Routing

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  • 1.  Passing multicast traffic to another subnet

    Posted 03-17-2009 13:59

    Hi there,

    We have a main office and two branch offices. All three offices have Netscreen 5GT devices and the two branch offices are connected back to the main office through route-based VPNs. 

     

    We have an IP phone system at our main office and remote phones deployed to the branch offices and they all work fine except when we try to make a conference call.  I was told by the vendor this is because the phone system uses multicast traffic for the conference audio.

     

    I see in my Netscreen 5GT configuration screens there is an area for configuring "MCast" Policies, and it looks promising. Will this allow me to forward multicast traffic to the other subnets? I am trying to find documentation on Juniper's support site but the site is either down or horrifically slow for me right now.

     

    Thanks,

    Mark



  • 2.  RE: Passing multicast traffic to another subnet
    Best Answer

    Posted 03-17-2009 23:13

    You will not be able to forward multicast with mcast policies. Basically the nature of multicast traffic is that it is not forwarded by routing devices. Multicast traffic is always seen as self traffic to layer 3 devices, and in order to forward you must have PIM dense mode enabled or PIM-SM or PIM-SSM with proper PIM or IGMP joins. This is not specific to Juniper devices, it applies to all layer 3 devices. Once you have PIM working then this is when the mcast policies would come into play to permit/deny the mcast stream.

     

    So the question to ask with regards to your IP phone system is does the IP phone use PIM-DM, PIM-SM or PIM-SSM? If PIM-SM then this is supported on ScreenOS 5.4.0. Your IP phone will need to send IGMP joins to a multicast group and receivers would also need tp send join to their nearest router. If PIM-SSM, then that is supported in later versions of ScreenOS but not on 5GT because latest for 5GT is 5.4.0. If PIM-DM then this is not supported on ScreenOS at all.

     

    Hope this helps.

    -Richard

    Message Edited by rkim on 03-17-2009 11:14 PM


  • 3.  RE: Passing multicast traffic to another subnet

    Posted 03-19-2009 07:20
    The phone system vendor (3Com NBX V3000) got back to me and told me the phone system uses dense mode. So it looks like I am out of luck. I appreciate your help!