</a>, which are defined by <a href="https://tools.ietf.org/html/rfc4007">RFC 4007</a>. In string form, an IP
with a scope index is written as <code>'IP%scope'</code> where scope is an interface name
or interface number.</em></p>
<p>Sets the default outgoing multicast interface of the socket to a chosen
interface or back to system interface selection. The <code>multicastInterface</code> must
be a valid string representation of an IP from the socket's family.</p>
<p>For IPv4 sockets, this should be the IP con