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Versions: 00                                                            
Intarea Working Group                                          R. Bonica
Internet-Draft                                          Juniper Networks
Intended status: Informational                             June 28, 2021
Expires: December 30, 2021


                Router Terminology: Functions and Paths
                   draft-bonica-intarea-func-path-00

Abstract

   This document distinguishes between the terms "function" and "path".
   It also recommends against use of the terms "fast path", "slow path",
   and "host path" in IETF documents.  However, it defines the terms
   "congestion vulnerable path" and "congestion critical path".

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 December 30, 2021.

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.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Functions . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Recommendations . . . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Function Versus Path  . . . . . . . . . . . . . . . . . .   3
     4.2.  Function Versus Plane . . . . . . . . . . . . . . . . . .   4
     4.3.  Path Through A Router . . . . . . . . . . . . . . . . . .   4
     4.4.  Path Through A Network  . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   Routers execute the following functions upon packets:

   o  Forward the packet.

   o  Consume the packet as part of a control function.

   o  Consume the packet as part of a management function.

   A packet follows a path through a router.  The path contains hardware
   components and can be determined by the function that the router
   executes upon the packet.

   Many routers dedicate hardware components to functions.  This has
   caused the IETF community to use the terms "function" and "path"
   interchangeably.  It has also caused the IETF community to use the
   terms "fast path" and "slow path".

   This document distinguishes between the terms "function" and "path".
   It also recommends against use of the terms "fast path", and "slow
   path", and "host path" in IETF documents.  However, it defines the
   terms "congestion vulnerable path" and "congestion critical path".

2.  Functions

   Routers perform forwarding, control, and management functions.  The
   forwarding function accepts a packet from an incoming interface,
   identifies an outgoing interface, and transmits the packet through
   the outgoing interface.  Most routers benefit from statistical
   multiplexing.  As a side effect of statistical multiplexing, the
   forwarding function is subject to congestion and packet loss.



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   The control function builds a Forwarding Information Base (FIB) that
   the forwarding function uses.  The FIB identifies the interface
   through which a packet should be transmitted.  Control functions
   include routing and signaling protocols.  While routing and signaling
   protocols can tolerate transient congestion and packet loss,
   prolonged congestion can cause serious forwarding plane failures.

   The management function allows controllers and network management
   stations to manage router behaviors.  It includes fault,
   configuration, and performance management protocols.  While
   management protocols can tolerate transient congestion and packet
   loss, they must always be available.  Loss of management function
   impairs an operator's ability to recover from failures.

3.  Paths

   A packet follows a path through a router.  The path contains various
   hardware components and depends upon router architecture.

   Some routers dedicate hardware components to functions.  For example,
   some Internet core routers have network processor cards and line
   cards.  A line card has one or more network interfaces and supports
   much higher throughput than the network processor card.  These core
   routers forward packets from one interface to another without
   traversing the network processor card.  This path through the router
   is sometimes called the "fast path".  While congestion is not
   desirable on the fast path, it is not catastrophic.

   Those same core routers send management and control packets to the
   network processor card.  This path through the router is sometimes
   called the "slow path" or the "host path".  While transient host path
   congestion is tolerable, persistent congestion can cause catastrophic
   failure.

   Other routers (e.g., home routers) do not dedicate hardware
   components to functions.  All packets traverse the same path through
   the router, regardless of their function.  Therefore, they do not
   have a "fast path" or a "slow path".

4.  Recommendations

4.1.  Function Versus Path

   The terms "function" and "path" have distinct meanings.  They should
   not be used interchangeably.

   A packet's function is an externally observable behavior and is
   independent of router architecture.  A packet's path through the



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   router is not externally observable and depends upon router
   architecture.

4.2.  Function Versus Plane

   The following terms are used interchangeably in the IETF:

   o  Forwarding Function and Forwarding Plane

   o  Control Function and Control Plane

   o  Management Function and Management Plane

   While these terms can be used interchangeably, the term "function" is
   more descriptive.

4.3.  Path Through A Router

   IETF documents should document a network device's externally
   observable behaviors.  They should avoid discussion of a network
   device's internal architecture.  Therefore, IETF documents should
   avoid the following terms:

   o  Slow path

   o  Fast path

   o  Host path

   However, some paths through a router can be more vulnerable to
   congestion than others.  These include:

   o  Low bandwidth paths

   o  Paths that cannot be protected by user configurable classifiers
      and rate limits

   o  Paths that, by default, are not protected by user configurable
      classifiers and rate limits

   IETF documents should refer to these as "congestion vulnerable
   paths".  When control or management traffic traverses a congestion
   vulnerable path, the path becomes a "congestion critical path".








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4.4.  Path Through A Network

   IETF documents should continue to use the term "path" when it refers
   to a packet's path through a network.  A packets path through a
   network does not depend on the architecture of any network device.

5.  Security Considerations

   This document addresses IETF terminology and does not introduce any
   security considerations.

6.  IANA Considerations

   This document makes no requests of IANA.

7.  Acknowledgements

   Thanks to John Scudder for reading this draft.

8.  Normative References

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

Author's Address

   Ron Bonica
   Juniper Networks
   2251 Corporate Park Drive
   Herndon, Virginia  20171
   USA

   Email: rbonica@juniper.net
















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