Re: [Roll] Comments on draft-dt-roll-p2p-rpl-01

["Anders Brandt" <[e-mail]>]

Comments inline
 
Cheers,
  Anders


________________________________

	From: [e-mail] [mailto:[e-mail]] On
Behalf Of JP Vasseur
	Sent: Wednesday, June 16, 2010 12:00
	To: Mukul Goyal; Emmanuel Baccelli
	Cc: ROLL WG
	Subject: [Roll] Comments on draft-dt-roll-p2p-rpl-01
	
	
	Dear authors,

	Since I had a number of comments I inserted them in the ID
itself. As you will notice:
	1) Some of them are purely editorial
	2) Others are more fundamental and may require just
clarifications, more discussion on the mailing list, ... In this case,
feel free to start a separate thread (note that ticket cannot be
assigned to non WG document).
	3) I also suggested new sections

	
	Internet Engineering Task Force                            M.
Goyal, Ed.
	Internet-Draft                         University of Wisconsin
Milwaukee
	Intended status: Informational                          E.
Baccelli, Ed.
	
	JP> Are you sure that you want to make it informational ?
	
	
	Expires: December 16, 2010
INRIA
	
P2P. Team
	                                                           June
14, 2010
	
	
	   Reactive Discovery of Point-to-Point Routes in Low Power and
Lossy
	                                Networks
	                        draft-dt-roll-p2p-rpl-01
	
	Abstract
	
	   This document describes a mechanism to discover and establish
"on
	   demand" one or more routes between two routers in a low power
and
	   lossy network.
	
	
	
	JP> Needs a bit more details + explicitly refer to IPv6 in the
abstract 
	and introduction.
	Status of this Memo This Internet-Draft is submitted to IETF 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
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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 December 16, 2010. Copyright Notice Copyright (c) 2010 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 Goyal,
et al. Expires December 16, 2010 [Page 1]  Internet-Draft
draft-dt-roll-p2p-rpl-01 June 2010 described in the Simplified BSD
License. Table of Contents 1. Introduction . . . . . . . . . . . . . . .
. . . . . . . . . . 3 2. Targeted Use Cases . . . . . . . . . . . . . .
. . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . .
. . . . . 4 4. Functional Overview . . . . . . . . . . . . . . . . . . .
. . 5 5. Propagation of Discovery Messages . . . . . . . . . . . . . . 7
5.1. The Route Discovery Option . . . . . . . . . . . . . . . . 7 5.2.
Setting a DIO Carrying a Route Discovery Option . . . . . 9 5.3.
Processing of a DIO Carrying a Route Discovery Option At An Intermediate
Node . . . . . . . . . . . . . . . . . 10 5.4. Processing of a DIO
Carrying a Route Discovery Option At The Target Router . . . . . . . . .
. . . . . . . . . . 12 6. Propagation of Discovery Reply Messages . . .
. . . . . . . . 13 6.1. The Discovery Reply Object (DRO) . . . . . . . .
. . . . . 13 6.1.1. The Source Route Option . . . . . . . . . . . . . .
. 15 6.2. DRO as Acknowledgement for Backward Source Routes . . . . 16
6.3. DRO as Carrier of Forward/Bidirectional Source Routes . . 17 6.4.
Establishing Hop-by-hop Routes Via DRO . . . . . . . . . . 17 7.
Security Considerations . . . . . . . . . . . . . . . . . . . 18 8. IANA
Considerations . . . . . . . . . . . . . . . . . . . . . 18 9. Authors
and Contributors . . . . . . . . . . . . . . . . . . . 18 10. References
. . . . . . . . . . . . . . . . . . . . . . . . . . 18 10.1. Normative
References . . . . . . . . . . . . . . . . . . . 18 10.2. Informative
References . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . .
. . . . . . . . . . . . . . . . . . . . . . 19 Goyal, et al. Expires
December 16, 2010 [Page 2]  Internet-Draft draft-dt-roll-p2p-rpl-01
June 2010 1. Introduction RPL [I-D.ietf-roll-rpl] provides
multipoint-to-point (MP2P) routes from routers in a low power and lossy
network (LLN) to a sink router by organizing the routers along a
Directed Acyclic Graph (DAG) rooted at the sink.  
	
	JP> low power and lossy .... Low Power and Lossy
	
	JP> RPL provides P2MP, MP2P and P2P routes too.
	
	
	The DAG root initiates the DAG formation by originating
	   a DODAG Information Object (DIO) message.  The DIO message is
sent
	   via link-local multicast and carries information about the
	   originating router's position (the "rank") in the DAG.  On
receiving
	   DIO messages sent by its neighbors, a router determines its
own
	   "rank" in the DAG and originates its own DIO message.
	
	
	JP> Without going too much in the details, you may just want to
add
	that a node decides to join a DODAG according to a number of
parameters
	(identity of the DODAG, OF, routing/constraints a specified in
the metric-ID,...).
	   RPL enables point-to-multipoint (P2MP) routing from a router
to its
	   descendants in the DAG by allowing a router to send a
Destination
	   Advertisement Object (DAO) upwards along the DAG.  The DAO
carries
	   the aggregated 
	
	JP> Potentially "aggregated"
	information regarding the descendants (and other local
	   prefixes) reachable through the originating router.
	
	   RPL also provides mechanisms for point-to-point (P2P) routing
between
	   any two routers in the DAG.  
	
