Multi-path Extension for the Optimized Link State Routing Protocol version 2 (OLSRv2)
draft-ietf-manet-olsrv2-multipath-12
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 8218.
|
|
|---|---|---|---|
| Authors | Jiazi Yi , Benoit Parrein | ||
| Last updated | 2017-05-04 (Latest revision 2017-04-19) | ||
| Replaces | draft-yi-manet-olsrv2-multipath | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
INTDIR Telechat review
by Zhen Cao
Ready w/issues
GENART Last Call review
by Peter Yee
Ready w/nits
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Stan Ratliff | ||
| Shepherd write-up | Show Last changed 2017-04-23 | ||
| IESG | IESG state | Became RFC 8218 (Experimental) | |
| Consensus boilerplate | Yes | ||
| Telechat date |
(None)
Needs a YES. |
||
| Responsible AD | Alvaro Retana | ||
| Send notices to | "Stan Ratliff" <sratliff@idirect.net>, aretana@cisco.com | ||
| IANA | IANA review state | IANA - Not OK |
draft-ietf-manet-olsrv2-multipath-12
Network Working Group J. Yi
Internet-Draft Ecole Polytechnique
Intended status: Experimental B. Parrein
Expires: October 21, 2017 University of Nantes
April 19, 2017
Multi-path Extension for the Optimized Link State Routing Protocol
version 2 (OLSRv2)
draft-ietf-manet-olsrv2-multipath-12
Abstract
This document specifies a multi-path extension for the Optimized Link
State Routing Protocol version 2 (OLSRv2) to discover multiple
disjoint paths, so as to improve reliability of the OLSRv2 protocol.
The interoperability with OLSRv2 is retained.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
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
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 21, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Motivation and Experiments to Be Conducted . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Applicability Statement . . . . . . . . . . . . . . . . . . . 6
4. Protocol Overview and Functioning . . . . . . . . . . . . . . 7
5. Parameters and Constants . . . . . . . . . . . . . . . . . . . 8
5.1. Router Parameters . . . . . . . . . . . . . . . . . . . . 8
6. Packets and Messages . . . . . . . . . . . . . . . . . . . . . 8
6.1. HELLO and TC messages . . . . . . . . . . . . . . . . . . 9
6.1.1. SOURCE_ROUTE TLV . . . . . . . . . . . . . . . . . . . 9
6.2. Datagram . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.2.1. Source Routing Header in IPv4 . . . . . . . . . . . . 9
6.2.2. Source Routing Header in IPv6 . . . . . . . . . . . . 10
7. Information Bases . . . . . . . . . . . . . . . . . . . . . . 10
7.1. SR-OLSRv2 Router Set . . . . . . . . . . . . . . . . . . . 10
7.2. Multi-path Routing Set . . . . . . . . . . . . . . . . . . 10
8. Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. HELLO and TC Message Generation . . . . . . . . . . . . . 11
8.2. HELLO and TC Message Processing . . . . . . . . . . . . . 12
8.3. MPR Selection . . . . . . . . . . . . . . . . . . . . . . 12
8.4. Datagram Processing at the MP-OLSRv2 Originator . . . . . 12
8.5. Multi-path Calculation . . . . . . . . . . . . . . . . . . 14
8.5.1. Requirements of Multi-path Calculation . . . . . . . . 14
8.5.2. Multi-path Dijkstra Algorithm . . . . . . . . . . . . 14
8.6. Multi-path Routing Set Updates . . . . . . . . . . . . . . 16
8.7. Datagram Forwarding . . . . . . . . . . . . . . . . . . . 16
9. Configuration Parameters . . . . . . . . . . . . . . . . . . . 16
10. Implementation Status . . . . . . . . . . . . . . . . . . . . 17
10.1. Multi-path extension based on nOLSRv2 . . . . . . . . . . 18
10.2. Multi-path extension based on olsrd . . . . . . . . . . . 18
10.3. Multi-path extension based on umOLSR . . . . . . . . . . . 19
11. Security Considerations . . . . . . . . . . . . . . . . . . . 19
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
12.1. Expert Review: Evaluation Guidelines . . . . . . . . . . . 20
12.2. Message TLV Types . . . . . . . . . . . . . . . . . . . . 20
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
14.1. Normative References . . . . . . . . . . . . . . . . . . . 21
14.2. Informative References . . . . . . . . . . . . . . . . . . 22
Appendix A. Examples of Multi-path Dijkstra Algorithm . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
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1. Introduction
The Optimized Link State Routing Protocol version 2 (OLSRv2)
[RFC7181] is a proactive link state protocol designed for use in
mobile ad hoc networks (MANETs). It generates routing messages
periodically to create and maintain a Routing Set, which contains
routing information to all the possible destinations in the routing
domain. For each destination, there exists a unique Routing Tuple,
which indicates the next hop to reach the destination.
This document specifies an extension of the OLSRv2 protocol
[RFC7181], to provide multiple disjoint paths when appropriate for a
source-destination pair. Because of the characteristics of MANETs
[RFC2501], especially the dynamic topology, having multiple paths is
helpful for increasing network throughput, improving forwarding
reliability and load balancing.
The Multi-path OLSRv2 (MP-OLSRv2) specified in this document uses
Multi-path Dijkstra algorithm by default to explore multiple disjoint
paths from a source router to a destination router based on the
topology information obtained through OLSRv2, and to forward the
datagrams in a load-balancing manner using source routing. MP-OLSRv2
is designed to be interoperable with OLSRv2.
