Trying to connect() to an IPv6 link-local multicast address by specifying the outgoing multicast interface doesn't work, you have to bind to a device first with an SO_BINDTODEVICE setsockopt() call. This patch allows the IPV6_MULTICAST_IF setting to also control which interface should be used for the connection, as specified in RFC 3493. Signed-off-by: Brian Haley ---