	JP> Yes.
	If the destination is within the
	   source's "range", the source may directly send packets to the
	   destination.  Otherwise, if the destination is a DAG
descendant and
	   the source maintains "downwards" routing state about this
descendant,
	   it can forward the packet along this route.  Otherwise, the
source
	   sends the packet to a DAG parent, which then applies the same
set of
	   rules to forward the packet further.  Thus, a packet travels
up the
	   DAG until it reaches a router that knows of the downwards
route to
	   the destination and then it travels down the DAG towards its
	   destination.  A router may or may not maintain routing state
about a
	   descendant depending on whether its immediate children send
it such
	   information in their DAOs and whether the router can store
this
	   information.  Thus, in the best case scenario, the "upwards"
segment
	   of the P2P route between a source and a destination ends at
the first
	   common ancestor of the source and the destination.  In the
worst
	   case, the "upwards" segment would extend all the way to the
DAG's
	   root.  If the destination did not originate a DAO, the packet
will
	   travel all the way to the DAG's root, where it will be
dropped.
	
	
	
	JP> This may require to be a bit more accurate here. If there is
no DAO,
	there RPL is used for MP2P routing only (that is not a protocol
design 
	characteristic though). 
	   The P2P routing functionality available in RPL suffers from
several
	   shortcomings
[I-D.brandt-roll-rpl-applicability-home-building]:
	
	
	
	JP> "suffering from several shortcomings" is a bit strong
though. You may
	want to say that additional mechanisms may be required to
address specific
	situation and list them.  

[ABR:]
I think that the wording is adequate and nobody objected to the
conclusions of the applicability draft so far.
The applicability draft evaluates the usefulness of the current RPL
proposal and concludes that
basic requirements are not met for home and building application spaces.

	   o  The need to maintain routes "proactively", i.e. every
possible
	      destination in the DAG must originate a DAO.
	
	   o  The constraint to route only along a DAG potentialy
leading to
	      significantly suboptimal P2P routes and traffic congestion
near
	      the DAG root.
	
	JP> 
	First bullet: you can mention that this requires to pro-actively
advertise the
	route and to keep refreshing the state accordingly
	Second bullet: just to be very accurate, mention that the route
may be sub-optimal.
	This is highly network topology / OF dependent.
	Goyal, et al. Expires December 16, 2010 [Page 3] 
Internet-Draft draft-dt-roll-p2p-rpl-01 June 2010 These shortcomings are
not compatible with the home and commercial building domain application
requirements described in [RFC5826] and
[I-D.ietf-roll-building-routing-reqs].  
	
	JP> Again, to be accurate, there are no MUST requirements listed
in
	these ID that are not satisfied by RPL (with regards to the
aforementioned
	issues). I am NOT saying that the proposed mechanism is not
useful 
	(by all means), just that the statement above is not correct. 

 
[ABR:]
I have to disagree.
 
RFC5826 says: 
The routing protocol MUST converge within 0.5 seconds if no nodes
   have moved (see Section 3.2 <outbind://43/#section-3.2>  for
motivation).

   The routing protocol MUST converge within four seconds if nodes have
   moved to re-establish connectivity within a time that a human
   operator would find tolerable as, for example, when moving a remote
   control unit.


	Such applications require a
	   mechanism providing source-initiated discovery of P2P routes
that are
	   not along a DAG.  
	
	JP> In some cases, it may be desirable to make use of
source-initiated ... 

[ABR:]
I have to disagree.
If I am looking for a light module and the DAG states represent broken
paths, I have a requirement for
source-initiated discovery. I cannot wait for the RPL DAG timers to
fire. 


	This document thus describes such a mechanism,
	   complementary to the basic RPL specification.
	
	   The specified scheme is based on a reactive on-demand
approach, which
	   enables a router to discover one or more "good-enough" routes
in
	   either direction between itself and another router in the LLN
without
	   any constraints regarding the existing DAG-membership of the
links
	   that such routes may use.  
	
	JP> This will be an aspect triggering some discussion. How
"good" is
	"good enough" ? You will need some text to elaborate here or
point 
	to another section explaining what is meant by "good enough"
	Such routes may be source-routes or hop-
	   by-hop ones.  
	
	JP> Just terminology: instead of referring to hop-by-hop routes,
you may
	want to say that once a route has been computed between two
nodes in 
	the network, IPv6 packet may be forward using a source routing
mechanism
	as specified in [XX] or in a hop by hop fashion.
	A complementary functionality, necessary to help decide
	   whether to initiate a route discovery, is a mechanism to
measure the
	   end-to-end cost of an existing route.  
	
	JP> s/cost/path cost
	Such functionality will be
	   described in a separate document.
	
	
	
	JP> But its use is described in this document ?
	2. Targeted Use Cases The mechanisms described in this document
are intended to be employed as complementary to RPL in specific
scenarios that need point-to- point (P2P) routes between arbitrary
routers. One target use case, common in a home environment, involves a
remote control (or a motion sensor) that suddenly needs to communicate
with a lamp module, whose network address it knows apriori. In this
case, the source of data (the remote control or the motion sensor) must
be able to discover a route to the destination (the lamp module) "on
demand". Another target use case, common in a large commercial building
environment, involves a large LLN deployment where P2P communication
along a particular DAG among hundreds (or thousands) of routers creates
severe traffic congestion near that DAG's root, and thus routes across
this DAG are desirable. Targeted use cases also include scenarios where
energy or delay constraints are not satisfied by the P2P routes along a
DAG because they involve traversing many more intermediate routers than
necessary to reach the destination. 
	
	JP> What I would suggest is to summarize it, put in the
introduction,
	and detail the use case in the applicability statement. 

[ABR:]
 
Good point

	3.  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
	
	
	
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	   [RFC2119].
	
	   Additionally, this document uses terminology from
	   [I-D.ietf-roll-terminology] and [I-D.ietf-roll-rpl], and
introduces
	   the following terminology:
	
	   Origin Router: The router initiating the route discovery.
The origin
	   router acts as one end point of the routes to be discovered.
	
	   Target Router: The other end point of the routes to be
discovered.
	
	   Intermediate Router: A router that is neither the origin nor
the
	   target.
	
