From: Geert Nijs (geert.nijs@simac.be)
Date: Mon Aug 09 2004 - 12:05:05 GMT-3
Sparse mode without a RP ?? This is impossible. If you want to keep running your group in sparse mode, you will
need a RP.
My guess is that you only have one broadcast domain, or one switch that has multicast routing enabled or you have
fallen back to dense mode.
From the moment that a router configured with "ip pim sparse-mode" receives a multicast packet, it will lookup
the RP. If it hasn't got a RP it will revert to dense mode. If it has a RP, it will forward the multicast packets
using unicast to that RP (register messages).
Also an application doesn't know if it is running in dense or sparse mode. A multicast sender just sends. It doesn't
care about sparse or dense mode. That is just a router thing.......
Regards,
Geert
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
tycampbell@comcast.net
Sent: maandag 9 augustus 2004 16:37
To: ccie2be; Lord, Chris; ccielab@groupstudy.com
Subject: Re: PIM-SM
I believe that the assumption that "If a pim router knows of a rp for the group, the group operates in sparse mode, otherwise it operates in dense mode." is incorrect.
If I understand what you are saying is correct, then I would be led to believe that in sparse mode, an rp must be defined
I have an application running on a network. The application is running in sparse mode without an rp. This application is setup on a layer 3 switch and is running perfectly. Therefore, at least for this case, I am running sparse mode without an rp. I did not want dense mode because of extra traffic. This is the only mulicast application running on this particular network, so I am not to concerned about it. The applcation is only used during off hours for OS images
Dense mode is not specified, so therefore the application is not running in dense mode. The rp does not always determine that the application only runs in sparse mode. If it does always need to be specified for dense mode, then the applcation should not be running at all
-------------- Original message --------------
> Chris,
>
> Your question can be restated as "What determines whether a mcast operates
> in Dense mode or Sparse mode?"
>
> Many people. it seems, have the misperception that the mode entered on the
> interface determines the mode in which the mcast group operates.
>
> THIS IS WRONG !!!
>
> Only one thing determines if a mcast group operates in sparse or dense mode
> and that is if an RP exists for the group and the given router knows where
> that rp is. If a pim router knows of a rp for the group, the group operates
> in sparse mode, otherwise it operates in dense mode.
>
> But, this does lead to an interesting question - a question I don't know the
> answer for.
>
> Suppose in a mcast domain all interfaces are configured with ip pim
> sparse-mode. And, there's an rp for some mcast groups but not for others.
> What happens with the groups that operate in dense mode? Will they run
> properly or will they experience problems? And, if so, what type of
> problems?
>
>
> ----- Original Message -----
> From: "Lord, Chris"
> To:
> Sent: Monday, August 09, 2004 5:00 AM
> Subject: PIM-SM
>
>
> > Please can someone help me to understand this......
> >
> > I have three routers:
> >
> > e0-R1-s0---s0-R2-s1---s0-R3-e0
> >
> > PIM-SM is configured on all of the interfaces.
> >
> > R1-e0 has an ip igmp join for three groups 224.1.1.1, 224.2.2.2 and
> 224.3.3.3
> >
> > R1 and R2 use R3-s0 as the RP for groups 224.1.1.1 and 224.2.2.2. There is
> no RP configured for 224.3.3.3
> >
> > Results - I can ping 224.1.1.1 and 224.2.2.2 from any router as expected.
> What I didn't expect is that I can also ping 224.3.3.3 from R1 and R2 (but
> not R3). When I look in ip mroute for 224.3.3.3 it is operating in DM on R1
> and R2 even though only PIM-SM is configured. Why is this?
> >
> > TIA.
> >
> > Chris.
> >
> >
> >
> >
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