply to consumer devices, such as
   smart devices (refrigerators, light bulbs, garage door openers,
   etc.), Internet of Things (IoT) devices, cell phones primarily used
   as an end user device (such as checking email, social media, games,
   and use as a voice device), and other devices of this class.  It is
   up to each provider or equipment purchaser to determine how best to
   apply this document to their environment.

   The intended use of this document is for operators to be able to
   point to a common set of functionality which should be available
   across all IPv6 implementations.  Several members of the community
   have argued there is no common set of IPv6 features; rather each
   deployment of IPv6 calls for different feature sets.  However, the
   authors of this draft believe outlining a common set of features
   expected of every IPv6 forwarding device is useful.  Specifically:

   o  If every IPv6 deployment situation is unique, and requires a
      different set of features, there will not be a solid definition of
      what an IPv6 forwarding device is, or performs.  This fragments
      the concept of IPv6 forwarding devices in an unhelpful way,
      especially as IPv6 deployment is already seen as difficult.

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   o  It encourages developers and vendors to code a multitude of
      different IPv6 stacks, one for each possible set of features.
      This fragments the experience with these stacks, potentially
      preventing the development of a well designed, fully featured
      stacks the entire community can rely on.

   Because this document is designed to be a reference point rather than
   a best common practice or a standard, this document does not use
   [RFC2119] upper case "must" and "should" throughout.  Rather, it uses
   lower case "must" and "should" throughout, anticipating operators
   will find such guidance clear and useful.

2.  Review of the Internet Architecture

   The Internet relies on a number of basic concepts and considerations.
   These concepts are not explicitly called out in any specification,
   nor do they necessarily impact protocol design or packet forwarding
   directly.  This section provides an overview of these concepts and
   considerations to help the reader understand the larger context of
   this document.

2.1.  Robustness Principle

   Every point where multiple protocols interact, is an interaction
   surface that can threaten the robustness of the overall system.
   While it may seem the global Internet has achieved a level of
   stability that makes it immune to such considerations, the reality is
   every network is a complex system, and is therefore subject to
   massive non repeatable unanticipated failures.  Postel's Robustness
   Principle countered this problem with a simple statement, explicated
   in [RFC1122]: "Be conservative in what you do, and liberal in what
   you accept from others."

   However, since this time, it has been noted that following this law
   allows errors in protocols to accumulate over time, with overall
   negative effects on the system as a whole.  [RFC1918] describes
   several points in conjunction with this principle that bear updating
   based on further experience with large-scale protocol and network
   deployments within the Internet community, including:

   o  Applications should deal with error states gracefully; an
      application should not degrade in a way that will cause the
      failure of adjacent systems when possible.  For instance, when a
      routing protocol implementation fails, it should not do so in a
      way that will cause the spreading of or continued existence of
      false reachability information, nor should it fail in a way that
      overloads adjacent routers or interacting protocols and causing a
      cascading failure.

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   o  It is best to assume the network is filled with poor
      implementations and malevolent actors, both of which will find
      every possible failure mode over time.

   o  It is best to assume every technology will be used to the limits
      of its technical capabilities, rather than assuming a particular
      protocol's scope of use will align (in any way) with the intent of
      the original designer(s).  [RFC5218] defines a wildly successful
      protocol as one that "far exceeds its original goals, in terms of
      purpose (being used in scenarios far beyond the initial design),
      in terms of scale (being deployed on a scale much greater than
      originally envisaged), or both."  Successful implementations
      attract more functionality, much like a few nodes in a scale free
      graph eventually become connectivity hubs.

   o  Protocols and implementations change over time.  A corollary of
      the assumption that protocols will be used until they reach their
      technical limits is that protocols will change over time as they
      gain new functionality.  [RFC5218] points out several problems
      with "wild success" in a protocol: undesirable side effects,
      performance problems, and becoming a high value attack target.
      Protocol and implementation design should take into account use
      cases that have not yet been thought of by building flexibility
      into protocols.  Protocols should also remained focused on a
      narrow range of use cases; it is often wise to invent a new
      protocol than to extend a single protocol into a broad set of use

   o  Protocols are sometimes replaced or updated to new versions in
      order to add new capabilities or features.  Updating a protocol
      requires great care in providing for a transition mechanism
      between older and newer versions.  [RFC8170] provides sound advice
      on protocol transition planning and mechanisms.

   o  Obscure, but legal, protocol features are often ignored or left
      unimplemented.  Protocols must handle receiving unexpected
      information gracefully so they do not fail because of incomplete
      or partial implementations.  Protocols should avoid specifying
      contradictory states, or features that will cause interoperability
      issues if multiple implementations choose to implement different
      feature sets.

   o  Monocultures are almost always bad.  While multiple
      implementations can represent an interaction surface which
      increases complexity, particularly if a broad set of protocol
      capabilities and/or implementation features are used, using the
      same implementation at every point in a deployment results in a
      mono-culture.  In a monoculture, a single event can trigger a

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      defect in every router, causing a network failure.  Mono-cultures
      must be carefully balanced against interaction surfaces; often
      this is best accomplished by using multiple implementations and
      minimal, widely implemented, and well understood protocol

   A summary of the points above might be this: It is important to work
   within the bounds of what is actually implemented in any given
   protocol, and to leave corner cases for another day.  It is often
   easy to assume "virtual oceans" are easier to boil than physical
   ones, or for an ocean to appear much smaller because it is being
   implemented in software.  This is often deceptive.  It is never
   helpful to boil the ocean whether in a design, an implementation, or
   a protocol.

2.2.  Complexity

   Complexity, as articulated by Mike O'Dell (see [RFC3439]), is "the
   primary mechanism which impedes efficient scaling, and as a result is
   the primary driver of increases in both capital expenditures (CAPEX)
   and operational expenditures (OPEX)."  At the same time, complexity
   cannot be "solved," but rather must be "managed."  The simplest and
   most obvious solution to any problem is often easy to design, deploy,
   and manage.  It's also often wrong and/or broken.  As much as
   developers, designers, and operators might like to make things as
   simple as possible, hard problems require complex solutions.  See
   Alderson and Doyle [COMPLEXHARD] for a discussion of the relationship
   between hard problems and complex solutions.

