Subject: [Roll] FW: Resolving #59: Request for clarification: Transit information option

From: "Pascal Thubert (pthubert)" <[email-masked]>
Date: Fri, 23 Jul 2010 11:16:08 +0200

Dear WG

The following text is proposed to clarify RPL for issue 59:

- ECMP is added for issue #60 by pairing path control bits.
- Some text on path sequence is added for issue #55
- text on lifetime is added for issue #56

"If a node sends a DAO message to one DAO parent, it MUST send a
            DAO with the same Sequence to all other DAO parents."

Was at the wrong place. It goes away but is replaced elsewhere with this

"Path Sequence:  This sequence counter is present in
            the Transit Information option in a DAO message. The purpose of
            this counter is to differentiate a movement where a newer route
            supersedes a stale one from a route redundancy scenario where
            multiple routes exist in parallel for a same target. The Path
            Sequence is globally significant in a DODAG and indicates the
            freshness of the route to the associated target. An older (lesser)
            value received from an originating router indicates that the
            originating router holds stale routing states and the originating
            router should not be considered anymore as a potential next-hop
            for the target. The Path Sequence is computed by the node that
            advertises the target, that is the target itself or a router that
            advertises a target on behalf of a host, and is unchanged as the
            DAO content is propagated towards the root by parent routers. If a
            host does not pass a counter to its router, then the router is in
            charge of computing the Path Sequence on behalf of the host and
            the host can only register to one router for that purpose. If a
            DAO message containing a same target is issued to multiple parents
            at a given point of time for the purpose of route redundancy, then
            the Path Sequence is the same in all the DAO messages for that
            same target."

Also

          "For a Target that is associated with (owned by) a node, that node
          MAY increment the Path Sequence counter, and generate a new DAO
          message, on occasion in order to refresh the downward routing
          information. In storing mode, the node generates such DAO to each of 
          its DAO parents in order to enable multipath.
          All DAOs generated at the same time for a same target MUST be sent
          with the same path sequence in the transit information."

Text on path sequence and DAO sequence is revisited.

The path control text is slightly incremented:

       " When a node sends a DAO to one of its DAO parents, it MUST select
       one or more of the set, active bits in the aggregated Path
       Control field.  The DAO it transmits to its parent MUST have
       these active bits set and all other active bits cleared."

Becomes

           "When a node sends a DAO message to one of its DAO parents, it
            MUST select one or more of the bits that are set active in the aggregated
            Path Control field to advertise to a that parent. A given bit can
            only be presented as active to one parent. The DAO message it
            transmits to its parent MUST have these active bits set and all
            other active bits cleared."

If you have an issue with this resolution please chime in : )

Pascal

> -----Original Message-----
> From: roll issue tracker [mailto:[email-masked]]
> Sent: Tuesday, July 13, 2010 1:22 PM
> To: Pascal Thubert (pthubert); [email-masked]
> Cc: [email-masked]
> Subject: [roll] #59: Request for clarification: Transit information 
> option
> 
> #59: Request for clarification: Transit information option
> -----------------------------+----------------------------------------
> -----------------------------+--
> -----------------------------+----
>  Reporter:  jpv@…            |       Owner:  pthubert@…
>      Type:  enhancement      |      Status:  new
>  Priority:  major            |   Milestone:
> Component:  rpl              |     Version:
>  Severity:  In WG Last Call  |    Keywords:
> -----------------------------+----------------------------------------
> -----------------------------+--
> -----------------------------+----
>  Email from Mathilde On July 9:
> 
>  From: [email-masked] [mailto:[email-masked]] On Behalf 
> Of Mathilde Durvy (mdurvy)
>  Sent: vendredi, 9. juillet 2010 15:17
>  To: Pascal Thubert (pthubert); ROLL WG
>  Subject: Re: [Roll] FW: Transit information option
> 
>  Hi Pascal,
> 
>  Thanks again for your reply. What you say makes sense although I 
> still  think that the separation of the fields between the target and 
> transit  options is somewhat arbitrary J However this is not a major 
> issue and  maybe at this point it’s more important to clarify the 
> specs with respect  to the meaning / usage of the path sequence, control, and lifetime.
>  - In storing mode, the path control is used to limit the DAO fan-out. 
> It  can also be used to set a preference between routes with the 
> limitation  that it cannot specify two routes which are equally 
> preferred (since path  control bits sent to different parents have to be disjoint).
>  - It seems to me that the path control usage is incompatible with the 
> sentence “If a node sends a DAO to one DAO parent, it MUST send a DAO 
> with  the same DAOSequence to all other DAO parents”. No?
>  - In the non storing mode, the path control is not used to limit the 
> DAO  fan-out as nodes send DAOs to only one of their DAO parents. I 
> guess it  can be used as a preference by the root when it computes the source  routes.
>  - How is the path sequence processed? Given that we have already a 
> DAO sequence is it possible to receive a stale path sequence? Isn’t it  redundant?
>  - What does the lifetime represent concretely? Is it a measure of the 
> lifetime of the link between the target and the transit?
> 
>  It’s a lot of questions, but I hope it will help make the DAO part 
> clearer  to everybody!
> 
>  Best,
>  Mathilde
> 
> --
> Ticket URL: <https://svn.tools.ietf.org/wg/roll/trac/ticket/59>
> roll <http://tools.ietf.org/wg/roll/>