Subject: Re: [Roll] [roll] #30: Clearly documenting Multicast mode of operation

From: "roll issue tracker" <[email-masked]>
Date: Sat, 29 May 2010 06:07:22 -0000

#30: Clearly documenting Multicast mode of operation
--------------------------------+-------------------------------------------
 Reporter:  jpv@…               |        Owner:  wintert@…      
     Type:  task                |       Status:  closed         
 Priority:  minor               |    Milestone:                 
Component:  rpl                 |      Version:                 
 Severity:  Active WG Document  |   Resolution:  fixed          
 Keywords:                      |  
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Changes (by jpv@…):

  * status:  new => closed
  * resolution:  => fixed

Comment:

 Multicast operation is now clearly documented in revision 08:

 9.  Multicast Operation

    This section describes further the multicast routing operations over
    an IPv6 RPL network, and specifically how unicast DAOs can be used to
    relay group registrations up.  Wherever the following text mentions
    Multicast Listener Discovery (MLD), one can read MLDv1 ([RFC2710]) or
    MLDv2 ([RFC3810]).

    As is traditional, a listener uses a protocol such as MLD with a
    router to register to a multicast group.

    Along the path between the router and the DODAG root, MLD requests
    are mapped and transported as DAO messages within the RPL protocol;
    each hop coalesces the multiple requests for a same group as a single
    DAO message to the parent(s), in a fashion similar to proxy IGMP, but

 Winter, et al.          Expires November 29, 2010              [Page 68]

 Internet-Draft           draft-ietf-roll-rpl-08                 May 2010

    recursively between child router and parent up to the root.

    A router might select to pass a listener registration DAO message to
    its preferred parent only, in which case multicast packets coming
    back might be lost for all of its sub-DODAG if the transmission fails
    over that link.  Alternatively the router might select to copy
    additional parents as it would do for DAO messages advertising
    unicast destinations, in which case there might be duplicates that
    the router will need to prune.

    As a result, multicast routing states are installed in each router on
    the way from the listeners to the root, enabling the root to copy a
    multicast packet to all its children routers that had issued a DAO
    message including a DAO for that multicast group, as well as all the
    attached nodes that registered over MLD.

    For unicast traffic, it is expected that the grounded root of an
    DODAG terminates RPL and MAY redistribute the RPL routes over the
    external infrastructure using whatever routing protocol is used in
    the other routing domain.  For multicast traffic, the root MAY proxy
    MLD for all the nodes attached to the RPL domain (this would be
    needed if the multicast source is located in the external
    infrastructure).  For such a source, the packet will be replicated as
    it flows down the DODAG based on the multicast routing table entries
    installed from the DAO message.

    For a source inside the DODAG, the packet is passed to the preferred
    parents, and if that fails then to the alternates in the DODAG.  The
    packet is also copied to all the registered children, except for the
    one that passed the packet.  Finally, if there is a listener in the
    external infrastructure then the DODAG root has to further propagate
    the packet into the external infrastructure.

    As a result, the DODAG Root acts as an automatic proxy Rendezvous
    Point for the RPL network, and as source towards the Internet for all
    multicast flows started in the RPL LLN.  So regardless of whether the
    root is actually attached to the Internet, and regardless of whether
    the DODAG is grounded or floating, the root can serve inner multicast
    streams at all times.

-- 
Ticket URL: <http://trac.tools.ietf.org/wg/roll/trac/ticket/30#comment:1>
roll <http://tools.ietf.org/wg/roll/>

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From: "roll issue tracker" <[email-masked]>
Date: Mon, 31 May 2010 21:16:58 -0000

#30: Clearly documenting Multicast mode of operation
--------------------------------+-------------------------------------------
 Reporter:  jpv@…               |        Owner:  wintert@…      
     Type:  task                |       Status:  reopened       
 Priority:  minor               |    Milestone:                 
Component:  rpl                 |      Version:                 
 Severity:  Active WG Document  |   Resolution:                 
 Keywords:                      |  
--------------------------------+-------------------------------------------
Changes (by jpv@…):

  * status:  closed => reopened
  * resolution:  fixed =>

Comment:

 Closed too soon ... requires more text.

-- 
Ticket URL: <http://trac.tools.ietf.org/wg/roll/trac/ticket/30#comment:2>
roll <http://tools.ietf.org/wg/roll/>