Socket options to support IPv6

A group of socket options is defined to support IPv6. These options are defined with a level of IPPROTO_IPV6. The individual options begin with IPV6_ or with MCAST_.

Restriction: The options that begin with IPV6_ are allowed only on AF_INET6 sockets.

In most cases, an IPV6_xxx option can be set on an AF_INET6 socket that is using IPv4-mapped IPv6 addresses but have no effect. For example, the IPV6_UNICAST_HOPS socket option is used to set a hop limit value in the IPv6 header. Because IPv4 packets are used with IPv4-mapped IPv6 addresses, the hop limit value is not used.

Guideline: The Sockets Extended macro/call APIs do not use level as an input to getsockopt() and setsockopt(). However, other IPv6-enabled APIs do use level as input. For detailed information about setsockopt() and getsockopt() input and output, see the API-specific information.

Table 1. Socket options for getsockopt() and setsockopt()
Socket options getsockopt() setsockopt()	z/OS® UNIX Assembler Callable services	C/C++ using Language Environment®	IP CICS® C sockets	REXX	Sockets Extended macro/call (includes CICS EZASOKET)
IPV6_ADDR_PREFERENCES	Yes	Yes	Yes	Yes	Yes
IPV6_UNICAST_HOPS	Yes	Yes	Yes	Yes	Yes
IPV6_MULTICAST_IF	Yes	Yes	Yes	Yes	Yes
IPV6_MULTICAST_LOOP	Yes	Yes	Yes	Yes	Yes
IPV6_MULTICAST_HOPS	Yes	Yes	Yes	Yes	Yes
IPV6_JOIN_GROUP	Yes	Yes	Yes	Yes	Yes
IPV6_LEAVE_GROUP	Yes	Yes	Yes	Yes	Yes
IPV6_V6ONLY	Yes	Yes	Yes	Yes	Yes
MCAST_BLOCK_SOURCE	Yes	Yes	Yes	Yes	Yes
MCAST_JOIN_GROUP	Yes	Yes	Yes	Yes	Yes
MCAST_JOIN_SOURCE_GROUP	Yes	Yes	Yes	Yes	Yes
MCAST_LEAVE_GROUP	Yes	Yes	Yes	Yes	Yes
MCAST_LEAVE_SOURCE_GROUP	Yes	Yes	Yes	Yes	Yes
MCAST_UNBLOCK_SOURCE	Yes	Yes	Yes	Yes	Yes