	   Forward Route: A route from the origin router to the target
router.
	
	   Backward Route: A route from the target router to the origin
router.
	
	   Bidirectional Route: A route that can be used in both
directions:
	   from the origin router to the target router and vice versa.
	
	   Source Route: A complete and ordered list of routers that can
be used
	   by a packet to travel from a source to a destination.  Such
source
	   routes can be carried by a packet in a proposed Type 4
Routing Header
	   [I-D.hui-6man-rpl-routing-header].
	
	   Hop-by-hop Route: A route from a source to a destination
where each
	   router in the route knows only the address of the next hop on
the
	   route.
	
	JP> I would suggest to change the definition for "routing
paradigm
	whereby packets are routed from their source to destination by 
	on a hop by hop basis where the packets is routed by a set of
routers
	along the path according to the routing table stored by each
router
	along the path".
	   In this document, the term 'router' refers to any LLN device
that can
	   forward packets generated at other devices.
	
	
	4.  Functional Overview
	
	   Router A originates a "Discovery" message listing router B as
the
	   target.  Node A also indicates in the message:
	
	   o  The nature of the routing cost, the method for
accumulating the
	      end-to-end cost 
	
	JP> This may de detailed hereafter but I guess that you will
point to 
	the metric-ID for the metric used?
	
	
	and the criteria used to determine if a route is
	      "good enough";
	
	   o  The direction (forward: router A to router B; backward:
router B
	      to router A; or both) of the route being discovered;
	
	   o  The desired number of routes;
	
	
	
	
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	   o  Whether the route is a source-route or a hop-by-hop one;
and
	
	   o  A limit on the "distance" the Discovery message may
travel.
	
	
	
	JP> Need to define the term "distance": is it a max path cost,
number of
	hops, ... ?
	The Discovery message propagates via link-local multicast 
	
	JP> Indicate "IPv6"
	with each
	   receiving router making the decision regarding whether to
forward the
	   message further based on the "distance" (from router A) that
this
	   particular copy of the message has already traveled.  Note
that this
	   document does not require a receiving router to use the "good
enough"
	   criteria to make the forwarding decision.  This is because
the
	   evaluation of such criteria may be too complex for a
constrained
	   intermediate router to perform for each received copy of the
	   Discovery message.  
	
	JP> So I guess that you define later what to do in both cases
(the node
	cannot process the "good enough" criteria or it can process it)
?
	The calculation of the "distance" that a copy of
	   the Discovery message has already travelled should be simple
enough
	   for a constrained router to perform.  
	
	JP> Again it is hard to tell from what you wrote if this can
reasonably be
	achieved; it depends on the definition of the term "distance".
	A router may optionally decide
	   not to forward a copy of the Discovery message further
because the
	   aggregated cost of the route so far fails the "good enough"
criteria.
	
	JP> You will nee to be more specific here. Is it a "may" or a
"MAY". 
	Define what happens in this case. You may provide more details
later
	in the document.
	   The underlying mechanism being used to propagate the
Discovery
	   message may put further restrictions on its propagation.  A
router
	   should not propagate the Discovery message further if
hop-by-hop
	   routes are desired and the router can not store state for
this route.
	
	   As a copy of the Discovery message travels towards router B,
it
	   accumulates the relevant forward/backward costs as well as
the route
	   it takes.  When router B receives a copy of the Discovery
message, it
	   determines whether the route traveled by the message meets
the "good
	   enough" criteria.
	
	JP> I think that you already mentioned this.
	   If router A had requested the discovery of backward
source-routes,
	
	JP> Didn't you mean "forward" ?
	   router B caches one or more good enough source-routes it
identifies.
	   Additionally, router B sends one or more "Discovery Reply"
message to
	   router A to acknowledge the discovery of these routes.  These
	   acknowledgements allow router A to judge the success of the
route
	   discovery.  The Discovery Reply messages can travel towards
router A
	   in any manner chosen by router B. For example, router B may
source-
	   route the messages or send them towards router A along a DAG.
	
	   If router A had requested the discovery of "n" forward
source-routes,
	   router B sends the "n" good enough source-routes it
identifies to
	   router A in one or more Discovery Reply messages.  Again,
these
	   Discovery Reply messages can travel towards router A in any
manner
	   chosen by router B.
	
	JP> What if the DAG is "broken": retry from A after expiration
of a local
	timer ?
	   If router A had requested the discovery of "n" bidirectional
source-
	   routes, router B caches the "n" good enough source-routes it
	   identifies and also sends these routes to router A in one or
more
	   Discovery Reply messages.  These Discovery Reply messages can
travel
	   towards router A in any manner chosen by router B.
	
	
	
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	   If router A had requested the discovery of "n"
forward/backward/
	   bidirectional hop-by-hop routes, router B sends out a
Discovery Reply
	   message to router A for each one of the "n" good enough
routes it
	   identifies.  
	
	JP> Do you need one "Discovery Reply message" per route or
next-hop
	in this case?
	The Discovery Reply message travels towards router A
	   using the source-route accumulated by the Discovery message.

	
	JP> In the case of hop-by-hop routes, source routes, both ?
	As this
	   message travels towards router A, it establishes appropriate
forward/
	   backward routing state in the en-route routers.  This "non
DAG"
	   routing state should be specially marked to associate it with
the
	   routing metrics 
	
	JP> Refer to metric ID ?
	used to discover the route and to distinguish such
	   state from other DAG-specific routing state the router may
have.
	
	JP> Not sure that you need to distinguish the state. Suppose
that you
	discover a hop-by-hop route (not a big fan of that terms as
pointed out
	above but let's continue to use it for the time being), a
storing node
	may indeed have two routes for the same destination: do you want
to
	state that it should always use the P2P routes discovered by
this
	mechanism or let it choose the best one according to the metric
in
	use?
	
