draft-ietf-homenet-prefix-assignment-05.txt   draft-ietf-homenet-prefix-assignment-06.txt 
Network Working Group P. Pfister Network Working Group P. Pfister
Internet-Draft B. Paterson Internet-Draft B. Paterson
Intended status: Standards Track Cisco Systems Intended status: Standards Track Cisco Systems
Expires: October 10, 2015 J. Arkko Expires: November 29, 2015 J. Arkko
Ericsson Ericsson
April 8, 2015 May 28, 2015
Distributed Prefix Assignment Algorithm Distributed Prefix Assignment Algorithm
draft-ietf-homenet-prefix-assignment-05 draft-ietf-homenet-prefix-assignment-06
Abstract Abstract
This document specifies a distributed algorithm for automatic prefix This document specifies a distributed algorithm for automatic prefix
assignment. Given a set of delegated prefixes, it ensures that at assignment. Given a set of delegated prefixes, it ensures that at
most one prefix is assigned from each delegated prefix to each link. most one prefix is assigned from each delegated prefix to each link.
Nodes may assign available prefixes to the links they are directly Nodes may assign available prefixes to the links they are directly
connected to, or for other private purposes. The algorithm connected to, or for other private purposes. The algorithm
eventually converges and ensures that all assigned prefixes do not eventually converges and ensures that all assigned prefixes do not
overlap. overlap.
skipping to change at page 1, line 38 skipping to change at page 1, line 38
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This Internet-Draft will expire on October 10, 2015. This Internet-Draft will expire on November 29, 2015.
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.
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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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Applicability statement . . . . . . . . . . . . . . . . . . . 5 2.1. Subroutine Specific Terminology . . . . . . . . . . . . . 5
4. Algorithm Specification . . . . . . . . . . . . . . . . . . . 6 3. Applicability Statement . . . . . . . . . . . . . . . . . . . 6
4.1. Algorithm Terminology . . . . . . . . . . . . . . . . . . 6 4. Algorithm Specification . . . . . . . . . . . . . . . . . . . 7
4.2. Prefix Assignment Algorithm Routine . . . . . . . . . . . 7 4.1. Prefix Assignment Algorithm Subroutine . . . . . . . . . 7
4.3. Overriding and Destroying Existing Assignments . . . . . 10 4.2. Overriding and Destroying Existing Assignments . . . . . 10
4.4. Other Events . . . . . . . . . . . . . . . . . . . . . . 11 4.3. Other Events . . . . . . . . . . . . . . . . . . . . . . 12
5. Prefix Selection Considerations . . . . . . . . . . . . . . . 12 5. Prefix Selection Considerations . . . . . . . . . . . . . . . 12
6. Implementation Capabilities and Node Behavior . . . . . . . . 14 6. Implementation Capabilities and Node Behavior . . . . . . . . 14
7. Algorithm Parameters . . . . . . . . . . . . . . . . . . . . 15 7. Algorithm Parameters . . . . . . . . . . . . . . . . . . . . 15
8. Security Considerations . . . . . . . . . . . . . . . . . . . 15 8. Security Considerations . . . . . . . . . . . . . . . . . . . 16
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
11.1. Normative References . . . . . . . . . . . . . . . . . . 17 11.1. Normative References . . . . . . . . . . . . . . . . . . 17
11.2. Informative References . . . . . . . . . . . . . . . . . 17 11.2. Informative References . . . . . . . . . . . . . . . . . 17
Appendix A. Static Configuration Example . . . . . . . . . . . . 17 Appendix A. Static Configuration Example . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction 1. Introduction
This document specifies a distributed algorithm for automatic prefix This document specifies a distributed algorithm for automatic prefix
assignment. Given a set of delegated prefixes, nodes may assign assignment. Given a set of delegated prefixes, Nodes may assign
available prefixes to links they are directly connected to, or for available prefixes to links they are directly connected to, or for
their private use. The algorithm ensures that the following their private use. The algorithm ensures that the following
assertions are eventually true: assertions are satisfied after a finite convergence 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 not included in and do not include other 2. Assigned prefixes are non-overlapping (i.e., an assigned prefix
assigned prefixes. 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 to
as the correctness conditions of the algorithm while the third 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 more advanced assignment policies. When assignment, allowing for custom assignment policies. When multiple
multiple nodes assign different prefixes from the same delegated Nodes assign different prefixes from the same delegated prefix to the
prefix to the same link, or when multiple nodes assign overlapping same link, or when multiple Nodes assign overlapping prefixes (to the
prefixes, the assignment with the highest priority is kept and other same link or to different links), the assignment with the greatest
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
faster than a given timing upper bound, the algorithm also ensures within a given time window, the algorithm also ensures that all
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. Terminology 2. Terminology
In this document, the key words "MAY", "MUST, "MUST NOT", "OPTIONAL", In this document, the key words "MAY", "MUST, "MUST NOT", "OPTIONAL",
and "SHOULD", are to be interpreted as described in [RFC2119]. and "SHOULD", are to be interpreted as described in [RFC2119].
