24-port NWay Ethernet Switch User’s Guide
Switch Management and Operating Concepts
107
Figure 5-17. IGMP Message Format
The IGMP Type codes are shown below:
Type Meaning
0X11
Membership Query (if Group Address is 0.0.0.0)
0x11
Specific Group Membership Query (if Group Address is
Present)
0x16
Membership Report (version 2)
0x17
Leave a Group (version 2)
0x12
Membership Report (version 1)
Table 5-11. IGMP Type Codes
Each host can join a mulitcast group or leave a mulitcast group
that it previously joined. IGMP packets are used by routers to
keep track of group member ships in their immediately
connected subnetworks. The following rules apply:
??
A host sends an IGMP “report” to join a group
??
A host will never send a report when it wants to leave a
group (for version 1).
??
A host will send a “leave” report when it wants to leave a
group (for version 2).
??
Multicast routers send IGMP queries (to the all-hosts
group address: 224.0.0.1) periodically to see whether any
group members exist on their subnetworks. If there is no