1.1. Motivation and Experiments to Be Conducted
This document is an experimental extension of OLSRv2 that can
increase the data forwarding reliability in dynamic and high-load
MANET scenarios by transmitting datagrams over multiple disjoint
paths using source routing. This mechanism is used because:
o Disjoint paths can avoid single route failures.
o Transmitting datagrams through parallel paths can increase
aggregated throughput.
o Some scenarios may require some routers must (or must not) be
used.
o Having control of the paths at the source benefits the load
balancing and traffic engineering.
o An application of this extension is in combination with Forward
Error Correction (FEC) coding applied across packets (erasure
coding) [WPMC11]. Because the packet drop is normally bursty in a
path (for example, due to route failure), erasure coding is less
effective in single path routing protocols. By providing multiple
disjoint paths, the application of erasure coding with multi-path
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protocol is more resilient to routing failures.
While in existing deployments, running code and simulations have
proven the interest of multi-path extension for OLSRv2 in certain
networks, more experiments and experiences are still needed to
understand the effects of the protocol. The multi-path extension for
OLSRv2 is expected to be revised and improved to the Standard Track,
once sufficient operational experience is obtained. Other than
general experiences including the protocol specification and
interoperability with base OLSRv2 implementations, the experiences in
the following aspects are highly appreciated:
o Optimal values for the number of multiple paths (NUMBER_OF_PATHS,
Section 5) to be used. This depends on the network topology and
router density.
o Optimal values used in the metric functions. Metric functions are
applied to increase the metric of used links and nodes so as to
obtain disjoint paths. What kind of disjointness is desired
(node-disjoint or link-disjoint) may depend on the layer 2
protocol used, and can be achieved by setting different sets of
metric functions.
o Use of different metric types. This multi-path extension can be
used with metric types that meet the requirement of OLSRv2, such
as [RFC7779]. The metric type used has also impact to the choice
of metric functions as indicated in the previous bullet point.
o The impact of partial topology information to the multi-path
calculation. OLSRv2 maintains a partial topology information base
to reduce protocol overhead. Although with existing experience,
multiple paths can be obtained even with such partial information,
the calculation might be impacted, depending on the MPR selection
algorithm used.
o Use of IPv6 loose source routing. In the current specification,
only strict source routing is used for IPv6 based on [RFC6554].
In [I-D.ietf-6man-segment-routing-header], the use of loose source
routing is also proposed in IPv6. In scenarios where the length
of the source routing header is critical, the loose source routing
can be considered.
o Optimal choice of "key" routers for loose source routing. In some
cases, loose source routing is used to reduce overhead or for
interoperability with OLSRv2 routers. Other than the basic rules
defined in the following of this document, optimal choices of
routers to put in the loose source routing header can be further
studied.
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o Different path-selection schedulers. By default, Round-Robin
scheduling is used to select a path to be used for datagrams. In
some scenarios, weighted scheduling can be considered: for
example, the paths with lower metrics (i.e., higher quality) can
transfer more datagrams compared to paths with higher metrics.
o The impacts of the delay variation due to multi-path routing.
[RFC2991] brings out some concerns of multi-path routing,
especially variable latencies. Although current experiment
results show that multi-path routing can reduce the jitter in
dynamic scenarios, some transport protocols or applications may be
sensitive to the datagram re-ordering.
o The disjoint multi-path protocol has interesting application with
erasure coding, especially for services like video/audio streaming
[WPMC11]. The combination of erasure coding mechanisms and this
extension is thus encouraged.
o Different algorithms to obtain multiple paths, other than the
default Multi-path Dijkstra algorithm introduced in this
specification.
o The use of multi-topology information. By using [RFC7722],
multiple topologies using different metric types can be obtained.
Although there is no work defining how this extension can make use
of the multi-topology information base yet, it is encouraged to
experiment with the use of multiple metrics for building multiple
paths.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
This document uses the terminology and notation defined in [RFC5444],
[RFC6130], [RFC7181]. Additionally, it defines the following
terminology:
OLSRv2 Routing Process - A routing process based on [RFC7181],
without multi-path extension specified in this document.
MP-OLSRv2 Routing Process - A multi-path routing process based on
this specification as an extension to [RFC7181].
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SR-OLSRv2 Routing Process - A OLSRv2 Routing Process that supports
source routing, or an MP-OLSRv2 Routing Process.
3. Applicability Statement
As an extension of OLSRv2, this specification is applicable to MANETs
for which OLSRv2 is applicable (see [RFC7181]). It can operate on
single, or multiple interfaces, to discover multiple disjoint paths
from a source router to a destination router. MP-OLSRv2 is designed
for networks with dynamic topology by avoiding single route failure.
It can also provide higher aggregated throughput and load balancing.
In a router supporting MP-OLSRv2, MP-OLSRv2 does not necessarily
replace OLSRv2 completely. The extension can be applied for certain
applications that are suitable for multi-path routing (mainly video
or audio streams), based on the information such as DiffServ Code
Point [RFC2474].
Compared to OLSRv2, this extension does not introduce new message
type. A new Message TLV Type is introduced to identify the routers
that support forwarding based on source routing header. It is
interoperable with OLSRv2 implementations that do not have this
extension: as the MP-OLSRv2 uses source routing, in IPv4 networks the
interoperability is achieved by using loose source routing header; in
IPv6 networks, it is achieved by eliminating routers that do not
support IPv6 strict source routing.
MP-OLSRv2 supports two different, but interoperable multi-path
calculation approaches: proactive and reactive. In the proactive
calculation, the paths to all the destinations are calculated before
needed. In the reactive calculation, only the paths to desired
destination(s) are calculated on demand. The proactive approach
requires more computational resources than the reactive one. The
reactive approach requires the IP forwarding plane to trigger the
multi-path calculation.