   The following sections contain observations which apply to the
   management of complexity in both protocol and network design.

2.2.1.  Elegance

   Elegance should be the goal of protocol and network design.  Rather
   than seeking out simple solutions because they are simple, seek out
   solutions that will solve the problem in the simplest way possible
   (and no simpler).  Often this will require:

   o  Ensuring the goal is actually the goal.  Many times the goal is
      taken from the operational realm into the protocol design realm
      before enough thought has been applied to ensure the correct
      problem is being addressed.

   o  Seeing the problem from different angles, trying to break the
      problem up in multiple ways; and trying, abandoning, and
      rebuilding ideas and implementations until a better way is found.

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   o  Sometimes the complexity of the solution will overwhelm the use
      case; sometimes it is better to leave the apparent problem
      unsolved, or allow the community time and space to find a simpler

2.2.2.  Trade-offs

   There are always trade-offs.  For any protocol, network, or
   operational design decision, there will always be a trade-off between
   at least two competing goals.  If some problem appears to have a
   single solution without trade-offs, this doesn't mean the trade-offs
   don't exist.  Rather, it means the trade-offs haven't been discovered
   yet.  In the area of protocol and network design, these trade-offs
   often take the form of common "choose two of three" situations, such
   as "quick, cheap, high quality."  In network and protocol design, the
   trade-offs are often:

   o  The amount of state carried in the system and the speed at which
      it changes, or simply the state.  The amount of state required to
      operate a system as it scales tends to be nonlinear.  Some
      instances of this are described in [RFC3439] section 2.2.1, the
      Amplification Principle.

   o  The number of interaction surfaces between the components that
      make up the complete system, and the depth of those interaction
      surfaces.  Some examples of surfaces are described in
      [RFC3439]section 2.2.2, the Coupling Principle.  Layering is
      essentially a form of abstraction; all abstractions are subject to
      the law of leaky abstractions, [LEAKYABS] which states: "all
      nontrivial abstractions leak."

   o  The desired optimization, including efficient use of network
      resources, optimal support for business objectives, and optimal
      support for a specific set of applications.

   These three make up a "triangle problem."  For instance, to increase
   the optimization of traffic flow through a network generally requires
   adding more state to the control plane, leading to problems in
   complexity due to amplification.  To reduce amplification, the
   control plane (or perhaps the various functions the control plane
   serves) can be broken up into subsystems, or modules.  Breaking the
   control plane up into subsystems, however, introduces interaction
   surfaces between the components, which is another form of complexity.
   [RFC7980] provides a good overview of network complexity; in
   particular, section 3 of that document provides some examples of
   complexity trade-offs.

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2.3.  Layered Structure

   The Internet data plane is organized around broad top and bottom
   layers, and much thinner middle layer.  This is illustrated in the
   figure below.

   \                         /
    \ HTTP, FTP, SNMP, ETC. /
     \                     /
       \     TCP, UDP    /
        \               /
          \    IPv6   /
          /   (IPv4)  \
        /               \
       /      (MPLS)      \
     /  Ethernet, Wireless \
    /    Physical Media     \
   /                         \

                                 Figure 1

   This layering emulates or mirrors many naturally occurring systems;
   it is a common strategy for managing complexity (see Meyer's
   presentation on complexity).  [COMPLEXLAYER] The single protocol in
   the center, IPv6, serves to separate the complexity of the lower
   layers from the complexity of the upper layers.  This center layer of
   the Internet ecosystem has traditionally been called the Network
   Layer, in reference to the Department of Defense (DoD) [DoD] and OSI
   models.  [OSI] The Internet ecosystem includes two different
   protocols in this central location.

   o  IPv4, an older network protocol that, it is anticipated, will be
      replaced over time as the Internet ecosystem standardizes on IPv6

   o  IPv6, a newer network protocol that is being adopted

   MPLS is often used as a "middle" sub-transport layer, and at other
   times as "middle" sub data link layer; hence MPLS is difficult to
   classify within the strictly hierarchical model depicted here.  These
   protocols are often treated as if they exist in strict hierarchical
   layers with a well defined and followed Application Programming
   Interface (API), data models, Remote Procedure Calls (RPCs), sockets,
   etc.  The reality, however, is there are often solid reasons for
   violating these layers, creating interaction surfaces that are often
   deeper than intended or understood without some experience.  Beyond
   this, such layering mechanisms act as information abstractions.  It
   is well known that all such abstractions leak (see above on the law
   of leaky abstractions).  Because of these intentional and

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   unintentional leakages of information, the interactions between
   protocols is often subtle.

2.4.  Routers

   A router connects to two or more logical interfaces and at least one
   physical interface.  A router processes packets by:

   o  Receiving a packet through an interface

   o  Stripping the data link, physical header, or tunnel encapsulation
      off the packet

   o  Examining the packet for errors, and determining if this packet
      needs to be punted to another process on the router

   o  Looking up the destination in a local forwarding table

   o  Rewriting the data link and/or physical layer header

   o  Transmitting the packet out an interface

   When consulting the forwarding table, the router searches for a match
   based on:

   o  The longest prefix containing the destination address (this is the
      most common matching element)

   o  A label, such as a flow label or MPLS label

   o  The source address or other header fields (not common)

   The router then examines the information in the matching entry to
   determine the next hop, or rather the next logically connected device
   to forward the packet to.  The next hop will either be another
   router, which will presumably carry the packet closer to the final
   destination, or it will be the destination host itself.  The
   following figure provides a conceptual model of a router; not all
   routers actually have this set of tables and interactions, and some
   have many more moving parts.  This model is simply used as a common
   reference to promote understanding.

