draft-ietf-homenet-prefix-assignment-08.txt   rfc7695.txt 
Network Working Group P. Pfister Internet Engineering Task Force (IETF) P. Pfister
Internet-Draft B. Paterson Request for Comments: 7695 B. Paterson
Intended status: Standards Track Cisco Systems Category: Standards Track Cisco Systems
Expires: February 25, 2016 J. Arkko ISSN: 2070-1721 J. Arkko
Ericsson Ericsson
August 24, 2015 November 2015
Distributed Prefix Assignment Algorithm Distributed Prefix Assignment Algorithm
draft-ietf-homenet-prefix-assignment-08
Abstract Abstract
This document specifies a distributed algorithm for dividing a set of This document specifies a distributed algorithm for dividing a set of
prefixes in a manner that allows for automatic assignment of sub- prefixes in a manner that allows for automatic assignment of sub-
prefixes that are unique and non-overlapping. Used in conjunction prefixes that are unique and non-overlapping. Used in conjunction
with a protocol that provides flooding of information among a set of with a protocol that provides flooding of information among a set of
participating nodes, prefix configuration within a network may be participating nodes, prefix configuration within a network may be
automated. automated.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
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 http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on February 25, 2016. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7695.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 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
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
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 . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Subroutine Specific Terminology . . . . . . . . . . . . . 5 2.1. Subroutine-Specific Terminology . . . . . . . . . . . . . 6
3. Applicability Statement . . . . . . . . . . . . . . . . . . . 7 3. Applicability Statement . . . . . . . . . . . . . . . . . . . 7
4. Algorithm Specification . . . . . . . . . . . . . . . . . . . 8 4. Algorithm Specification . . . . . . . . . . . . . . . . . . . 9
4.1. Prefix Assignment Algorithm Subroutine . . . . . . . . . 9 4.1. Prefix Assignment Algorithm Subroutine . . . . . . . . . 9
4.2. Overriding and Destroying Existing Assignments . . . . . 12 4.2. Overriding and Destroying Existing Assignments . . . . . 12
4.3. Other Events . . . . . . . . . . . . . . . . . . . . . . 13 4.3. Other Events . . . . . . . . . . . . . . . . . . . . . . 13
5. Prefix Selection Considerations . . . . . . . . . . . . . . . 13 5. Prefix Selection Considerations . . . . . . . . . . . . . . . 14
6. Implementation Capabilities and Node Behavior . . . . . . . . 16 6. Implementation Capabilities and Node Behavior . . . . . . . . 16
7. Algorithm Parameters . . . . . . . . . . . . . . . . . . . . 17 7. Algorithm Parameters . . . . . . . . . . . . . . . . . . . . 17
8. Security Considerations . . . . . . . . . . . . . . . . . . . 17 8. Security Considerations . . . . . . . . . . . . . . . . . . . 17
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
11.1. Normative References . . . . . . . . . . . . . . . . . . 18 11.1. Normative References . . . . . . . . . . . . . . . . . . 18
11.2. Informative References . . . . . . . . . . . . . . . . . 18 11.2. Informative References . . . . . . . . . . . . . . . . . 18
Appendix A. Static Configuration Example . . . . . . . . . . . . 19 Appendix A. Static Configuration Example . . . . . . . . . . . . 19
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction 1. Introduction
This document specifies a distributed algorithm for automatic prefix This document specifies a distributed algorithm for automatic prefix
assignment. The algorithm provides a generic alternative to assignment. The algorithm provides a generic alternative to
centralized (human or software based) approaches for network prefix centralized (human- or software-based) approaches for network prefix
and address assignment. Although it does not require to be and address assignment. Although it does not have to be configured
configured to operate properly, it supports custom configuration by to operate properly, it supports custom configuration by means of
means of variable priority assignments, and can therefore be used in variable priority assignments, and can therefore be used in fully
fully autonomic as well as configured networks. This document autonomic as well as configured networks. This document focuses on
focuses on the algorithm itself and therefore leaves as out of scope the algorithm itself and therefore context-specific considerations
context-specific considerations, such as the process of selecting a (such as the process of selecting a prefix value and length when
prefix value and length when making a new assignment. making a new assignment) are out of scope.
The algorithm makes use of a flooding mechanism allowing The algorithm makes use of a flooding mechanism allowing
participating Nodes to advertise prefixes assigned to the links they participating nodes to advertise prefixes assigned to the links to
are directly connected to or for other purposes, e.g., for private which they are directly connected or for other purposes, e.g., for
assignment or prefix delegation. Advertising a prefix therefore private assignment or prefix delegation. Advertising a prefix
serves two purposes. It is a claim that a prefix is in use, meaning therefore serves two purposes. It is a claim that a prefix is in
that no other Node may advertise an overlapping prefix (unless it has use, meaning that no other node may advertise an overlapping prefix
a greater priority). And it is a way for other Nodes to know which (unless it has a greater priority). And, it is a way for other nodes
prefixes have been assigned to the links they are directly connected to know which prefixes have been assigned to the links to which they
to. are directly connected.
The algorithm is given a set of delegated prefixes, and ensures that The algorithm is given a set of delegated prefixes and ensures that
the following assertions are satisfied after a finite convergence the following assertions are satisfied after a finite convergence
period: period:
1. At most one prefix from each delegated prefix is assigned to each 1. At most one prefix from each delegated prefix is assigned to each
link. link.
2. Assigned prefixes are non-overlapping (i.e., an assigned prefix 2. Assigned prefixes are non-overlapping (i.e., an assigned prefix
never includes another assigned prefix). never includes another assigned prefix).
3. Assigned prefixes do not change in the absence of topology or 3. Assigned prefixes do not change in the absence of topology or
configuration changes. configuration changes.
In the rest of this document the two first conditions are referred to In the rest of this document, the two first conditions are referred
as the correctness conditions of the algorithm while the third to as the correctness conditions of the algorithm, while the third
condition is referred to as its convergence condition. condition is referred to as its convergence condition.
Each assignment has a priority specified by the Node making the Each assignment has a priority specified by the node making the
assignment, allowing for custom assignment policies. When multiple assignment, allowing for custom assignment policies. When multiple
Nodes assign different prefixes from the same delegated prefix to the nodes assign different prefixes from the same delegated prefix to the
same link, or when multiple Nodes assign overlapping prefixes (to the same link, or when multiple nodes assign overlapping prefixes (to the
same link or to different links), the assignment with the greatest same link or to different links), the assignment with the greatest
priority is kept and other assignments are removed. priority is kept and other assignments are removed.
The prefix assignment algorithm requires that participating Nodes The prefix assignment algorithm requires that participating nodes
share information through a flooding mechanism. If the flooding share information through a flooding mechanism. If the flooding
mechanism ensures that all messages are propagated to all Nodes mechanism ensures that all messages are propagated to all nodes
within a given time window, the algorithm also ensures that all within a given time window, the algorithm also ensures that all
assigned prefixes used for networking operations (e.g., host assigned prefixes used for networking operations (e.g., host
configuration) remain unchanged, unless another Node assigns an configuration) remain unchanged, unless another node assigns an
overlapping prefix with a higher assignment priority, or the topology overlapping prefix with a higher assignment priority, or the topology
changes and renumbering cannot be avoided. changes and renumbering cannot be avoided.
2. Definitions 2. Definitions
In this document, the key words "MUST", "MUST NOT", "REQUIRED", In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in [RFC2119]. and "OPTIONAL" are to be interpreted as described in [RFC2119].
