What is the difference between IPV6_ADD_MEMBERSHIP and IPV6_JOIN_GROUP?

Question

I notice that most OSs that define IPv6 multicast define two sets of socket options; IPV6_ADD_MEMBERSHIP / IPV6_DROP_MEMBERSHIP and IPV6_JOIN_GROUP / IPV6_LEAVE_GROUP . Whenever I find them, they are documented as synonyms, taking the same parameter value. In fact, some reach the #define one to literally mean the other; eg

 #define IPV6_JOIN_GROUP IPV6_ADD_MEMBERSHIP 

Is there any difference here, or is it just historical baggage - two names for the same?

Answer 1

They are identical. Synonyms, just like you said.