   +-------------+            +-------------+
   | Candidate   |            | Startup     |
   | Config      |<--+    +-->| Config      |
   +--+----------+   |    |   +-------+-----+
      |              |    |           |
      v              |    |           v

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   | Running Configuration                  |
       | // configuration transformations
   | Intended Configuration                 |
       | // changes applied subject to local factors
   | Operational Configuration              +------>----------+
   +---+----------+----------+----------+---+                 |
       |          |          |          |                     |
       v          |          |          |                     |
   +-------+      |          |          |                     |
   | IS-IS |<-----------------------------------> Adjacent    |
   +---+---+      v          |          |         Routers     |
       |      +-------+      |          |                     |
       |      |  BGP  |<------------------------> Peers       |
       |      +---+---+      v          |                     |
       |          |      +-------+      |                     |
       |          |      | OSPF  |<-------------> Adjacent    |
       |          |      +---+---+      v         Routers     |
       |          |          |      +-------+                 |
       |          |          |      | Other |                 |
       |          |          |      +---+---+                 |
       |          |          |          |                     |
   +---+----------+----------+----------+---+                 |
   | RIB Manager                            |                 |
   +---+------------------------------------+                 |
       |                                                      |
   +---+------------------------------------+                 |
   | Routing Information Base (RIB)         |                 |
   +---+------------------------------------+                 |
       |                                                      |
   +---+------------------------------------+                 |
   | Forwarding Information Base (FIB)      |                 |
   +---+----------+---------------------+---+                 |
       |          |                     |                     |
   +---+---+  +---+---+             +---+---+                 |
   | Int 1 |  | Int 2 |     ...     | Int X | <---------------+
   +-------+  +-------+             +-------+
       ^                                |
       |                                v
   Packets In                       Packets Out

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                                 Figure 2

   The configuration datastores in this figure follow [RFC8342].

3.  Requirements Related to Device Management and Security

   Network engineering began in the era of Command Line Interfaces
   (CLIs), and has generally stayed with these CLIs even as the
   Graphical User Interface (GUI) has become the standard way of
   interacting with almost every other computing device.  Direct human
   interaction with routers and middleboxes in large-scale and complex
   environments, however, tends to result in an unacceptably low Mean
   Time Between Mistakes (MTBM), directly impacting the overall
   availability of the network.  In reaction to this, operators have
   increased their reliance on automation, specifically targeting
   machine to machine interfaces, such as Remote Procedure Calls (RPCs)
   and Application Programming Interface (API) solutions, to manage and
   configure routers and middleboxes.  This section considers the
   various components of device management.

   Across all interface types, devices should provide and use complete,
   idempotent, stateless configurations.  Further, default settings
   should be accessible in some way, even if they are hidden by default
   for configuration readability.

3.1.  Programmable Device Access

   Configuration primarily relates to the startup, candidate, running,
   intended, and operational configurations in the router model shown
   above.  In order to deploy networks at scale, operators rely on
   automated management of router configuration.  This effort has
   traditionally focused on screen scraping and other proprietary
   methods of "reading" and "writing" configuration information through
   a CLI.  In the future, operators expect to move towards open source/
   open standards YANG models, regardless of how these are encoded and/
   or carried (or marshaled).

   Vendors and implementors should implement machine readable interfaces
   with overlays to support human interaction, rather than human
   readable interfaces with overlays to support machine to machine
   interaction.  Emphasis should be placed on machine to machine
   interaction for day to day operations, rather than on human readable
   interfaces, which are largely used in the process of troubleshooting.
   Within the realm of machine to machine interfaces, emphasis should be
   placed on marshaling information in YANG models.

   To support automated router configuration, IPv6 routers and routers
   should support YANG configuration, including (but not limited to):

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   o  Openconfig models [OPENCONF] related to the protocols configured
      on the device, interface state, and device state

   o  [RFC8343]: A YANG Data Model for Interface Management

   o  [RFC7224]: IANA Interface Type YANG Module

   o  [RFC8344]: A YANG Data Model for IP Management

   o  [RFC7317]: A YANG Data Model for System Management

   o  [RFC8349]: A YANG Data Model for Routing Management (NMDA Version)

3.2.  Human Readable Device Access

   To operate a network at scale, operators rely on the ability to
   access routers and middleboxes to troubleshoot and gather state
   manually through a number of different interfaces.  These interfaces
   should provide current device configuration, current device state
   (such as interface state, packets drops, etc.), and current control
   plane contents (such as the RIB in the figure above).  In other
   words, manual interfaces should provide information about the router
   (the whole device stack).

   To support manual state gathering and troubleshooting, IPv6 routers
   and middleboxes should support:

   o  TELNET ([RFC0854]): TELNET should be disabled by default, but
      should be available for operational purposes as required or as
      configured by the operator

   o  SSH ([RFC4253]): SSH should be the default access for IPv6 capable

   o  All network devices supporting IPv6 must support zccess through an
      Ethernet management port

3.3.  Supporting Zero Touch Provisioning for Connected Devices

   To operate a network at scale, operators rely on protocols and
   mechanisms that reduce provisioning time to a minimum.  The preferred
   state is zero touch provisioning; plug a new router in and it just
   works without any manual configuration.  The closer an operator can
   come to this ideal, the more MTBM and Operational Expenses (OPEX) can
   be reduced -- important goals in the real world.  IPv6 routers should
   support several standards, including, but not limited to:

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   o  [I-D.ietf-dhc-rfc3315bis]: Dynamic Configuration Protocol for IPv6
      must be supported.

   o  [RFC4862]: IPv6 Stateless Address Autoconfiguration (SLAAC) must
      be supported, and must be enabled by default on all router
      interfaces.  SLAAC must be able to be disabled by operators who
      prefer to use some other mechanism for address management and
      assignment (specifically for customer facing edge ports).

   o  [RFC7217]: Semantically Opaque Interface Identifiers should be
      supported unless there's a need to embed MAC address.

   o  [RFC7934]: Host Address Availability, the ability to assign
      multiple addresses to a host, should be supported.

   o  [RFC7527]: Enhanced Duplicate Address Detection should be

   o  [RFC7527]: Enhanced Duplicate Address Detection may be disabled
      for manually configured interfaces.

   o  [RFC8028]: First-Hop Router Selection by Hosts, specifically
      section 2.1, which says a router should be able to send a PIO with
      both the L and A bits cleared.

   o  [RFC3810]: Routers supporting IPv6 must support Multicast Listener
      Discovery Version 2

   o  [RFC7772]: Routers supporting IPv6 should support Reducing Energy
      Consumption of Router Advertisements

   o  [RFC8273]: Routers supporting IPv6 should support Unique IPv6
      Prefix per Host

   The provisioning of Domain Name Systems (DNS) system information is a
   contentious topic, based on provider, operating system, interface,
   and other requirements.  This document therefore addresses the
   mechanisms that must be included in IPv6 router implementations, but
   leaves the option of what to configure and deploy to the network
   operator.  Routers supporting IPv6, and intended for user facing
   connections, must support:

   o  [RFC3646]: DNS Configuration options for Dynamic Host
      Configuration Protocol for IPv6 (DHCPv6) if DHCPv6 is supported.

   o  [RFC8106]: IPv6 Router Advertisement Options for DNS
      Configuration.  This includes the ability to send Router
      Advertisements (RAs) with DNS information.