This document makes use of the following terminology. The terms This document makes use of the following terminology. The terms
defined here are ordered in such a way as to try to avoid forward defined here are ordered in such a way as to try to avoid forward
references, and therefore are not sorted alphabetically. references, and therefore are not sorted alphabetically.
Node: An entity executing the algorithm specified in this document Node: An entity executing the algorithm specified in this document
and able to communicate with other Nodes using the Flooding and able to communicate with other Nodes using the Flooding
Mechanism. Mechanism.
Flooding Mechanism: A mechanism allowing participating Nodes to Flooding Mechanism: A mechanism allowing participating Nodes to
reliably share information with all other participating Nodes. reliably share information with all other participating Nodes.
Link: An object the distributed algorithm will assign prefixes to. Link: An object to which the distributed algorithm will assign
A Node may only assign prefixes to Links it is directly connected prefixes. A Node may only assign prefixes to Links to which it is
to. A Link is either Shared or Private. directly connected. A Link is either Shared or Private.
Shared Link: A Link multiple Nodes may be connected to. Most of Shared Link: A Link to which multiple Nodes may be connected. Most
the time, a Shared Link is a multi-access link or point-to-point of the time, a Shared Link is a multi-access link or point-to-
link, virtual or physical, requiring prefixes to be assigned to point link, virtual or physical, requiring prefixes to be assigned
it. to it.
Private Link: A Private Link is an abstract concept defined for the Private Link: A Private Link is an abstract concept defined for the
sake of this document. It allows Nodes to make assignments for sake of this document. It allows Nodes to make assignments for
their private use or delegation. For instance, every DHCPv6-PD their private use or delegation. For instance, every DHCPv6-PD
[RFC3633] requesting router may be considered as a different [RFC3633] requesting router may be considered as a different
Private Link. Private Link.
Delegated Prefix: A prefix provided to the algorithm and used as a Delegated Prefix: A prefix provided to the algorithm and used as a
prefix pool for Assigned Prefixes. prefix pool for Assigned Prefixes.
Node ID: A value identifying a given participating Node. The set Node ID: A value identifying a given participating Node. The set
of identifiers MUST be strictly and totally ordered (e.g., using of identifiers MUST be strictly and totally ordered (e.g., using
the alphanumeric order). The mechanism used to assign Node IDs, the alphanumeric order). The mechanism used to assign Node IDs,
whether manual or automated, is out of the scope of this document. whether manual or automated, is out of scope for this document.
Flooding Delay: A value which MUST be provided by the Flooding Flooding Delay: A value that MUST be provided by the Flooding
Mechanism and SHOULD be a deterministic or likely upper bound on Mechanism and SHOULD be a deterministic or likely upper bound on
the information propagation delay among participating Nodes. the information propagation delay among participating Nodes.
Advertised Prefix: A prefix advertised by another Node and Advertised Prefix: A prefix advertised by another Node and
delivered to the local Node by the Flooding Mechanism. It has an delivered to the local Node by the Flooding Mechanism. It has an
Advertised Prefix Priority and, when assigned to a directly Advertised Prefix Priority and, when assigned to a directly
connected Shared Link, is associated with that Shared Link. connected Shared Link, is associated with that Shared Link.
Advertised Prefix Priority: A value that defines the priority of an Advertised Prefix Priority: A value that defines the priority of an
Advertised Prefix received from the Flooding Mechanism or a Advertised Prefix received from the Flooding Mechanism or a
published Assigned Prefix. Whenever multiple Advertised Prefixes published Assigned Prefix. Whenever multiple Advertised Prefixes
are conflicting (i.e., overlapping or from the same Delegated are conflicting (i.e., overlapping or from the same Delegated
Prefix and assigned to the same link), all Advertised Prefixes but Prefix and assigned to the same link), all Advertised Prefixes but
the one with the greatest priority will eventually be removed. In the one with the greatest priority will eventually be removed. In
case of a tie, the assignment advertised by the Node with the case of a tie, the assignment advertised by the Node with the
greatest Node ID is kept and others are removed. In order to greatest Node ID is kept, and others are removed. In order to
ensure convergence, the range of priority values MUST have an ensure convergence, the range of priority values MUST have an
upper bound. upper bound.
Assigned Prefix: A prefix included in a Delegated Prefix and Assigned Prefix: A prefix included in a Delegated Prefix and
assigned to a Shared or Private Link. It represents a local assigned to a Shared or Private Link. It represents a local
decision to assign a given prefix from a given Delegated Prefix to decision to assign a given prefix from a given Delegated Prefix to
a given Link. The algorithm ensures that there is never more than a given Link. The algorithm ensures that there is never more than
one Assigned Prefix per Delegated Prefix and Link pair. When one Assigned Prefix per Delegated Prefix and Link pair. When
destroyed, an Assigned Prefix is set as not applied, ceases to be destroyed, an Assigned Prefix is set as not applied, ceases to be
advertised, and is removed from the set of Assigned Prefixes. advertised, and is removed from the set of Assigned Prefixes.
skipping to change at page 5, line 29 skipping to change at page 5, line 32
through the Flooding Mechanism as assigned to its associated Link. through the Flooding Mechanism as assigned to its associated Link.
A published Assigned Prefix MUST have an Advertised Prefix A published Assigned Prefix MUST have an Advertised Prefix
Priority. It will appear as an Advertised Prefix to other Nodes, Priority. It will appear as an Advertised Prefix to other Nodes,
once received from the Flooding Mechanism. once received from the Flooding Mechanism.
Destroy (an Assigned Prefix): Local action of removing an Assigned Destroy (an Assigned Prefix): Local action of removing an Assigned
Prefix from the set of Assigned Prefixes. If applied, the prefix Prefix from the set of Assigned Prefixes. If applied, the prefix
is unapplied. If published, the prefix stops being advertised is unapplied. If published, the prefix stops being advertised
through the Flooding Mechanism. through the Flooding Mechanism.
Prefix Adoption: When an Advertised Prefix which does not conflict Prefix Adoption: When an Advertised Prefix that does not conflict
with any other Advertised Prefix or published Assigned Prefix with any other Advertised Prefix or published Assigned Prefix
stops being advertised, any other Node connected to the same Link stops being advertised, any other Node connected to the same Link
may, after some random delay, start advertising the same prefix. may, after some random delay, start advertising the same prefix.
This procedure is called adoption and provides seamless assignment This procedure is called adoption and provides seamless assignment
transfer from a Node to another, e.g., in case of Node failure. transfer from a Node to another, e.g., in case of Node failure.
Backoff Timer: Every Delegated Prefix and Link pair is associated Backoff Timer: Every Delegated Prefix and Link pair is associated
with a timer counting down to zero. It is used to reduce the with a timer counting down to zero. By delaying the creation of
probability of colliding assignments made by multiple Nodes by new Assigned Prefixes or the advertisement of adopted Assigned
delaying the creation of new Assigned Prefixes or the Prefixes by a random amount of time, it reduces the probability of
advertisement of adopted Assigned Prefixes by a random amount of colliding assignments made by multiple Nodes.
time.
Renumbering: Event occurring when an Assigned Prefix which was Renumbering: Event occurring when an Assigned Prefix that was
applied is destroyed. Renumbering is undesirable as it usually applied is destroyed. Renumbering is undesirable as it usually
implies reconfiguring routers or hosts. implies reconfiguring routers or hosts.
