Re: PIM Sparse Mode and SPT switchover

You need to find out what exactly SW4 is doing when the source starts
pinging the Mcast address: Is SW4 sending out PIM-JOIN message for S,G with
the SPT-bit set AND PIM-Prune message for S,G with the RPT-bit set?? If so,
it is trying to switch to the Shortest Path Tree, if not, everything is
working as intended. SW4 should continue sending PIM- JOINS with the RPT-bit
set and nothing else) Clear the mroute tables and set the spt-threshold
infinity BEFORE doing the test.

I've noticed odd behavior with the spt-threshold command, in that once a a
router starts using the SPT tree it wont switch back to the Shared tree
until the mroute table clears. If things are working correctly, you will NOT
see a S,G entry at all. Just a *,G entry.

Cheers

-Yuri

On Wed, Jul 27, 2011 at 3:52 AM, Shane K <shanekgs_at_gmail.com> wrote:

> True! So, here is what I did in an effort to understand.
> I've done some reading on this... and I know this is something to do with
> there being only one path but what I want to know is WHY.
>
>
> Build the shared tree from destination to RP
>
> SW4 - IGMP join coming in on VLAN10:
> 3d21h: IGMP(0): Send v2 Report for 224.10.10.10 on Vlan10
> 3d21h: IGMP(0): Received v2 Report on Vlan10 from 155.1.10.10 for
> 224.10.10.10
> 3d21h: IGMP(0): Received Group record for group 224.10.10.10, mode 2 from
> 155.1.10.10 for 0 sources
> 3d21h: IGMP(0): Updating EXCLUDE group timer for 224.10.10.10
> 3d21h: IGMP(0): MRT Add/Update Vlan10 for (*,224.10.10.10) by 0
>
>
> SW2 - received the PIM join message from SW4:
> *Mar 4 21:36:13.234: PIM(0): Received v2 Join/Prune on Port-channel1 from
> 155.1.108.10, to us
> *Mar 4 21:36:13.234: PIM(0): Join-list: (*, 224.10.10.10), RPT-bit set,
> WC-bit set, S-bit set
> *Mar 4 21:36:13.234: PIM(0): Update Port-channel1/155.1.108.10 to (*,
> 224.10.10.10), Forward state, by PIM *G Join
> *Mar 4 21:36:18.359: PIM(0): Received RP-Reachable on Vlan58 from
> 150.1.5.5
> *Mar 4 21:36:18.359: PIM(0): Received RP-Reachable on Vlan58 from
> 150.1.5.5
>
>
> PIM Join forwarded Upstream to R5 from SW2:
> *Jul 27 09:07:36.372: PIM(0): Received v2 Join/Prune on FastEthernet0/0
> from
> 155.1.58.8, to us
> *Jul 27 09:07:36.372: PIM(0): Join-list: (*, 224.10.10.10), RPT-bit set,
> WC-bit set, S-bit set
> *Jul 27 09:07:36.372: PIM(0): Update FastEthernet0/0/155.1.58.8 to (*,
> 224.10.10.10), Forward state, by PIM *G Join
> *Jul 27 09:07:37.556: PIM(0): Send RP-reachability for 224.10.10.10 on
> FastEthernet0/0
>
>
> Now SW4, SW2 and R5 should all have *,G (Confirmed).
>
> R5:
> (*, 224.10.10.10), 00:04:37/00:02:50, RP 150.1.5.5, flags: S
> Incoming interface: Null, RPF nbr 0.0.0.0
> Outgoing interface list:
> FastEthernet0/0, Forward/Sparse, 00:04:12/00:02:50
>
> SW2:
> (*, 224.10.10.10), 00:04:58/00:02:53, RP 150.1.5.5, flags: S
> Incoming interface: Vlan58, RPF nbr 155.1.58.5
> Outgoing interface list:
> Port-channel1, Forward/Sparse, 00:04:33/00:02:53
> SW4:
> (*, 224.10.10.10), 00:05:14/00:02:27, RP 150.1.5.5, flags: SCL
> Incoming interface: Port-channel1, RPF nbr 155.1.108.8
> Outgoing interface list:
> Vlan10, Forward/Sparse, 00:04:49/00:02:27, H
>
>
> R6 will start pinging 224.10.10.10, R4 will send a PIM register message (as
> the DR) to the RP (R5).
> R5 will acknowledge this by sending a PIM register stop back to R4.
>
> R5:
>
> *Jul 27 09:12:37.944: PIM(0): Received v2 Register on Serial0/1/0 from
> 155.1.146.6
> *Jul 27 09:12:37.944: PIM(0): Send v2 Register-Stop to 155.1.146.6 for
> 0.0.0.0, group 0.0.0.0
>
>
> At this stage we should see that R6, R4 and R5 will have *,G and S,G
> entries
>
> R6:
> (*, 224.10.10.10), 00:06:20/stopped, RP 150.1.5.5, flags: SPF
> Incoming interface: FastEthernet0/0.146, RPF nbr 155.1.146.4
> Outgoing interface list: Null
>
> (155.1.146.6, 224.10.10.10), 00:06:20/00:02:48, flags: PFT
> Incoming interface: FastEthernet0/0.146, RPF nbr 0.0.0.0, Registering
> Outgoing interface list: Null
>
> R4:
>
> (*, 224.10.10.10), 00:06:50/stopped, RP 150.1.5.5, flags: S
> Incoming interface: Serial0/1/0, RPF nbr 155.1.45.5
> Outgoing interface list:
> FastEthernet0/1, Forward/Dense, 00:06:50/00:00:00
>
> (155.1.146.6, 224.10.10.10), 00:06:50/00:02:50, flags: T
> Incoming interface: FastEthernet0/1, RPF nbr 155.1.146.6
> Outgoing interface list:
> Serial0/1/0, Forward/Sparse, 00:06:51/00:02:33
>
>
>
>
> R5:
>
>
> (*, 224.10.10.10), 00:13:52/00:03:16, RP 150.1.5.5, flags: S
> Incoming interface: Null, RPF nbr 0.0.0.0
> Outgoing interface list:
> FastEthernet0/0, Forward/Sparse, 00:13:27/00:02:31
> Serial0/1/0, Forward/Sparse, 00:06:09/00:03:16
>
> (155.1.146.6, 224.10.10.10), 00:07:07/00:02:34, flags: T
> Incoming interface: Serial0/1/0, RPF nbr 155.1.45.4
> Outgoing interface list:
> FastEthernet0/0, Forward/Sparse, 00:07:07/00:03:21
>
>
>
>
>
> Now configure ip pim spt-threshold infinity on SW4 but there is no change.
> I'm not seeing anything specific in the logs.
>
>
>
>
>
>
>
>
> Cheers,
>
> S
>
>
>
>
>
>
>
>
> On Wed, Jul 27, 2011 at 2:59 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 Wed Jul 27 2011 - 09:06:19 ART