From: ccie2be (ccie2be@nyc.rr.com)
Date: Mon Aug 09 2004 - 10:55:08 GMT-3
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" <chris.lord@lorien.co.uk>
To: <ccielab@groupstudy.com>
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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