2.1. Subroutine Specific Terminology 2.1. Subroutine-Specific Terminology
In addition to the terms defined in Section 2, the subroutine In addition to the terms defined in Section 2, the subroutine
specified in Section 4 makes use of the following terms. specified in Section 4 makes use of the following terms.
Current Assignment: For a given Delegated Prefix and Link, the Current Assignment: For a given Delegated Prefix and Link, the
Current Assignment is the Assigned Prefix (if any) included in the Current Assignment is the Assigned Prefix (if any) included in the
Delegated Prefix and assigned to the given Link by the Node Delegated Prefix and assigned to the given Link by the Node
executing the algorithm. At some point in time, the Current executing the algorithm. At some point in time, the Current
Assignment from different Nodes may differ, but the algorithm Assignment from different Nodes may differ, but the algorithm
ensures that eventually, all Nodes directly connected to a Shared ensures that, eventually, all Nodes directly connected to a Shared
Link have the same Current Assignment for any given Delegated Link have the same Current Assignment for any given Delegated
Prefix. Prefix.
Precedence: An Advertised Prefix takes precedence over an Assigned Precedence: An Advertised Prefix takes precedence over an Assigned
Prefix if and only if one of the following conditions is met: Prefix if and only if one of the following conditions is met:
* The Assigned Prefix is not published. * The Assigned Prefix is not published.
* The Assigned Prefix is published and the Advertised Prefix * The Assigned Prefix is published, and the Advertised Prefix
Priority from the Advertised Prefix is strictly greater than Priority from the Advertised Prefix is strictly greater than
the Advertised Prefix Priority from the Assigned Prefix. the Advertised Prefix Priority from the Assigned Prefix.
* The Assigned Prefix is published, the priorities are identical, * The Assigned Prefix is published, the priorities are identical,
and the Node ID from the Node advertising the Advertised Prefix and the Node ID from the Node advertising the Advertised Prefix
is strictly greater than the local Node ID. is strictly greater than the local Node ID.
Best Assignment: For a given Delegated Prefix and Link, the Best Best Assignment: For a given Delegated Prefix and Link, the Best
Assignment is computed as the unique Advertised Prefix (if any) Assignment is computed as the unique Advertised Prefix (if any)
that: that:
skipping to change at page 7, line 14 skipping to change at page 7, line 20
* No Advertised Prefix including or included in the same * No Advertised Prefix including or included in the same
Delegated Prefix as the Assigned Prefix and assigned to the Delegated Prefix as the Assigned Prefix and assigned to the
same Link takes precedence over the Assigned Prefix. same Link takes precedence over the Assigned Prefix.
3. Applicability Statement 3. Applicability Statement
Although the algorithm was primarily designed as an autonomic prefix Although the algorithm was primarily designed as an autonomic prefix
assignment tool for home networks, it is applicable to other areas. assignment tool for home networks, it is applicable to other areas.
In particular, it can operate without any kind of configuration as In particular, it can operate without any kind of configuration as
well as using advanced prefix assignment rules. Additionally, it can well as use advanced prefix assignment rules. Additionally, it can
be applied to any address space and can be used to manage multiple be applied to any address space and can be used to manage multiple
address spaces simultaneously. For instance, an implementation can address spaces simultaneously. For instance, an implementation can
make use of IPv4-mapped IPv6 addresses [RFC4291] in order to manage make use of IPv4-mapped IPv6 addresses [RFC4291] in order to manage
both IPv4 and IPv6 prefix assignment using a single prefix space. both IPv4 and IPv6 prefix assignment using a single prefix space.
Each Node MUST have a set of non-overlapping Delegated Prefixes Each Node MUST have a set of non-overlapping Delegated Prefixes
(i.e., which do not include each other). This set MAY change over (i.e., that do not include each other). This set MAY change over
time and be different from one Node to another at some point, but time and be different from one Node to another at some point, but
Nodes MUST eventually have the same set of non-overlapping Delegated Nodes MUST eventually have the same set of non-overlapping Delegated
Prefixes. Prefixes.
Given this set of non-overlapping Delegated Prefixes, Nodes may Given this set of non-overlapping Delegated Prefixes, Nodes may
assign available prefixes from each Delegated Prefix to the Links assign available prefixes from each Delegated Prefix to the Links
they are directly connected to. The algorithm ensures that at most they are directly connected to. The algorithm ensures that at most
one prefix from a given Delegated Prefix is assigned to any given one prefix from a given Delegated Prefix is assigned to any given
Link. Prefixes may also be assigned for private use. For example, Link. Prefixes may also be assigned for private use. For example,
an assigned prefix may be delegated to some other entity that does an assigned prefix may be delegated to some other entity that does
not implement this algorithm [RFC3633], or associated with a high not implement this algorithm [RFC3633], or associated with a high
priority in order to prevent other nodes from assigning any priority in order to prevent other nodes from assigning any
overlapping prefix [RFC6603]. overlapping prefix [RFC6603].
The algorithm supports dynamically changing topologies and therefore The algorithm supports dynamically changing topologies and therefore
will converge if the topology remains unmodified for a long enough will converge if the topology remains unmodified for a long enough
period of time (That time depends on the Flooding Mechanism period of time. (That time depends on the Flooding Mechanism
properties). Nevertheless, some topology changes may induce properties.) Nevertheless, some topology changes may induce
renumbering, while others do not. In particular, Nodes joining the renumbering, while others do not. In particular, Nodes joining the
set of participating Nodes do not cause renumbering. Similarly, set of participating Nodes do not cause renumbering. Similarly,
Nodes leaving the network may be dealt with without renumbering by Nodes leaving the network may be handled without renumbering by using
using the prefix adoption procedure. On the other hand, Links the prefix adoption procedure. On the other hand, Links that merge
junction or split may break correctness conditions, and therefore or split may break correctness conditions, and therefore cause
cause renumbering. renumbering.
All Nodes MUST run a common Flooding Mechanism in order to share All Nodes MUST run a common Flooding Mechanism in order to share
published Assigned Prefixes. The set of participating Nodes is published Assigned Prefixes. The set of participating Nodes is
defined as the set of Nodes participating in the Flooding Mechanism. defined as the set of Nodes participating in the Flooding Mechanism.
The Flooding Mechanism MUST: The Flooding Mechanism MUST:
o Provide a way to flood Assigned Prefixes assigned to a directly o Provide a way to flood Assigned Prefixes assigned to a directly
connected Link along with their respective Advertised Prefix connected Link along with their respective Advertised Prefix
Priority and the Node ID of the Node which is advertising them. Priority and the Node ID of the Node that is advertising them.
o Specify whether an Advertised Prefix is assigned to a directly o Specify whether an Advertised Prefix is assigned to a directly
connected Shared Link, and if so, on which one. This information connected Shared Link, and if so, which one. This information
also needs to be updated in case of links junction or split. also needs to be updated in case of Links that merge or split.
o Provide a Flooding Delay value, which SHOULD represent a o Provide a Flooding Delay value, which SHOULD represent a
deterministic or likely upper bound on the information propagation deterministic or likely upper bound on the information propagation
delay among participating Nodes. Whenever the Flooding Mechanism delay among participating Nodes. Whenever the Flooding Mechanism
is unable to adhere to the provided Flooding Delay, renumbering is unable to adhere to the provided Flooding Delay, renumbering
may happen. As such a delay often depends on the size of the may happen. As such, a delay often depends on the size of the
network, it MAY change over time and MAY be different from one network, it MAY change over time and MAY be different from one
Node to another. Furthermore, the process of selecting this value Node to another. Furthermore, the process of selecting this value
is subject to a tradeoff between convergence speed and lower is subject to a tradeoff between convergence speed and lower
renumbering probability (e.g., the value 0 may be used when renumbering probability (e.g., the value 0 may be used when
renumbering is harmless), and is therefore out of scope of this renumbering is harmless), and is therefore out of scope for this
document. document.
