According to the 7.1 of RFC3376 (IGMP V3)
7.1. Query Version Distinctions
The IGMP version of a Membership Query message is determined as
follows:
IGMPv1 Query: length = 8 octets AND Max Resp Code field is zero
IGMPv2 Query: length = 8 octets AND Max Resp Code field is
non-zero
IGMPv3 Query: length >= 12 octets
I have a question about that. For Ethernet the IGMP V2 Query is always encapsulated in a 64
bytes packet. da+sa+tpid+ip header+IGMP query+padding+fcs=64 bytes,that means after 8 bytes
Query fields,there are some padding "zeros".For this packet the TOTAL LENGTH filed of IP
header is 46. So it seems that it's impossible for a snooping switch to tell the IGMP QUERY
version from the IP header length. any other method?
Somebody told me use the Checksum of IGMP to verify whether the Query is V2 OR V3. But i
think it's not effient for a L2 switch to do that. For the switch which only support V2
snooping ,it just need let V3 query flood to all ports. Then how can the switch recognize
the version of the Query?
I have an idea,let the switch just read the QQIC field,if QQIC !=0,it is V3,otherwise it's
V1 or V2.Can this method work well? Thank you
Klein
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