TCP/IP Tutorial and Technical Overview - IBM Redbooks

Figure 6-3 illustrates the expanded version 3 membership query packet.
0 8 16 31
Type - 0x11 Max. Resp. Code Checksum
Group Address
Resv S QRV QQIC Number of Sources (N)
Source Address [1]
Source Address [2]
Source Address [N]
Figure 6-3 The IGMPv3 membership query message
The fields from this message are as follows:
► Type: This remains unchanged and, in the case of the membership query
message, has a value of 0x’11’.
► Max resp code: This field is has been changed from the IGMPv2 convention,
and distinguishes between a maximum response code and a maximum
response time. The time can be determined from the code as follows:
– If the maximum response code is less than 128, the value of maximum
response code is also the maximum response time.
– If the maximum response code is greater than 128, the maximum
response code represents a floating-point value denoted as follows:
Byte 0 = 1
Bytes 1-3 = exp
Bytes 4-7 = mant
Maximum response time = (mant OR 0x’10)