	JP> What if there are two routes using different metrics?
	
	5.  Propagation of Discovery Messages
	
	   RPL uses DIO message propagation to build a DAG.  The DIO
message
	   travels via link-local multicast.  
	
	JP> Add everywhere "IPv6 link-local multicast addresses"
	
	
	Each router joining the DAG
	   determines a rank for itself and ignores the subsequent DIO
messages
	   received from lower (higher in numerical value) ranked
neighbors.
	   Thus, the DIO messages propagate outwards rather than return
inwards
	   towards the DAG root.  
	
	JP> I would suggest to align to the RPL terminology.
Inward/outward
	are not used anymore.
	
	
	The DIO message generation at a router is
	   further controlled by a trickle timer that allows a router to
avoid
	   generating unnecessary messages.  
	
	JP> Add a reference to the Trickle ID
	
	
	The link-local multicast based
	   propagation, trickle-controlled generation and the rank-based
	   poisoning of messages traveling in the wrong direction
(towards the
	   DAG root) provide powerful incentives to use the DIO message
as the
	   Discovery message and propagate the DIO/Discovery message by
creating
	   a "temporary" DAG.
	
	5.1.  The Route Discovery Option
	
	       0                   1                   2
3
	        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
8 9 0 1
	
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	       |   Type = 9    | Option Length | D |S|  N  | L |O|  Max
Rank   |
	
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	       |
|
	       |                       Target Address
|
	       |
|
	       |
|
	
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	       |              OCP              |
	       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	
	
	              Figure 1: Format of the Route Discovery Option
	
	   In order to be used as a Discovery message, a DIO MUST carry
a "Route
	   Discovery" option illustrated in Figure 1.  A DIO MUST NOT
carry more
	
	
	
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	   than one Route Discovery options.  
	
	JP> Explain what you do if more than one is present:
		* Ignore the second one?
		* Ignore the entire message?
	
	
	A Route Discovery option consists
	   of the following fields:
	
	   o  Option Type = 0x09 (to be confirmed by IANA).
	
	   o  Option Length = 20 or 22 octets depending on whether the
OCP field
	      is included or not.
	
	   o  D: A 2-bit field that indicates the direction of the
desired
	      routes:
	
	      *  D = 0x00: Forward;
	
	      *  D = 0x01: Backward;
	
	      *  D = 0x02: Bidirectional.
	
	   o  S: A flag that indicates whether source routes are
desired.  The
	      flag is set if the source routes are desired.  The flag is
clear
	      if hop-by-hop routes are desired.
	
	   o  N: A 3-bit unsigned integer indicating the number of
routes
	      desired.
	
	   o  L: A 2-bit field indicating the minimum "Life Time" of the
	      temporary DAG, i.e., the minimum duration a router joining
the
	      temporary DAG must maintain its membership in the DAG:
	
	      *  L = 0x00: Minimum life time is 5 seconds;
	
	      *  L = 0x01: Minimum life time is 10 seconds;
	
	      *  L = 0x02: Minimum life time is 1 minute;
	
	      *  L = 0x03: Minimum life time is 10 minutes.
	
	
	
	JP> Placeholder ... indicate what happens if a node cannot store
that
	additional state (add a manageability section).
	   o  O: A flag that indicates whether the same OCP is used for
route
	      discovery as well as temporary DAG formation.  If this
flag is
	      clear, the OCP contained in the DODAG Configuration option
in the
	      DIO is used for route discovery as well.  Otherwise, the
OCP
	      specified in the Route Discovery option is used for route
	      selection 
	
	JP> s/route selection/route discovery
	
	
	and the metrics/constraints used for route selection are
	      carried in a Metrics Container option immediately
following the
	      Route Discovery option.
	
	JP> Since OF is decoupled from metrics, you always need to
indicate
	the metric in use. That said, I do not see your point here.
Indeed, the 
	temporary DAG is built according to some OF and metrics so the 
	resulting routes will inherit these metrics?
	   o  Max Rank: A 7-bit unsigned integer that indicates the
maximum rank
	      allowed in the temporary DAG advertised by the DIO
message.  This
	      upper limit on the DAG rank serves as the "distance"
referred to
	
	
	
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	      in Section 4 and provides a control over how far the Route
	      Discovery option contained in the DODAG Configuration
option in
	      the DIO message may travel.  
	
	JP> You may discuss it later in this document ... but the
distance is tied
	to how you compute the rank.
	A router MUST not 
	
	JP> s/MUST not/MUST NOT
	join the temporary
	      DAG if its rank in the DAG will exceed this limit.  Later
versions
	      of this draft will map the 128 value space available in
this field
	      to 16-bit long limits on the DAG rank.
	
	   o  Target Address: The IPv6 address of the target router.
	
	   o  OCP: 16 bit unsigned integer.  An optional field, present
only if
	      the O flag is set, that indicates the objective code point
(OCP)
	      to be used for route selection.
	
	5.2.  Setting a DIO Carrying a Route Discovery Option
	
	   A DIO message that carries a Route Discovery option MUST set
the Base
	   Object, described in [I-D.ietf-roll-rpl], in the following
manner:
	
	   o  RPLInstanceID: RPLInstanceID MUST be a local value as
described in
	      Section 4.1 of [I-D.ietf-roll-rpl].
	
	   o  Grounded (G) Flag: MUST be clear since the objective of
DAG
	      formation is the propagation of Route Discovery option.
This DAG
	      is temporary in nature and is not used for routing
purpose.
	
	   o  Destination Advertisement Supported (A) Flag: MUST be
clear for
	      same reasons as described above.
	
	   o  Destination Advertisement Trigger (T) Flag: MUST be clear.
	
	   o  Mode of Operation (MOP): Since the temporary DAG is not to
be used
	      for routing purposes, the value of this field is
immaterial.  To
	      allow constrained routers to join the DAG, the MOP field
SHOULD be
	      set to 00 (non-storing).
	
