Options to control sending of multicast packets

These options allow an application to control certain features in the transmission of IPv6 multicast packets. These socket options do not have to be set to send multicast packets. Supplying a multicast address as the destination address is the only thing required to send an IPv6 multicast packet.

IPV6_MULTICAST_IF

This socket option allows an application to control the outgoing interface used for a multicast packet. The socket option value is the interface index of the interface to be used.

A getsockopt() with this option returns the value set by setsockopt(). If a setsockopt() has not been done, the value 0 is returned.

Tip: This function is similar to the IPv4 socket option IP_MULTICAST_IF.

IPV6_MULTICAST_HOPS

The IPv6 header contains a hop limit field that controls the number of hops over which a datagram can be sent before being discarded. This is similar to the TTL field in the IPv4 header. The IPV6_MULTICAST_HOPS socket option can be used to set the default hop limit value for an outgoing multicast packet. The socket option value should be in the range 0 – 255. A socket option value of -1 is used to clear the socket option. This causes the default value 1 to be used.

A getsockopt() with this option returns the value set by a setsockopt(). If a setsockopt() has not been done, the default value 1 is returned.

The default value is 1. An application must be APF-authorized or have superuser authority to set this option to a value greater than the value of HOPLIMIT on the IPCONFIG6 statement. See z/OS Communications Server: IP Configuration Guide for more information about the IPCONFIG6 statement.

Tip: This function is similar to the IPv4 socket option IP_MULTICAST_TTL.

IPV6_MULTICAST_LOOP

When a multicast packet is sent, if the sender belongs to the multicast group to which the packet was sent, then this option controls whether the sender receives a copy of the packet. If this option is enabled, then the sender receives a copy of the packet. The socket option value should be 1 to enable the option, or 0 to disable the option.

A getsockopt() with this option returns the value set by a setsockopt(). If a setsockopt() has not been done, the default value of 1 (enabled) is returned.

Tip: This function is similar to the IPv4 socket option IP_MULTICAST_LOOP.