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   Whether these are enabled by default, or require extra configuration,
   is left as an exercise for providers and implementation developers to
   determine on a case by case basis.

3.4.  Device Protection against Denial of Service Attacks

   Denial of Service (DoS) and Distributed Denial of Service (DDoS)
   attacks are unfortunately common in the Internet globally; these
   types of attacks cost network operators a great deal in opportunity
   and operational costs in prevention and responses.  To provide for
   effective counters to DoS and DDoS attacks directly on routers:

   o  Manufacturers and system integrators should test and clearly
      report the packet/traffic load handling capabilities of devices
      with and without various encryption methods enabled

   o  Routers should be able to police traffic destined to the control
      plane based on the rate of traffic received, including the ability
      to police individual flows, targeted services, etc., at individual
      rates as described in [RFC6192]

   o  Ideally, devices should be able to statefully filter traffic
      destined to the control plane

   There are other useful techniques for dealing with DDoS attacks at
   the network level, including: transferring sessions to a new address
   and abandoning the address under attack, using BGP communities to
   spread the attack over multiple ingress ports and "consume" it, and
   requiring mutual authentication before allocating larger resource
   pools to a connection.  These techniques are not "device level," and
   hence are not considered further here.

4.  Requirements Related to Telemetry

   Telemetry relates to information devices push to systems used to
   monitor and track the state of the network.  This applies to
   individual devices as well as the network as a system.  Two major
   challenges face operators in the area of telemetry:

   o  Information that is laid out primarily for human, rather than
      machine, consumption.  While human consumption of telemetry is
      important in some situations, this information should be supplied
      in a form that focuses on machine readability with an overlay or
      interpretor that allows human consumption.

   o  Software systems that require information to be queried (or polled
      or even pushed) on a per-item basis.  This form of organization
      can produce a lot of information, and a lot of individual packets,

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      very quickly, overwhelming monitoring systems and consuming a
      large amount of available network resources.  Instead, telemetry
      should be focused on bulk collection.

   There are three broad categories of telemetry: device state and
   traceability, topology state and traceability, and flow traceability.
   These three roughly correspond to the management plane, the control
   plane, and the forwarding plane of the network.  Each of the sections
   below considers one of these three telemetry types.

4.1.  Device State and Traceablity

   Ideally, the entire network could be monitored using a single
   modeling language to ease implementation of telemetry systems and
   increase the pace at which new software can be deployed in production
   environments.  In real deployments, it is often impossible to reach
   this ideal; however, reducing the languages and methods used, while
   focusing on machine readability, can greatly ease the deployment and
   management of a large-scale network.  Specifically, IPv6 routers
   should support:

   o  [RFC6241] and [RFC8040]: NETCONF/RESTCONF transporting telemetry
      formatted according to YANG (see above)

   o  [I-D.ietf-i2rs-yang-l2-network-topology]: An I2RS model for layer
      2 topologies

   o  [I-D.ietf-netconf-yang-push]: YANG Datastore Subscription

   o  [RFC5424]: Syslog

   o  gRPC based telemetry interfaces [GRPC]

   o  Simple Network Management Protocol (SNMP) MIBs as appropriate

   Syslog and SNMP access for telemetry should be considered "legacy,"
   and should not be the focus of new telemetry access development

4.2.  Topology State and Traceability

   IPv6 routers are part of a system of devices that, combined, make up
   the entire network.  Viewing the network as a system is often crucial
   for operational purposes.  For instance, being able to understand
   changes in the topology and utilization of a network can lead to
   insights about traffic flow and network growth that lead to a greater
   understanding of how the network is operating, where problems are
   developing, and how to improve the network's performance.  To support

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   systemic monitoring of the network topology, IPv6 devices should
   support at least:

   o  [RFC5424]: North-Bound Distribution of Link-State and Traffic
      Engineering (TE) Information using BGP

   o  [I-D.ietf-i2rs-yang-l2-network-topology]: An I2RS model for layer
      2 topologies

   o  [RFC8346]: An I2RS model for layer 3 topologies

   o  [RFC8345]: A Data Model for Network Topologies

4.3.  Flow State and Traceability

   Network operators frequently need to observe and understand the
   types, sources, and destinations of traffic passing through devices.
   For example, information about traffic flows may be used to identify
   abuse (such as DDOS attacks) or to plan network expansions based on
   traffic patterns.  To support insight and analysis of this traffic,
   IPv6 devices should support IPFIX as described in [RFC7011], PSAMP as
   described in [RFC5474], or some other flow state mechanism.

   In-situ Operational and Management (iOAM) is a technology that being
   developed at the time of this writing; see [I-D.ietf-ippm-ioam-data].
   Operators and vendors should consider the deployment of iOAM to
   provide deeper information about flow and topology information.

5.  Requirements Related to IPv6 Forwarding and Addressing

   There are a number of capabilities that a device should have to be
   deployed into an IPv6 network, and several forwarding plane
   considerations operators and vendors need to bear in mind.  The
   sections below explain these considerations.

5.1.  The IPv6 Address is not a Host Identifier

   The IPv6 address is commonly treated as a host identifier; it is not.
   Rather, it is an interface identifier that describes the topological
   point where a particular host connects to the Internet.

   o  The IPv6 address will change when a device changes where it
      connects to the network.

   o  A single host can have multiple addresses.  For instance, a host
      may have one address per interface, or multiple addresses assigned

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      through different mechanisms, or through multiple connection

   o  A single IPv6 address may represent many hosts, as in the case of
      a group of hosts reachable through a multicast address, or a set
      of services reachable through an anycast address.

