< draft-ietf-babel-applicability-08.txt   draft-ietf-babel-applicability-09.txt >
Network Working Group J. Chroboczek Network Working Group J. Chroboczek
Internet-Draft IRIF, University of Paris-Diderot Internet-Draft IRIF, University of Paris-Diderot
Intended status: Informational August 5, 2019 Intended status: Informational August 7, 2019
Expires: February 6, 2020 Expires: February 8, 2020
Applicability of the Babel routing protocol Applicability of the Babel routing protocol
draft-ietf-babel-applicability-08 draft-ietf-babel-applicability-09
Abstract Abstract
Babel is a routing protocol based on the distance-vector algorithm Babel is a routing protocol based on the distance-vector algorithm
augmented with mechanisms for loop avoidance and starvation augmented with mechanisms for loop avoidance and starvation
avoidance. This document describes a number of niches where Babel avoidance. This document describes a number of niches where Babel
has been found to be useful and that are arguably not adequately has been found to be useful and that are arguably not adequately
served by more mature protocols. served by more mature protocols.
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 6, 2020. This Internet-Draft will expire on February 8, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction and background . . . . . . . . . . . . . . . . . 2 1. Introduction and background . . . . . . . . . . . . . . . . . 2
1.1. Technical overview of the Babel protocol . . . . . . . . 2 1.1. Technical overview of the Babel protocol . . . . . . . . 2
2. Properties of the Babel protocol . . . . . . . . . . . . . . 3 2. Properties of the Babel protocol . . . . . . . . . . . . . . 3
2.1. Simplicity and implementability . . . . . . . . . . . . . 3 2.1. Simplicity and implementability . . . . . . . . . . . . . 3
2.2. Robustness . . . . . . . . . . . . . . . . . . . . . . . 3 2.2. Robustness . . . . . . . . . . . . . . . . . . . . . . . 3
2.3. Extensibility . . . . . . . . . . . . . . . . . . . . . . 4 2.3. Extensibility . . . . . . . . . . . . . . . . . . . . . . 5
2.4. Limitations . . . . . . . . . . . . . . . . . . . . . . . 5 2.4. Limitations . . . . . . . . . . . . . . . . . . . . . . . 5
3. Successful deployments of Babel . . . . . . . . . . . . . . . 6 3. Successful deployments of Babel . . . . . . . . . . . . . . . 6
3.1. Heterogeneous networks . . . . . . . . . . . . . . . . . 6 3.1. Heterogeneous networks . . . . . . . . . . . . . . . . . 6
3.2. Large scale overlay networks . . . . . . . . . . . . . . 7 3.2. Large scale overlay networks . . . . . . . . . . . . . . 7
3.3. Pure mesh networks . . . . . . . . . . . . . . . . . . . 7 3.3. Pure mesh networks . . . . . . . . . . . . . . . . . . . 7
3.4. Small unmanaged networks . . . . . . . . . . . . . . . . 7 3.4. Small unmanaged networks . . . . . . . . . . . . . . . . 7
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8 7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informational References . . . . . . . . . . . . . . . . 8 7.2. Informational References . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction and background 1. Introduction and background
Babel [RFC6126bis] is a routing protocol based on the familiar Babel [RFC6126bis] is a routing protocol based on the familiar
distance-vector algorithm (sometimes known as distributed Bellman- distance-vector algorithm (sometimes known as distributed Bellman-
Ford) augmented with mechanisms for loop avoidance (there is no Ford) augmented with mechanisms for loop avoidance (there is no
"counting to infinity") and starvation avoidance. This document "counting to infinity") and starvation avoidance. This document
describes a number of niches where Babel is useful and that are describes a number of niches where Babel is useful and that are
arguably not adequately served by more mature protocols such as OSPF arguably not adequately served by more mature protocols such as OSPF
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transitive, and it does not require that the metric be discrete transitive, and it does not require that the metric be discrete
(continuous metrics are possible, reflecting for example packet loss (continuous metrics are possible, reflecting for example packet loss
rates). This is in contrast to link-state routing protocols such as rates). This is in contrast to link-state routing protocols such as
OSPF [RFC5340] or IS-IS [RFC1195], which incorporate a reliable OSPF [RFC5340] or IS-IS [RFC1195], which incorporate a reliable
flooding algorithm and make stronger requirements on the underlying flooding algorithm and make stronger requirements on the underlying
network and metric. network and metric.
