Multicast over BT MPLS

Unanswered Question
Feb 1st, 2009


Requirement is to multicast music on hold RTP stream from a Data Center to a remote site over BT IP Clear MPLS network. Catalyst 3750 switches (both running IP Services Image) will BGP peer with BT PE equipment. The Catalyst 3750 switches will also be configured with PIM-SM.

Does BT MPLS support IP Multicast? I could not find any info on the web so I am hoping people have tried it and (hopefully) it worked for them!

I have this problem too.
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Paolo Bevilacqua Mon, 02/02/2009 - 02:18


I think you will find that multicast is not supported on MPLS. Consequently, you will need to setup GRE tunnels to carry multicast. Since the 3750s are not apt for that, you will need dedicated routers.

Ayodeji oladipo... Mon, 02/02/2009 - 04:33


you can configure the remote site routers to stream MOH from flash because MPLS network will not support multicast.

I just did an install over BT IP Clear MPLS network and it was okay.

Here is a link to configuring this. You must follow every step of it. In some cases after you configure the gateway you may need to reload for it to work, I had to do this.

Below is a sample configuration I used.

NB Ensure the MOH file you use is in router's flash memory.

interface Loopback0

ip address

ip pim sparse-dense-mode

h323-gateway voip interface

h323-gateway voip bind srcaddr


interface FastEthernet0/0

no ip address

ip pim sparse-dense-mode

duplex auto

speed auto


interface FastEthernet0/0.50

description Data VLAN 50

encapsulation dot1Q 50

ip address

ip pim sparse-dense-mode


interface FastEthernet0/0.144

description Voice VLAN 144

encapsulation dot1Q 144

ip address

ip helper-address

ip pim sparse-dense-mode


ccm-manager music-on-hold



max-conferences 8 gain -6

transfer-system full-consult

ip source-address port 2000

max-ephones 42

max-dn 144 dual-line

system message primary WAN Circuit Down

transfer-pattern .T

pickup 4625

call-forward pattern .T

moh SampleAudioSource.ulaw.wav

multicast moh port 16384 route 10.144.50.


gsidhu Mon, 02/02/2009 - 05:10

Thanks for the replies so far.

MoH is requred for external callers (over PRI ISDN circuits) as well as internal callers. My understanding that 'Non-Fallback Mode' will not provide MoH over POTs interfaces.

Looks like my options are limited.

If I deploy standalone MoH server, does this have to be on the same LAN as the UCM cluster or can it be on the remote site (RTT is less than 30 ms between the sites)?

Ayodeji oladipo... Mon, 02/02/2009 - 05:35

This will work for external and internal callers in NON-Fallback Mode.

Please take a minute to read the documentation. This will work even if the router is not in SRST Mode, which is what you want

gsidhu Mon, 02/02/2009 - 05:57

Thanks - I'll have a look through the documnentation. I'm glad it worked for you. I appreciate the configuration.

The SRND for 6.x mentions multicasting moh over 'local Cisco Communications devices' for Non-Fallback mode (no mention of POTS interfaces) and 'analog and digital ports within the chassis' for Fallback mode, which is why I queried this.


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