   Because the host address may change at any time, it is generally
   harmful to embed IPv6 addresses inside upper layer headers to
   identify a particular host.

5.2.  Router IPv6 Addresses

   Internet Routing Registries may allocate a network operator a wide
   range of prefix lengths (see [RFC6177] for further information).
   Within this allocation, network operators will often suballocate
   address space along nibble boundaries (/48, /52, /56, /60, and /64)
   for ease of configuration and management.  Several common practices

   o  Each multiaccess interface is allocated a /64

   o  Point-to-point links are allocated a /64, but should be addressed
      with a longer prefix length to prevent certain kinds of denial of
      service attacks ([RFC6547] originally mandated 64 bit prefix
      lengths on point-to-point links; [RFC6164] explains possible
      security issues with assigning a 64 bit prefix length to a point-
      to-point, and recommends a /127 instead)

   o  Although aggregation is typically only performed to the nibble
      boundaries noted above, variances are possible

   o  Loopback addresses are assigned a /128

   Given these common practices, routers designed to run IPv6 should
   support the following addressing conventions:

   o  The default prefix length on any interface other than a loopback
      should be a /64

   o  Configuring a prefix length longer than a /64 on any multi-access
      interface should require additional configuration steps to prevent
      manual configuration errors

   o  Routers must not assume IPv6 prefix lengths only on nibble

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   o  Routers should support any prefix length shorter or greater than

   o  Loopback interfaces should default to a /128 prefix length unless
      some additional configuration is undertaken to override this
      default setting

   o  Routers must be able to generate link local addresses on all links
      and/or interfaces using stateless address autoconfiguration (see

5.3.  The Maximum Transmission Unit

   The long history of the Maximum Transmission Unit (MTU) in networks
   is not a happy one.  Specific problems with MTU sizing include:

   o  Many different default sizes on different media types, from very
      small (576 bytes on X.25) to very large (17914 bytes on 16Mbps
      Token Ring)

   o  Many different ways to calculate the MTU on any given link; for
      instance a 9000 byte MTU can be calculated as 8184 bytes on one
      operating system, 8972 on another, and 9000 on a third

   o  The increasing use of tunnel encapsulations in the network; for
      instance MPLS over GRE over IP over...

   o  The wide variety of default MTUs across many different end hosts
      and operating systems

   o  The general ineffectiveness of path MTU discovery to operate
      correctly in the face of packet filters and rate limiters (see the
      section on ICMP filtering below)

   o  Lower speed links at the network edge which require a lot of time
      to serialize a packet with a large MTU

   o  Increased jitter caused by the disparity between large and small
      packet size across a lower bandwidth links

   The final point requires some further elucidation.  The time required
   to serialize various packets at various speeds are:

   o  64 byte packet onto a 10Mb/s link: .5ms

   o  1500 byte packet onto a 10Mb/s link: 1.2ms

   o  9000 byte packet onto a 10Mb/s link: 7.2ms

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   o  64 byte packet onto a 100Mb/s link: .05ms

   o  1500 byte packet onto a 100Mb/s link: .12ms

   o  9000 byte packet onto a 100Mb/s link: .72ms

   A 64 byte packet trapped behind a single 1500 byte packet on a 10Mb/s
   link suffers 1.2ms of serialization delay.  Each additional 1500 byte
   packet added to the queue in front of the 64 byte packet adds and
   additional 1.2ms of delay.  In contrast, a 64 byte packet trapped
   behind a single 9000 byte packet on a 10Mb/s link suffers 7.7ms of
   serialization delay.  Each additional 9000 byte packet added to the
   queue adds an additional 7.2ms of serialization delay.  The practical
   result is that larger MTU sizes on lower speed links can add a
   significant amount of delay and jitter into a flow.  On the other
   hand, increasing the MTU on higher speed links appears to add
   negligible additional delay and jitter.

   The result is that it costs less in terms of overall systemic
   performance to use higher MTUs on higher speed links than on lower
   speed links.  Based on this, increasing the MTU across any particular
   link may not increase overall end-to-end performance, but can greatly
   enhance the performance of local applications (such as a local BGP
   peering session, or a large/long standing elephant flow used to
   transfer data across a local fabric), while also providing room for
   tunnel encapsulations to be added with less impact on lower MTU end

   The general rule of thumb is to assume the largest size MTU should be
   used on higher speed transit only links in order to support a wide
   array of available link sizes, default MTUs, and tunnel
   encapsulations.  Routers designed for a network core, data center
   core, or use on the global Internet should support at least 9000 byte
   MTUs on all interfaces.  MTU detection mechanisms, such as IS-IS
   hello padding, described in [RFC3719], should be enabled to ensure
   correct point-to-point MTU configuration.  Devices should also

   o  [RFC8201]: Path MTU Discovery for IP version 6

   o  [RFC4821]: Packetization Layer Path MTU Discovery

5.4.  ICMP Considerations

   Internet Control Message Protocol (ICMP) is described in [RFC0792]
   and [RFC4443].  ICMP is often used to perform a traceroute through a
   network (normally by using a TTL expired ICMP message), for Path MTU
   discovery, and, in IPv6, for autoconfiguration and neighbor

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   discovery.  ICMP is often blocked by middleboxes of various kinds
   and/or ICMP filters configured on the ingress edge of a provider
   network, most often to prevent the discovery of reachable hosts and
   network topology.  Routers implementing IPv6:

   o  Should rate limit the generation of ICMP echo and echo responses
      by default (for instance, using a token bucket method as described
      in [RFC4443]).  The device should support the configuration of not
      generating ICMP echo, echo response, and time exceeded packets to
      prevent topology discovery.

   o  Should rate limit the generation of ICMP error messages with a
      token bucket method as described in [RFC4443].  Rate limits should
      be narrow enough to (a) protect the device's ability to generate
      packets and (b) reduce the usefulness of ICMP error packets as
      part of a distributed denial of service attack.  Limits should be
      generous enough to allow successful path MTU discovery and
      traceroute.  For example, in a small/mid-size device, the possible
      defaults could be bucket size=100, refill rate=100/s.  Larger
      devices can afford more generous rate limits.

   o  Should implement the filtering suggestions in

   o  Should not filter Destination Unreachable or Packet Too Big ICMP
      error messages by default, as this has negative impacts on many
      aspects of IPv6 operation, particularly path MTU discovery.

