4 Replies Latest reply on Aug 26, 2014 2:25 PM by stevepiette

    ummon multicast usage

    New Member



      We are setting new servers that will be using ummon that will use multicast for resolving topics. When we are doing checking with the multicast setup with mTool, we found some strange behavior.


      We have some servers which can send msg through the multicast interface but not receiving. While some existing servers can use ummon but can't send / receive msg successfully with mTool.


      That make multicat testing a bit difficult. Two questions below.


      1. Would there be a document for how mTool works ?

      2. Would there be any server / network level setting required for mTool to work ?

      3. Would there be any server / network level setting required for UM multicast to work (ummon, twngd etc) ?


      We would like to get some hint for our troubleshooting for the multicast setup.


      Thanks and Regards,


        • 1. Re: ummon multicast usage
          New Member



          I can have one of my engineers open a support request to assist you.


          I'm not sure what ummon is, there is an example program lbmmon that demonstrates how to use the UM monitor statistics.Is that what your refering to?


          MTools Informatica MTools is an unsupported debugging tool and the distribution provides detailed documentation with the source code. The code uses standard OS interfaces for testing multicast operation in much the same way as UM does for the LBTRM transport and for Multicast Topic Resolution.


          It sounds like you have some issues with the configuration of your network routers, have you spoken to your networking staff?


          Let me know if you require a support case to assist on this issue.



          • 2. Re: ummon multicast usage
            New Member

            Thanks Steve, we are troubleshooting with the unix / networks guys.


            Would there be any kernel parameters tunning required for the the multicast topic resolution or LBTRM transport on RedHat 6 ?

            • 3. Re: ummon multicast usage
              New Member

              Hi Tim,


              I am not aware of any kernel parameter changes needed for multicast IP routing to work on RedHat 6 systems.


              It is the default firewall rules that tend to cause me problems when setting up a new system.



              • 4. Re: ummon multicast usage
                New Member

                Sherwin is correct, we don't change any multicast kernel settings.


                The only kernel option we regularly have to point out is to increase the size of the maximum UDP socket buffers. This isn't multicast specific.


                If you don't change the kernel value then you won't be able to request larger buffers in the UM config and get error messages like:

                Core-5688-3290: INFO: unicast rcv could only get SO_RCVBUF 262142 (desired 1048576)

                Core-5688-3340: lbm_socket_sendtob: msg dropped (EWOULDBLOCK): adjust rate limit or buffers


                The default Max UDP Buffer size on most linux systems is very small, usually between 128K and 256K bytes.


                sysctl -w net.core.rmem_max=8388603

                sysctl -w net.core.wmem_max=8388608


                Sets the max size for read and write to 8 megabytes on a linux platform. This just changes the amount you can ask for, you still have to request a larger socket buffer in UM by setting:

                "context resolver_multicast_receiver_socket_buffer 8388603"

                "context transport_lbtrm_receiver_socket_buffer 8388603"

                and if required

                "context transport_lbtrm_source_socket_buffer 8388603"


                If you are seeing UDP drops in netstat you need to increase the size of your receive socket buffers.