Re: PIM Sparse Mode and SPT switchover

There are a few scenarios where you cannot prevent SPT switchover. Most
likely in your case, R5 is attempting to prevent a loop.
As Joseph mentioned, we will need to have a look at the debug ip pim output.

This behaviour is not documented well - the best explanation I have come
across is a blog entry by Brian McGahan:
http://blog.ine.com/2011/01/14/understanding-advanced-pim-shared-tree-designs/

HTH,
Nasser.

On Wed, Jul 27, 2011 at 11:59 AM, Joseph L. Brunner <joe_at_affirmedsystems.com
> wrote:

> Shane,
>
> No one here can give you a better answer than the router itself.
>
> What was the result of running debug ip pim on R5?
>
> I'm willing to be in plain English (ok, ciscoese) the RP will let you know
> the before and after condition.
>
> (Hint: how many paths do you have in this network for multicast traffic to
> flow down)
>
> -Joe
>
> -----Original Message-----
> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
> Shane K
> Sent: Tuesday, July 26, 2011 4:36 PM
> To: Cisco certification
> Subject: PIM Sparse Mode and SPT switchover
>
> Hey guys,
>
> I'm having difficulty understanding this, here is the basic topology -
>
>
> R6-------R4 -----R5------SW2-------SW4
>
>
>
> R5 is configured as the RP, SW4 has joined the multicast group
> 224.10.10.10.
> I am pinging 224.10.10.10 from R6 and I am expecting to see *,G and S,G
> entries on the RP (which I do).
>
> However, on R1 and R2 I am seeing port *,G and S,G entries.
> I have configured *ip pim spt-threshold infinity* on SW4 to prevent the SPT
> switchover, cleared the mroutes and started a ping from R6 again - still I
> get the same results.
>
>
>
> R5:
> Rack1R5#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
>
> (*, 224.10.10.10), 00:07:18/00:03:08, RP 150.1.5.5, flags: S
> Incoming interface: Null, RPF nbr 0.0.0.0
> Outgoing interface list:
> FastEthernet0/0, Forward/Sparse, 00:07:18/00:03:08
> Serial0/1/0, Forward/Sparse, 00:05:55/00:02:31
>
> (155.1.146.6, 224.10.10.10), 00:06:54/00:03:20, flags: T
> Incoming interface: Serial0/1/0, RPF nbr 155.1.45.4
> Outgoing interface list:
> FastEthernet0/0, Forward/Sparse, 00:06:54/00:03:08
>
> (*, 224.0.1.40), 00:08:13/00:03:27, RP 150.1.5.5, flags: SJCL
> Incoming interface: Null, RPF nbr 0.0.0.0
> Outgoing interface list:
> FastEthernet0/0, Forward/Sparse, 00:08:07/00:03:19
> Serial0/1/0, Forward/Sparse, 00:06:57/00:03:27
>
> Rack1R5#
>
>
>
>
>
> SW2 Output:
> 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
>
> (*, 224.10.10.10), 00:08:02/00:03:18, RP 150.1.5.5, flags: S
> Incoming interface: Vlan58, RPF nbr 155.1.58.5
> Outgoing interface list:
> Port-channel1, Forward/Sparse, 00:08:02/00:03:18
>
> (155.1.146.6, 224.10.10.10), 00:07:38/00:03:22, flags: T
> Incoming interface: Vlan58, RPF nbr 155.1.58.5
> Outgoing interface list:
> Port-channel1, Forward/Sparse, 00:07:38/00:03:18
>
> (*, 224.0.1.40), 00:08:52/00:03:19, RP 150.1.5.5, flags: SJCL
> Incoming interface: Vlan58, RPF nbr 155.1.58.5
> Outgoing interface list:
> Port-channel1, Forward/Sparse, 00:08:02/00:03:19
>
>
> SW4 output:
> 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
> Y - Joined MDT-data group, y - Sending to MDT-data group
> Outgoing interface flags: H - Hardware switched, A - Assert winner
> Timers: Uptime/Expires
> Interface state: Interface, Next-Hop or VCD, State/Mode
>
> (*, 224.10.10.10), 00:10:37/stopped, RP 150.1.5.5, flags: SCL
> Incoming interface: Port-channel1, RPF nbr 155.1.108.8
> Outgoing interface list:
> Vlan10, Forward/Sparse, 00:10:37/00:02:41, H
>
> (155.1.146.6, 224.10.10.10), 00:00:10/00:02:59, flags: LJT
> Incoming interface: Port-channel1, RPF nbr 155.1.108.8
> Outgoing interface list:
> Vlan10, Forward/Sparse, 00:00:10/00:02:49, H
>
> (*, 224.0.1.40), 00:10:37/00:02:50, RP 150.1.5.5, flags: SPCL
> Incoming interface: Port-channel1, RPF nbr 155.1.108.8
> Outgoing interface list: Null
>
> Rack1SW4#
>
>
>
>
> SW4 config -
> ip pim spt-threshold infinity
>
> interface vl25
> ip igmp join 224.10.10.10
>
>
>
>
>
>
>
> Any suggestions?
> Maybe I'm misunderstanding something here?
>
>
>
> Thanks
>
>
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>
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Received on Fri Jul 29 2011 - 13:28:00 ART