Compex Systems SGX3226 - Manual (Page 55)

Chapter 7 Advanced Configuration for Compex SGX3226
45
7.2 IGMP Config
Internet Group Management Protocol (IGMP) is an Internet protocol that provides a
way for an Internet computer to report its multicast group membership to adjacent
routers. It allows Compex SGX3226 to forward multicast traffic intelligently. The
switch "snoops" the IGMP query and report messages and forwards traffic to only the
ports that request the multicast traffic. This prevents the switch from broadcasting the
traffic to all ports and possibly affecting network performance.
The membership of a host group is dynamic - hosts may join and leave groups at any
time. There is no restriction on the location or number of members in a host group. A
host may be a member of more than one group at a time. A host need not be a member
of a group to send datagrams to it.
Host Group Addresses
Host groups are identified by class D IP addresses, i.e., those with "1110" as their
high-order four bits. Class E IP addresses, i.e., those with "1111" as their high-order
four bits, are reserved for future addressing modes.
In Internet standard "dotted decimal" notation, host group addresses range from
224.0.0.0 to 239.255.255.255. The address 224.0.0.0 is guaranteed not to be
assigned to any group, and 224.0.0.1 is assigned to the permanent group of all IP
hosts (including gateways). This is used to address all multicast hosts on the directly
connected network. There is no multicast address (or any other IP address) for all
hosts on the total Internet. The addresses of other well-known, permanent groups are
to be published in "Assigned Numbers".