These weak requirements make Babel a robust protocol: These weak requirements make Babel a robust protocol:
o robust with respect to unusual networks: an unusual network (non- o robust with respect to unusual networks: an unusual network (non-
transitive links, unstable metrics, etc.) does most likely not transitive links, unstable link costs, etc.) is likely not to
violate the assumptions of the protocol; violate the assumptions of the protocol;
o robust with respect to novel metrics: no matter how strange your o robust with respect to novel metrics: an unusual metric
metric (continuous, constantly fluctuating, etc.), it does most (continuous, constantly fluctuating, etc.) is likely not to
likely not violate the assumptions of the protocol. violate the assumptions of the protocol.
Section 3 below gives examples of successful deployments of Babel
that illustrate these properties.
In addition to the above, our implementation experience indicates In addition to the above, our implementation experience indicates
that Babel tends to be robust with respect to bugs: more often than that Babel tends to be robust with respect to bugs: in many cases, an
not, an implementation bug does not violate the properties on which implementation bug does not violate the properties on which Babel
Babel relies, and therefore slows down convergence or causes sub- relies, and therefore slows down convergence or causes sub-optimal
optimal routing rather than causing the network to collapse. routing rather than causing the network to collapse.
These robustness properties have important consequences for the These robustness properties have important consequences for the
applicability of the protocol: Babel works (more or less efficiently) applicability of the protocol: Babel works (more or less efficiently)
in a wide range of circumstances where traditional routing protocols in a range of circumstances where traditional routing protocols don't
give up. work well (or at all).
2.3. Extensibility 2.3. Extensibility
Babel's packet format has a number of features that make the protocol Babel's packet format has a number of features that make the protocol
extensible (see Appendix C of [RFC6126bis]), and a number of extensible (see Appendix C of [RFC6126bis]), and a number of
extensions have been designed to make Babel work better in situations extensions have been designed to make Babel work better in situations
that were not envisioned when the protocol was initially designed. that were not envisioned when the protocol was initially designed.
The ease of extensibility is not an accident, but a consequence of The ease of extensibility is not an accident, but a consequence of
the design of the protocol: it is reasonably easy to check whether a the design of the protocol: it is reasonably easy to check whether a
given extension violates the assumptions on which Babel relies. given extension violates the assumptions on which Babel relies.
All of the extensions designed to date interoperate with the base All of the extensions designed to date interoperate with the base
protocol and with each other. This, again, is a consequence of the protocol and with each other. This, again, is a consequence of the
protocol design: in order to check that two extensions to the Babel protocol design: in order to check that two extensions to the Babel
protocol are interoperable, it is enough to verify that the protocol are interoperable, it is enough to verify that the
interaction of the two does not violate the base protocol's interaction of the two does not violate the base protocol's
assumptions. assumptions.
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where applicable, and can be configured to filter out redundant where applicable, and can be configured to filter out redundant
announcements (manual aggregation). Just like specialised mesh announcements (manual aggregation). Just like specialised mesh
protocols, Babel doesn't by default assume that links are transitive protocols, Babel doesn't by default assume that links are transitive
or symmetric, can dynamically compute metrics based on an estimation or symmetric, can dynamically compute metrics based on an estimation
of link quality, and carries large numbers of host routes efficiently of link quality, and carries large numbers of host routes efficiently
by omitting common prefixes. by omitting common prefixes.
Because of these properties, Babel has seen a number of successful Because of these properties, Babel has seen a number of successful
deployments in medium-sized heterogeneous networks, networks that deployments in medium-sized heterogeneous networks, networks that
combine a wired, aggregated backbone with meshy wireless bits at the combine a wired, aggregated backbone with meshy wireless bits at the
edges. No other routing protocol known to us is similarly robust and edges.
efficient in this particular kind of topology.
Efficient operation in heterogeneous networks requires the Efficient operation in heterogeneous networks requires the
implementation to distinguish between wired and wireless links, and implementation to distinguish between wired and wireless links, and
to perform link quality estimation on wireless links. to perform link quality estimation on wireless links.
3.2. Large scale overlay networks 3.2. Large scale overlay networks
The algorithms used by Babel (loop avoidance, hysteresis, delayed The algorithms used by Babel (loop avoidance, hysteresis, delayed
updates) allow it to remain stable and efficient in the presence of updates) allow it to remain stable and efficient in the presence of
unstable metrics, even in the presence of a feedback loop. For this unstable metrics, even in the presence of a feedback loop. For this
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