MP-OLSRv2 forwards datagrams using the source routing header. As
there are multiple paths to each destination, MP-OLSRv2 requires the
IP forwarding plane to be able to choose which source route to be put
in the source routing header based on the path scheduler defined by
MP-OLSRv2. For IPv4 networks, implementation of loose source routing
is required following [RFC0791]. For IPv6 networks, implementation
of strict source routing is required following the source routing
header generation and processing defined in [RFC6554].
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4. Protocol Overview and Functioning
This specification uses OLSRv2 [RFC7181] to:
o Identify all the reachable routers in the network.
o Identify a sufficient subset of links in the networks, so that
routes can be calculated to all reachable destinations.
o Provide a Routing Set containing shortest routes from this router
to all destinations.
In addition, the MP-OLSRv2 Routing Process identifies the routers
that support source routing by adding a new Message TLV in HELLO and
TC messages. Based on the above information acquired, every MP-
OLSRv2 Routing Process is aware of a reduced topology map of the
network and the routers supporting source routing.
A Multi-path Routing Set containing the multi-path information is
maintained. It may either be proactively calculated or reactively
calculated:
o In the proactive approach, multiple paths to all possible
destinations are calculated and updated based on control message
exchange. The routes are thus available before they are actually
needed.
o In the reactive approach, a multi-path algorithm is invoked on
demand, i.e., only when there is a datagram to be sent from the
source to the destination, and there is no available Routing Tuple
in the Multi-path Routing Set. This requires the IP forwarding
information base to trigger the multi-path calculation specified
in Section 8.5 when no Multi-path Routing Tuple is available. The
reactive operation is local in the router and no additional
routing control messages exchange is required. When the paths are
being calculated, the datagrams SHOULD be buffered unless the
router does not have enough memory.
Routers in the same network may choose either proactive or reactive
multi-path calculation independently according to their computation
resources. The Multi-path Dijkstra algorithm (defined in
Section 8.5) is introduced as the default algorithm to generate
multiple disjoint paths from a source to a destination, and such
information is kept in the Multi-path Routing Set.
The datagram is forwarded based on source routing. When there is a
datagram to be sent to a destination, the source router acquires a
path from the Multi-path Routing Set (MAY be Round-Robin, or other
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scheduling algorithms). The path information is stored in the
datagram header as source routing header.
5. Parameters and Constants
In addition to the parameters and constants defined in [RFC7181],
this specification uses the parameters and constants described in
this section.
5.1. Router Parameters
NUMBER_OF_PATHS The number of paths desired by the router.
MAX_SRC_HOPS The maximum number of hops allowed to be put in the
source routing header. A value set zero means there is no
limitation on the maximum number of hops. In an IPv6 network, it
MUST be set to 0 because [RFC6554] supports only strict source
routing. All the intermediate routers MUST be included in the
source routing header, which makes the number of hops to be kept a
variable. In an IPv4 network, it MUST be strictly less than 11
and greater than 0 due to the limit of the IPv4 header.
CUTOFF_RATIO The ratio that defines the maximum metric of a path
compared to the shortest path kept in the OLSRv2 Routing Set. For
example, the metric to a destination is R_metric based on the
Routing Set. Then the maximum metric allowed for a path is
CUTOFF_RATIO * R_metric. CUTOFF_RATIO MUST be greater than or
equal to 1. Note that setting the value to 1 means looking for
equal length paths, which may not be possible in some networks.
SR_TC_INTERVAL The maximum time between the transmission of two
successive TC messages by a MP-OLSRv2 Routing Process.
SR_HOLD_TIME_MULTIPLIER The multiplier to calculate the minimal time
that a SR-OLSRv2 Router Tuple SHOULD be kept in the SR-OLSRv2
Router Set. It is the value of the Message TLV with Type =
SOURCE_ROUTE.
6. Packets and Messages
This extension employs the routing control messages HELLO and TC
(Topology Control) as defined in OLSRv2 [RFC7181] to obtain network
topology information. For the datagram, to support source routing, a
source routing header is added to each datagram routed by this
extension. Depending on the IP version used, the source routing
header is defined in this section.
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6.1. HELLO and TC messages
HELLO and TC messages used by MP-OLSRv2 Routing Process use the same
format as defined in [RFC7181]. In addition, a new Message TLV type
is defined, to identify the originator of the HELLO or TC message
that supports source route forwarding. The new Message TLV type is
introduced for enabling MP-OLSRv2 as an extension of OLSRv2: only the
routers supporting source-route forwarding can be used in the source
routing header of a datagram, because adding a router that does not
understand the source routing header will cause routing failure.
6.1.1. SOURCE_ROUTE TLV
SOURCE_ROUTE TLV is a Message TLV signalling that the message is
generated by a router that supports source-route forwarding. It can
be an MP-OLSRv2 Routing Process, or an OLSRv2 Routing Process that
supports source-route forwarding.
Every HELLO or TC message generated by a MP-OLSRv2 Routing Process
MUST have exactly one SOURCE_ROUTE TLV.
+--------------+-----------+----------------------------------------+
| Type | Value | Value |
| | Length | |
+--------------+-----------+----------------------------------------+
| SOURCE_ROUTE | 1 octet | The parameter SR_HOLD_TIME_MULTIPLIER |
| | | (unsigned integer) |
+--------------+-----------+----------------------------------------+
Table 1: SOURCE_ROUTE TLV Definition
Every HELLO or TC message generated by an OLSRv2 Routing Process MUST
have exactly one SOURCE_ROUTE TLV, if the OLSRv2 Routing Process
supports source-route forwarding, and is willing to join the source
route generated by other MP-OLSRv2 Routing Processes. The existence
of SOURCE_ROUTE TLV MUST be consistent for a specific OLSRv2 Routing
Process, i.e., either it adds SOURCE_ROUTE TLV to all its HELLO/TC
messages, or it does not add SOURCE_ROUTE TLV to any HELLO/TC
messages.