	
	
	JP> I'd rather suggest to specify a new MOP value (0x02)
	   o  DODAGPreference (Prf): TBD
	
	   o  Destination Advertisement Trigger Sequence Number (DTSN):
TBD
	
	
	
	JP> To be discussed on the mailing list ?
	   o  DODAGID: IPv6 address of the router initiating the route
	      discovery.
	
	
	
	JP> Origin router.
	   The other fields in the Base Object are set as per the rules
	   described in [I-D.ietf-roll-rpl].
	
	   The DODAG Configuration option, carried in the DIO message,
specifies
	   the parameters for the trickle timer operation that governs
the
	   generation of DIO messages by the routers joining the
temporary DAG.
	
	
	
	JP> Also according to RPL ID or would you recommend different
	default values ? Default values for RPL are TBD but we could
easily
	think of different values in this case. To be revisited in the
future.
	
	
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	   The other fields defined in the DODAG Configuration option
are set as
	   follows:
	
	   o  The MaxRankIncrease field MUST be set to 0 to disable
local repair
	      of the temporary DAG.
	
	   o  This document RECOMMENDS a value 1 for the MinHopRankInc
field.
	
	   o  Objective Code Point (OCP): The OCP to be used for
temporary DAG
	      formation.  This document RECOMMENDS RPL Objective
Function 0, as
	      defined in [I-D.ietf-roll-of0], for use as the objective
function
	      for the formation of the temporary DAG.
	
	   A DIO, that contains a Route Discovery option with O flag
set, MUST
	   also contain a Metric Container option immediately following
the
	   Route Discovery option.  This Metric Container option carries
the
	   values for the routing metrics as well as the constraints
	   (constituting the "good enough" criteria) used for route
selection.
	
	JP> This is confusing: the metric and constraint carried within
the Metric
	Container are used for the DODAG formation. Do you want to use
them
	for a different purpose ? At this point, you have not yet
defined the use of
	the good enough criteria but one can guess that you would use
the good
	enough metrics to control the flooding and the metric/OF to
effectively 
	build the temporary DAG and discover the routes. If so, the good
enough
	metrics are of different use.
	   Note that if O flag in the Route Discovery option is clear,
the OCP
	   and Metric Container used for temporary DAG formation are
used for
	   route selection as well.
	
	   A DIO, carrying a Route Discovery option, MUST not carry any
Route
	
	JP> s/MUST not/MUST NOT
	   Information or Prefix Information options described in
	   [I-D.ietf-roll-rpl].
	
	5.3.  Processing of a DIO Carrying a Route Discovery Option At
An
	      Intermediate Node
	
	   The rules for DIO processing and transmission, described in
Section 7
	   of RPL [I-D.ietf-roll-rpl], apply to DIOs carrying a Route
Discovery
	   option as well except as modified in this document.
	
	   When an intermediate router joins a temporary DAG advertized
by a DIO
	   carrying the Route Discovery option, it MUST maintain its
membership
	   in the DAG for the Minimum Life Time duration listed in the
Route
	   Discovery option.  
	
	JP> What if it cannot ? Just not join the DAG and log an error ?
	Maintaining membership in the DAG implies
	   remembering:
	
	   o  The RPLInstanceID, the DODAGID and the DODAGVersionNumber
for the
	      temporary DAG;
	
	   o  The router's rank in the temporary DAG;
	
	   o  The best Metric Container, 
	
	JP> you mean the best path cost?
	along with the associated source route
	      from the initiator of route discovery till this router
(carried in
	      a Record Route IPv6 Extension Header proposed in
	      [I-D.thubert-6man-reverse-routing-header]), for the Route
	
	
	
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	      Discovery option being propagated by the temporary DAG.
If the
	      router can not compare Metric Containers, it MUST remember
the
	      latest Metric Container it has received, along with the
associated
	      source route.
	
	JP> Requires clarification on what you mean by "compare"
	   A router belonging to a temporary DAG need not remember the
identity
	   of its DAG parents since the temporary DAG is not used for
routing.
	
	JP> Are you sure ? What is a hop-by-hop route is needed ? Don't
you
	need to remember your parent, or do you still record the route ?


[ABR:] 
I would guess that neighboring information could be used by the node to
update the neighbor caches
for the "normal" DODAGs that the nodes already use.
The temporary DODAGID is mainly a unique handle for the discovery
session to avoid loops and control
the number of transmissions by an individual node during the discovery
time window.

	   The main purpose of a temporary DAG's existence is to
facilitate the
	   propagation of the Route Discovery option.
	
	   The router does not process a Route Discovery option,
contained in
	   the received DIO, any further if any of the following
conditions are
	   true:
	
	   o  The router does not support the objective function 
	
	JP> and/or metrics
	being used for
	      route discovery
	
	   o  The router does not have sufficient information to
calculate the
	      relevant routing metrics/constraints in the right
direction (as
	      specified by the D field).
	
	   o  The S field is clear, i.e. hop-by-hop routes are desired,
but the
	      router can not participate in a hop-by-hop route.
	
	   o  The router is an intermediate router and the router's rank
in the
	      temporary DAG, calculated on the basis of the rank and
objective
	      function carried in the Base Object in the DIO, exceeds
the Max
	      Rank value specified in the Route Discovery option.
	
	   A router MUST discard the DIO if the Route Discovery option
contained
	   in the message does not need further processing.  
	
	JP> Log an error ?
	Otherwise, the
	   Route Discovery option is processed as follows.
	
	   The router updates the Metrics Container associated with the
received
	   Route Discovery option as per the specified objective
function.  
	
