PIM-SM mroute have (S,G) !

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

Reply to
DÆ°Æ¡ng VÅ©
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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

Reply to
DÆ°Æ¡ng VÅ©

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.

Reply to
Martin Gallagher

Reply to
D??ng V?

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.

Reply to
Martin Gallagher

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.

Reply to
DÆ°Æ¡ng VÅ©

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)

Reply to
Jim Reynolds

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