What is the difference between IPV6_ADD_MEMBERSHIP and IPV6_JOIN_GROUP?

Question

I notice that most OSes 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 option value. In fact some go as far as to #define one to literally mean the other; for example

#define IPV6_JOIN_GROUP IPV6_ADD_MEMBERSHIP

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

Answer 1

They're identical. Synonyms, just like you said.