This document makes use of the following terminology: This document makes use of the following terminology. The terms
defined here are ordered in such a way as to avoid forward
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
reliably share information with all other participating Nodes.
Link: An object the distributed algorithm will assign prefixes to. Link: An object the distributed algorithm will assign prefixes to.
A Node may only assign prefixes to Links it is directly connected A Node may only assign prefixes to Links it is directly connected
to. A Link is either Shared or Private. to. A Link is either Shared or Private.
Shared Link: A Link multiple Nodes may be connected to. Most of
the time, a Shared Link is a multi-access link or point-to-point
link, virtual or physical, requiring prefixes to be assigned 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.
Shared Link: A Link multiple nodes may be connected to. Most of
the time, a Shared Link is a multi-access link or point-to-point
link, virtual or physical, requiring prefixes to be assigned to
it.
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 alphanumeric order).
Flooding Mechanism: A mechanism allowing participating nodes to Flooding Delay: A value which MUST be provided by the Flooding
reliably share information with all other participating nodes. Mechanism and SHOULD be a deterministic or likely upper bound on
the information propagation delay among participating Nodes.
Flooding Delay: Value which SHOULD be provided by the Flooding
Mechanism indicating a deterministic or likely upper bound of the
information propagation delay. When the Flooding Mechanism does
not provide a value, it is set to DEFAULT_FLOODING_DELAY
(Section 7).
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 a 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, all Advertised Prefixes but the one with the are conflicting (i.e., overlapping or from the same Delegated
greatest priority will eventually be removed. In case of tie, the Prefix and assigned to the same link), all Advertised Prefixes but
assignment advertised by the node with the greatest Node ID is the one with the greatest priority will eventually be removed. In
kept and others are removed. In order to ensure convergence, the case of a tie, the assignment advertised by the Node with the
range of priority values MUST have an upper bound. greatest Node ID is kept and others are removed. In order to
ensure convergence, the range of priority values MUST have an
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 never is 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.
Applied (Assigned Prefix): When an Assigned Prefix is applied, it Applied (Assigned Prefix): When an Assigned Prefix is applied, it
MAY be used (e.g., for host configuration, routing protocol MAY be used (e.g., for host configuration, routing protocol
configuration, prefix delegation). When not applied, it MUST NOT configuration, prefix delegation). When not applied, it MUST NOT
be used for any other purposes than the prefix assignment be used for any purpose outside of the prefix assignment
algorithm. Each Assigned Prefix is associated with a timer (Apply algorithm. Each Assigned Prefix is associated with a timer (Apply
Timer) used to apply the Assigned Prefix. An Assigned Prefix is Timer) used to apply the Assigned Prefix. An Assigned Prefix is
unapplied when destroyed. unapplied when destroyed.
Published (Assigned Prefix): The Assigned Prefix is advertised Published (Assigned Prefix): The Assigned Prefix is advertised
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 through the Flooding Mechanism. once received through the Flooding Mechanism.
Prefix Adoption: When an Advertised Prefix which does not conflict Prefix Adoption: When an Advertised Prefix which 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 avoid multiple with a timer counting down to zero. It is used to reduce the
nodes from making colliding assignments by delaying the creation probability of colliding assignments made by multiple Nodes by
of 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. advertisement of adopted Assigned Prefixes by a random amount of
time.
Renumbering: Event occurring when an Assigned Prefix which was Renumbering: Event occurring when an Assigned Prefix which was
applied is destroyed. It is undesirable as it usually implies applied is destroyed. Renumbering is undesirable as it usually
reconfiguring routers or hosts. implies reconfiguring routers or hosts.
