PIM-SM mroute have (S,G) !

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Hi guys,
Pls help me to explain a multicast problem:
I have a topology like this:
source(224.6.6.6)--R1---R2(RP)---R4---R5---R6---Receiver

I use GNS3 lab, PIM-SM, R2 is RP.
So I think between R2--R4--R5--R6 just see the shared tree, but when i show ip mroute on R4, i see (S,G) !!! pls tell me why !
I have config ip pim spt-threshold infinity, but (S,G) is still here !!!!

Pls help !
Thank so much.

Duong Vu

Re: PIM-SM mroute have (S,G) !
The mroute output:
R4#show ip mroute
IP Multicast Routing Table
Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected,
       L - Local, P - Pruned, R - RP-bit set, F - Register flag,
       T - SPT-bit set, J - Join SPT, M - MSDP created entry,
       X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement,
       U - URD, I - Received Source Specific Host Report,
       Z - Multicast Tunnel, z - MDT-data group sender,
       Y - Joined MDT-data group, y - Sending to MDT-data group,
       V - RD & Vector, v - Vector
Outgoing interface flags: H - Hardware switched, A - Assert winner
 Timers: Uptime/Expires
 Interface state: Interface, Next-Hop or VCD, State/Mode

(*, 224.6.6.6), 00:00:58/stopped, RP 2.2.2.2, flags: S
  Incoming interface: GigabitEthernet2/0, RPF nbr 10.0.24.2
  Outgoing interface list:
    GigabitEthernet1/0, Forward/Sparse, 00:00:51/00:02:38

(10.0.12.1, 224.6.6.6), 00:00:09/00:03:29, flags: T
  Incoming interface: GigabitEthernet2/0, RPF nbr 10.0.24.2
  Outgoing interface list:
    GigabitEthernet1/0, Forward/Sparse, 00:00:09/00:03:20

(*, 224.0.1.40), 00:01:00/00:02:59, RP 2.2.2.2, flags: SCL
  Incoming interface: GigabitEthernet2/0, RPF nbr 10.0.24.2
  Outgoing interface list:
    GigabitEthernet1/0, Forward/Sparse, 00:00:46/00:02:43

Duong Vu
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Re: PIM-SM mroute have (S,G) !
D??ng V? wrote:

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 I just did much the same thing and don't see (S,G) with spt-threshold
infinity and do when it's 0.

 Run debug ip pim 224.6.6.6 on R[1-6] and see if you still get (S,G) join
even with spt-threshold infinity.

--  
Rgds,
Martin

Re: PIM-SM mroute have (S,G) !
Hi Martin,
Thank for your reply !
But could you pls tell me why R5 and R4,6 have (S,G) on multicast routing t
able?
I think they are on Shared tree, and just have only (*,G), except R6-Edge R
outer connect to member.

Duong Vu.
On Friday, September 12, 2014 4:51:26 PM UTC+7, Martin Gallagher wrote:
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p

Re: PIM-SM mroute have (S,G) !

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 I don't know why the (S,G) are there, but 'debug ip pim' might give you a
clue if R6 is sending a join anyway.

--  
Rgds,
Martin

Re: PIM-SM mroute have (S,G) !
On Saturday, September 13, 2014 3:52:01 PM UTC+7, Martin Gallagher wrote:
Hi Martin,
Many thanks for your reply.
Here is the debug output (I config ip pim spt-threshold infinity on R4,R5,R6:
R4:
*Sep 13 16:28:54.587: PIM(0): Received v2 Join/Prune on GigabitEthernet1/0 from 10.0.45.5, to us
*Sep 13 16:28:54.591: PIM(0): Join-list: (1.1.1.1/32, 224.6.6.6), S-bit set
*Sep 13 16:28:54.595: PIM(0): Update GigabitEthernet1/0/10.0.45.5 to (1.1.1.1, 224.6.6.6), Forward state, by PIM SG Join
*Sep 13 16:28:55.515: PIM(0): Insert (1.1.1.1,224.6.6.6) join in nbr 10.0.24.2's queue
*Sep 13 16:28:55.519: PIM(0): Building Join/Prune packet for nbr 10.0.24.2
*Sep 13 16:28:55.523: PIM(0):  Adding v2 (1.1.1.1/32, 224.6.6.6), S-bit Join
*Sep 13 16:28:55.527: PIM(0): Send v2 join/prune to 10.0.24.2 (GigabitEthernet2/0)

R5:
*Sep 13 16:28:53.699: PIM(0): Insert (1.1.1.1,224.6.6.6) join in nbr 10.0.45.4's queue
*Sep 13 16:28:53.703: PIM(0): Building Join/Prune packet for nbr 10.0.45.4
*Sep 13 16:28:53.707: PIM(0):  Adding v2 (1.1.1.1/32, 224.6.6.6), S-bit Join
*Sep 13 16:28:53.711: PIM(0): Send v2 join/prune to 10.0.45.4 (GigabitEthernet1/0)
R5#


R6-connect to client-edge router:
*Sep 13 16:28:42.727: PIM(0): Building Periodic (*,G) Join / (S,G,RP-bit) Prune message for 224.6.6.6
*Sep 13 16:28:42.731: PIM(0): Insert (*,224.6.6.6) join in nbr 10.0.56.5's queue
*Sep 13 16:28:42.739: PIM(0): Building Join/Prune packet for nbr 10.0.56.5
*Sep 13 16:28:42.739: PIM(0):  Adding v2 (2.2.2.2/32, 224.6.6.6), WC-bit, RPT-bit, S-bit Join
*Sep 13 16:28:42.739: PIM(0): Send v2 join/prune to 10.0.56.5 (GigabitEthernet2/0)

You can see? the (S,G) is add from R5 !!!, R5 is not the edge router, it's just the normal transit router. Do u know why it do that? how it know about the source.
From my knowledge, R5 just know about RP.


Thanks so much !
Duong Vu.


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Re: PIM-SM mroute have (S,G) !
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You should see a S,G entry because it indicates the presence of multicast in the
forwarding plane i.e. if everything is on the shared tree you will still see S,G
because it is indicating that traffic is actually flowing from a multicast
sender. If there are no receivers you will still see S,G from the source to the
RP but not beyond. You will also see S,G on routers between the receiver router
and the RP because it indicates that traffic is flowing.
You need to understand that S,G results from traffic flowing and NOT from
someone doing a join. A join results in a *,G entry being created or an existing
one modified (e.g. an interface added to the OIL)

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