Muticast question

in this example The Linux socket and network programming on multicasting client-server with C program example why they assign

localInterface.s_addr = inet_addr("203.106.93.94");

in the sender?

I notice many other example don't do this.

Code:

---

/* Set local interface for outbound multicast datagrams. */

---

Many computers have more that one network interface.

gg