   There are implications for path MTU discovery and other useful
   mechanisms in filtering and rate limiting ICMP.  The trade-off here
   is between allowing unlimited ICMP, which would allow path MTU
   detection to work, or limiting ICMP in a way that prevents negative
   side effects for individual devices, and hence the operational
   capabilities of the network as a whole.  Operators rightly limit ICMP
   to reduce the attack surface against their network, as well as the
   opportunity for "perfect storm" events that inadvertently reduce the
   capability of routers and middleboxes.  Hence ICMP can be treated as
   "quasi-reliable" in many situations; existence of an ICMP message can
   prove, for instance, that a particular host is unreachable.  The non-
   existence of an ICMP message, however, does not prove a particular
   host exists or does not.

5.5.  Machine Access to the Forwarding Table

   In order to support treating the "network as a whole" as a single
   programmable system, it is important for each router have the ability
   to directly program forwarding information.  This programmatic
   interface allows controllers, which are programmed to support

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   specific business logic and applications, to modify and filter
   traffic flows without interfering with the distributed control plane.
   While there are several programmatic interfaces available, this
   document suggests that the I2RS interface to the RIB be supported in
   all IPv6 routers.  Specifically, these drafts should be supported to
   enable network programmability:

   o  [I-D.ietf-i2rs-fb-rib-data-model]: Filter-Based RIB Data Model

   o  [I-D.ietf-i2rs-fb-rib-info-model]: Filter-Based RIB Information

   o  [I-D.ietf-i2rs-rib-data-model]: A YANG Data Model for Routing
      Information Base (RIB)

   o  [RFC7922]: I2RS Traceability

5.6.  Processing IPv6 Extension Headers

   (To be added)

5.7.  IPv6 Operation by Default

   If a device forwards and/or originates IPv4 packets by default
   (without explicit configuration by the operator), it should forward
   and/or originate IPv6 packets by default.  See the security
   considerations section below for reflections on the automatic
   configuration of IPv6 forwarding in parallel with IPv4.

5.8.  IPv6 Only Operation

   While the transition to IPv6 only networks may take years (or perhaps
   decades), a number of operators are moving to deploy IPv6 on internal
   networks supporting transport and data center fabric applications
   more quickly.  Routers and middleboxes that support IPv6 should
   support IPv6 only operation, including:

   o  Link Local addressing must be configurable and usable as the
      primary address on all interfaces on a device.

   o  IPv4 and/or MPLS should not be required for proper device
      operation.  For instance, an IPv4 address should not be required
      to determine the router ID for any protocol.  See [RFC6540]
      section 2.

   o  Any control plane protocol implementations must support the
      recommendations in [RFC7404] for operation using link local
      addresses only.

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5.9.  Prefix Length Handling in IPv6 Packet Forwarding

   Routers must support IPv6 destination lookups in the forwarding
   process on a single bit prefix length increments, in accordance with

5.10.  IPv6 Mobility Support

   Mobile IPv6 [RFC6275] and associated specifications, including
   [RFC3776] and [RFC4877] allow a node to change its point of
   attachment within the Internet, while maintaining (and using) a
   permanent address.  All communication using the permanent address
   continues to proceed as expected even as the node moves around.  At
   the present time, Mobile IP has seen only limited implementation.
   More usage and deployment experience is needed with mobility before
   any specific approach can be recommended for broad implementation in
   hosts and routers.  Consequently, routers may support [RFC6275] and
   associated specifications (these specifications are not required for
   IPv6 routers).

6.  Security Considerations

   This document addresses several ways in which devices designed to
   support IPv6 forwarding.  Some of the recommendations here are
   designed to increase device security; for instance, see the section
   on device access.  Others may intersect with security, but are not
   specifically targeted at security, such as running IPv6 link local
   only on links.  These are not discussed further here, as they improve
   the security stance of the network.  Other areas discussed in this
   draft are more nuanced.  This section gathers the intersection
   between operational concerns and security concerns into one place.

   ICMP security is already considered in the section on ICMP; it will
   not be considered further here.  Link local only addressing will
   increase security by removing transit only links within the network
   as a reachable destination.

6.1.  Robustness and Security

   Robustness, particularly in the area of error handling, largely
   improves security if designed and implemented correctly.  Many
   attacks take advantage of mistakes in implementations and variations
   in protocols.  In particular, any feature that is unevenly
   implemented among a number of implementations often offers an attack
   surface.  Hence, reducing protocol complexity helps reduce the
   breadth of attack surfaces.

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   Another point to consider at the intersection of robustness and
   security is the issue of monocultures.  Monocultures are in and of
   themselves a potential attack surface, in that finding a single
   failure mode can be exploited to take an entire network (or operator)
   down.  On the other hand, reducing the number of implementations for
   any particular protocol will decrease the set of "random" features
   deployed in the network.  These two goals will often be opposed to
   one another.  Network designers and operators need to consider these
   two sides of this trade-off, and make an intelligent decision about
   how much diversity to implement versus how to control the attack
   surface represented by deploying a wide array of implementations.

6.2.  Programmable Device Access and Security

   Programmable interfaces, including programmable configuration,
   telemetry, and machine interface to the routing table, introduce a
   large attack surface; operators should be careful to ensure this
   attack surface is properly secured.  Specifically:

   o  Prevent external access to any administrative access points used
      for device programmability

   o  Use AAA systems to ensure only valid devices and/or users access

   o  Rate limit the change rate and protect management interfaces from
      DoS and DDoS attacks

   Such interfaces should be treated no differently than SSH, SFTP, and
   other interfaces available to manage routers and middleboxes.

6.3.  Zero Touch Provisioning and Security

   Zero touch provisioning opens a new attack surface; insider attackers
   can simply install a new device, and assume it will be autoconfigured
   into the network.  A "simple" solution would be to install door
   locks, but this will likely not be enough; defenses need to be
   layered to be effective.  It is recommended that devices installed in
   the network need to contain a hardware or software identification
   system that allows the operator to identify devices that are
   installed in the network.