3. Applicability statement
Each node MUST have a set of disjoint Delegated Prefixes (i.e., which
do not include each other). This set MAY change over time and be
different from one node to another at some point, but nodes MUST
eventually have the same set of disjoint Delegated Prefixes.
Given this set of disjoint Delegated Prefixes, nodes may assign
available prefixes from each Delegated Prefix to the Links they are
directly connected to. The algorithm ensures that at most one prefix
from a given Delegated Prefix is assigned to a given Link.
The algorithm can be applied to any address space and can be used to
manage multiple address spaces simultaneously. For instance, an
implementation can make use of IPv4-mapped IPv6 addresses [RFC4291]
in order to manage both IPv4 and IPv6 prefix assignment using a
single prefix space.
The algorithm supports dynamically changing topologies:
o Nodes may join or leave the set of participating nodes.
o Nodes may join or leave Links.
o Links may be joined or split.
All nodes MUST run a common Flooding Mechanism in order to share
published Assigned Prefixes. The set of participating nodes is
defined as the set of nodes participating in the Flooding Mechanism.
The Flooding Mechanism MUST:
o Provide a way to flood Assigned Prefixes assigned to a directly
connected Link along with their respective Advertised Prefix
Priority and the Node ID of the node which advertises it.
o Specify whether an Advertised Prefix was assigned to a directly
connected Shared Link, and if so, on which one.
In addition, a Flooding Delay SHOULD be specified and respected in
order to avoid renumbering. If not specified, or whenever the
Flooding Mechanism is unable to respect the provided delay,
renumbering may happen. As such delay often depends on the size of
the network, it MAY change over time and MAY be different from one
node to another.
The algorithm ensures that whenever the Flooding Delay is provided
and respected, and in the absence of topology change or Delegated
Prefix removal, renumbering only happens when a node deliberately
overrides an existing assignment.
Each node MUST have a Node ID. Node IDs MAY change over time and be
the same on multiple nodes at some point, but each node MUST
eventually have a Node ID which is unique among the set of
participating nodes.
4. Algorithm Specification
This section specifies the behavior of nodes implementing the prefix
assignment algorithm.
4.1. Algorithm Terminology 2.1. Subroutine Specific Terminology
The algorithm makes use of the following terms: In addition to the terms defined in Section 2, the subroutine
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, 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 the Advertised Prefix (if any): Assignment is the unique Advertised Prefix (if any) that:
* Including or included in the Delegated Prefix. * Includes or is included in the Delegated Prefix (i.e., the
Advertised Prefix is a sub-prefix of the Delegated Prefix, or
the Delegated Prefix is a sub-prefix of the Advertised Prefix).
* Assigned on the given Link. * Is assigned on the given Link.
* Having the greatest Advertised Prefix Priority among Advertised * Has the greatest Advertised Prefix Priority among Advertised
Prefixes fulfilling the two preceding conditions (and, in case Prefixes fulfilling the two preceding conditions (and, in case
of tie, the prefix advertised by the node with the greatest of a tie, the prefix advertised by the Node with the greatest
Node ID among all prefixes with greatest priority). Node ID among all prefixes with greatest priority).
* Taking precedence over the Current Assignment associated with * Takes precedence over the Current Assignment associated with
the same Link and Delegated Prefix (if any). the same Link and Delegated Prefix (if any).
Valid (Assigned Prefix): An Assigned Prefix is valid if and only if Valid (Assigned Prefix): An Assigned Prefix is valid if and only if
the two following conditions are met: the following two conditions are met:
* No Advertised Prefix including or included in the Assigned * No Advertised Prefix including or included in the Assigned
Prefix takes precedence over the Assigned Prefix. Prefix takes precedence over the Assigned Prefix.
* 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.
4.2. Prefix Assignment Algorithm Routine 3. Applicability Statement
This section specifies the prefix assignment algorithm routine. It Each Node MUST have a set of non-overlapping Delegated Prefixes
is defined for a given Delegated Prefix and Link pair and may be run (i.e., which do not include each other). This set MAY change over
either as triggered by the Backoff Timer or as triggered by another time and be different from one Node to another at some point, but
event. Nodes MUST eventually have the same set of disjoint Delegated
Prefixes.