	JP> And routing metrics
	
	
	The
	   router may optionally check the Metric Container to determine
if the
	   aggregated values for the routing metrics meet all the
constraints
	   listed in the Metric Container.  
	
	JP> The aggregated values are for the metrics. Constraints are
used to
	prune potential path.
	If not, the Route Discovery option
	   is discarded 
	
	JP> You mean the DIO message.
	without further processing.  Otherwise, the router
	   updates its in-memory copy of the latest/best Metric
Container for
	   this Route Discovery option along with the associated source
route
	   updated in the correct direction (based on the D field of the
Route
	   Discovery option).  Any change in the in-memory copy also
requires
	   resetting the trickle timer and generating a new DIO carrying
the
	   Route Discovery option, the updated latest/best Metric
Container and
	   the associated source route (in a Record Route IPv6 extension
header
	   proposed in [I-D.thubert-6man-reverse-routing-header]) when
the timer
	   fires.  
	
	JP> If the changes occur during the lifetime window.
	Note that the Metric Container MUST immediately follow the
	
	
	
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	   Route Discovery option if the O flag in the Route Discovery
option is
	   set.
	
	5.4.  Processing of a DIO Carrying a Route Discovery Option At
The
	      Target Router
	
	   When the target router joins the temporary DAG advertized by
a DIO
	   carrying the Route Discovery option, it MUST maintain its
membership
	   in the DAG for the Minimum Life Time duration listed in the
Route
	   Discovery option.  Maintaining membership in the DAG implies
	   remembering:
	
	   o  The RPLInstanceID, the DODAGID and the DODAGVersionNumber
for the
	      temporary DAG;
	
	   o  The router's rank in the temporary DAG;
	
	   The target router does not process a Route Discovery option,
	   contained in the received DIO, any further if any of the
following
	   conditions are true:
	
	   o  The router does not support the objective function used
for route
	      discovery
	
	   o  The router does not have sufficient information to
calculate the
	      relevant routing metrics/constraints in the right
direction (as
	      specified by the D field).
	
	
	
	JP> or does not support the metric.
	The target router MUST discard the DIO if the Route Discovery
option contained in the message does not need further processing.
	
	JP> ? How does it knows (simply because it reaches the
destination) ? 

[ABR:]
 
e.g. if the updated rank exceeds the limit, i.e. "TTL == 0"

	   Otherwise, the Route Discovery option is processed as
follows.
	
	   The target router updates the Metrics Container associated
with the
	   received Route Discovery option as per the specified
objective
	   function.  
	
	JP> and routing metrics (remember they are decoupled).
	
	
	The target router then checks the Metric Container to
	   determine if the aggregated values for the routing metrics
meet all
	   the constraints listed in the Metric Container.  
	
	JP> See previous comments.
	
	
	If not, the Route
	   Discovery option is discarded without further processing.
Otherwise,
	   the router MAY select the source route accumulated by the
received
	   DIO as one of the discovered routes.  
	
	JP> "MAY" ? When ?
	The target router MUST send one
	   or more RPL Control Messages carrying a Discovery Reply
Object
	   (defined in the next section) back to the origin router
(identified
	   by the DODAGID field in the DIO Base Object) as discussed in
the
	   following sections.
	
	   The target router MUST NOT forward a DIO carrying a Route
Discovery
	   option that lists one of its own addresses as the Target
Address.
	
	
	
	
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	6.  Propagation of Discovery Reply Messages
	
	6.1.  The Discovery Reply Object (DRO)
	
	       0                   1                   2
3
	        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
8 9 0 1
	
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	       | RPLInstanceID |    Version    | D |S|  N  |
Reserved      |
	
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	       |
|
	       |                         DODAGID
|
	       |
|
	       |
|
	
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	       |
|
	       |                       Target Address
|
	       |
|
	       |
|
	
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	       | Option(s)...
	       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...
	
	
	           Figure 2: Format of the Discovery Reply Object (DRO)
	
	   This document defines a new RPL Control Message type, the
Discovery
	   Reply Object (DRO) with code 0x04 (to be confirmed by IANA),
that
	   serves the following functions:
	
	   o  An acknowledgement from the target router to the origin
router
	      regarding the successful discovery of backward source
routes;
	
	
	JP> ACK of routes from the origin to the target: you may not
have routes
	in the opposite direction. 

[ABR:]
True - and in that case, the requester most likely retries the
discovery. Randomization causes other
routes to be found in the second attempt - or the the "B" node also
starts a discovery.
I agree that the doc should be clearer on this aspect.

	   o  Carries one or more forward/bidirectional source routes
from the
	      target to the origin router;
	
	   o  Establishes a hop-by-hop forward/backward/bidirectional
route as
	      it travels from the target to the origin router.
	
	   The format for a Discovery Reply Object (DRO) is shown in
Figure 2.
	   A DRO consists of the following fields:
	
	   o  RPLInstanceID: The RPLInstanceID of the temporary DAG used
for
	      route discovery.
	
	   o  Version: The Version of the temporary DAG used for route
	      discovery.
	
	
	
	
	
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	   o  DODAGID: The DODAGID of the temporary DAG used for route
	      discovery.  The DODAGID also identifies the origin router.
The
	      RPLInstanceID, the Version and the DODAGID together
uniquely
	      identify the temporary DAG used for route discovery and
can be
	      copied from the Base Object of the DIO advertizing the
temporary
	      DAG.
	
	   o  D: A 2-bit field that indicates the direction of the
discovered
	      routes:
	
	      *  D = 0x00: Forward;
	
	      *  D = 0x01: Backward;
	
	      *  D = 0x02: Bidirectional.
	