The algorithm ensures that whenever the Flooding Delay is provided The algorithm ensures that whenever the Flooding Delay is provided
and held, and in the absence of any topology change or Delegated and held, and in the absence of any topology change or Delegated
Prefix removal, renumbering only happens when a Node deliberately Prefix removal, renumbering only happens when a Node deliberately
overrides an existing assignment. In the absence of such deliberate overrides an existing assignment. In the absence of such deliberate
override, the algorithm converges within an absolute worst case override, the algorithm converges within an absolute worst-case
timespan of '2 * Flooding Delay * L' seconds, where L in the number timespan of (2 * Flooding Delay * L) seconds, where L is the number
of links. of links.
Each Node MUST have a Node ID. In the absence of colliding Each Node MUST have a Node ID. In the situation where multiple nodes
assignments, the algorithm will not suffer from multiple nodes having have the same Node ID, the algorithm will not suffer, assuming there
the same Node ID, but in order for collisions to be resolved, such are no colliding assignments. However, in order for collisions to be
situation MUST be transient. resolved, that situation MUST be transient.
Finally, leaving the Flooding Mechanism or Node ID assignment process Finally, leaving the Flooding Mechanism or Node ID assignment process
unsecured makes the network vulnerable to deny of service attacks, as unsecured makes the network vulnerable to denial-of-service attacks,
detailed in Section 8. Additionally, as this algorithm requires all as detailed in Section 8. Additionally, as this algorithm requires
Nodes to know which Node has made which assignment, it may be all Nodes to know which Node has made which assignment, it may be
unsuitable depending on privacy requirements among participating unsuitable depending on privacy requirements among participating
Nodes. Nodes.
4. Algorithm Specification 4. Algorithm Specification
This section specifies the behavior of Nodes implementing the prefix This section specifies the behavior of Nodes implementing the prefix
assignment algorithm. The terms 'Current Assignment', 'Precedence', assignment algorithm. The terms 'Current Assignment', 'Precedence',
'Best Assignment' and 'Valid' are used as defined in Section 2.1. 'Best Assignment', and 'Valid' are used as defined in Section 2.1.
4.1. Prefix Assignment Algorithm Subroutine 4.1. Prefix Assignment Algorithm Subroutine
This section specifies the prefix assignment algorithm subroutine. This section specifies the prefix assignment algorithm subroutine.
It is defined for a given Delegated Prefix and Link pair and takes a It is defined for a given Delegated Prefix and Link pair and takes a
BackoffTriggered boolean as parameter (indicating whether the BackoffTriggered boolean as parameter (indicating whether the
subroutine execution was triggered by the Backoff Timer or by another subroutine execution was triggered by the Backoff Timer or by another
event). The subroutine also makes use of the two following event). The subroutine also makes use of the two following
configuration parameters: ADOPT_MAX_DELAY and BACKOFF_MAX_DELAY, configuration parameters: ADOPT_MAX_DELAY and BACKOFF_MAX_DELAY,
which meanings are detailed in Section 7. which are defined in Section 7.
For a given Delegated Prefix and Link pair, the subroutine MUST be For a given Delegated Prefix and Link pair, the subroutine MUST be
run with the BackoffTriggered boolean set to false whenever: run with the BackoffTriggered boolean set to false whenever:
o An Advertised Prefix including or included in the considered o An Advertised Prefix including or included in the considered
Delegated Prefix is added or removed. Delegated Prefix is added or removed.
o An Assigned Prefix included in the considered Delegated Prefix and o An Assigned Prefix included in the considered Delegated Prefix and
associated with a different Link than the considered Link was associated with a different Link than the considered Link was
destroyed, while there is no Current Assignment associated with destroyed, while there is no Current Assignment associated with
skipping to change at page 9, line 43 skipping to change at page 9, line 49
o An Assigned Prefix included in the considered Delegated Prefix and o An Assigned Prefix included in the considered Delegated Prefix and
associated with the considered Link is destroyed outside of the associated with the considered Link is destroyed outside of the
context of the subroutine, as specified in Section 4.2. context of the subroutine, as specified in Section 4.2.
Furthermore, for a given Delegated Prefix and Link pair, the Furthermore, for a given Delegated Prefix and Link pair, the
subroutine MUST be run with the BackoffTriggered boolean set to true subroutine MUST be run with the BackoffTriggered boolean set to true
whenever: whenever:
o The Backoff Timer associated with the considered Delegated Prefix o The Backoff Timer associated with the considered Delegated Prefix
and Link pair fires while there is no Current Assignment and Link pair fires while there is no Current Assignment associated
associated with the given pair. with the given pair.
When such an event occurs, a Node MAY delay the execution of the When such an event occurs, a Node MAY delay the execution of the
subroutine instead of executing it immediately, e.g., while receiving subroutine instead of executing it immediately, e.g., while receiving
an update from the Flooding Mechanism, or for security reasons (see an update from the Flooding Mechanism, or for security reasons (see
Section 8). Even if other events occur in the meantime, the Section 8). Even if other events occur in the meantime, the
subroutine MUST be run only once. It is also assumed that, whenever subroutine MUST be run only once. It is also assumed that if one of
one of these events is the Backoff Timer firing while there is no these events is the firing of the Backoff Timer while there is no
Current Assignment associated with the given pair, the subroutine is Current Assignment associated with the given pair, the subroutine is
executed with the BackoffTriggered boolean set to true. executed with the BackoffTriggered boolean set to true.
In order to execute the subroutine for a given Delegated Prefix and In order to execute the subroutine for a given Delegated Prefix and
Link pair, first get the Current Assignment and compute the Best Link pair, first get the Current Assignment and compute the Best
Assignment associated with the Delegated Prefix and Link pair, then Assignment associated with the Delegated Prefix and Link pair, then
execute the corresponding case: execute the steps depending on the following cases:
1. If there is no Best Assignment and no Current Assignment: Decide 1. If there is no Best Assignment and no Current Assignment: Decide
whether the creation of a new assignment for the given Delegated whether the creation of a new assignment for the given Delegated
Prefix and Link pair is desired (As any result would be valid, Prefix and Link pair is desired. (As any result would be valid,
the process of making this decision is out of the scope of this the process of making this decision is out of scope for this
document) and do the following: document.) And, do the following:
* If it is not desired, stop the execution of the subroutine. * If it is not desired, stop the execution of the subroutine.
* Else if the Backoff Timer is running, stop the execution of * Else if the Backoff Timer is running, stop the execution of
the subroutine. the subroutine.
* Else if the BackoffTriggered boolean is set to false, set the * Else if the BackoffTriggered boolean is set to false, set the
Backoff Timer to some random delay between ADOPT_MAX_DELAY and Backoff Timer to some random delay between ADOPT_MAX_DELAY and
BACKOFF_MAX_DELAY (see Section 7) and stop the execution of BACKOFF_MAX_DELAY (see Section 7) and stop the execution of the
the subroutine. subroutine.
* Else, continue the execution of the subroutine. * Else, continue the execution of the subroutine.