For a given Delegated Prefix and Link pair, the routine MUST be run Given this set of disjoint Delegated Prefixes, Nodes may assign
as not triggered by the Backoff Timer whenever: available prefixes from each Delegated Prefix to the Links they are
directly connected to. The algorithm ensures that at most one prefix
from a given Delegated Prefix is assigned to any given Link.
The algorithm can be applied to any address space and can be used to
manage multiple address spaces simultaneously. For instance, an
implementation can make use of IPv4-mapped IPv6 addresses [RFC4291]
in order to manage both IPv4 and IPv6 prefix assignment using a
single prefix space.
The algorithm supports dynamically changing topologies:
o Nodes may join or leave the set of participating Nodes.
o Nodes may join or leave Links.
o Links may be joined or split.
All Nodes MUST run a common Flooding Mechanism in order to share
published Assigned Prefixes. The set of participating Nodes is
defined as the set of Nodes participating in the Flooding Mechanism.
The Flooding Mechanism MUST:
o Provide a way to flood Assigned Prefixes assigned to a directly
connected Link along with their respective Advertised Prefix
Priority and the Node ID of the Node which is advertising them.
o Specify whether an Advertised Prefix was assigned to a directly
connected Shared Link, and if so, on which one.
o Provide a Flooding Delay value, which SHOULD represent a
deterministic or likely upper bound on the information propagation
delay among participating Nodes. Whenever the Flooding Mechanism
is unable to adhere to the provided Flooding Delay, renumbering
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
Node to another. Furthermore, the process of selecting this value
is subject to a tradeoff between convergence speed and lower
renumbering probability (e.g., the value 0 may be used when
renumbering is harmless), and is therefore out of scope of this
document.
The algorithm ensures that whenever the Flooding Delay is provided
and respected, and in the absence of any topology change or Delegated
Prefix removal, renumbering only happens when a Node deliberately
overrides an existing assignment.
Each Node MUST have a Node ID. Node IDs MAY change over time and be
the same on multiple Nodes at some point, but each Node MUST
eventually have a Node ID which is unique among the set of
participating Nodes.
4. Algorithm Specification
This section specifies the behavior of Nodes implementing the prefix
assignment algorithm. The terms 'Current Assignment', 'Precedence',
'Best Assignment' and 'Valid' are used as defined in Section 2.1.
4.1. 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
BackoffTriggered boolean as parameter (indicating whether the
subroutine execution was triggered by the Backoff Timer or by another
event).
For a given Delegated Prefix and Link pair, the subroutine MUST be
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
the given pair. This case MAY be ignored if the creation of a new the given pair. This case MAY be ignored if the creation of a new
Assigned Prefix associated with the considered pair is not Assigned Prefix associated with the considered pair is not
desired. desired.
o The considered Delegated Prefix is added. o The considered Delegated Prefix is added.
o The considered Link is added. o The considered Link is added.
o The Node ID is modified. o The Node ID is modified.
Additionally, for a given Delegated Prefix and Link pair, the routine Furthermore, for a given Delegated Prefix and Link pair, the
MUST be run as triggered by the Backoff Timer whenever: subroutine MUST be run with the BackoffTriggered boolean set to true
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 with the given pair. associated 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
routine instead of executing it immediately, e.g. while receiving an subroutine instead of executing it immediately, e.g., while receiving
update from the Flooding Mechanism, or for security reasons (see an update from the Flooding Mechanism, or for security reasons (see
Section 8). Even though other events occur in the meantime, the Section 8). Even if other events occur in the meantime, the
routine MUST be run only once. It is also assumed that, whenever one subroutine MUST be run only once. It is also assumed that, whenever
of these events is the Backoff Timer firing, the routine is executed one of these events is the Backoff Timer firing, the subroutine is
as triggered by the Backoff Timer. executed with the BackoffTriggered boolean set to true.
In order to execute the routine for a given Delegated Prefix and Link In order to execute the subroutine for a given Delegated Prefix and
pair, first look for the Best Assignment and Current Assignment Link pair, first look for the Best Assignment and Current Assignment
associated with the Delegated Prefix and Link pair, then execute the associated with the Delegated Prefix and Link pair, then execute the
corresponding case: corresponding case:
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 way the decision is made is out of the scope of this the process of making this decision is out of the scope of this
document) and do the following: document) and do the following:
* If it is not desired, stop the execution of the routine. * 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 routine. the subroutine.