	      This field has the same value as the corresponding field
in the
	      Route Discovery option.
	
	   o  S: A flag that is clear if the Discovery Reply Object is
	      establishing an hop-by-hop route.  The flag is set if the
	      Discovery Reply Object carries (or is an acknowledgement
for the
	      discovery of) one or more source routes.
	
	   o  N: A 3-bit field that indicates the number of source
routes
	      carried or acknowledged in the Discovery Reply Object.
	
	   o  Target Address: The IPv6 address of the target router
originating
	      the Discovery Reply Object.
	
	   o  Reserved: These bits are reserved for future use.  These
bits MUST
	      be set to zero on transmission and MUST be ignored on
reception.
	
	   o  Options: The Discovery Reply Object MAY carry up to 7
Source Route
	      options (defined in the next section) with each such
option
	      carrying a complete forward/bidirectional source route and
	      optionally followed by a Metric Container option that
lists the
	      aggregated values for the routing metrics for the source
route.
	
	JP> This may not be an aggregated value but recorded metric too.
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Route Option 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type
= 10 | Option Length | Compr | Pad | Resvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | .
Addresses[1..n] . . . | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure
3: Format of the Source Route Option The Source Route option,
illustrated in Figure 3, carries a complete forward/bidirectional source
route from the target router to the origin router. A Source Route option
can only be a part of the Discovery Reply Object and MAY be immediately
followed by a Metric Container option that contains the aggregated
values of the routing metrics for this source route. A Route Discovery
option consists of the following fields: o Option Type = 0x0A (to be
confirmed by IANA). o Option Length = Variable, depending on the size of
the Addresses vector. o Compr: 4-bit unsigned interger indicating the
number of prefix octets that are elided from each address. For example,
Compr value will be 0 if full IPv6 addresses are carried in the
Addresses vector. o Pad: 4-bit unsigned integer. Number of octets that
are used for padding between Address[n] and the end of the Source Route
option. o Address[1..n]: Vector of addresses, numbered 1 to n. Each
vector element has size (16 - Compr) octets. A common network
configuration for an RPL domain is that all routers within an LLN share
a common prefix. The Source Route option uses the Compr field to allow
compaction of the Addresses[1..n] vector when all entries share the same
prefix as the DODAGID or the Target Address of the encapsulating
Discovery Reply Object. The shared prefix octets are not carried within
the Source Route option and each entry in Address[1..n] has size (16 -
Compr) octets. When Compr is Goyal, et al. Expires December 16, 2010
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there may exist unused octets between the last entry, Address[n], and
the end of the Source Route option. The Pad field indicates the number
of unused octets that are used for padding. Note that when Compr is 0,
Pad MUST be null and carry a value 0. The Source Route option MUST NOT
specify a path that visits a router more than once. When generating a
Source Route option, the target router may not know the mapping between
IPv6 addresses and routers. Minimally, the target router MUST ensure
that: o The IPv6 Addresses do not appear more than once; o The IPv6
addresses of the origin and the target routers do not appear in the
Address vector; o The Address vector represents a source route in
forward direction with Address[1] being the next hop for the origin
router. Multicast addresses MUST NOT appear in a Source Route option. 
	
	
	JP> you may want to add a ref to RH4 since the format is very
similar.
	6.2.  DRO as Acknowledgement for Backward Source Routes
	
	   When a target router discovers a backward source route, 
	
	JP> I have an issue with your terminology. When the target
receives the
	DIO with route discovery option, what is discovered is a forward
route ?
	
	
	it sends a
	   DRO message to the origin router as an acknowlegement for the
	   discovered route.  Optionally, a target router MAY send a DRO
	   acknowledgement to the origin router after discovering
multiple
	   backward source routes.  A DRO, serving as an acknowledgement
for
	   backward source route discovery, has its D field set to 0x01
	   (indicating backward) while the S flag is set to 1
(indicating source
	   route).  The N field is set to indicate the number of
discovered
	   backward source routes being acknowledged.  Such a DRO
message MUST
	   NOT contain any option.
	
	   This document does not require a particular method for
sending such a
	   DRO message to the origin router.  The target router MAY send
the DRO
	   message to the origin router in any fashion, including:
	
	   o  Using a source route carried in a Type 4 Routing header
	      [I-D.hui-6man-rpl-routing-header];
	
	   o  Along any DAG connecting the target and the origin
routers;
	
	   o  Along the temporary DAG created for route discovery,
provided that
	      the target router is reasonably sure that the DAG's life
time is
	      sufficiently long and the routers in the DAG do remember
one or
	      more of their parents in the DAG.
	
	JP> You may want to explain a bit more why you the origin router
	would be interested in receiving an ACK without the route itself
(case
	6.3): hop-by-hop routes.
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Forward/Bidirectional Source Routes When a target router discovers a
forward source route, 
	
	JP> Here, I agree that this is a forward route.
	it sends a DRO
	   message to the origin router carrying the discovered source
route
	   inside a Source Route option.  Similarly, when a target
router
	   discovers a bidirectional source route, it caches the route
for its
	   own use and then sends a DRO message to the origin router
carrying
	   the discovered route inside a Source Route option.  Rather
than
	   immediately sending a discovered route back to the origin
router, a
	   target router MAY optionally send one DRO message after
discovering
	   multiple forward/bidirectional source routes with the sent
DRO
	   carrying the discovered source routes (in multiple Source
Route
	   options).
	
	JP> Note that the algorithm for "best route" selection is
outside the scope
	of this document, so does the use of a timer on the target side
to determine
	how much time to wait before answering, ...  
	 

[ABR:]
Well, if I am in a hurry, I can live with the best enough route, i.e.
the first one received, while in
other cases, I can accept waiting for some time to get a number of
backup routes in the same message.