Select a prefix for the new assignment (see Section 5 for Select a prefix for the new assignment (see Section 5 for
guidance regarding prefix selection). This prefix MUST be guidance regarding prefix selection). This prefix MUST be
included in or be equal to the considered Delegated Prefix and included in or be equal to the considered Delegated Prefix and
MUST NOT include or be included in any Advertised Prefix. If a MUST NOT include or be included in any Advertised Prefix. If a
suitable prefix is found, use it to create a new Assigned Prefix: suitable prefix is found, use it to create a new Assigned Prefix:
* Assigned to the considered Link. * Assigned to the considered Link.
* Set as not applied. * Set as not applied.
* The Apply Timer set to '2 * Flooding Delay'. * The Apply Timer set to (2 * Flooding Delay).
* Published with some selected Advertised Prefix Priority. * Published with some selected Advertised Prefix Priority.
2. If there is a Best Assignment but no Current Assignment: First 2. If there is a Best Assignment but no Current Assignment: First,
check if the Best Assignment is equal to or included in the check if the Best Assignment is equal to or included in the
Delegated Prefix. If not, stop the execution of the subroutine. Delegated Prefix. If not, stop the execution of the subroutine.
Otherwise, cancel the Backoff Timer and use the prefix from the Otherwise, cancel the Backoff Timer and use the prefix from the
Best Assignment to create a new Assigned Prefix: Best Assignment to create a new Assigned Prefix:
* Assigned to the considered Link. * Assigned to the considered Link.
* Set as not applied. * Set as not applied.
* The Apply Timer set to '2 * Flooding Delay'. * With the Apply Timer set to (2 * Flooding Delay).
* Set as not published. * Set as not published.
3. If there is a Current Assignment but no Best Assignment: 3. If there is a Current Assignment but no Best Assignment:
* If the Current Assignment is not valid, destroy it, and * If the Current Assignment is not valid, destroy it, and
execute the subroutine again with the BackoffTriggered boolean execute the subroutine again with the BackoffTriggered boolean
set to false. set to false.
* If the Current Assignment is valid and published, stop the * If the Current Assignment is valid and published, stop the
execution of the subroutine. execution of the subroutine.
* If the Current Assignment is valid and not published, the Node * If the Current Assignment is valid and not published, the Node
MUST either: MUST either:
+ Adopt the prefix by canceling the Apply Timer and set the + Adopt the prefix by canceling the Apply Timer and set the
Backoff Timer to some random delay between 0 and Backoff Timer to some random delay between 0 and
ADOPT_MAX_DELAY (see Section 7). This procedure is used to ADOPT_MAX_DELAY (see Section 7). This procedure is used to
avoid renumbering when the Node advertising the prefix left avoid renumbering when the Node advertising the prefix left
the Shared Link, and SHOULD therefore be preferred. the Shared Link, and it SHOULD therefore be preferred.
+ Destroy it and go to case 1, allowing a different prefix to + Destroy it and go to case 1, allowing a different prefix to
be assigned, or the prefix to be removed. When the Current be assigned, or the prefix to be removed. When the Current
Assignment is applied, this causes renumbering. Assignment is applied, this causes renumbering.
4. If there is a Current Assignment and a Best Assignment: 4. If there is a Current Assignment and a Best Assignment:
* Cancel the Backoff Timer. * Cancel the Backoff Timer.
* If the two prefixes are identical, set the Current Assignment * If the two prefixes are identical, set the Current Assignment
as not published. If the Current Assignment is not applied as not published. If the Current Assignment is not applied
and the Apply Timer is not set, set the Apply Timer to '2 * and the Apply Timer is not set, set the Apply Timer to (2 *
Flooding Delay'. Flooding Delay).
* If the two prefixes are not identical, destroy the Current * If the two prefixes are not identical, destroy the Current
Assignment and go to case 2. Assignment and go to case 2.
When the prefix assignment algorithm subroutine requires an When the prefix assignment algorithm subroutine requires an
assignment to be created or adopted, any Advertised Prefix Priority assignment to be created or adopted, any Advertised Prefix Priority
value can be used. Other documents MAY provide restrictions over value can be used. Other documents MAY provide restrictions over
this value depending on the context the algorithm is operating in, or this value depending on the context in which the algorithm is
leave it as implementation-specific. operating or leave it as implementation specific.
4.2. Overriding and Destroying Existing Assignments 4.2. Overriding and Destroying Existing Assignments
In addition to the behaviors specified in Section 4.1, the following In addition to the behaviors specified in Section 4.1, the following
procedures MAY be used in order to provide additional behavior procedures MAY be used in order to provide additional behavior
options (Section 6): options (Section 6).
Overriding Existing Assignments: For any given Link and Delegated Overriding Existing Assignments: For any given Link and Delegated
Prefix, a Node MAY create a new Assigned Prefix using a chosen Prefix, a Node MAY create a new Assigned Prefix using a chosen
prefix and Advertised Prefix Priority such that: prefix and Advertised Prefix Priority such that:
* The chosen prefix is included in or is equal to the considered * The chosen prefix is included in or is equal to the considered
Delegated Prefix. Delegated Prefix.
* The Current Assignment, if any, as well as all existing * The Current Assignment, if any, as well as all existing
Assigned Prefixes which include or are included inside the Assigned Prefixes that include or are included inside the
chosen prefix, are destroyed. chosen prefix are destroyed.
* It is not applied. * It is not applied.
* The Apply Timer is set to '2 * Flooding Delay'. * The Apply Timer is set to (2 * Flooding Delay).
* It is published. * It is published.
* The Advertised Prefix Priority is greater than the Advertised * The Advertised Prefix Priority is greater than the Advertised
Prefix Priority from all Advertised Prefixes which include or Prefix Priority from all Advertised Prefixes that include or
are included in the chosen prefix. are included in the chosen prefix.
* The Advertised Prefix Priority is greater than the Advertised * The Advertised Prefix Priority is greater than the Advertised
Prefix Priority from all Advertised Prefixes which include or Prefix Priority from all Advertised Prefixes that include or
are included in the considered Delegated Prefix and are are included in the considered Delegated Prefix and are
assigned to the considered Link. assigned to the considered Link.
In order to ensure algorithm convergence: In order to ensure algorithm convergence:
* Such overriding assignments MUST NOT be created unless there * Such overriding assignments MUST NOT be created unless there
was a change in the Node configuration, a Link was added, or an was a change in the Node configuration, a Link was added, or an
Advertised Prefix was added or removed. Advertised Prefix was added or removed.
* The chosen Advertised Prefix Priority for the new Assigned * The chosen Advertised Prefix Priority for the new Assigned
Prefix SHOULD be greater than all priorities from the destroyed Prefix SHOULD be greater than all priorities from the destroyed
Assigned Prefixes. If not, simple topologies with only two Assigned Prefixes. If not, simple topologies with only two
Nodes may not converge. Nodes which do not adhere to this rule Nodes may not converge. Nodes that do not adhere to this rule
MUST implement a mechanism which detects whether the MUST implement a mechanism that detects if the distributed
distributed algorithm does not converge and, whenever this algorithm does not converge and, when this occurs, they MUST
would happen, stop creating overriding Assigned Prefixes which stop creating overriding Assigned Prefixes that do not adhere
do not adhere to this rule. The specifications for such safety to this rule. The specifications for such safety procedures
procedures are out of the scope of this document. are out of scope for this document.