* Else if the routine was not executed as triggered by the * Else if the BackoffTriggered boolean is set to false, set the
Backoff Timer, set the Backoff Timer to some random delay Backoff Timer to some random delay between ADOPT_MAX_DELAY and
between ADOPT_MAX_DELAY and BACKOFF_MAX_DELAY (see Section 7) BACKOFF_MAX_DELAY (see Section 7) and stop the execution of
and stop the execution of the routine. the subroutine.
* Else, continue the execution of the routine. * 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.
* 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: Cancel 2. If there is a Best Assignment but no Current Assignment: Cancel
the Backoff Timer and use the prefix from the Best Assignment to the Backoff Timer and use the prefix from the Best Assignment to
create a new Assigned Prefix: create a new Assigned Prefix:
* Assigned to the considered Link. * Assigned to the considered Link.
* Not applied. * Set as not applied.
* The Apply Timer set to '2 * Flooding Delay'. * The Apply Timer set to '2 * Flooding Delay'.
* 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 routine again, as not triggered by the Backoff execute the subroutine again with the BackoffTriggered boolean
Timer. 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 routine. 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 cancelling 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. the Shared Link.
+ Destroy it and go to case 1. + Destroy it and go to case 1.
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 routine requires an assignment When the prefix assignment algorithm subroutine requires an
to be created or adopted, any Advertised Prefix Priority value can be assignment to be created or adopted, any Advertised Prefix Priority
used. Other documents MAY provide restrictions over this value value can be used. Other documents MAY provide restrictions over
depending on the context the algorithm is operating in, or leave it this value depending on the context the algorithm is operating in, or
as implementation-specific. leave it as implementation-specific.
When the prefix assignment algorithm routine requires an assignment
to be created or adopted, the chosen Advertised Prefix Priority is
unspecified (any value would be valid). The values to be used in
such situations MAY be specified by other documents making use of the
prefix assignment algorithm or be left as an implementation specific
choice.
4.3. Overriding and Destroying Existing Assignments 4.2. Overriding and Destroying Existing Assignments
In addition to the behaviors specified in Section 4.2, the following In addition to the behaviors specified in Section 4.1, the following
procedures MAY be used in order to provide more advanced behavior procedures MAY be used in order to provide additional behavior
(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 which 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 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 which 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 which 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 respect this rule Nodes may not converge. Nodes which do not adhere to this rule
MUST implement a mechanism which detects whether the MUST implement a mechanism which detects whether the
distributed algorithm do not converge and, whenever this would distributed algorithm does not converge and, whenever this
happen, stop creating overriding Assigned Prefixes which do not would happen, stop creating overriding Assigned Prefixes which
hold this rule. The specifications for such safety procedures do not adhere to this rule. The specifications for such safety
are out of the scope of this document. procedures are out of the scope of 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 from a node which is published. Such an event reflects the desire of a Node
to not assign a prefix from a given Delegated Prefix to a given to not assign a prefix from a given Delegated Prefix to a given
Link anymore. In order to ensure algorithm convergence, such Link 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. Additionally, whenever an Assigned Prefix is Node configuration. Furthermore, whenever an Assigned Prefix is
destroyed this way, the prefix assignment algorithm routine MUST destroyed in this way, the prefix assignment algorithm subroutine
be run for the Delegated Prefix and Link pair associated with the MUST be run for the Delegated Prefix and Link pair associated with
deleted Assigned Prefix. the destroyed Assigned Prefix.
These procedures are OPTIONAL. They could be used for various The two procedures specified in this section are OPTIONAL. They
purposes, e.g., for providing custom prefix assignment configuration could be used for various purposes, e.g., for providing custom prefix
or reacting to prefix space exhaustion (by overriding short Assigned assignment configuration or reacting to prefix space exhaustion (by
Prefixes and assigning longer ones). overriding short Assigned Prefixes and assigning longer ones).