6.2. Datagram
6.2.1. Source Routing Header in IPv4
In IPv4 [RFC0791] networks, the MP-OLSRv2 routing process employs
loose source routing header, as defined in [RFC0791]. It exists as
an option header, with option class 0, and option number 3.
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The source route information is kept in the "route data" field of the
loose source route header.
6.2.2. Source Routing Header in IPv6
In IPv6 [I-D.ietf-6man-rfc2460bis] networks, the MP-OLSRv2 routing
process employs the source routing header as defined in section 3 of
[RFC6554], but with IPv6 Routing Type 254 (experimental).
The source route information is kept in the "Addresses" field of the
routing header.
7. Information Bases
Each MP-OLSRv2 routing process maintains the information bases as
defined in [RFC7181]. Additionally, a Multipath Information Base is
used for this specification. It includes the protocol sets as
defined below.
7.1. SR-OLSRv2 Router Set
The SR-OLSRv2 Router Set records the routers that support source-
route forwarding. This includes routers that run MP-OLSRv2 Routing
Process, or OLSRv2 Routing Process with source-route forwarding
support. The set consists of SR-OLSRv2 Router Tuples:
(SR_addr, SR_time)
where:
SR_addr - is the network address of the router that supports
source-route forwarding;
SR_time - is the time until which the SR-OLSRv2 Router Tuple is
considered valid.
7.2. Multi-path Routing Set
The Multi-path Routing Set records the full path information of
different paths to the destination. It consists of Multi-path
Routing Tuples:
(MR_dest_addr, MR_path_set)
where:
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MR_dest_addr - is the network address of the destination, either
the network address of an interface of a destination router or the
network address of an attached network;
MP_path_set - contains the multiple paths to the destination. It
consists of a set of Path Tuples.
Each Path Tuple is defined as:
(PT_metric, PT_address[1], PT_address[2], ..., PT_address[n])
where:
PT_metric - is the metric of the path to the destination, measured
in LINK_METRIC_TYPE defined in [RFC7181];
PT_address[1, ..., n-1] - are the addresses of intermediate routers
to be visited numbered from 1 to n-1, where n is the number of
routers in the path, i.e., the hop count.
8. Protocol Details
This protocol is based on OLSRv2, and extended to discover multiple
disjoint paths from a source router to a destination router. It
retains the basic routing control packets formats and processing of
OLSRv2 to obtain topology information of the network. The main
differences between OLSRv2 routing process are the datagram
processing at the source router and datagram forwarding.
8.1. HELLO and TC Message Generation
HELLO messages are generated according to Section 15.1 of [RFC7181],
plus a single message TLV with Type := SOURCE_ROUTE included.
TC message are generated according to Section 16.1 of [RFC7181] plus
a single message TLV with Type := SOURCE_ROUTE included. At least
one TC message MUST be generated by an MP-OLSRv2 Routing Process
during SR_TC_INTERVAL (Section 5). The TC message generation based
on SR_TC_INTERVAL does not replace the ordinary TC message generation
specified in [RFC7181] and MUST not carry any advertised neighbor
addresses. This is due to the fact that not all routers will
generate TC messages based on OLSRv2. The TC generation based on
SR_TC_INTERVAL serves for those routers to advertise SOURCE_ROUTE TLV
so that the other routers can be aware of the source-route enabled
routers so as to be used as destinations of multipath routing. The
SR_TC_INTERVAL is set to a longer value than TC_INTERVAL.
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8.2. HELLO and TC Message Processing
HELLO and TC messages are processed according to section 15.3 and
16.3 of [RFC7181].
In addition to the reasons specified in [RFC7181] for discarding a
HELLO message or a TC message on reception, a HELLO or TC message
received MUST be discarded if it has more than one Message TLV with
Type = SOURCE_ROUTE.
For every HELLO or TC message received, if there is a Message TLV
with Type := SOURCE_ROUTE, create or update (if the Tuple exists
already) the SR-OLSR Router Tuple with
o SR_addr := originator address of the HELLO or TC message
o SR_time := current_time + SR_HOLD_TIME_MULTIPLIER * validity time
of the TC or HELLO message defined in [RFC7181], unless the
existing SR_time is greater than the newly calculated the SR_time.
8.3. MPR Selection
Each MP-OLSRv2 Routing Process selects routing MPRs and flooding MPRs
following Section 18 of [RFC7181]. In a mixed network with OLSRv2-
only routers, the following considerations apply when calculating
MPRs:
o MP-OLSRv2 routers SHOULD be preferred as routing MPRs to increase
the possiblity of finding disjoint paths using MP-OLSRv2 routers.
o The number of routing MPRs that run MP-OLSRv2 Routing Process MUST
be equal or greater than NUMBER_OF_PATHS if there are enough MP-
OLSRv2 symmetric neighbors. Or else, all the MP-OLSRv2 routers
are selected as routing MPRs.
8.4. Datagram Processing at the MP-OLSRv2 Originator
If datagrams without source routing header need to be forwarded using
multiple paths (for example, based on the information of DiffServ
Code Point [RFC2474]), the MP-OLSRv2 routing process will try to find
the Multi-path Routing Tuple where:
o MR_dest_addr = destination of the datagram
If no matching Multi-path Routing Tuple is found and the Multi-path
Routing Set is maintained proactively, it indicates that there is no
route available to the desired destination. The datagram is
discarded.
