Definition Of Multicasting
A multicast message is, by definition, one packet in length. When a QP transmits a multicast message at the behest of a local application program, the packet's destination address defines to which ports (the multicast group members) the message is delivered.
As the packet arrives at each switch, the switch uses the packet's multicast DLID address to perform a lookup in its Multicast Forwarding Table (see “Multicast Forwarding Table Implemented” on page 675). The table lookup determines through which of the switch's exit ports (see Figure 22-1 on page 564) the packet is to be forwarded.
Figure 22-1. Switch Performing a Multicast
When the packet arrives at a CA port (see Figure 22-2 on page 565), it is delivered to all ...
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