Removing an Assigned Prefix: A Node MAY destroy any Assigned Prefix Removing an Assigned Prefix: A Node MAY destroy any Assigned Prefix
which is published. Such an event reflects the desire of a Node that is published. Such an event reflects the desire of a Node to
to not assign a prefix from a given Delegated Prefix to a given not assign a prefix from a given Delegated Prefix to a given Link
Link anymore. In order to ensure algorithm convergence, such a anymore. In order to ensure algorithm convergence, such a
procedure MUST NOT be executed unless there was a change in the procedure MUST NOT be executed unless there was a change in the
Node configuration. Furthermore, whenever an Assigned Prefix is Node configuration. Furthermore, whenever an Assigned Prefix is
destroyed in this way, the prefix assignment algorithm subroutine destroyed in this way, the prefix assignment algorithm subroutine
MUST be run for the Delegated Prefix and Link pair associated with MUST be run for the Delegated Prefix and Link pair associated with
the destroyed Assigned Prefix. the destroyed Assigned Prefix.
The two procedures specified in this section are OPTIONAL. They The two procedures specified in this section are OPTIONAL. They
could be used for various purposes, e.g., for providing custom prefix could be used for various purposes, e.g., for providing custom prefix
assignment configuration or reacting to prefix space exhaustion (by assignment configuration or reacting to prefix space exhaustion (by
overriding short Assigned Prefixes and assigning longer ones). overriding short Assigned Prefixes and assigning longer ones).
4.3. Other Events 4.3. Other Events
When the Apply Timer fires, the associated Assigned Prefix MUST be When the Apply Timer fires, the associated Assigned Prefix MUST be
applied. applied.
When the Backoff Timer associated with a given Delegated Prefix and When the Backoff Timer associated with a given Delegated Prefix and
Link pair fires while there is a Current Assignment associated with Link pair fires while there is a Current Assignment associated with
the same pair, the Current Assignment MUST be published with some the same pair, the Current Assignment MUST be published with some
associated Advertised Prefix Priority and, if the prefix is not associated Advertised Prefix Priority and, if the prefix is not
applied, the Apply Timer MUST be set to '2 * Flooding Delay'. applied, the Apply Timer MUST be set to (2 * Flooding Delay).
When a Delegated Prefix is removed from the set of Delegated Prefixes When a Delegated Prefix is removed from the set of Delegated Prefixes
(e.g., when the Delegated Prefix expires), all Assigned Prefixes (e.g., when the Delegated Prefix expires), all Assigned Prefixes
included in the removed Delegated Prefix MUST be destroyed. included in the removed Delegated Prefix MUST be destroyed.
When one Delegated Prefix is replaced by another one that includes or When one Delegated Prefix is replaced by another one that includes or
is included in the deleted Delegated Prefix, all Assigned Prefixes is included in the deleted Delegated Prefix, all Assigned Prefixes
which were included in the deleted Delegated Prefix but are not that were included in the deleted Delegated Prefix but are not
included in the added Delegated Prefix MUST be destroyed. Others MAY included in the added Delegated Prefix MUST be destroyed. Others MAY
be kept. be kept.
When a Link is removed, all Assigned Prefixes assigned to that Link When a Link is removed, all Assigned Prefixes assigned to that Link
MUST be destroyed. MUST be destroyed.
5. Prefix Selection Considerations 5. Prefix Selection Considerations
When the prefix assignment algorithm subroutine specified in When the prefix assignment algorithm subroutine specified in
Section 4.1 requires a new prefix to be selected, the prefix MUST be Section 4.1 requires a new prefix to be selected, the prefix MUST be
selected either: selected either:
o Among prefixes included in the considered Delegated Prefix which o Among prefixes included in the considered Delegated Prefix that
were previously assigned and applied on the considered Link. For were previously assigned and applied on the considered Link. For
that purpose, Applied Prefixes may be stored in stable storage that purpose, Applied Prefixes may be stored in stable storage
along with their associated Link. along with their associated Link.
o Randomly, picked in a set of at least RANDOM_SET_SIZE (see o Randomly, picked from a set of prefixes, where the set is of at
Section 7) prefixes included in the considered Delegated Prefix least RANDOM_SET_SIZE (see Section 7). The prefixes are those
and not including or included in any Assigned or Advertised included in the considered Delegated Prefix and not including or
Prefix. If less than RANDOM_SET_SIZE candidates are found, the included in any Assigned or Advertised Prefix. If less than
prefix MUST be picked among all candidates. RANDOM_SET_SIZE candidates are found, the prefix MUST be picked
among all candidates.
o Based on some custom selection process specified in the o Based on some custom selection process specified in the
configuration. configuration.
A simple implementation MAY randomly pick the prefix among all A simple implementation MAY randomly pick the prefix among all
available prefixes, but this strategy is inefficient in terms of available prefixes, but this strategy is inefficient in terms of
address space use as a few long prefixes may exhaust the pool of address space use as a few long prefixes may exhaust the pool of
available short prefixes. available short prefixes.
The rest of this section describes a more efficient approach which The rest of this section describes a more efficient approach that MAY
MAY be applied any time a Node needs to pick a prefix for a new be applied any time a Node needs to pick a prefix for a new
assignment. The two following definitions are used: assignment. The two following definitions are used:
Available prefix: The prefix of the form Prefix/PrefixLength is Available prefix: The prefix of the form Prefix/PrefixLength is
available if and only if it satisfies the three following available if and only if it satisfies the three following
conditions: conditions:
* It is included in the considered Delegated Prefix. * It is included in the considered Delegated Prefix.
* It does not include and is not included in any Assigned or * It does not include and is not included in any Assigned or
Advertised Prefix. Advertised Prefix.
* It is equal to the considered Delegated Prefix or Prefix/ * It is equal to the considered Delegated Prefix or
(PrefixLength-1) includes an Assigned or Advertised Prefix. Prefix/(PrefixLength-1) includes an Assigned or Advertised
Prefix.
Candidate prefix: A prefix of desired length which is included in Candidate prefix: A prefix of desired length that is included in or
or is equal to an available prefix. is equal to an available prefix.
The procedure described in this section takes the three following The procedure described in this section takes the three following
criteria into account: criteria into account:
Prefix Stability: In some cases, it is desirable that the selected Prefix Stability: In some cases, it is desirable that the selected
prefix should remain the same across executions and reboots. For prefix should remain the same across executions and reboots. For
this purpose, prefixes previously applied on the Link or pseudo- this purpose, prefixes previously applied on the Link or
random prefixes generated based on Node- and Link-specific values pseudorandom prefixes generated based on Node- and Link-specific
may be considered. values may be considered.
Randomness: When no stored or pseudo-random prefix is chosen, a Randomness: When no stored or pseudorandom prefix is chosen, a
prefix may be randomly picked among RANDOM_SET_SIZE candidates of prefix may be randomly picked among RANDOM_SET_SIZE candidates of
desired length. If less than RANDOM_SET_SIZE candidates can be desired length. If less than RANDOM_SET_SIZE candidates can be
found, the prefix is picked among all candidates. found, the prefix is picked among all candidates.
Addressing-space usage efficiency: In the process of assigning Addressing-space usage efficiency: In the process of assigning
prefixes, a small set of badly chosen long prefixes may prevent prefixes, a small set of badly chosen long prefixes may prevent
any shorter prefix from being assigned. For this reason, the set any shorter prefix from being assigned. For this reason, the set
of RANDOM_SET_SIZE candidates is created from available prefixes of RANDOM_SET_SIZE candidates is created from available prefixes
with longest prefix lengths and, in case of a tie, preferring with longest prefix lengths, and, in case of a tie, numerically
numerically small prefix values. small prefix values are preferred.