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If no matching Multi-path Routing Tuple is found and the Multi-path
Routing Set is maintained reactively, the multi-path algorithm
defined in Section 8.5 is invoked, to calculate the Multi-path
Routing Tuple to the destination. If the calculation does not return
any Multi-path Routing Tuple, the following steps are aborted and the
datagram is forwarded following OLSRv2 routing process.
If a matching Multi-path Routing Tuple is obtained, the Path Tuples
of the Multi-path Routing Tuple are applied to the datagrams using
Round-robin scheduling. For example, there are 2 path Tuples
(Path-1, Path-2) for destination router D. A series of datagrams
(Packet-1, Packet-2, Packet-3, ... etc.) are to be sent router D.
Path-1 is then chosen for Packet-1, Path-2 for Packet-2, Path-1 for
Packet 3, etc. Other path scheduling mechanisms are also possible
and will not impact the interoperability of different
implementations.
The addresses in PT_address[1, ..., n-1] of the chosen Path Tuple are
thus added to the datagram header as the source routing header. For
IPv6 networks, strict source routing is used, thus all the
intermediate routers in the path are stored in the source routing
header following format defined in section 3 of [RFC6554] with
Routing Type set to 3.
For IPv4 networks, loose source routing is used, with following
rules:
o Only the addresses that exist in SR-OLSR Router Set can be added
to the source routing header.
o If the length of the path (n) is greater than MAX_SRC_HOPS
(Section 5), only the "key" routers in the path are kept. By
default, the key routers are uniformly chosen in the path. If
further information such as capacity of the routers (e.g., battery
life) or the routers' willingness in forwarding data is available,
the routers with higher capacity and willingness are preferred.
o The routers that are considered not appropriate for forwarding
indicated by external policies should be avoided.
It is RECOMMENDED to use MTU sizes considering the source routing
header to avoid fragmentation. Depending on the size of the routing
domain, the MTU should be at least 1280 + 40 (for outer IP header) +
16 * diameter of the network in number of hops (for source routing
header). If the links in the network have different MTU sizes, by
using technologies like Path MTU Discovery, the routers are able to
be aware of the MTU along the path. The size of the datagram plus
the size of IP headers (including the source routing header) SHOULD
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NOT exceed the minimum MTU along the path.
8.5. Multi-path Calculation
8.5.1. Requirements of Multi-path Calculation
The Multi-path Routing Set maintains the information of multiple
paths to the destination. The Path Tuples of the Multi-path Routing
Set (Section 7.2) are generated based on a multi-path algorithm.
For each path to a destination, the algorithm must provide:
o The metric of the path to the destination,
o The list of intermediate routers on the path.
For IPv6 networks, as strict source routing is used, only the routers
that exist in SR-OLSRv2 Router Set are considered in the path
calculation, i.e., only the source-routing supported routers can
exist in the path.
After the calculation of multiple paths, the metric of paths (denoted
c_i for path i) to the destination is compared to the R_metric of the
OLSRv2 Routing Tuple ([RFC7181]) to the same destination. If the
metric c_i is greater than R_metric * CUTOFF_RATIO (Section 5), the
corresponding path i SHOULD NOT be used. If less than 2 paths are
found with metrics less than R_metric * CUTOFF_RATIO, the router
SHOULD fall back to OLSRv2 Routing Process without using multipath
routing. This can happen if there are too much OLSRv2-only routers
in the network, and requiring multipath routing may result in
inferior paths.
By invoking the multi-path algorithm, NUMBER_OF_PATHS paths are
obtained and added to the Multi-path Routing Set, by creating a
Multi-path Routing Tuple with:
o MR_dest_addr := destination of the datagram
o A MP_path_set with calculated Path Tuples. Each Path Tuple
corresponds to a path obtained in Multi-path Dijkstra algorithm,
with PT_metric := metric of the calculated path and PT_address[1,
..., n-1] := list of intermediate routers.
8.5.2. Multi-path Dijkstra Algorithm
This section introduces Multi-path Dijkstra Algorithm as a default
algorithm. It tries to obtain disjoint paths when appropriate, but
does not guarantee strict disjoint paths. The use of other
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algorithms is not prohibited, as long as the requirements described
in Section 8.5.1 are met. Using different multi-path algorithms will
not impact the interoperability.
The general principle of the Multi-path Dijkstra Algorithm [ADHOC11]
is using Dijkstra algorithm for multiple iterations, and at iteration
i to look for the shortest path P[i] to the destination d. After
each iteration, the cost of used links is increased. Compared to the
original Dijkstra algorithm, the main modification consists in adding
two incremental functions named metric functions fp and fe in order
to prevent the next steps resulting in similar paths:
o fp(c) is used to increase metrics of arcs belonging to the
previous path P[i-1] (with i>1), where c is the value of the
previous metric. This encourages future paths to use different
arcs but not different vertices.
o fe(c) is used to increase metrics of the arcs that lead to
intermediate vertices of the previous path P[i-1] (with i>1),
where c is the value of the previous metric. The "lead to" means
that only one vertex of the arc belongs to the previous path
P[i-1], while the other vertex is not. The "intermediate" means
that the source and destination vertices are not considered.
Considering the simple example in Figure 1: a path P[i] S--A--D is
obtained at step i. For the next step, the metric of link S--A and
A--D are to be increased using fp(c), because they belong to the path
P[i]. A--B is to be increased using fe(c), because A is an
intermediate vetex of path P[i], and B is not part of P[i]. B--D is
unchanged.
