• Michal Tesar's avatar
    igmp: Make igmp group member RFC 3376 compliant · 7ababb78
    Michal Tesar authored
    5.2. Action on Reception of a Query
    
     When a system receives a Query, it does not respond immediately.
     Instead, it delays its response by a random amount of time, bounded
     by the Max Resp Time value derived from the Max Resp Code in the
     received Query message.  A system may receive a variety of Queries on
     different interfaces and of different kinds (e.g., General Queries,
     Group-Specific Queries, and Group-and-Source-Specific Queries), each
     of which may require its own delayed response.
    
     Before scheduling a response to a Query, the system must first
     consider previously scheduled pending responses and in many cases
     schedule a combined response.  Therefore, the system must be able to
     maintain the following state:
    
     o A timer per interface for scheduling responses to General Queries.
    
     o A per-group and interface timer for scheduling responses to Group-
       Specific and Group-and-Source-Specific Queries.
    
     o A per-group and interface list of sources to be reported in the
       response to a Group-and-Source-Specific Query.
    
     When a new Query with the Router-Alert option arrives on an
     interface, provided the system has state to report, a delay for a
     response is randomly selected in the range (0, [Max Resp Time]) where
     Max Resp Time is derived from Max Resp Code in the received Query
     message.  The following rules are then used to determine if a Report
     needs to be scheduled and the type of Report to schedule.  The rules
     are considered in order and only the first matching rule is applied.
    
     1. If there is a pending response to a previous General Query
        scheduled sooner than the selected delay, no additional response
        needs to be scheduled.
    
     2. If the received Query is a General Query, the interface timer is
        used to schedule a response to the General Query after the
        selected delay.  Any previously pending response to a General
        Query is canceled.
    --8<--
    
    Currently the timer is rearmed with new random expiration time for
    every incoming query regardless of possibly already pending report.
    Which is not aligned with the above RFE.
    It also might happen that higher rate of incoming queries can
    postpone the report after the expiration time of the first query
    causing group membership loss.
    
    Now the per interface general query timer is rearmed only
    when there is no pending report already scheduled on that interface or
    the newly selected expiration time is before the already pending
    scheduled report.
    Signed-off-by: default avatarMichal Tesar <mtesar@redhat.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    7ababb78
igmp.c 72.3 KB