4.4. 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 When a Delegated Prefix is removed from the set of Delegated Prefixes
Prefixes, all Assigned Prefixes included in the removed Delegated (e.g., when the Delegated Prefix expires), all Assigned Prefixes
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 which 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 routine specified in Section 4.2 When the prefix assignment algorithm subroutine specified in
requires a new prefix to be selected, the prefix MUST be selected Section 4.1 requires a new prefix to be selected, the prefix MUST be
either: selected either:
o Among prefixes included in the considered Delegated Prefix which o Among prefixes included in the considered Delegated Prefix which
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 in a set of at least RANDOM_SET_SIZE (see
Section 7) prefixes included in the considered Delegated Prefix Section 7) prefixes included in the considered Delegated Prefix
and not including or included in any Assigned or Advertised and not including or included in any Assigned or Advertised
Prefix. If less than RANDOM_SET_SIZE candidates are found, the Prefix. If less than RANDOM_SET_SIZE candidates are found, the
skipping to change at page 12, line 46 skipping to change at page 13, line 6
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 which
MAY be applied any time a node needs to pick a prefix for a new MAY 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 A/N is available if and only if it Available prefix: The prefix of the form Prefix/PrefixLength is
holds the three following conditions: available if and only if it satisfies the three following
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 but Advertised Prefix.
* It is equal to the considered Delegated Prefix or A/(N-1) * It is equal to the considered Delegated Prefix or Prefix/
includes an Assigned or Advertised 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 which is included in
or is equal to an available prefix. or 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:
Stability: In some cases, it is desirable that the selected prefix Prefix Stability: In some cases, it is desirable that the selected
remains the same across executions and reboots. For this purpose, prefix should remain the same across executions and reboots. For
prefixes previously applied on the Link or pseudo-random prefixes this purpose, prefixes previously applied on the Link or pseudo-
generated based on node and Link specific values may be random prefixes generated based on Node- and Link-specific values
considered. may be considered.
Randomness: When no stored or pseudo-random prefix is chosen, a Randomness: When no stored or pseudo-random 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 tie, preferring small with longest prefix lengths and, in case of a tie, preferring
prefix values. numerically small prefix values.
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.
3. If the desired prefix length was not specified, select one. The 3. If the desired prefix length was not specified, select one. The
available prefixes count computed previously may be used to help available prefixes count computed previously may be used to help
picking a prefix length such that: pick a prefix length such that:
* There is at least one candidate prefix. * There is at least one candidate prefix.
* The prefix length is chosen great enough to not exhaust the * The prefix length is chosen large enough to not exhaust the
address space. address space.
Let N be the chosen prefix length. Let N be the chosen prefix length.
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 pseudo-
randomly chosen based on Node and Link specific values. For each randomly chosen based on Node- and Link-specific values. For
pseudo-random prefix, check if the prefix is equal to a candidate each pseudo-random prefix, check if the prefix is equal to a
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 trie.
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 4.3. The node considerations specified in Section 5 or Section 4.2. The Node
never checks existing assignments validity, which makes this never checks the validity of existing assignments, which makes
behavior particularly suited to lightweight devices which can rely this behavior particularly suited to lightweight devices which can
on more capable neighbors to make assignments on directly rely 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 which 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 4.3. 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 4.3. It is considerations specified in Section 5 and Section 4.2. It is
suited when the administrator desires some particular prefix to be suited when the administrator desires some particular prefix to be
assigned on a given Link, or some Links to be assigned prefixes assigned on a given Link, or some Link to be assigned prefixes
with a greater priority. with a greater priority when there are not enough prefixes
available for all Links.
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
given Delegated Prefix to the given Link, no prefix from the given
Delegated Prefix will ever be assigned to the Link (and such existing
prefixes will be removed). This situation may be detected by
watching whether no prefix from a given Delegated Prefix has been
assigned to the Link for longer than 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, low verbosity (less traffic is generated by the Flooding addressing, reduced control traffic (generated by the Flooding
Mechanism), and low collision probability. Mechanism), and low collision probability.
ADOPT_MAX_DELAY (respectively BACKOFF_MAX_DELAY) represents the ADOPT_MAX_DELAY (respectively BACKOFF_MAX_DELAY) represents the
maximum backoff time a node may wait before adopting an assignment maximum backoff time a Node may wait before adopting an assignment
(respectively making a new assignment). BACKOFF_MAX_DELAY MUST be (respectively making a new assignment). BACKOFF_MAX_DELAY MUST be
greater than or equal to ADOPT_MAX_DELAY. The greater greater than or equal to ADOPT_MAX_DELAY. The greater
ADOPT_MAX_DELAY and (BACKOFF_MAX_DELAY - ADOPT_MAX_DELAY), the lower ADOPT_MAX_DELAY and (BACKOFF_MAX_DELAY - ADOPT_MAX_DELAY), the lower
the collision probability and the verbosity, but the greater the the collision probability and the lesser the amount of control
convergence time. 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 a random
prefix will be picked from. The greater RANDOM_SET_SIZE, the better prefix will be picked from. The greater RANDOM_SET_SIZE, the better
the convergence time and the lower the collision probability, but the the convergence time and the lower the collision probability, but the
worse the addressing-space usage efficiency. worse the addressing-space usage efficiency.