B
/ \
/ \
/ \
S---------A-----------D
Figure 1
It is possible to choose different fp and fe to get link-disjoint
paths or node-disjoint paths as desired. A recommendation of
configuration of fp and fe is given in Section 9.
To get NUMBER_OF_PATHS different paths, for each path P[i] (i = 1,
..., NUMBER_OF_PATHS) do:
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1. Run Dijkstra algorithm to get the shortest path P[i] for the
destination d.
2. Apply metric function fp to the metric of links (in both
directions) in P[i].
3. Apply metric function fe to the metric of links (in both
directions) that lead to routers used in P[i].
A simple example of Multi-path Dijkstra Algorithm is illustrated in
Appendix A.
8.6. Multi-path Routing Set Updates
The Multi-path Routing Set MUST be updated when the Local Information
Base, the Neighborhood Information Base, or the Topology Information
Base indicate a change (including of any potentially used outgoing
neighbor metric values) of the known symmetric links and/or attached
networks in the MANET, hence changing the Topology Graph, as
described in section 17.7 of [RFC7181]. How the Multi-path Routing
Set is updated depends on the set is maintained reactively or
proactively:
o In reactive mode, all the Tuples in the Multi-path Routing Set are
removed. The new arriving datagrams will be processed as
specified in Section 8.4;
o In proactive mode, the route to all the destinations are updated
according to Section 8.5.
8.7. Datagram Forwarding
In IPv4 networks, datagrams are forwarded using loose source routing
as specified in Section 3.1 of [RFC0791].
In IPv6 networks, datagrams are forwarded using strict source routing
as specified in Section 4.2 of [RFC6554], except the applied routers
are MP-OLSRv2 routers rather than RPL routers. The last hop of the
source route MUST remove the source routing header.
9. Configuration Parameters
This section gives default values and guideline for setting
parameters defined in Section 5. Network administrators may wish to
change certain, or all the parameters for different network
scenarios. As an experimental protocol, the users of this protocol
are also encouraged to explore different parameter setting in various
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network environments, and provide feedback.
o NUMBER_OF_PATHS := 3. This parameter defines the number of
parallel paths used in datagram forwarding. Setting it to one
makes the specification identical to OLSRv2. Setting it to too
large values may lead to unnecessary computational overhead and
inferior paths.
o MAX_SRC_HOPS := 10, for IPv4 networks. For IPv6 networks, it MUST
be set to 0, i.e., no constraint on maximum number of hops.
o CUTOFF_RATIO := 1.5. It MUST be strictly greater than 1.
o SR_TC_INTERVAL := 10 x TC_INTERVAL. It SHOULD be significantly
greater than TC_INTERVAL to reduce unnecessary TC message
generations.
o SR_HOLD_TIME_MULTIPLIER := 32. It MUST be greater than 1 and less
than 255. It SHOULD be greater than 30.
If Multi-path Dijkstra Algorithm is applied:
o fp(c) := 4*c, where c is the original metric of the link.
o fe(c) := 2*c, where c is the original metric of the link.
The setting of metric functions fp and fc defines the preference of
obtained multiple disjoint paths. If id is the identity function,
i.e., fp(c)=c, 3 cases are possible:
o if id=fe<fp: only increase the metric of related links;
o if id<fe=fp: apply equal increase to the metric of related nodes
and links;
o if id<fe<fp: apply more increase to the metric of related links.
Increasing the metric of related links or nodes means avoiding the
use of such links or nodes in the next path to be calculated.
10. Implementation Status
The RFC Editor is advised to remove the entire section before
publication, as well as the reference to RFC 7942.
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
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Internet-Draft, and based on a proposal described in [RFC7942]. The
description of implementations in this section is intended to assist
the IETF in its decision processes in progressing drafts to RFCs.
Please note that the listing of any individual implementation here
does not imply endorsement by the IETF. Furthermore, no effort has
been spent to verify the information presented here that was supplied
by IETF contributors. This is not intended as, and must not be
construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
Until April 2015, there are 3 open source implementations of the
protocol specified in this document, for both testbed and simulation
use.
10.1. Multi-path extension based on nOLSRv2
The implementation is conducted by University of Nantes, France, and
is based on Niigata University's nOLSRv2 implementation. It is an
open source implementation. The code is available at
https://github.com/yijiazi/mpolsr_qualnet and
http://jiaziyi.com/index.php/research-projects/mp-olsr .
It can be used for Qualnet simulations, and be exported to run in a
testbed. All the specification is implemented in this
implementation.
Implementation experience and test data can be found at [ADHOC11].
10.2. Multi-path extension based on olsrd
The implementation is conducted under SEREADMO (Securite des Reseaux
Ad Hoc & Mojette) project, and supported by French research agency
(RNRT2803). It is based on olsrd (http://www.olsr.org/)
implementation, and is open sourced. The code is available at
https://github.com/yijiazi/mpolsr_testbed and
http://jiaziyi.com/index.php/research-projects/sereadmo .
The implementation is for testing the specification in the field.
All the specification is implemented in this implementation.
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Implementation experience and test data can be found at [ADHOC11] and
[GIIS14].
10.3. Multi-path extension based on umOLSR
The implementation is conducted by University of Nantes, France, and
is based on um-olsr implementation
(http://masimum.inf.um.es/fjrm/development/um-olsr/). The code is
available at https://github.com/yijiazi/mpolsr_ns2 and
http://jiaziyi.com/index.php/research-projects/mp-olsr under GNU GPL
license.
The implementation is for network simulation for NS2 network
simulator. All the specification is implemented in this
implementation.
Implementation experience and test data can be found at [WCNC08].
