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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Unused Reference: 'RFC8126' is defined on line 211, but no explicit reference was found in the text Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Intarea Working Group R. Bonica 3 Internet-Draft Juniper Networks 4 Intended status: Informational June 28, 2021 5 Expires: December 30, 2021 7 Router Terminology: Functions and Paths 8 draft-bonica-intarea-func-path-00 10 Abstract 12 This document distinguishes between the terms "function" and "path". 13 It also recommends against use of the terms "fast path", "slow path", 14 and "host path" in IETF documents. However, it defines the terms 15 "congestion vulnerable path" and "congestion critical path". 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at https://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on December 30, 2021. 34 Copyright Notice 36 Copyright (c) 2021 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (https://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 52 2. Functions . . . . . . . . . . . . . . . . . . . . . . . . . . 2 53 3. Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 4. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 3 55 4.1. Function Versus Path . . . . . . . . . . . . . . . . . . 3 56 4.2. Function Versus Plane . . . . . . . . . . . . . . . . . . 4 57 4.3. Path Through A Router . . . . . . . . . . . . . . . . . . 4 58 4.4. Path Through A Network . . . . . . . . . . . . . . . . . 5 59 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 60 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 61 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 62 8. Normative References . . . . . . . . . . . . . . . . . . . . 5 63 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 65 1. Introduction 67 Routers execute the following functions upon packets: 69 o Forward the packet. 71 o Consume the packet as part of a control function. 73 o Consume the packet as part of a management function. 75 A packet follows a path through a router. The path contains hardware 76 components and can be determined by the function that the router 77 executes upon the packet. 79 Many routers dedicate hardware components to functions. This has 80 caused the IETF community to use the terms "function" and "path" 81 interchangeably. It has also caused the IETF community to use the 82 terms "fast path" and "slow path". 84 This document distinguishes between the terms "function" and "path". 85 It also recommends against use of the terms "fast path", and "slow 86 path", and "host path" in IETF documents. However, it defines the 87 terms "congestion vulnerable path" and "congestion critical path". 89 2. Functions 91 Routers perform forwarding, control, and management functions. The 92 forwarding function accepts a packet from an incoming interface, 93 identifies an outgoing interface, and transmits the packet through 94 the outgoing interface. Most routers benefit from statistical 95 multiplexing. As a side effect of statistical multiplexing, the 96 forwarding function is subject to congestion and packet loss. 98 The control function builds a Forwarding Information Base (FIB) that 99 the forwarding function uses. The FIB identifies the interface 100 through which a packet should be transmitted. Control functions 101 include routing and signaling protocols. While routing and signaling 102 protocols can tolerate transient congestion and packet loss, 103 prolonged congestion can cause serious forwarding plane failures. 105 The management function allows controllers and network management 106 stations to manage router behaviors. It includes fault, 107 configuration, and performance management protocols. While 108 management protocols can tolerate transient congestion and packet 109 loss, they must always be available. Loss of management function 110 impairs an operator's ability to recover from failures. 112 3. Paths 114 A packet follows a path through a router. The path contains various 115 hardware components and depends upon router architecture. 117 Some routers dedicate hardware components to functions. For example, 118 some Internet core routers have network processor cards and line 119 cards. A line card has one or more network interfaces and supports 120 much higher throughput than the network processor card. These core 121 routers forward packets from one interface to another without 122 traversing the network processor card. This path through the router 123 is sometimes called the "fast path". While congestion is not 124 desirable on the fast path, it is not catastrophic. 126 Those same core routers send management and control packets to the 127 network processor card. This path through the router is sometimes 128 called the "slow path" or the "host path". While transient host path 129 congestion is tolerable, persistent congestion can cause catastrophic 130 failure. 132 Other routers (e.g., home routers) do not dedicate hardware 133 components to functions. All packets traverse the same path through 134 the router, regardless of their function. Therefore, they do not 135 have a "fast path" or a "slow path". 137 4. Recommendations 139 4.1. Function Versus Path 141 The terms "function" and "path" have distinct meanings. They should 142 not be used interchangeably. 144 A packet's function is an externally observable behavior and is 145 independent of router architecture. A packet's path through the 146 router is not externally observable and depends upon router 147 architecture. 149 4.2. Function Versus Plane 151 The following terms are used interchangeably in the IETF: 153 o Forwarding Function and Forwarding Plane 155 o Control Function and Control Plane 157 o Management Function and Management Plane 159 While these terms can be used interchangeably, the term "function" is 160 more descriptive. 162 4.3. Path Through A Router 164 IETF documents should document a network device's externally 165 observable behaviors. They should avoid discussion of a network 166 device's internal architecture. Therefore, IETF documents should 167 avoid the following terms: 169 o Slow path 171 o Fast path 173 o Host path 175 However, some paths through a router can be more vulnerable to 176 congestion than others. These include: 178 o Low bandwidth paths 180 o Paths that cannot be protected by user configurable classifiers 181 and rate limits 183 o Paths that, by default, are not protected by user configurable 184 classifiers and rate limits 186 IETF documents should refer to these as "congestion vulnerable 187 paths". When control or management traffic traverses a congestion 188 vulnerable path, the path becomes a "congestion critical path". 190 4.4. Path Through A Network 192 IETF documents should continue to use the term "path" when it refers 193 to a packet's path through a network. A packets path through a 194 network does not depend on the architecture of any network device. 196 5. Security Considerations 198 This document addresses IETF terminology and does not introduce any 199 security considerations. 201 6. IANA Considerations 203 This document makes no requests of IANA. 205 7. Acknowledgements 207 Thanks to John Scudder for reading this draft. 209 8. Normative References 211 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 212 Writing an IANA Considerations Section in RFCs", BCP 26, 213 RFC 8126, DOI 10.17487/RFC8126, June 2017, 214 . 216 Author's Address 218 Ron Bonica 219 Juniper Networks 220 2251 Corporate Park Drive 221 Herndon, Virginia 20171 222 USA 224 Email: rbonica@juniper.net