The sysctl igmp_max_memberships is not enforced on Red Hat Enterprise Linux

Issue

• From what we gathered, limitation on IGMP subscriptions can be set by using the following parameter:  igmp_max_memberships (default to '20').  However, on some of our servers where we left the default value, we noticed that our ethernet card is subscribed to more than 700 different IGMP Groups:

  # head -4 /proc/net/igmp:
  Idx     Device    : Count Querier       Group    Users Timer    Reporter
  1       lo        :     0      V3
                                  010000E0     1 0:00000000               0
  2       eth0      :   711      V2