From: Bob Sinclair (bsinclair@netmasterclass.net)
Date: Mon Jun 13 2005 - 15:34:33 GMT-3
Hi John,
If you have just a (*,G) entry, then it probably has the DCL flags,
indicating dense-mode, Connnected and Local. I see this whenever I configure
PIM on an interface, sparse, dense, or sparse-dense. It indicates you are a
client for auto-rp. That is, this router is a member of that group, it is
listening for auto-rp announcements from the MA. Unless you see an (S,G) for
this group, you are not actually receiving MA announcements.
HTH,
Bob Sinclair
CCIE #10427, CCSI 30427, CISSP
www.netmasterclass.net
----- Original Message -----
From: Sheahan, John
To: Anthony Sequeira
Cc: ccielab@groupstudy.com
Sent: Monday, June 13, 2005 11:02 AM
Subject: RE: Multicast ( *, G) question
Thanks Anthony,
One more quick question, I am running in IP PIM DENSE MODE only. I am
surprised that I am getting the (*, 224.0.1.40)...I thought that was
only used in sparse mode?
-----Original Message-----
From: Anthony Sequeira [mailto:terry.francona@gmail.com]
Sent: Monday, June 13, 2005 11:00 AM
To: Sheahan, John
Cc: ccielab@groupstudy.com
Subject: Re: Multicast ( *, G) question
Yes - you are correct - Cisco routers build a "parent" (*,G) entry
from which they derive other entries. This entry itself is not
actually used for packet forwarding. Incoming and outgoing interface
entries are actually taken from this list for subsequent entries.
On 6/13/05, Sheahan, John <John.Sheahan@priceline.com> wrote:
> Yes, there is a domain controller on one side and one on the other
side.
> As soon as I turn on multicast, I get the (*, 224.0.1.24), but no flow
> exists. After about 5 minutes, I get the flow which looks like
> (10.1.1.1, 224.0.1.24)...then it goes away and I'm left with (*,
> 224.0.1.24) again.
>
> I know it's normal behavior for the MS DS servers to send to this
> address, I'm wondering why I get the (*, 224.0.1.24) on the routers
> before the flow actually starts?
>
> I also have a couple of servers that are sending out join messages to
> 223.22.22.25. As soon as I turn on multicast, I get (*, 223.22.22.25)
on
> the router closest to the server that is sending the joint request for
> 223.22.22.25....but there is no source traffic from the server, only a
> join request.
>
> I'm thinking that the router will automatically put a (*,G) entry in
for
> the multicast network whenever it gets a join request for a multicast
> group?
>
> -----Original Message-----
> From: Anthony Sequeira [mailto:terry.francona@gmail.com]
> Sent: Monday, June 13, 2005 10:47 AM
> To: Sheahan, John
> Cc: ccielab@groupstudy.com
> Subject: Re: Multicast ( *, G) question
>
> What you should be seeing are automatic entries generated for
> 224.0.1.40. This is caused by Cisco's Auto-RP process. Auto-RP
> actually relies upon multicast for its functionality, and therefore,
> your routers are ready to participate in and route for this group.
>
> If you are truly seeing the address 224.0.1.24 showing up
> automatically - I am a bit puzzled - when I looked this address up -
> it seems to be a Microsoft related Multicast address. I assume you
> have Microsoft servers attached to your routers?
>
>
> On 6/13/05, Sheahan, John <John.Sheahan@priceline.com> wrote:
> > When you first turn up multicast with the command "ip
> multicast-routing"
> > and add the appropriate PIM statements on the interfaces, you
usually
> > get a (*,G) for a certain multicast group destination. For instance,
> (*,
> > 224.0.1.24).
> >
> >
> >
> > I see that this will occur even when you have no source traffic to
the
> > destination (in this case, 224.0.1.24).
> >
> > When the source starts up, you will then see (10.1.1.1, 224.0.1.24)
in
> > the mroute table.
> >
> >
> >
> > My question is, what causes the router to know about and put in the
> > (*,224.0.1.24) entry when there is no source? Is this caused by a
> > join-request for that group? How does the router initially know
about
> > this multicast destination and why does it not note the source?
> >
> >
> >
> > thanks
> >
> >
>
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