	 
	A DRO message carrying one or more Source Route options MUST
have its D field set to 0x00 (for forward routes) or 0x02 (for
bidirectional routes). The S flag MUST be set to 1 and the N field MUST
indicate the number of Source Route options in the message. A Source
Route option MAY immediately be followed by a Metric Container option
that carries the aggregated 
	
	JP> or recorded
	values of the routing metrics for this source
	   route.  The target router may send this DRO message to the
origin
	   router in any fashion it desires including the options listed
in
	   Section 6.2.
	
	6.4.  Establishing Hop-by-hop Routes Via DRO
	
	   In order to establish a hop-by-hop route, the target router
sends a
	   DRO message along the reverse of the discovered route (via a
Type 4
	   Routing Header specified in
[I-D.hui-6man-rpl-routing-header]).  The
	   D field of the message is set to convey the route's direction
	   (forward/backward/bidirectional) and the S flag MUST be clear
	   (indicating hop-by-hop).  The N field MUST be set to 1.  Such
a DRO
	   MUST NOT contain any option.
	
	   A router receiving such a DRO message SHOULD establish
hop-by-hop
	   state in the right direction corresponding to the route
carried in
	   the Type 4 Routing Header of the DRO message.  If a router
does not
	   establish such state, it MUST drop the DRO message.
Otherwise, it
	   MUST forward the DRO message along the source route contained
in Type
	   4 Routing Header of the received message.
	
	
	
	JP> Any error log if it does not ? (optional) ICMP sent to the
target node?
	   A router SHOULD associate the hop-by-hop routing state, thus
	   established, with the objective function and metrics used for
route
	   discovery.
	
	
	
	
	
	
	
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	JP> New section to indicate how to clean-up the temporary DAG ?
	7.  Security Considerations
	
	   TBA
	
	
	8.  IANA Considerations
	
	   TBA
	
	
	9.  Authors and Contributors
	
	   In addition to the editor, the authors of this document
include the
	   following individuals (listed in alphabetical order).
	
	   Anders Brandt, Sigma Designs, Emdrupvej 26A, 1., Copenhagen,
Dk-2100,
	   Denmark.  Phone: [phone]; Email: [e-mail]
	
	   Robert Cragie, Gridmerge Ltd, 89 Greenfield Crescent,
Wakefieldm WF4
	   4WA, UK.  Phone: [phone]; Email:
[e-mail]
	
	   Jerald Martocci, Johnson Controls, Milwaukee, WI 53202, USA.
Phone:
	   [phone]; Email:[e-mail]
	
	   Charles Perkins, Tellabs Inc., USA.
Email:[e-mail]
	
	   Authors gratefully acknowledge the contributions of Richard
Kelsey
	   and Zach Shelby in the development of this document.
	
	
	10.  References
	
	10.1.  Normative References
	
	   [RFC2119]  Bradner, S., "Key words for use in RFCs to
Indicate
	              Requirement Levels", BCP 14, RFC 2119, March 1997.
	
	10.2.  Informative References
	
	   [I-D.brandt-roll-rpl-applicability-home-building]
	              Brandt, A., Baccelli, E., and R. Cragie,
"Applicability
	              Statement: The use of RPL in Building and Home
	              Environments",
	
draft-brandt-roll-rpl-applicability-home-building-00 (work
	              in progress), April 2010.
	
	   [I-D.hui-6man-rpl-routing-header]
	              Hui, J., Vasseur, J., and D. Culler, "A Source
Routing
	
	
	
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	              Header for RPL",
draft-hui-6man-rpl-routing-header-00
	              (work in progress), May 2010.
	
	   [I-D.ietf-roll-building-routing-reqs]
	              Martocci, J., Riou, N., Mil, P., and W. Vermeylen,
	              "Building Automation Routing Requirements in Low
Power and
	              Lossy Networks",
draft-ietf-roll-building-routing-reqs-09
	              (work in progress), January 2010.
	
	   [I-D.ietf-roll-of0]
	              Thubert, P., "RPL Objective Function 0",
	              draft-ietf-roll-of0-02 (work in progress), June
2010.
	
	   [I-D.ietf-roll-routing-metrics]
	              Vasseur, J., Kim, M., Networks, D., and H. Chong,
"Routing
	              Metrics used for Path Calculation in Low Power and
Lossy
	              Networks", draft-ietf-roll-routing-metrics-07
(work in
	              progress), June 2010.
	
	   [I-D.ietf-roll-rpl]
	              Winter, T., Thubert, P., and R. Team, "RPL: IPv6
Routing
	              Protocol for Low power and Lossy Networks",
	              draft-ietf-roll-rpl-09 (work in progress), June
2010.
	
	   [I-D.ietf-roll-terminology]
	              Vasseur, J., "Terminology in Low power And Lossy
	              Networks", draft-ietf-roll-terminology-03 (work in
	              progress), March 2010.
	
	   [I-D.thubert-6man-reverse-routing-header]
	              Thubert, P., "Reverse Routing Header",
	              draft-thubert-6man-reverse-routing-header-00 (work
in
	              progress), June 2010.
	
	   [RFC5826]  Brandt, A., Buron, J., and G. Porcu, "Home
Automation
	              Routing Requirements in Low-Power and Lossy
Networks",
	              RFC 5826, April 2010.
	
	
	
	
	
	
	
	
	
	
	
	
	
	
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	Authors' Addresses
	
	   Mukul Goyal (editor)
	   University of Wisconsin Milwaukee
	   3200 N Cramer St
	   Milwaukee, WI  53211
	   USA
	
	   Phone: [phone]
	   Email: [e-mail]
	
	
	   Emmanuel Baccelli (editor)
	   INRIA
	
	   Phone: [phone]
	   Email: [e-mail]
	   URI:   http://www.emmanuelbaccelli.org/
	
	
	   P2P Team
	
	
	JP> Remove P2P Team unless you list the people.
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