[cisco-voip] Determining if multicast is working properly for CallManager's Music On Hold (MOH)

[Andy Saykao]

Hi There,

We are using CallManager 5.1 and I believe I've set up the network to be
multicast ready, but I don't know how to confirm that multicast is
working properly for Music On Hold which is currently being streamed
using multicast datagrams from our two CallManager servers.
 
Here's a brief overview of the current set up.
 
We have all our Cisco IP phones (7961's) set up on vlan 40.
There's only one core router involved with this set up and various PoE
switches.
 
------------------------------------------------------------------------
------------------------------------------
Core Router (cisco 7206VXR (NPE300))

------------------------------------------------------------------------
------------------------------------------

* I've enabled multicast on this router and set up PIM on the respective
sub-interface.
 
ip multicast-routing
 
interface FastEthernet0/0.40
 description Cisco IP Phone System
 encapsulation dot1Q 40
 ip address 172.16.55.1 255.255.255.0
 ip pim dense-mode

------------------------------------------------------------------------
------------------------------------------
switch1-voip

------------------------------------------------------------------------
------------------------------------------

* The switches all are have igmp snooping enabled as seen below for
vlan40.
 
switch1-voip#sh ip igmp snooping vlan 40

Global IGMP Snooping configuration:
-------------------------------------------
IGMP snooping                : Enabled
IGMPv3 snooping (minimal)    : Enabled
Report suppression           : Enabled
TCN solicit query            : Disabled
TCN flood query count        : 2
Robustness variable          : 2
Last member query count      : 2
Last member query interval   : 1000
 
Vlan 40:
--------
IGMP snooping                       : Enabled
IGMPv2 immediate leave              : Disabled
Multicast router learning mode      : pim-dvmrp
CGMP interoperability mode          : IGMP_ONLY
Robustness variable                 : 2
Last member query count             : 2
Last member query interval          : 1000

------------------------------------------------------------------------
------------------------------------------
 
I can see that the multicast group exists on the core router.
172.16.55.5 = callmanager1 
172.16.55.6 = callmanager2
 
core-routerr#sh 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
Outgoing interface flags: H - Hardware switched
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD, State/Mode

(*, 239.1.2.1), 1d03h/00:02:59, RP 0.0.0.0, flags: DP
  Incoming interface: Null, RPF nbr 0.0.0.0
  Outgoing interface list: Null
 
(172.16.55.6, 239.1.2.1), 00:01:10/00:01:49, flags: PT
  Incoming interface: FastEthernet0/0.40, RPF nbr 0.0.0.0
  Outgoing interface list: Null
 
(*, 239.1.1.1), 1d03h/00:02:59, RP 0.0.0.0, flags: DP
  Incoming interface: Null, RPF nbr 0.0.0.0
  Outgoing interface list: Null
 
(172.16.55.5, 239.1.1.1), 00:01:06/00:01:53, flags: PT
  Incoming interface: FastEthernet0/0.40, RPF nbr 0.0.0.0
  Outgoing interface list: Null

But I don't understand why no hosts (ip phones) are joining this
multicast group (0 joins, 0 leaves)
 
core-routerr#sh ip igmp interface fa0/0.40
FastEthernet0/0.40 is up, line protocol is up
  Internet address is 172.16.55.1/24
  IGMP is enabled on interface
  Current IGMP host version is 2
  Current IGMP router version is 2
  IGMP query interval is 60 seconds
  IGMP querier timeout is 120 seconds
  IGMP max query response time is 10 seconds
  Last member query count is 2
  Last member query response interval is 1000 ms
  Inbound IGMP access group is not set
  IGMP activity: 0 joins, 0 leaves
  Multicast routing is enabled on interface
  Multicast TTL threshold is 0
  Multicast designated router (DR) is 172.16.55.1 (this system)
  IGMP querying router is 172.16.9.50
  No multicast groups joined by this system

I've followed this troubleshooting article and everything appears
correct within the switch network:
 
http://www.cisco.com/en/US/products/hw/switches/ps708/products_tech_note
09186a008059a9df.shtml
 
This CCIE also has a simple set up which I followed but can't confirm if
multicast is properly working bc I don't see the join counter increasing
on the sub interface.
 
http://cciev.wordpress.com/2006/06/17/moh-settings-for-multicast/
 
Strange enough, MOH is still working eventhough multicast doesn't appear
to be working. Why would this be the case?
 
How do I confirm multicast is properly working with CallManager's MOH
within the network?
 
Any help or page reference would be greatly appreciated.
 
--
 
Regards,
 
Andy

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