When executing the procedure, do as follows: When executing the procedure, do as follows:
1. For each prefix stored in stable storage, check if the prefix is 1. For each prefix stored in stable storage, check if the prefix is
included in or equal to an available prefix. If so, pick that included in or equal to an available prefix. If so, pick that
prefix and stop. prefix and stop.
2. For each prefix length, count the number of available prefixes of 2. For each prefix length, count the number of available prefixes of
the given length. the given length.
skipping to change at page 15, line 43 skipping to change at page 16, line 5
4. Iterate over available prefixes starting with prefixes of length 4. Iterate over available prefixes starting with prefixes of length
N down to length 0 and create a set of RANDOM_SET_SIZE candidate N down to length 0 and create a set of RANDOM_SET_SIZE candidate
prefixes of length exactly N included in or equal to available prefixes of length exactly N included in or equal to available
prefixes. The end goal here is to create a set of prefixes. The end goal here is to create a set of
RANDOM_SET_SIZE candidate prefixes of length N included in a set RANDOM_SET_SIZE candidate prefixes of length N included in a set
of available prefixes of maximized prefix length. In case of a of available prefixes of maximized prefix length. In case of a
tie, smaller prefix values (as defined by the bit-wise tie, smaller prefix values (as defined by the bit-wise
lexicographical order) are preferred. lexicographical order) are preferred.
5. Generate a set of prefixes of desired length, which are pseudo- 5. Generate a set of prefixes of desired length, which are
randomly chosen based on Node- and Link-specific values. For pseudorandomly chosen based on Node- and Link-specific values.
each pseudo-random prefix, check if the prefix is equal to a For each pseudorandom prefix, check if the prefix is equal to a
candidate prefix. If so, pick that prefix and stop. candidate prefix. If so, pick that prefix and stop.
6. Choose a random prefix from the set of selected candidates. 6. Choose a random prefix from the set of selected candidates.
The complexity of this procedure is equivalent to the complexity of The complexity of this procedure is equivalent to the complexity of
iterating over available prefixes. Such operation may be iterating over available prefixes. Such operation may be
accomplished in linear time, e.g., by storing Advertised and Assigned accomplished in linear time, e.g., by storing Advertised and Assigned
Prefixes in a binary trie. Prefixes in a binary tree.
6. Implementation Capabilities and Node Behavior 6. Implementation Capabilities and Node Behavior
Implementations of the prefix assignment algorithm may vary from very Implementations of the prefix assignment algorithm may vary from very
basic to highly customizable, enabling different types of fully basic to highly customizable, enabling different types of fully
interoperable behaviors. The three following behaviors are given as interoperable behaviors. The three following behaviors are given as
examples: examples:
Listener: The Node only acts upon assignments made by other Nodes, Listener: The Node only acts upon assignments made by other Nodes,
i.e, it never creates new assignments nor adopts existing ones. i.e, it never creates new assignments nor adopts existing ones.
Such behavior does not require the implementation of the Such behavior does not require the implementation of the
considerations specified in Section 5 or Section 4.2. The Node considerations specified in Section 4.2 or 5. The Node never
never checks the validity of existing assignments, which makes checks the validity of existing assignments, which makes this
this behavior particularly suited to lightweight devices which can behavior particularly suited to lightweight devices that can rely
rely on more capable neighbors to make assignments on directly on more capable neighbors to make assignments on directly
connected Shared Links. connected Shared Links.
Basic: The Node is capable of assigning new prefixes or adopting Basic: The Node is capable of assigning new prefixes or adopting
prefixes which do not conflict with any other existing assignment. prefixes that do not conflict with any other existing assignment.
Such behavior does not require the implementation of the Such behavior does not require the implementation of the
considerations specified in Section 4.2. It is suited to considerations specified in Section 4.2. It is suited to
situations where there is no preference over which prefix should situations where there is no preference over which prefix should
be assigned to which Link, and there is no priority between be assigned to which Link, and there is no priority between
different Links. different Links.
Advanced: The Node is capable of assigning new prefixes, adopting Advanced: The Node is capable of assigning new prefixes, adopting
existing ones, making overriding assignments and destroying existing ones, making overriding assignments, and destroying
existing ones. Such behavior requires the implementation of the existing ones. Such behavior requires the implementation of the
considerations specified in Section 5 and Section 4.2. It is considerations specified in Sections 4.2 and 5. It is suitable
suited when the administrator desires some particular prefix to be when the administrator desires some particular prefix to be
assigned on a given Link, or some Link to be assigned prefixes assigned on a given Link, or some Link to be assigned prefixes
with a greater priority when there are not enough prefixes with a greater priority when there are not enough prefixes
available for all Links. available for all Links.
Note that if all Nodes directly connected to some Link are listener Note that if all Nodes directly connected to some Link are listener
Nodes or none of these Nodes are willing to make an assignment from a Nodes or none of these Nodes are willing to make an assignment from a
given Delegated Prefix to the given Link, no prefix from the given given Delegated Prefix to the given Link, no prefix from the given
Delegated Prefix will ever be assigned to the Link. This situation Delegated Prefix will ever be assigned to the Link. This situation
may be detected by watching whether no prefix from a given Delegated may be detected by monitoring whether any prefix from a given
Prefix has been assigned to the Link for longer than Delegated Prefix has been assigned to the Link for longer than
BACKOFF_MAX_DELAY plus the Flooding Delay. BACKOFF_MAX_DELAY plus the Flooding Delay.
7. Algorithm Parameters 7. Algorithm Parameters
This document does not provide values for ADOPT_MAX_DELAY, This document does not provide values for ADOPT_MAX_DELAY,
BACKOFF_MAX_DELAY and RANDOM_SET_SIZE. The algorithm ensures BACKOFF_MAX_DELAY, and RANDOM_SET_SIZE. The algorithm ensures
convergence and correctness for any chosen values, even when these convergence and correctness for any chosen values, even when these
are different from Node to Node. They MAY be adjusted depending on are different from Node to Node. They MAY be adjusted depending on
the context, providing a tradeoff between convergence time, efficient the context, providing a tradeoff between convergence time, efficient
addressing, reduced control traffic (generated by the Flooding addressing, control traffic (generated by the Flooding Mechanism),
Mechanism), and low collision probability. and collision probability.
ADOPT_MAX_DELAY (respectively BACKOFF_MAX_DELAY) represents the ADOPT_MAX_DELAY represents the maximum backoff time a Node may wait
maximum backoff time a Node may wait before adopting an assignment before adopting an assignment; BACKOFF_MAX_DELAY represents the
(respectively making a new assignment). BACKOFF_MAX_DELAY MUST be maximum backoff time a Node may wait before making a new assignment.
greater than or equal to ADOPT_MAX_DELAY. The greater BACKOFF_MAX_DELAY MUST be greater than or equal to ADOPT_MAX_DELAY.
ADOPT_MAX_DELAY and (BACKOFF_MAX_DELAY - ADOPT_MAX_DELAY), the lower The greater ADOPT_MAX_DELAY and (BACKOFF_MAX_DELAY -
the collision probability and the lesser the amount of control ADOPT_MAX_DELAY), the lower the collision probability and the lesser
traffic, but the greater the convergence time. the amount of control traffic, but the greater the convergence time.
