Internet DRAFT - draft-bonica-intarea-func-path
draft-bonica-intarea-func-path
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
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This Internet-Draft will expire on December 30, 2021.
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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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