6.4.  Defaulting to IPv6 Forwarding and Security

   Operators should be aware that devices which forward IPv6 by default
   can introduce a new attack surface or new threats without explicit
   configuration.  Operators should verify that IPv6 policies, including
   filtering, match or fulfill the same intent as any existing IPv4

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   policies when deploying devices capable of forwarding both IPv4 and

7.  IANA Considerations

   This document has no actions for IANA.

8.  Conclusion

   The deployment of IPv6 throughout the Internet marks a point in time
   where it is good to review the overall Internet architecture, and
   assess the impact on operations of these changes.  This document
   provides an overview of a lot of these changes and lessons learned,
   as well as providing pointers to many of the relevant documents to
   understand each topic more deeply.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

9.2.  Informative References

              Alderson, D. and J. Doyle, "Contrasting Views of
              Complexity and Their Implications For Network-Centric
              Infrastructures", 2010,

              Meyer, D., "Macro Trends, Architecture, and the Hidden
              Nature of Complexity", 2010,

   [DoD]      Wikipedia, "The Internet Protocol Suite", 2016,

   [GRPC]     gRPC, "gRPC", 2016, <>.

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              Gont, F., Hunter, R., Massar, J., and W. LIU, "Defeating
              Attacks which employ Forged ICMPv4/ICMPv6 Error Messages",
              draft-gont-opsec-icmp-ingress-filtering-03 (work in
              progress), July 2017.

              Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
              Richardson, M., Jiang, S., Lemon, T., and T. Winters,
              "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
              bis", draft-ietf-dhc-rfc3315bis-13 (work in progress),
              April 2018.

              Hares, S., Kini, S., Dunbar, L., Krishnan, R., Bogdanovic,
              D., and R. White, "Filter-Based RIB Data Model", draft-
              ietf-i2rs-fb-rib-data-model-01 (work in progress), March

              Kini, S., Hares, S., Dunbar, L., Ghanwani, A., Krishnan,
              R., Bogdanovic, D., and R. White, "Filter-Based RIB
              Information Model", draft-ietf-i2rs-fb-rib-info-model-00
              (work in progress), June 2016.

              Wang, L., Chen, M., Dass, A., Ananthakrishnan, H., Kini,
              S., and N. Bahadur, "A YANG Data Model for Routing
              Information Base (RIB)", draft-ietf-i2rs-rib-data-model-15
              (work in progress), May 2018.

              Dong, J. and X. Wei, "A YANG Data Model for Layer-2
              Network Topologies", draft-ietf-i2rs-yang-l2-network-
              topology-04 (work in progress), March 2018.

              Brockners, F., Bhandari, S., Pignataro, C., Gredler, H.,
              Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
              P., Chang, R.,, d., and J. Lemon,
              "Data Fields for In-situ OAM", draft-ietf-ippm-ioam-
              data-02 (work in progress), March 2018.

              Clemm, A., Voit, E., Prieto, A., Tripathy, A., Nilsen-
              Nygaard, E., Bierman, A., and B. Lengyel, "YANG Datastore
              Subscription", draft-ietf-netconf-yang-push-15 (work in
              progress), February 2018.

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              Spolsky, J., "The Law of Leaky Abstractions", 2002,

              OpenConfig, "Openconfig release YANG models", 2016,

   [OSI]      Wikipedia, "OSI Model", 2016,

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, DOI 10.17487/RFC0792, September 1981,

   [RFC0854]  Postel, J. and J. Reynolds, "Telnet Protocol
              Specification", STD 8, RFC 854, DOI 10.17487/RFC0854, May
              1983, <>.

   [RFC1122]  Braden, R., Ed., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122,
              DOI 10.17487/RFC1122, October 1989,

   [RFC1812]  Baker, F., Ed., "Requirements for IP Version 4 Routers",
              RFC 1812, DOI 10.17487/RFC1812, June 1995,

   [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,

   [RFC3439]  Bush, R. and D. Meyer, "Some Internet Architectural
              Guidelines and Philosophy", RFC 3439,
              DOI 10.17487/RFC3439, December 2002,

   [RFC3646]  Droms, R., Ed., "DNS Configuration options for Dynamic
              Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
              DOI 10.17487/RFC3646, December 2003,

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   [RFC3719]  Parker, J., Ed., "Recommendations for Interoperable
              Networks using Intermediate System to Intermediate System
              (IS-IS)", RFC 3719, DOI 10.17487/RFC3719, February 2004,

   [RFC3776]  Arkko, J., Devarapalli, V., and F. Dupont, "Using IPsec to
              Protect Mobile IPv6 Signaling Between Mobile Nodes and
              Home Agents", RFC 3776, DOI 10.17487/RFC3776, June 2004,

   [RFC3810]  Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
              Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
              DOI 10.17487/RFC3810, June 2004,

   [RFC4253]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,
              January 2006, <>.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
              Control Message Protocol (ICMPv6) for the Internet
              Protocol Version 6 (IPv6) Specification", STD 89,
              RFC 4443, DOI 10.17487/RFC4443, March 2006,

   [RFC4821]  Mathis, M. and J. Heffner, "Packetization Layer Path MTU
              Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007,

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,

   [RFC4877]  Devarapalli, V. and F. Dupont, "Mobile IPv6 Operation with
              IKEv2 and the Revised IPsec Architecture", RFC 4877,
              DOI 10.17487/RFC4877, April 2007,

   [RFC5218]  Thaler, D. and B. Aboba, "What Makes for a Successful
              Protocol?", RFC 5218, DOI 10.17487/RFC5218, July 2008,

   [RFC5424]  Gerhards, R., "The Syslog Protocol", RFC 5424,
              DOI 10.17487/RFC5424, March 2009,

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   [RFC5474]  Duffield, N., Ed., Chiou, D., Claise, B., Greenberg, A.,
              Grossglauser, M., and J. Rexford, "A Framework for Packet
              Selection and Reporting", RFC 5474, DOI 10.17487/RFC5474,
              March 2009, <>.