11. Security Considerations
As an extension of [RFC7181], the security considerations and
security architecture illustrated in [RFC7181] are applicable to this
MP-OLSRv2 specification. The implementations without security
mechanisms are vulnerable to threats discussed in
[I-D.ietf-manet-olsrv2-sec-threats].
In a mixed network with OLSRv2-only routers, a compromised router can
add SOURCE_ROUTE TLVs in its TC and HELLO messages, which will make
other MP-OLSRv2 Routing Process believes that it supports source
routing. This will increase the possibility of being chosen as MPRs
and be put into the source routing header. The former will make it
possible to manipulate the flooding of TC messages and the latter
will make the datagram pass through the compromised router.
As [RFC7181], a conformant implementation of MP-OLSRv2 MUST, at
minimum, implement the security mechanisms specified in [RFC7183] to
provide integrity and replay protection of routing control messages.
MP-OLSRv2 Routing Process MUST drop datagrams entering or exiting a
OLSRv2/MP-OLSRv2 routing domain that contain a source routing header.
Compared to OLSRv2, the use of source routing header in this
specification introduces vulnerabilities related to source routing
attacks, which include bypassing filtering devices, bandwidth
exhaustion of certain routers, etc. Those attacks are discussed in
Section 5 of [RFC6554] and [RFC5095]. The influence is limited to
the OLSRv2/MP-OLSRv2 routing domain, because the source routing
header is used only in the current routing domain.
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If the multiple paths are calculated reactively, the datagrams SHOULD
be buffered while the paths are being calculated. Because the path
calculation is local and no control message is exchanged, the
buffering time should be trivial. However, depending on the CPU
power and memory of the router, a maximum buffer size SHOULD be set
to avoid occupying too much memory of the router. When the buffer is
full, the ancient datagrams are dropped. A possible attack that a
malicious application could launch is that, it initiates large amount
of datagrams to all the other routers in the network, thus triggering
path calculation to all the other routers and during which, the
datagrams are buffered. This might flush other legitimate datagrams.
But the impact of the attack is transient: once the path calculation
is finished, the datagrams are forwarded and the buffer goes back to
empty.
12. IANA Considerations
This section adds one new Message TLV, allocated as a new Type
Extension to an existing Message TLV.
12.1. Expert Review: Evaluation Guidelines
For the registry where an Expert Review is required, the designated
expert SHOULD take the same general recommendations into
consideration as are specified by [RFC5444].
12.2. Message TLV Types
This specification updates the Message Type 7 by adding the new Type
Extension SOURCE_ROUTE, as illustrated in Table 2.
+-----------+--------------+------------------------+---------------+
| Type | Name | Description | Reference |
| Extension | | | |
+-----------+--------------+------------------------+---------------+
| TBD | SOURCE_ROUTE | Indicates that the | This |
| | | originator of the | specification |
| | | message supports | |
| | | source route | |
| | | forwarding. The value | |
| | | is a multiplier for | |
| | | calculating the hold | |
| | | time of SR-OLSRv2 | |
| | | Router Tuples. | |
+-----------+--------------+------------------------+---------------+
Table 2: SOURCE_ROUTE type for RFC 5444 Type 7 Message TLV Type
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Extensions
13. Acknowledgments
The authors would like to thank Sylvain David, Asmaa Adnane, Eddy
Cizeron, Salima Hamma, Pascal Lesage and Xavier Lecourtier for their
efforts in developing, implementing and testing the specification.
The authors also appreciate valuable discussions with Thomas Clausen,
Ulrich Herberg, Justin Dean, Geoff Ladwig, Henning Rogge , Marcus
Barkowsky and especially Christopher Dearlove for his multiple rounds
of reviews during the working group last calls.
14. References
14.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<http://www.rfc-editor.org/info/rfc791>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC5444] Clausen, T., Dearlove, C., Dean, J., and C. Adjih,
"Generalized Mobile Ad Hoc Network (MANET) Packet/Message
Format", RFC 5444, DOI 10.17487/RFC5444, February 2009,
<http://www.rfc-editor.org/info/rfc5444>.
[RFC6130] Clausen, T., Dearlove, C., and J. Dean, "Mobile Ad Hoc
Network (MANET) Neighborhood Discovery Protocol (NHDP)",
RFC 6130, DOI 10.17487/RFC6130, April 2011,
<http://www.rfc-editor.org/info/rfc6130>.
[RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
Routing Header for Source Routes with the Routing Protocol
for Low-Power and Lossy Networks (RPL)", RFC 6554,
DOI 10.17487/RFC6554, March 2012,
<http://www.rfc-editor.org/info/rfc6554>.
[RFC7181] Clausen, T., Dearlove, C., Jacquet, P., and U. Herberg,
"The Optimized Link State Routing Protocol Version 2",
RFC 7181, DOI 10.17487/RFC7181, April 2014,
<http://www.rfc-editor.org/info/rfc7181>.
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[RFC7183] Herberg, U., Dearlove, C., and T. Clausen, "Integrity
Protection for the Neighborhood Discovery Protocol (NHDP)
and Optimized Link State Routing Protocol Version 2
(OLSRv2)", RFC 7183, DOI 10.17487/RFC7183, April 2014,
<http://www.rfc-editor.org/info/rfc7183>.
14.2. Informative References
[ADHOC11] Yi, J., Adnane, A-H., David, S., and B. Parrein,
"Multipath optimized link state routing for mobile ad hoc
networks", In Elsevier Ad Hoc Journal, vol.9, n. 1, 28-47,
January, 2011.