RANDOM_SET_SIZE represents the desired size of the set a random RANDOM_SET_SIZE represents the desired size of the set from which a
prefix will be picked from. The greater RANDOM_SET_SIZE, the better random prefix will be picked. The greater RANDOM_SET_SIZE, the
the convergence time and the lower the collision probability, but the better the convergence time and the lower the collision probability,
worse the addressing-space usage efficiency. but the worse the addressing-space usage efficiency.
8. Security Considerations 8. Security Considerations
The prefix assignment algorithm functions on top of two distinct The prefix assignment algorithm functions on top of two distinct
mechanisms, the Flooding Mechanism and the Node ID assignment mechanisms, the Flooding Mechanism and the Node ID assignment
mechanism. mechanism.
An attacker able to publish Advertised Prefixes through the An attacker able to publish Advertised Prefixes through the
Flooding Mechanism may perform the following attacks: Flooding Mechanism may perform the following attacks:
skipping to change at page 18, line 20 skipping to change at page 18, line 24
An attacker able to publish Advertised Prefixes using a Node ID An attacker able to publish Advertised Prefixes using a Node ID
used by another Node may impede the ability to resolve prefix used by another Node may impede the ability to resolve prefix
assignment collisions. assignment collisions.
Whenever the security of the Flooding Mechanism and Node ID Whenever the security of the Flooding Mechanism and Node ID
assignment mechanism cannot be ensured, the convergence of the assignment mechanism cannot be ensured, the convergence of the
algorithm may be prevented. In environments where such attacks may algorithm may be prevented. In environments where such attacks may
be performed, the execution of the prefix assignment algorithm be performed, the execution of the prefix assignment algorithm
subroutine SHOULD be rate limited, as specified in Section 4.1. subroutine SHOULD be rate limited, as specified in Section 4.1.
9. IANA Considerations 9. References
This document has no actions for IANA.
10. Acknowledgments
The authors would like to thank those who participated in the
previous document's version development as well as the present one.
In particular, the authors would like to thank Tim Chown, Fred Baker,
Mark Townsley, Lorenzo Colitti, Ole Troan, Ray Bellis, Markus
Stenberg, Wassim Haddad, Joel Halpern, Samita Chakrabarti, Michael
Richardson, Anders Brandt, Erik Nordmark, Laurent Toutain, Ralph
Droms, Acee Lindem, Steven Barth and Juliusz Chroboczek for
interesting discussions and document review.
11. References
11.1. Normative References 9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, DOI
10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
11.2. Informative References 9.2. Informative References
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633, Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003. DOI 10.17487/RFC3633, December 2003,
<http://www.rfc-editor.org/info/rfc3633>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006. Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <http://www.rfc-editor.org/info/rfc4291>.
[RFC6603] Korhonen, J., Savolainen, T., Krishnan, S., and O. Troan, [RFC6603] Korhonen, J., Ed., Savolainen, T., Krishnan, S., and O.
"Prefix Exclude Option for DHCPv6-based Prefix Troan, "Prefix Exclude Option for DHCPv6-based Prefix
Delegation", RFC 6603, May 2012. Delegation", RFC 6603, DOI 10.17487/RFC6603, May 2012,
<http://www.rfc-editor.org/info/rfc6603>.
Appendix A. Static Configuration Example Appendix A. Static Configuration Example
This section describes an example of how custom configuration of the This section describes an example of how custom configuration of the
prefix assignment algorithm may be implemented. prefix assignment algorithm may be implemented.
The Node configuration is specified as a finite set of rules. A rule The Node configuration is specified as a finite set of rules. A rule
is defined as: is defined as:
o A prefix to be used. o A prefix to be used.
o A Link on which the prefix may be assigned. o A Link on which the prefix may be assigned.
o An Assigned Prefix Priority (smallest possible Assigned Prefix o An Assigned Prefix Priority (the smallest possible Assigned Prefix
Priority if the rule may not override other Assigned Prefixes). Priority if the rule may not override other Assigned Prefixes).
o A rule priority (0 if the rule may not override existing o A rule priority (0 if the rule may not override existing
Advertised Prefixes). Advertised Prefixes).
In order to ensure the convergence of the algorithm, the Assigned In order to ensure the convergence of the algorithm, the Assigned
Prefix Priority MUST be an increasing function (not necessarily Prefix Priority MUST be an increasing function (not necessarily
strictly) of the configuration rule priority (i.e., the greater is strictly) of the configuration rule priority (i.e., the greater the
the configuration rule priority, the greater the Assigned Prefix configuration rule priority is, the greater the Assigned Prefix
Priority must be). Priority must be).
Each Assigned Prefix is associated with a rule priority. Assigned Each Assigned Prefix is associated with a rule priority. Assigned
Prefixes which are created as specified in Section 4.1 are given a Prefixes that are created as specified in Section 4.1 are given a
rule priority of 0. rule priority of 0.
Whenever the configuration is changed or the prefix assignment Whenever the configuration is changed or the prefix assignment
algorithm subroutine is run: For each Link/Delegated Prefix pair, algorithm subroutine is run, for each Link/Delegated Prefix pair,
look for the configuration rule with the greatest configuration rule look for the configuration rule with the greatest configuration rule
priority such that: priority such that:
o The prefix specified in the configuration rule is included in the o The prefix specified in the configuration rule is included in the
considered Delegated Prefix. considered Delegated Prefix.
o The Link specified in the configuration rule is the considered o The Link specified in the configuration rule is the considered
Link. Link.
o All the Assigned Prefixes which would need to be destroyed in case o All the Assigned Prefixes that would need to be destroyed in case
a new Assigned Prefix is created from that configuration rule (as a new Assigned Prefix is created from that configuration rule (as
specified in Section 4.2) have an associated rule priority which specified in Section 4.2) have an associated rule priority that is
is strictly lower than the one of the considered configuration strictly lower than the one of the considered configuration rule.
rule.
o The assignment would be valid when published with an Advertised o The assignment would be valid when published with an Advertised
Prefix Priority equal to the one specified in the configuration Prefix Priority equal to the one specified in the configuration
rule. rule.
If a rule is found, a new Assigned Prefix is created based on that If a rule is found, a new Assigned Prefix is created based on that
rule as specified in Section 4.2. The new Assigned Prefix is rule as specified in Section 4.2. The new Assigned Prefix is
associated with the Advertised Prefix Priority and the rule priority associated with the Advertised Prefix Priority and the rule priority
specified in the considered configuration rule. specified in the considered configuration rule.
Note that the use of rule priorities ensures the convergence of the Note that the use of rule priorities ensures the convergence of the
algorithm. algorithm.
Acknowledgments
The authors would like to thank those who participated in the
development of draft versions of this document as well as the present
document. In particular, the authors would like to thank Tim Chown,
Fred Baker, Mark Townsley, Lorenzo Colitti, Ole Troan, Ray Bellis,
Markus Stenberg, Wassim Haddad, Joel Halpern, Samita Chakrabarti,
Michael Richardson, Anders Brandt, Erik Nordmark, Laurent Toutain,
Ralph Droms, Acee Lindem, Steven Barth, and Juliusz Chroboczek for
interesting discussions and document review.
Authors' Addresses Authors' Addresses
Pierre Pfister Pierre Pfister
Cisco Systems Cisco Systems
Paris Paris
France France
Email: pierre.pfister@darou.fr Email: pierre.pfister@darou.fr
Benjamin Paterson Benjamin Paterson
 End of changes. 98 change blocks. 
208 lines changed or deleted 204 lines changed or added

This html diff was produced by rfcdiff 1.42. The latest version is available from http://tools.ietf.org/tools/rfcdiff/