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Spirent TestCenter: What is the setting "Unsolicited Report Interval" in IGMP used for?

Environment/Versions
  • Spirent TestCenter
    • IGMP
Answer
Setting this parameter sets the time between the initial STC IGMP host's "initial report" and subsequent repetitions of it.
  • The Help file describes the “Unsolicited Report Interval" (URI) with:
    • Enter the period of time (in seconds) between sending repetitions of the initial report of membership in a group
  • Next, RFC 2236 - IGMP, section 6, "start timer",  indicates that the URI is used to specify an interval (0, URI].
    • "start timer" for the group on the interface, ....  If this is an unsolicited Report, the timer is set to a delay value chosen uniformly from the interval (0, [Unsolicited Report Interval] ].
    • so when a device sends its initial join (i.e., after the user clicks on the "Send report for IGMP groups" command):
      • a delay value is chosen between (0, URI]
      • the "start timer" begins to count down
      • when the "start timer" expires, the next join (assuming the robustness variable is > 1) is sent
  • This is what it'd look like in a timeline:
             0---------------------------+-----------------------+
              ^                          ^                       ^
              |                  <------ | ----->                |                    
       initial report               delay chosen                URI
        (i.e., join)               when next join         the upper bound
            sent                      is sent               on the delay
     
  • Now, the number of subsequent joins are set with the "Robustness variable" parameter.
    • The default of the robustness variable is 2.
      • This value can be changed to a higher value but still this is only used for the initial report.
    • After these <robustness variable> reports are sent, the only other reports he will see is if the client receives a query from the DUT.
      • the response from the STC IGMP host is a Solicited Report.
Other comments/observations:
  • Of course you could also resend reports either manually or use the command sequencer.
  • A client would not periodically send any other unsolicited reports.
  • If the router needs to know if a client still wants to receive multicast traffic, then the router will send a query to the client.
  • Once the client receives the query it will respond with a report.
     
  • If you are seeing the IGMP routes disappearing please check article KNI11970

Product : Spirent TestCenter,IGMP/MLD,Multicast