From: Ashok M A (ashok_ccie@yahoo.co.in)
Date: Sun Oct 16 2005 - 06:52:32 GMT-3
Hi Simon, Andrew, Jian,
Thank you very much for the explanation..
Ashok
--- simon hart <simon@harttel.com> wrote:
> Hi all,
>
> I think everyone has done an eloquent job in
> explaining the difference
> between IGMP and PIM Joins, however I do not believe
> that this goes to the
> heart of Ashok's question.
>
> When a router's interface is enabled for either pim
> sparse or pim
> sparse-dense mode (not sure about dense will have to
> lab it up). Then that
> interface will immediately send out igmp joins to
> any listening multicast
> router on that subnet, as well as sending out pim
> hello's.
>
> Why does it send out IGMP joins. Well the router is
> in sparse mode and
> therefore needs to know how to get to the Rendevouz
> point. The only way it
> knows how to do this is to join the discovery and
> announcement groups of
> 224.0.1.40 and 224.0.1.39, thus it will send out an
> IGMP join.
>
> The router that recieves this IGMP join from its
> PIM neighbor will send a
> PIM Join to the Rendevouz point so that the
> initiating router can join the
> group.
>
> Remember that if the router is not next to the
> discovery agent, then
> everything breaks in sparse mode as the initiating
> router does not know how
> to get to the RP - this is the catch 22 that pim
> sparse-dense mode is
> trying to overcome as is autorp listener
>
> Hope that helps
>
> Simon
>
> -----Original Message-----
> From: nobody@groupstudy.com
> [mailto:nobody@groupstudy.com]On Behalf Of
> Andrew Lissitz (alissitz)
> Sent: 16 October 2005 05:11
> To: Jian Gu; Ashok M A
> Cc: ccielab@groupstudy.com; C&S GroupStudy
> Subject: RE: IGMP join & PIM join
>
>
> Hey Group,
>
> Jian says it well, igmp join messages are spoken by
> hosts. PIM messages
> are sent by the PIM protocol (I know that sounds
> simple ...) which is
> typically run only by routers. PIM is a control
> plane protocol used by
> routers to set up and control multicast traffic.
>
> When you configure an interface for multicast, you
> must configure the
> PIM protocol. This command enables the protocol on
> the interface as
> well as tells PIM how to behave on that interface;
> sparse, sparse-dense,
> and dense mode. PIM is not smart enough to know how
> to behave, you are
> telling it to try and operate as configured. Notice
> I said try ... If
> you configured sparse-dense mode, but your router
> can not find the RP
> ... What will happen? It certainly will not be
> sparse mode, but will
> fall back to dense mode ... Zzzis not good.
>
> When a router receives a igmp join message on it's
> interface, it then
> knows that it has a receiver requesting traffic for
> a group. What does
> it do now with this knowledge? Well in the case of
> sparse mode, it
> needs to tell the RP that it is interested in
> receiving traffic for this
> group. It will do this by using the PIM protocol.
> In the case of dense
> mode, it will be sure that it will NOT send a prune
> messages for the
> requested group.
>
> Ashok, I am not sure I answered your question. Are
> you also thinking of
> config options, such as igmp join-group?
>
>
>
>
> -----Original Message-----
> From: nobody@groupstudy.com
> [mailto:nobody@groupstudy.com] On Behalf Of
> Jian Gu
> Sent: Saturday, October 15, 2005 3:18 PM
> To: Ashok M A
> Cc: ccielab@groupstudy.com
> Subject: Re: IGMP join & PIM join
>
> They are very different, IGMP joins are from end
> host to last hop
> router, when last hop router receives a IGMP join,
> it will initiate a
> PIM join upstream to RP and create (*,G) entry
> locally, PIM joins are
> between routers.
>
> On 10/14/05, Ashok M A <ashok_ccie@yahoo.co.in>
> wrote:
> >
> > Hi GS,
> >
> > This might be silly question; but i can't explanin
> this well.
> >
> > What is the differnece between IGMP join and PIM
> join messages?
> >
> > Confusion arises as IGMP will be automatically
> enabled by configuring
> > PIM sparse or dense or sparse-dense mode over an
> interface.
> >
> > TIA,
> > Ashok
> >
> >
> >
> >
> >
>
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