   [RFC6164]  Kohno, M., Nitzan, B., Bush, R., Matsuzaki, Y., Colitti,
              L., and T. Narten, "Using 127-Bit IPv6 Prefixes on Inter-
              Router Links", RFC 6164, DOI 10.17487/RFC6164, April 2011,

   [RFC6177]  Narten, T., Huston, G., and L. Roberts, "IPv6 Address
              Assignment to End Sites", BCP 157, RFC 6177,
              DOI 10.17487/RFC6177, March 2011,

   [RFC6192]  Dugal, D., Pignataro, C., and R. Dunn, "Protecting the
              Router Control Plane", RFC 6192, DOI 10.17487/RFC6192,
              March 2011, <>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,

   [RFC6275]  Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility
              Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July
              2011, <>.

   [RFC6434]  Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node
              Requirements", RFC 6434, DOI 10.17487/RFC6434, December
              2011, <>.

   [RFC6540]  George, W., Donley, C., Liljenstolpe, C., and L. Howard,
              "IPv6 Support Required for All IP-Capable Nodes", BCP 177,
              RFC 6540, DOI 10.17487/RFC6540, April 2012,

   [RFC6547]  George, W., "RFC 3627 to Historic Status", RFC 6547,
              DOI 10.17487/RFC6547, February 2012,

   [RFC7011]  Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
              "Specification of the IP Flow Information Export (IPFIX)
              Protocol for the Exchange of Flow Information", STD 77,
              RFC 7011, DOI 10.17487/RFC7011, September 2013,

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   [RFC7217]  Gont, F., "A Method for Generating Semantically Opaque
              Interface Identifiers with IPv6 Stateless Address
              Autoconfiguration (SLAAC)", RFC 7217,
              DOI 10.17487/RFC7217, April 2014,

   [RFC7224]  Bjorklund, M., "IANA Interface Type YANG Module",
              RFC 7224, DOI 10.17487/RFC7224, May 2014,

   [RFC7317]  Bierman, A. and M. Bjorklund, "A YANG Data Model for
              System Management", RFC 7317, DOI 10.17487/RFC7317, August
              2014, <>.

   [RFC7404]  Behringer, M. and E. Vyncke, "Using Only Link-Local
              Addressing inside an IPv6 Network", RFC 7404,
              DOI 10.17487/RFC7404, November 2014,

   [RFC7527]  Asati, R., Singh, H., Beebee, W., Pignataro, C., Dart, E.,
              and W. George, "Enhanced Duplicate Address Detection",
              RFC 7527, DOI 10.17487/RFC7527, April 2015,

   [RFC7608]  Boucadair, M., Petrescu, A., and F. Baker, "IPv6 Prefix
              Length Recommendation for Forwarding", BCP 198, RFC 7608,
              DOI 10.17487/RFC7608, July 2015,

   [RFC7663]  Trammell, B., Ed. and M. Kuehlewind, Ed., "Report from the
              IAB Workshop on Stack Evolution in a Middlebox Internet
              (SEMI)", RFC 7663, DOI 10.17487/RFC7663, October 2015,

   [RFC7772]  Yourtchenko, A. and L. Colitti, "Reducing Energy
              Consumption of Router Advertisements", BCP 202, RFC 7772,
              DOI 10.17487/RFC7772, February 2016,

   [RFC7922]  Clarke, J., Salgueiro, G., and C. Pignataro, "Interface to
              the Routing System (I2RS) Traceability: Framework and
              Information Model", RFC 7922, DOI 10.17487/RFC7922, June
              2016, <>.

   [RFC7934]  Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi,
              "Host Address Availability Recommendations", BCP 204,
              RFC 7934, DOI 10.17487/RFC7934, July 2016,

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   [RFC7980]  Behringer, M., Retana, A., White, R., and G. Huston, "A
              Framework for Defining Network Complexity", RFC 7980,
              DOI 10.17487/RFC7980, October 2016,

   [RFC7991]  Hoffman, P., "The "xml2rfc" Version 3 Vocabulary",
              RFC 7991, DOI 10.17487/RFC7991, December 2016,

   [RFC8028]  Baker, F. and B. Carpenter, "First-Hop Router Selection by
              Hosts in a Multi-Prefix Network", RFC 8028,
              DOI 10.17487/RFC8028, November 2016,

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,

   [RFC8106]  Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
              "IPv6 Router Advertisement Options for DNS Configuration",
              RFC 8106, DOI 10.17487/RFC8106, March 2017,

   [RFC8170]  Thaler, D., Ed., "Planning for Protocol Adoption and
              Subsequent Transitions", RFC 8170, DOI 10.17487/RFC8170,
              May 2017, <>.

   [RFC8201]  McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
              "Path MTU Discovery for IP version 6", STD 87, RFC 8201,
              DOI 10.17487/RFC8201, July 2017,

   [RFC8273]  Brzozowski, J. and G. Van de Velde, "Unique IPv6 Prefix
              per Host", RFC 8273, DOI 10.17487/RFC8273, December 2017,

   [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore Architecture
              (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,

   [RFC8343]  Bjorklund, M., "A YANG Data Model for Interface
              Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,

   [RFC8344]  Bjorklund, M., "A YANG Data Model for IP Management",
              RFC 8344, DOI 10.17487/RFC8344, March 2018,

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   [RFC8345]  Clemm, A., Medved, J., Varga, R., Bahadur, N.,
              Ananthakrishnan, H., and X. Liu, "A YANG Data Model for
              Network Topologies", RFC 8345, DOI 10.17487/RFC8345, March
              2018, <>.

   [RFC8346]  Clemm, A., Medved, J., Varga, R., Liu, X.,
              Ananthakrishnan, H., and N. Bahadur, "A YANG Data Model
              for Layer 3 Topologies", RFC 8346, DOI 10.17487/RFC8346,
              March 2018, <>.

   [RFC8349]  Lhotka, L., Lindem, A., and Y. Qu, "A YANG Data Model for
              Routing Management (NMDA Version)", RFC 8349,
              DOI 10.17487/RFC8349, March 2018,

Authors' Addresses

   Zaid Ali Kahn (editor)


   John Brzozowski (editor)


   Russ White (editor)
   Oak Island, NC  28465


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