IGMP membership query max response time

When employing multicast, the maximum response time of IGMP membership reports is defined in the IGMP membership query:


The value found within the Max Resp Time (MRT) field in an IGMP message is only meaningful within a general membership query, and it refers to the maximum response time that the router allows the hosts to set their random response timers to.

Notice that in the router advertisement shown above, the value is 10 seconds, which is the default. However, in all membership reports as well as leave group messages sent by hosts, the MRT field is set to 0 as shown below:



This is because this field is ignored completely in such messages.

According to RFC 2236 which describes the Max Response Time field, it states:

The Max Response Time field is meaningful only in Membership Query messages, and specifies the maximum allowed time before sending a responding report in units of 1/10 second. In all other messages, it is set to zero by the sender and ignored by receivers.

The random time chosen by each host is actually maintained internally and is not shared in any messages, so you will never see the value chosen by any particular host in any field of an IGMP message.