When the Flooding Mechanism does not provide a Flooding Delay, it is
set to DEFAULT_FLOODING_DELAY. As participating nodes do not need to
agree on a common Flooding Delay value, this default value MAY be
different from one node to another. If the context in which the
algorithm is used does not suffer from renumbering, the value 0 MAY
be used. Otherwise it depends on the Flooding Mechanism properties
and the desired renumbering probability, and is therefore out of
scope of this document.
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:
* Publish a single overriding assignment for a whole Delegated * Publish a single overriding assignment for a whole Delegated
Prefix or for the whole address space, thus preventing any node Prefix or for the whole address space, thus preventing any Node
from assigning prefixes to Links. from assigning prefixes to Links.
* Quickly publish and remove Advertised Prefixes, generating * Quickly publish and remove Advertised Prefixes, generating
traffic at the Flooding Mechanism layer and causing multiple traffic at the Flooding Mechanism layer and causing multiple
executions of the prefix assignment algorithm in all executions of the prefix assignment algorithm in all
participating nodes. participating Nodes.
* Publish and remove Advertised Prefixes in order to prevent the * Publish and remove Advertised Prefixes in order to prevent the
convergence of the execution. convergence of the algorithm.
An attacker able to prevent other nodes from accessing a portion An attacker able to prevent other Nodes from accessing a portion
or the whole set of Advertised Prefixes may compromise the or the whole set of Advertised Prefixes may compromise the
correctness of the execution. correctness of the algorithm.
An attacker able to cause repetitive Node ID changes may induce An attacker able to cause repetitive Node ID changes may cause
traffic generation from the Flooding Mechanism and multiple traffic to be generated in the Flooding Mechanism and multiple
executions of the prefix assignment algorithm in all participating executions of the prefix assignment algorithm in all participating
nodes. Nodes.
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 prevent the correctness and convergence used by another Node may prevent the correctness and convergence
of the execution. of the algorithm or cause the result to violate the correctness
conditions.
Whenever the security of the Flooding Mechanism and Node ID Whenever the security of the Flooding Mechanism and Node ID
assignment mechanism could not be ensured, the convergence of the assignment mechanism cannot be ensured, the convergence of the
execution 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
routine SHOULD be rate limited, as specified in Section 4.2. subroutine SHOULD be rate limited, as specified in Section 4.1.
9. IANA Considerations 9. IANA Considerations
This document has no actions for IANA. This document has no actions for IANA.
10. Acknowledgments 10. Acknowledgments
The authors would like to thank those who participated in the The authors would like to thank those who participated in the
previous document's version development as well as the present one. previous document's version development as well as the present one.
In particular, the authors would like to thank Tim Chown, Fred Baker, In particular, the authors would like to thank Tim Chown, Fred Baker,
skipping to change at page 17, line 26 skipping to change at page 17, line 37
[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. December 2003.
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 (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 execution, 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 the strictly) of the configuration rule priority (i.e., the greater is
configuration rule priority, the greater the Assigned Prefix Priority the configuration rule priority, the greater the Assigned Prefix
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 4.2 are given a Prefixes which 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 routine is run: For each Link/Delegated Prefix pair, look algorithm subroutine is run: For each Link/Delegated Prefix pair,
for the configuration rule with the highest 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 which 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 4.3) have an associated rule priority which specified in Section 4.2) have an associated rule priority which
is strictly lower than the one of the considered configuration is 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 in conformance with Section 4.3. 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
execution. algorithm.
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
Cisco Systems Cisco Systems
Paris Paris
France France
Email: benjamin@paterson.fr Email: paterson.b@gmail.com
Jari Arkko Jari Arkko
Ericsson Ericsson
Jorvas 02420 Jorvas 02420
Finland Finland
Email: jari.arkko@piuha.net Email: jari.arkko@piuha.net
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