[GIIS14] Macedo, R., Melo, R., Santos, A., and M. Nogueria,
"Experimental performance comparison of single-path and
multipath routing in VANETs", In Global Information
Infrastructure and Networking Symposium (GIIS), 2014 ,
vol. 1, no. 6, pp. 15-19, 2014.
[I-D.ietf-6man-rfc2460bis]
Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", draft-ietf-6man-rfc2460bis-09 (work
in progress), March 2017.
[I-D.ietf-6man-segment-routing-header]
Previdi, S., Filsfils, C., Raza, K., Leddy, J., Field, B.,
daniel.voyer@bell.ca, d., daniel.bernier@bell.ca, d.,
Matsushima, S., Leung, I., Linkova, J., Aries, E., Kosugi,
T., Vyncke, E., Lebrun, D., Steinberg, D., and R. Raszuk,
"IPv6 Segment Routing Header (SRH)",
draft-ietf-6man-segment-routing-header-06 (work in
progress), March 2017.
[I-D.ietf-manet-olsrv2-sec-threats]
Clausen, T., Herberg, U., and J. Yi, "Security Threats to
the Optimized Link State Routing Protocol version 2
(OLSRv2)", draft-ietf-manet-olsrv2-sec-threats-04 (work in
progress), January 2017.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<http://www.rfc-editor.org/info/rfc2474>.
[RFC2501] Corson, S. and J. Macker, "Mobile Ad hoc Networking
(MANET): Routing Protocol Performance Issues and
Evaluation Considerations", RFC 2501, DOI 10.17487/
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RFC2501, January 1999,
<http://www.rfc-editor.org/info/rfc2501>.
[RFC2991] Thaler, D. and C. Hopps, "Multipath Issues in Unicast and
Multicast Next-Hop Selection", RFC 2991, DOI 10.17487/
RFC2991, November 2000,
<http://www.rfc-editor.org/info/rfc2991>.
[RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
of Type 0 Routing Headers in IPv6", RFC 5095,
DOI 10.17487/RFC5095, December 2007,
<http://www.rfc-editor.org/info/rfc5095>.
[RFC7722] Dearlove, C. and T. Clausen, "Multi-Topology Extension for
the Optimized Link State Routing Protocol Version 2
(OLSRv2)", RFC 7722, DOI 10.17487/RFC7722, December 2015,
<http://www.rfc-editor.org/info/rfc7722>.
[RFC7779] Rogge, H. and E. Baccelli, "Directional Airtime Metric
Based on Packet Sequence Numbers for Optimized Link State
Routing Version 2 (OLSRv2)", RFC 7779, DOI 10.17487/
RFC7779, April 2016,
<http://www.rfc-editor.org/info/rfc7779>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<http://www.rfc-editor.org/info/rfc7942>.
[WCNC08] Yi, J., Cizeron, E., Hamma, S., and B. Parrein,
"Simulation and performance analysis of MP-OLSR for mobile
ad hoc networks", In Proceeding of IEEE Wireless
Communications and Networking Conference, 2008.
[WPMC11] Yi, J., Parrein, B., and D. Radu, "Multipath routing
protocol for manet: Application to H.264/SVC video content
delivery", In Proceeding of 14th International Symposium
on Wireless Personal Multimedia Communications.
Appendix A. Examples of Multi-path Dijkstra Algorithm
This appendix gives two examples of multi-path Dijkstra algorithm.
A network topology is depicted in Figure 2.
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.-----A-----(2)
(1) / \ \
/ / \ \
S (2) (1) D
\ / \ /
(1) / \ / (2)
B----(3)----C
Figure 2
The capital letters are name of routers. An arbitrary metric with
value between 1 and 3 is used. The initial metrics of all the links
are indicated in the parenthesis. The incremental functions fp(c)=4c
and fe(c)=2c are used in this example. Two paths from router S to
router D are demanded.
On the first run of the Dijkstra algorithm, the shortest path S->A->D
with metric 3 is obtained.
The incremental function fp is applied to increase the metric of the
link S-A and A-D. fe is applied to increase the metric of the link
A-B and A-C. Figure 3 shows the link metrics after the punishment.
.-----A-----(8)
(4) / \ \
/ / \ \
S (4) (2) D
\ / \ /
(1) / \ / (2)
B----(3)----C
Figure 3
On the second run of the Dijkstra algorithm, the second path
S->B->C->D with metric 6 is obtained.
As mentioned in Section 8.5, the Multi-path Dijkstra Algorithm does
not guarantee strict disjoint path to avoid choosing inferior paths.
For example, given the topology in Figure 4, two paths from node S to
D are desired. On the top of the figure, there is a high cost path
between S and D.
If a algorithm tries to obtain strict disjoint paths, the two paths
obtained will be S--B--D and S--(high cost path)--D, which are
extremely unbalanced. It is undesired because it will cause huge
delay variance between the paths. By using the Multi-path Dijkstra
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algorithm, which is based on the punishing scheme, S--B--D and
S--B--C--D will be obtained.
--high cost path-
/ \
/ \
S----B--------------D
\ /
\---C-----/
Figure 4
Authors' Addresses
Jiazi Yi
Ecole Polytechnique
91128 Palaiseau Cedex,
France
Phone: +33 (0) 1 77 57 80 85
Email: jiazi@jiaziyi.com
URI: http://www.jiaziyi.com/
Benoit Parrein
University of Nantes
IRCCyN lab - IVC team
Polytech Nantes, rue Christian Pauc, BP50609
44306 Nantes cedex 3
France
Phone: +33 (0) 2 40 68 30 50
Email: Benoit.Parrein@polytech.univ-nantes.fr
URI: http://www.irccyn.ec-nantes.fr/~parrein
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